[babeltrace.git] / src / plugins / ctf / lttng-live / lttng-live.cpp

/*
 * SPDX-License-Identifier: MIT
 *
 * Copyright 2019 Francis Deslauriers <francis.deslauriers@efficios.com>
 * Copyright 2016 Jérémie Galarneau <jeremie.galarneau@efficios.com>
 * Copyright 2016 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * Babeltrace CTF LTTng-live Client Component
 */

#include <glib.h>
#include <unistd.h>

#include "common/assert.h"
#include "cpp-common/bt2c/fmt.hpp"
#include "cpp-common/vendor/fmt/format.h"

#include "plugins/common/muxing/muxing.h"
#include "plugins/common/param-validation/param-validation.h"

#include "data-stream.hpp"
#include "lttng-live.hpp"
#include "metadata.hpp"

#define MAX_QUERY_SIZE                     (256 * 1024)
#define URL_PARAM                          "url"
#define INPUTS_PARAM                       "inputs"
#define SESS_NOT_FOUND_ACTION_PARAM        "session-not-found-action"
#define SESS_NOT_FOUND_ACTION_CONTINUE_STR "continue"
#define SESS_NOT_FOUND_ACTION_FAIL_STR     "fail"
#define SESS_NOT_FOUND_ACTION_END_STR      "end"

void lttng_live_stream_iterator_set_state(struct lttng_live_stream_iterator *stream_iter,
                                          enum lttng_live_stream_state new_state)
{
    BT_CPPLOGD_SPEC(stream_iter->logger,
                    "Setting live stream iterator state: viewer-stream-id={}, "
                    "old-state={}, new-state={}",
                    stream_iter->viewer_stream_id, stream_iter->state, new_state);

    stream_iter->state = new_state;
}

#define LTTNG_LIVE_LOGD_STREAM_ITER(live_stream_iter)                                              \
    do {                                                                                           \
        BT_CPPLOGD_SPEC((live_stream_iter)->logger,                                                \
                        "Live stream iterator state={}, "                                          \
                        "last-inact-ts-is-set={}, last-inact-ts-value={}, "                        \
                        "curr-inact-ts={}",                                                        \
                        (live_stream_iter)->state, (live_stream_iter)->last_inactivity_ts.is_set,  \
                        (live_stream_iter)->last_inactivity_ts.value,                              \
                        (live_stream_iter)->current_inactivity_ts);                                \
    } while (0);

bool lttng_live_graph_is_canceled(struct lttng_live_msg_iter *msg_iter)
{
    bool ret;

    if (!msg_iter) {
        ret = false;
        goto end;
    }

    ret = bt_self_message_iterator_is_interrupted(msg_iter->self_msg_iter);

end:
    return ret;
}

static struct lttng_live_trace *
lttng_live_session_borrow_trace_by_id(struct lttng_live_session *session, uint64_t trace_id)
{
    uint64_t trace_idx;
    struct lttng_live_trace *ret_trace = NULL;

    for (trace_idx = 0; trace_idx < session->traces->len; trace_idx++) {
        struct lttng_live_trace *trace =
            (lttng_live_trace *) g_ptr_array_index(session->traces, trace_idx);
        if (trace->id == trace_id) {
            ret_trace = trace;
            goto end;
        }
    }

end:
    return ret_trace;
}

static void lttng_live_destroy_trace(struct lttng_live_trace *trace)
{
    BT_CPPLOGD_SPEC(trace->logger, "Destroying live trace: trace-id={}", trace->id);

    BT_ASSERT(trace->stream_iterators);
    g_ptr_array_free(trace->stream_iterators, TRUE);

    BT_TRACE_PUT_REF_AND_RESET(trace->trace);
    BT_TRACE_CLASS_PUT_REF_AND_RESET(trace->trace_class);

    lttng_live_metadata_fini(trace);
    delete trace;
}

static struct lttng_live_trace *lttng_live_create_trace(struct lttng_live_session *session,
                                                        uint64_t trace_id)
{
    BT_CPPLOGD_SPEC(session->logger, "Creating live trace: session-id={}, trace-id={}", session->id,
                    trace_id);

    lttng_live_trace *trace = new lttng_live_trace {session->logger};
    trace->session = session;
    trace->id = trace_id;
    trace->trace_class = NULL;
    trace->trace = NULL;
    trace->stream_iterators =
        g_ptr_array_new_with_free_func((GDestroyNotify) lttng_live_stream_iterator_destroy);
    BT_ASSERT(trace->stream_iterators);
    trace->metadata_stream_state = LTTNG_LIVE_METADATA_STREAM_STATE_NEEDED;
    g_ptr_array_add(session->traces, trace);

    return trace;
}

struct lttng_live_trace *
lttng_live_session_borrow_or_create_trace_by_id(struct lttng_live_session *session,
                                                uint64_t trace_id)
{
    struct lttng_live_trace *trace;

    trace = lttng_live_session_borrow_trace_by_id(session, trace_id);
    if (trace) {
        goto end;
    }

    /* The session is the owner of the newly created trace. */
    trace = lttng_live_create_trace(session, trace_id);

end:
    return trace;
}

int lttng_live_add_session(struct lttng_live_msg_iter *lttng_live_msg_iter, uint64_t session_id,
                           const char *hostname, const char *session_name)
{
    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Adding live session: "
                    "session-id={}, hostname=\"{}\", session-name=\"{}\"",
                    session_id, hostname, session_name);

    lttng_live_session *session = new lttng_live_session {lttng_live_msg_iter->logger};
    session->self_comp = lttng_live_msg_iter->self_comp;
    session->id = session_id;
    session->traces = g_ptr_array_new_with_free_func((GDestroyNotify) lttng_live_destroy_trace);
    BT_ASSERT(session->traces);
    session->lttng_live_msg_iter = lttng_live_msg_iter;
    session->new_streams_needed = true;
    session->hostname = g_string_new(hostname);
    BT_ASSERT(session->hostname);

    session->session_name = g_string_new(session_name);
    BT_ASSERT(session->session_name);

    g_ptr_array_add(lttng_live_msg_iter->sessions, session);

    return 0;
}

static void lttng_live_destroy_session(struct lttng_live_session *session)
{
    if (!session) {
        goto end;
    }

    BT_CPPLOGD_SPEC(session->logger,
                    "Destroying live session: "
                    "session-id={}, session-name=\"{}\"",
                    session->id, session->session_name->str);
    if (session->id != -1ULL) {
        if (lttng_live_session_detach(session)) {
            if (!lttng_live_graph_is_canceled(session->lttng_live_msg_iter)) {
                /* Old relayd cannot detach sessions. */
                BT_CPPLOGD_SPEC(session->logger, "Unable to detach lttng live session {}",
                                session->id);
            }
        }
        session->id = -1ULL;
    }

    if (session->traces) {
        g_ptr_array_free(session->traces, TRUE);
    }

    if (session->hostname) {
        g_string_free(session->hostname, TRUE);
    }

    if (session->session_name) {
        g_string_free(session->session_name, TRUE);
    }

    delete session;

end:
    return;
}

static void lttng_live_msg_iter_destroy(struct lttng_live_msg_iter *lttng_live_msg_iter)
{
    if (!lttng_live_msg_iter) {
        goto end;
    }

    if (lttng_live_msg_iter->sessions) {
        g_ptr_array_free(lttng_live_msg_iter->sessions, TRUE);
    }

    if (lttng_live_msg_iter->viewer_connection) {
        live_viewer_connection_destroy(lttng_live_msg_iter->viewer_connection);
    }
    BT_ASSERT(lttng_live_msg_iter->lttng_live_comp);
    BT_ASSERT(lttng_live_msg_iter->lttng_live_comp->has_msg_iter);

    /* All stream iterators must be destroyed at this point. */
    BT_ASSERT(lttng_live_msg_iter->active_stream_iter == 0);
    lttng_live_msg_iter->lttng_live_comp->has_msg_iter = false;

    delete lttng_live_msg_iter;

end:
    return;
}

void lttng_live_msg_iter_finalize(bt_self_message_iterator *self_msg_iter)
{
    struct lttng_live_msg_iter *lttng_live_msg_iter;

    BT_ASSERT(self_msg_iter);

    lttng_live_msg_iter =
        (struct lttng_live_msg_iter *) bt_self_message_iterator_get_data(self_msg_iter);
    BT_ASSERT(lttng_live_msg_iter);
    lttng_live_msg_iter_destroy(lttng_live_msg_iter);
}

static enum lttng_live_iterator_status
lttng_live_iterator_next_check_stream_state(struct lttng_live_stream_iterator *lttng_live_stream)
{
    switch (lttng_live_stream->state) {
    case LTTNG_LIVE_STREAM_QUIESCENT:
    case LTTNG_LIVE_STREAM_ACTIVE_DATA:
        break;
    case LTTNG_LIVE_STREAM_ACTIVE_NO_DATA:
        /* Invalid state. */
        BT_CPPLOGF_SPEC(lttng_live_stream->logger, "Unexpected stream state \"ACTIVE_NO_DATA\"");
        bt_common_abort();
    case LTTNG_LIVE_STREAM_QUIESCENT_NO_DATA:
        /* Invalid state. */
        BT_CPPLOGF_SPEC(lttng_live_stream->logger, "Unexpected stream state \"QUIESCENT_NO_DATA\"");
        bt_common_abort();
    case LTTNG_LIVE_STREAM_EOF:
        break;
    }
    return LTTNG_LIVE_ITERATOR_STATUS_OK;
}

/*
 * For active no data stream, fetch next index. As a result of that it can
 * become either:
 * - quiescent: won't have events for a bit,
 * - have data: need to get that data and produce the event,
 * - have no data on this stream at this point: need to retry (AGAIN) or return
 *   EOF.
 */
static enum lttng_live_iterator_status lttng_live_iterator_next_handle_one_no_data_stream(
    struct lttng_live_msg_iter *lttng_live_msg_iter,
    struct lttng_live_stream_iterator *lttng_live_stream)
{
    enum lttng_live_iterator_status ret = LTTNG_LIVE_ITERATOR_STATUS_OK;
    enum lttng_live_stream_state orig_state = lttng_live_stream->state;
    struct packet_index index;

    if (lttng_live_stream->trace->metadata_stream_state ==
        LTTNG_LIVE_METADATA_STREAM_STATE_NEEDED) {
        BT_CPPLOGD_SPEC(
            lttng_live_msg_iter->logger,
            "Need to get an update for the metadata stream before proceeding further with this stream: "
            "stream-name=\"{}\"",
            lttng_live_stream->name->str);
        ret = LTTNG_LIVE_ITERATOR_STATUS_CONTINUE;
        goto end;
    }

    if (lttng_live_stream->trace->session->new_streams_needed) {
        BT_CPPLOGD_SPEC(
            lttng_live_msg_iter->logger,
            "Need to get an update of all streams before proceeding further with this stream: "
            "stream-name=\"{}\"",
            lttng_live_stream->name->str);
        ret = LTTNG_LIVE_ITERATOR_STATUS_CONTINUE;
        goto end;
    }

    if (lttng_live_stream->state != LTTNG_LIVE_STREAM_ACTIVE_NO_DATA &&
        lttng_live_stream->state != LTTNG_LIVE_STREAM_QUIESCENT_NO_DATA) {
        goto end;
    }
    ret = lttng_live_get_next_index(lttng_live_msg_iter, lttng_live_stream, &index);
    if (ret != LTTNG_LIVE_ITERATOR_STATUS_OK) {
        goto end;
    }

    BT_ASSERT_DBG(lttng_live_stream->state != LTTNG_LIVE_STREAM_EOF);

    if (lttng_live_stream->state == LTTNG_LIVE_STREAM_QUIESCENT) {
        uint64_t last_inact_ts = lttng_live_stream->last_inactivity_ts.value,
                 curr_inact_ts = lttng_live_stream->current_inactivity_ts;

        if (orig_state == LTTNG_LIVE_STREAM_QUIESCENT_NO_DATA && last_inact_ts == curr_inact_ts) {
            /*
             * Because the stream is in the QUIESCENT_NO_DATA
             * state, we can assert that the last_inactivity_ts was
             * set and can be safely used in the `if` above.
             */
            BT_ASSERT(lttng_live_stream->last_inactivity_ts.is_set);

            ret = LTTNG_LIVE_ITERATOR_STATUS_AGAIN;
            LTTNG_LIVE_LOGD_STREAM_ITER(lttng_live_stream);
        } else {
            ret = LTTNG_LIVE_ITERATOR_STATUS_CONTINUE;
        }
        goto end;
    }

    lttng_live_stream->base_offset = index.offset;
    lttng_live_stream->offset = index.offset;
    lttng_live_stream->len = index.packet_size / CHAR_BIT;

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Setting live stream reading info: stream-name=\"{}\", "
                    "viewer-stream-id={}, stream-base-offset={}, stream-offset={}, stream-len={}",
                    lttng_live_stream->name->str, lttng_live_stream->viewer_stream_id,
                    lttng_live_stream->base_offset, lttng_live_stream->offset,
                    lttng_live_stream->len);

end:
    if (ret == LTTNG_LIVE_ITERATOR_STATUS_OK) {
        ret = lttng_live_iterator_next_check_stream_state(lttng_live_stream);
    }
    return ret;
}

/*
 * Creation of the message requires the ctf trace class to be created
 * beforehand, but the live protocol gives us all streams (including metadata)
 * at once. So we split it in three steps: getting streams, getting metadata
 * (which creates the ctf trace class), and then creating the per-stream
 * messages.
 */
static enum lttng_live_iterator_status
lttng_live_get_session(struct lttng_live_msg_iter *lttng_live_msg_iter,
                       struct lttng_live_session *session)
{
    enum lttng_live_iterator_status status;
    uint64_t trace_idx;

    if (!session->attached) {
        BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger, "Attach to session: session-id={}",
                        session->id);
        enum lttng_live_viewer_status attach_status =
            lttng_live_session_attach(session, lttng_live_msg_iter->self_msg_iter);
        if (attach_status != LTTNG_LIVE_VIEWER_STATUS_OK) {
            if (lttng_live_graph_is_canceled(lttng_live_msg_iter)) {
                /*
                 * Clear any causes appended in
                 * `lttng_live_attach_session()` as we want to
                 * return gracefully since the graph was
                 * cancelled.
                 */
                bt_current_thread_clear_error();
                status = LTTNG_LIVE_ITERATOR_STATUS_AGAIN;
            } else {
                status = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
                BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                             "Error attaching to LTTng live session");
            }
            goto end;
        }
    }

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Updating all data streams: "
                    "session-id={}, session-name=\"{}\"",
                    session->id, session->session_name->str);

    status = lttng_live_session_get_new_streams(session, lttng_live_msg_iter->self_msg_iter);
    switch (status) {
    case LTTNG_LIVE_ITERATOR_STATUS_OK:
        break;
    case LTTNG_LIVE_ITERATOR_STATUS_END:
        /*
                 * We received a `_END` from the `_get_new_streams()` function,
                 * which means no more data will ever be received from the data
                 * streams of this session. But it's possible that the metadata
                 * is incomplete.
                 * The live protocol guarantees that we receive all the
                 * metadata needed before we receive data streams needing it.
                 * But it's possible to receive metadata NOT needed by
                 * data streams after the session was closed. For example, this
                 * could happen if a new event is registered and the session is
                 * stopped before any tracepoint for that event is actually
                 * fired.
                 */
        BT_CPPLOGD_SPEC(
            lttng_live_msg_iter->logger,
            "Updating streams returned _END status. Override status to _OK in order fetch any remaining metadata:"
            "session-id={}, session-name=\"{}\"",
            session->id, session->session_name->str);
        status = LTTNG_LIVE_ITERATOR_STATUS_OK;
        break;
    default:
        goto end;
    }

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Updating metadata stream for session: "
                    "session-id={}, session-name=\"{}\"",
                    session->id, session->session_name->str);

    trace_idx = 0;
    while (trace_idx < session->traces->len) {
        struct lttng_live_trace *trace =
            (lttng_live_trace *) g_ptr_array_index(session->traces, trace_idx);

        status = lttng_live_metadata_update(trace);
        switch (status) {
        case LTTNG_LIVE_ITERATOR_STATUS_END:
        case LTTNG_LIVE_ITERATOR_STATUS_OK:
            trace_idx++;
            break;
        case LTTNG_LIVE_ITERATOR_STATUS_CONTINUE:
        case LTTNG_LIVE_ITERATOR_STATUS_AGAIN:
            goto end;
        default:
            BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                         "Error updating trace metadata: "
                                         "stream-iter-status={}, trace-id={}",
                                         status, trace->id);
            goto end;
        }
    }

    /*
     * Now that we have the metadata we can initialize the downstream
     * iterator.
     */
    status = lttng_live_lazy_msg_init(session, lttng_live_msg_iter->self_msg_iter);

end:
    return status;
}

static void
lttng_live_force_new_streams_and_metadata(struct lttng_live_msg_iter *lttng_live_msg_iter)
{
    uint64_t session_idx, trace_idx;

    for (session_idx = 0; session_idx < lttng_live_msg_iter->sessions->len; session_idx++) {
        struct lttng_live_session *session =
            (lttng_live_session *) g_ptr_array_index(lttng_live_msg_iter->sessions, session_idx);
        BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                        "Force marking session as needing new streams: "
                        "session-id={}",
                        session->id);
        session->new_streams_needed = true;
        for (trace_idx = 0; trace_idx < session->traces->len; trace_idx++) {
            struct lttng_live_trace *trace =
                (lttng_live_trace *) g_ptr_array_index(session->traces, trace_idx);
            BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                            "Force marking trace metadata state as needing an update: "
                            "session-id={}, trace-id={}",
                            session->id, trace->id);

            BT_ASSERT(trace->metadata_stream_state != LTTNG_LIVE_METADATA_STREAM_STATE_CLOSED);

            trace->metadata_stream_state = LTTNG_LIVE_METADATA_STREAM_STATE_NEEDED;
        }
    }
}

static enum lttng_live_iterator_status
lttng_live_iterator_handle_new_streams_and_metadata(struct lttng_live_msg_iter *lttng_live_msg_iter)
{
    enum lttng_live_iterator_status status;
    enum lttng_live_viewer_status viewer_status;
    uint64_t session_idx = 0, nr_sessions_opened = 0;
    struct lttng_live_session *session;
    enum session_not_found_action sess_not_found_act =
        lttng_live_msg_iter->lttng_live_comp->params.sess_not_found_act;

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Update data and metadata of all sessions: "
                    "live-msg-iter-addr={}",
                    fmt::ptr(lttng_live_msg_iter));
    /*
     * In a remotely distant future, we could add a "new
     * session" flag to the protocol, which would tell us that we
     * need to query for new sessions even though we have sessions
     * currently ongoing.
     */
    if (lttng_live_msg_iter->sessions->len == 0) {
        if (sess_not_found_act != SESSION_NOT_FOUND_ACTION_CONTINUE) {
            BT_CPPLOGD_SPEC(
                lttng_live_msg_iter->logger,
                "No session found. Exiting in accordance with the `session-not-found-action` parameter");
            status = LTTNG_LIVE_ITERATOR_STATUS_END;
            goto end;
        } else {
            BT_CPPLOGD_SPEC(
                lttng_live_msg_iter->logger,
                "No session found. Try creating a new one in accordance with the `session-not-found-action` parameter");
            /*
             * Retry to create a viewer session for the requested
             * session name.
             */
            viewer_status = lttng_live_create_viewer_session(lttng_live_msg_iter);
            if (viewer_status != LTTNG_LIVE_VIEWER_STATUS_OK) {
                if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_ERROR) {
                    status = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
                    BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                                 "Error creating LTTng live viewer session");
                } else if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_INTERRUPTED) {
                    status = LTTNG_LIVE_ITERATOR_STATUS_AGAIN;
                } else {
                    bt_common_abort();
                }
                goto end;
            }
        }
    }

    for (session_idx = 0; session_idx < lttng_live_msg_iter->sessions->len; session_idx++) {
        session =
            (lttng_live_session *) g_ptr_array_index(lttng_live_msg_iter->sessions, session_idx);
        status = lttng_live_get_session(lttng_live_msg_iter, session);
        switch (status) {
        case LTTNG_LIVE_ITERATOR_STATUS_OK:
        case LTTNG_LIVE_ITERATOR_STATUS_END:
            /*
             * A session returned `_END`. Other sessions may still
             * be active so we override the status and continue
             * looping if needed.
             */
            break;
        default:
            goto end;
        }
        if (!session->closed) {
            nr_sessions_opened++;
        }
    }

    if (sess_not_found_act != SESSION_NOT_FOUND_ACTION_CONTINUE && nr_sessions_opened == 0) {
        status = LTTNG_LIVE_ITERATOR_STATUS_END;
    } else {
        status = LTTNG_LIVE_ITERATOR_STATUS_OK;
    }

end:
    return status;
}

static enum lttng_live_iterator_status
emit_inactivity_message(struct lttng_live_msg_iter *lttng_live_msg_iter,
                        struct lttng_live_stream_iterator *stream_iter, const bt_message **message,
                        uint64_t timestamp)
{
    enum lttng_live_iterator_status ret = LTTNG_LIVE_ITERATOR_STATUS_OK;
    bt_message *msg = NULL;

    BT_ASSERT(stream_iter->trace->clock_class);

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Emitting inactivity message for stream: ctf-stream-id={}, "
                    "viewer-stream-id={}, timestamp={}",
                    stream_iter->ctf_stream_class_id.value, stream_iter->viewer_stream_id,
                    timestamp);

    msg = bt_message_message_iterator_inactivity_create(lttng_live_msg_iter->self_msg_iter,
                                                        stream_iter->trace->clock_class, timestamp);
    if (!msg) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Error emitting message iterator inactivity message");
        goto error;
    }

    *message = msg;
end:
    return ret;

error:
    ret = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
    bt_message_put_ref(msg);
    goto end;
}

static enum lttng_live_iterator_status lttng_live_iterator_next_handle_one_quiescent_stream(
    struct lttng_live_msg_iter *lttng_live_msg_iter,
    struct lttng_live_stream_iterator *lttng_live_stream, const bt_message **message)
{
    enum lttng_live_iterator_status ret = LTTNG_LIVE_ITERATOR_STATUS_OK;

    if (lttng_live_stream->state != LTTNG_LIVE_STREAM_QUIESCENT) {
        return LTTNG_LIVE_ITERATOR_STATUS_OK;
    }

    /*
     * Check if we already sent an inactivty message downstream for this
     * `current_inactivity_ts` value.
     */
    if (lttng_live_stream->last_inactivity_ts.is_set &&
        lttng_live_stream->current_inactivity_ts == lttng_live_stream->last_inactivity_ts.value) {
        lttng_live_stream_iterator_set_state(lttng_live_stream,
                                             LTTNG_LIVE_STREAM_QUIESCENT_NO_DATA);

        ret = LTTNG_LIVE_ITERATOR_STATUS_CONTINUE;
        goto end;
    }

    ret = emit_inactivity_message(lttng_live_msg_iter, lttng_live_stream, message,
                                  lttng_live_stream->current_inactivity_ts);

    lttng_live_stream->last_inactivity_ts.value = lttng_live_stream->current_inactivity_ts;
    lttng_live_stream->last_inactivity_ts.is_set = true;
end:
    return ret;
}

static int live_get_msg_ts_ns(struct lttng_live_msg_iter *lttng_live_msg_iter,
                              const bt_message *msg, int64_t last_msg_ts_ns, int64_t *ts_ns)
{
    const bt_clock_snapshot *clock_snapshot = NULL;
    int ret = 0;

    BT_ASSERT_DBG(msg);
    BT_ASSERT_DBG(ts_ns);

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Getting message's timestamp: iter-data-addr={}, msg-addr={}, "
                    "last-msg-ts={}",
                    fmt::ptr(lttng_live_msg_iter), fmt::ptr(msg), last_msg_ts_ns);

    switch (bt_message_get_type(msg)) {
    case BT_MESSAGE_TYPE_EVENT:
        clock_snapshot = bt_message_event_borrow_default_clock_snapshot_const(msg);
        break;
    case BT_MESSAGE_TYPE_PACKET_BEGINNING:
        clock_snapshot = bt_message_packet_beginning_borrow_default_clock_snapshot_const(msg);
        break;
    case BT_MESSAGE_TYPE_PACKET_END:
        clock_snapshot = bt_message_packet_end_borrow_default_clock_snapshot_const(msg);
        break;
    case BT_MESSAGE_TYPE_DISCARDED_EVENTS:
        clock_snapshot =
            bt_message_discarded_events_borrow_beginning_default_clock_snapshot_const(msg);
        break;
    case BT_MESSAGE_TYPE_DISCARDED_PACKETS:
        clock_snapshot =
            bt_message_discarded_packets_borrow_beginning_default_clock_snapshot_const(msg);
        break;
    case BT_MESSAGE_TYPE_MESSAGE_ITERATOR_INACTIVITY:
        clock_snapshot = bt_message_message_iterator_inactivity_borrow_clock_snapshot_const(msg);
        break;
    default:
        /* All the other messages have a higher priority */
        BT_CPPLOGD_STR_SPEC(lttng_live_msg_iter->logger,
                            "Message has no timestamp: using the last message timestamp.");
        *ts_ns = last_msg_ts_ns;
        goto end;
    }

    ret = bt_clock_snapshot_get_ns_from_origin(clock_snapshot, ts_ns);
    if (ret) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Cannot get nanoseconds from Epoch of clock snapshot: "
                                     "clock-snapshot-addr={}",
                                     fmt::ptr(clock_snapshot));
        goto error;
    }

    goto end;

error:
    ret = -1;

end:
    if (ret == 0) {
        BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                        "Found message's timestamp: iter-data-addr={}, msg-addr={}, "
                        "last-msg-ts={}, ts={}",
                        fmt::ptr(lttng_live_msg_iter), fmt::ptr(msg), last_msg_ts_ns, *ts_ns);
    }

    return ret;
}

static enum lttng_live_iterator_status lttng_live_iterator_next_handle_one_active_data_stream(
    struct lttng_live_msg_iter *lttng_live_msg_iter,
    struct lttng_live_stream_iterator *lttng_live_stream, const bt_message **message)
{
    enum lttng_live_iterator_status ret = LTTNG_LIVE_ITERATOR_STATUS_OK;
    enum ctf_msg_iter_status status;
    uint64_t session_idx, trace_idx;

    for (session_idx = 0; session_idx < lttng_live_msg_iter->sessions->len; session_idx++) {
        struct lttng_live_session *session =
            (lttng_live_session *) g_ptr_array_index(lttng_live_msg_iter->sessions, session_idx);

        if (session->new_streams_needed) {
            BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                            "Need an update for streams: "
                            "session-id={}",
                            session->id);
            ret = LTTNG_LIVE_ITERATOR_STATUS_CONTINUE;
            goto end;
        }
        for (trace_idx = 0; trace_idx < session->traces->len; trace_idx++) {
            struct lttng_live_trace *trace =
                (lttng_live_trace *) g_ptr_array_index(session->traces, trace_idx);
            if (trace->metadata_stream_state == LTTNG_LIVE_METADATA_STREAM_STATE_NEEDED) {
                BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                                "Need an update for metadata stream: "
                                "session-id={}, trace-id={}",
                                session->id, trace->id);
                ret = LTTNG_LIVE_ITERATOR_STATUS_CONTINUE;
                goto end;
            }
        }
    }

    if (lttng_live_stream->state != LTTNG_LIVE_STREAM_ACTIVE_DATA) {
        ret = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Invalid state of live stream iterator"
                                     "stream-iter-status={}",
                                     lttng_live_stream->state);
        goto end;
    }

    status = ctf_msg_iter_get_next_message(lttng_live_stream->msg_iter, message);
    switch (status) {
    case CTF_MSG_ITER_STATUS_EOF:
        ret = LTTNG_LIVE_ITERATOR_STATUS_END;
        break;
    case CTF_MSG_ITER_STATUS_OK:
        ret = LTTNG_LIVE_ITERATOR_STATUS_OK;
        break;
    case CTF_MSG_ITER_STATUS_AGAIN:
        /*
         * Continue immediately (end of packet). The next
         * get_index may return AGAIN to delay the following
         * attempt.
         */
        ret = LTTNG_LIVE_ITERATOR_STATUS_CONTINUE;
        break;
    case CTF_MSG_ITER_STATUS_ERROR:
    default:
        ret = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "CTF message iterator failed to get next message: "
                                     "msg-iter={}, msg-iter-status={}",
                                     fmt::ptr(lttng_live_stream->msg_iter), status);
        break;
    }

end:
    return ret;
}

static enum lttng_live_iterator_status
lttng_live_iterator_close_stream(struct lttng_live_msg_iter *lttng_live_msg_iter,
                                 struct lttng_live_stream_iterator *stream_iter,
                                 const bt_message **curr_msg)
{
    enum lttng_live_iterator_status live_status = LTTNG_LIVE_ITERATOR_STATUS_OK;

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Closing live stream iterator: stream-name=\"{}\", "
                    "viewer-stream-id={}",
                    stream_iter->name->str, stream_iter->viewer_stream_id);

    /*
     * The viewer has hung up on us so we are closing the stream. The
     * `ctf_msg_iter` should simply realize that it needs to close the
     * stream properly by emitting the necessary stream end message.
     */
    enum ctf_msg_iter_status status =
        ctf_msg_iter_get_next_message(stream_iter->msg_iter, curr_msg);

    if (status == CTF_MSG_ITER_STATUS_ERROR) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Error getting the next message from CTF message iterator");
        live_status = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
        goto end;
    } else if (status == CTF_MSG_ITER_STATUS_EOF) {
        BT_CPPLOGI_SPEC(lttng_live_msg_iter->logger,
                        "Reached the end of the live stream iterator.");
        live_status = LTTNG_LIVE_ITERATOR_STATUS_END;
        goto end;
    }

    BT_ASSERT(status == CTF_MSG_ITER_STATUS_OK);

end:
    return live_status;
}

/*
 * helper function:
 *            handle_no_data_streams()
 *              retry:
 *                - for each ACTIVE_NO_DATA stream:
 *                  - query relayd for stream data, or quiescence info.
 *                    - if need metadata, get metadata, goto retry.
 *                    - if new stream, get new stream as ACTIVE_NO_DATA, goto retry
 *                  - if quiescent, move to QUIESCENT streams
 *                  - if fetched data, move to ACTIVE_DATA streams
 *                (at this point each stream either has data, or is quiescent)
 *
 *
 * iterator_next:
 *            handle_new_streams_and_metadata()
 *                  - query relayd for known streams, add them as ACTIVE_NO_DATA
 *                  - query relayd for metadata
 *
 *            call handle_active_no_data_streams()
 *
 *            handle_quiescent_streams()
 *                - if at least one stream is ACTIVE_DATA:
 *                  - peek stream event with lowest timestamp -> next_ts
 *                  - for each quiescent stream
 *                    - if next_ts >= quiescent end
 *                      - set state to ACTIVE_NO_DATA
 *                - else
 *                  - for each quiescent stream
 *                      - set state to ACTIVE_NO_DATA
 *
 *            call handle_active_no_data_streams()
 *
 *            handle_active_data_streams()
 *                - if at least one stream is ACTIVE_DATA:
 *                    - get stream event with lowest timestamp from heap
 *                    - make that stream event the current message.
 *                    - move this stream heap position to its next event
 *                      - if we need to fetch data from relayd, move
 *                        stream to ACTIVE_NO_DATA.
 *                    - return OK
 *                - return AGAIN
 *
 * end criterion: ctrl-c on client. If relayd exits or the session
 * closes on the relay daemon side, we keep on waiting for streams.
 * Eventually handle --end timestamp (also an end criterion).
 *
 * When disconnected from relayd: try to re-connect endlessly.
 */
static enum lttng_live_iterator_status
lttng_live_iterator_next_msg_on_stream(struct lttng_live_msg_iter *lttng_live_msg_iter,
                                       struct lttng_live_stream_iterator *stream_iter,
                                       const bt_message **curr_msg)
{
    enum lttng_live_iterator_status live_status;

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Advancing live stream iterator until next message if possible: "
                    "stream-name=\"{}\", viewer-stream-id={}",
                    stream_iter->name->str, stream_iter->viewer_stream_id);

    if (stream_iter->has_stream_hung_up) {
        /*
         * The stream has hung up and the stream was properly closed
         * during the last call to the current function. Return _END
         * status now so that this stream iterator is removed for the
         * stream iterator list.
         */
        live_status = LTTNG_LIVE_ITERATOR_STATUS_END;
        goto end;
    }

retry:
    LTTNG_LIVE_LOGD_STREAM_ITER(stream_iter);

    /*
     * Make sure we have the most recent metadata and possibly some new
     * streams.
     */
    live_status = lttng_live_iterator_handle_new_streams_and_metadata(lttng_live_msg_iter);
    if (live_status != LTTNG_LIVE_ITERATOR_STATUS_OK) {
        goto end;
    }

    live_status =
        lttng_live_iterator_next_handle_one_no_data_stream(lttng_live_msg_iter, stream_iter);
    if (live_status != LTTNG_LIVE_ITERATOR_STATUS_OK) {
        if (live_status == LTTNG_LIVE_ITERATOR_STATUS_END) {
            /*
             * We overwrite `live_status` since `curr_msg` is
             * likely set to a valid message in this function.
             */
            live_status =
                lttng_live_iterator_close_stream(lttng_live_msg_iter, stream_iter, curr_msg);
        }
        goto end;
    }

    live_status = lttng_live_iterator_next_handle_one_quiescent_stream(lttng_live_msg_iter,
                                                                       stream_iter, curr_msg);
    if (live_status != LTTNG_LIVE_ITERATOR_STATUS_OK) {
        BT_ASSERT(!*curr_msg);
        goto end;
    }
    if (*curr_msg) {
        goto end;
    }
    live_status = lttng_live_iterator_next_handle_one_active_data_stream(lttng_live_msg_iter,
                                                                         stream_iter, curr_msg);
    if (live_status != LTTNG_LIVE_ITERATOR_STATUS_OK) {
        BT_ASSERT(!*curr_msg);
    }

end:
    if (live_status == LTTNG_LIVE_ITERATOR_STATUS_CONTINUE) {
        BT_CPPLOGD_SPEC(
            lttng_live_msg_iter->logger,
            "Ask the relay daemon for an updated view of the data and metadata streams");
        goto retry;
    }

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Returning from advancing live stream iterator: status={}, "
                    "stream-name=\"{}\", viewer-stream-id={}",
                    live_status, stream_iter->name->str, stream_iter->viewer_stream_id);

    return live_status;
}

static bool is_discarded_packet_or_event_message(const bt_message *msg)
{
    const enum bt_message_type msg_type = bt_message_get_type(msg);

    return msg_type == BT_MESSAGE_TYPE_DISCARDED_EVENTS ||
           msg_type == BT_MESSAGE_TYPE_DISCARDED_PACKETS;
}

static enum lttng_live_iterator_status
adjust_discarded_packets_message(bt_self_message_iterator *iter, const bt_stream *stream,
                                 const bt_message *msg_in, bt_message **msg_out,
                                 uint64_t new_begin_ts)
{
    enum lttng_live_iterator_status status = LTTNG_LIVE_ITERATOR_STATUS_OK;
    enum bt_property_availability availability;
    const bt_clock_snapshot *clock_snapshot;
    uint64_t end_ts;
    uint64_t count;

    clock_snapshot = bt_message_discarded_packets_borrow_end_default_clock_snapshot_const(msg_in);
    end_ts = bt_clock_snapshot_get_value(clock_snapshot);

    availability = bt_message_discarded_packets_get_count(msg_in, &count);
    BT_ASSERT_DBG(availability == BT_PROPERTY_AVAILABILITY_AVAILABLE);

    *msg_out = bt_message_discarded_packets_create_with_default_clock_snapshots(
        iter, stream, new_begin_ts, end_ts);
    if (!*msg_out) {
        status = LTTNG_LIVE_ITERATOR_STATUS_NOMEM;
        goto end;
    }

    bt_message_discarded_packets_set_count(*msg_out, count);
end:
    return status;
}

static enum lttng_live_iterator_status
adjust_discarded_events_message(bt_self_message_iterator *iter, const bt_stream *stream,
                                const bt_message *msg_in, bt_message **msg_out,
                                uint64_t new_begin_ts)
{
    enum lttng_live_iterator_status status = LTTNG_LIVE_ITERATOR_STATUS_OK;
    enum bt_property_availability availability;
    const bt_clock_snapshot *clock_snapshot;
    uint64_t end_ts;
    uint64_t count;

    clock_snapshot = bt_message_discarded_events_borrow_end_default_clock_snapshot_const(msg_in);
    end_ts = bt_clock_snapshot_get_value(clock_snapshot);

    availability = bt_message_discarded_events_get_count(msg_in, &count);
    BT_ASSERT_DBG(availability == BT_PROPERTY_AVAILABILITY_AVAILABLE);

    *msg_out = bt_message_discarded_events_create_with_default_clock_snapshots(
        iter, stream, new_begin_ts, end_ts);
    if (!*msg_out) {
        status = LTTNG_LIVE_ITERATOR_STATUS_NOMEM;
        goto end;
    }

    bt_message_discarded_events_set_count(*msg_out, count);
end:
    return status;
}

static enum lttng_live_iterator_status
handle_late_message(struct lttng_live_msg_iter *lttng_live_msg_iter,
                    struct lttng_live_stream_iterator *stream_iter, int64_t late_msg_ts_ns,
                    const bt_message *late_msg)
{
    const bt_clock_class *clock_class;
    const bt_stream_class *stream_class;
    enum bt_clock_class_cycles_to_ns_from_origin_status ts_ns_status;
    int64_t last_inactivity_ts_ns;
    enum lttng_live_iterator_status stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_OK;
    enum lttng_live_iterator_status adjust_status;
    bt_message *adjusted_message;

    /*
     * The timestamp of the current message is before the last message sent
     * by this component. We CANNOT send it as is.
     *
     * The only expected scenario in which that could happen is the
     * following, everything else is a bug in this component, relay daemon,
     * or CTF parser.
     *
     * Expected scenario: The CTF message iterator emitted discarded
     * packets and discarded events with synthesized beginning and end
     * timestamps from the bounds of the last known packet and the newly
     * decoded packet header. The CTF message iterator is not aware of
     * stream inactivity beacons. Hence, we have to adjust the beginning
     * timestamp of those types of messages if a stream signalled its
     * inactivity up until _after_ the last known packet's beginning
     * timestamp.
     *
     * Otherwise, the monotonicity guarantee of message timestamps would
     * not be preserved.
     *
     * In short, the only scenario in which it's okay and fixable to
     * received a late message is when:
     *  1. the late message is a discarded packets or discarded events
     *  message,
     *  2. this stream produced an inactivity message downstream, and
     *  3. the timestamp of the late message is within the inactivity
     *  timespan we sent downstream through the inactivity message.
     */

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Handling late message on live stream iterator: "
                    "stream-name=\"{}\", viewer-stream-id={}",
                    stream_iter->name->str, stream_iter->viewer_stream_id);

    if (!stream_iter->last_inactivity_ts.is_set) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Invalid live stream state: "
                                     "have a late message when no inactivity message "
                                     "was ever sent for that stream.");
        stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
        goto end;
    }

    if (!is_discarded_packet_or_event_message(late_msg)) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Invalid live stream state: "
                                     "have a late message that is not a packet discarded or "
                                     "event discarded message: late-msg-type={}",
                                     static_cast<bt2::MessageType>(bt_message_get_type(late_msg)));
        stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
        goto end;
    }

    stream_class = bt_stream_borrow_class_const(stream_iter->stream);
    clock_class = bt_stream_class_borrow_default_clock_class_const(stream_class);

    ts_ns_status = bt_clock_class_cycles_to_ns_from_origin(
        clock_class, stream_iter->last_inactivity_ts.value, &last_inactivity_ts_ns);
    if (ts_ns_status != BT_CLOCK_CLASS_CYCLES_TO_NS_FROM_ORIGIN_STATUS_OK) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Error converting last "
                                     "inactivity message timestamp to nanoseconds");
        stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
        goto end;
    }

    if (last_inactivity_ts_ns <= late_msg_ts_ns) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Invalid live stream state: "
                                     "have a late message that is none included in a stream "
                                     "inactivity timespan: last-inactivity-ts-ns={}, "
                                     "late-msg-ts-ns={}",
                                     last_inactivity_ts_ns, late_msg_ts_ns);
        stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
        goto end;
    }

    /*
     * We now know that it's okay for this message to be late, we can now
     * adjust its timestamp to ensure monotonicity.
     */
    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Adjusting the timestamp of late message: late-msg-type={}, "
                    "msg-new-ts-ns={}",
                    static_cast<bt2::MessageType>(bt_message_get_type(late_msg)),
                    stream_iter->last_inactivity_ts.value);
    switch (bt_message_get_type(late_msg)) {
    case BT_MESSAGE_TYPE_DISCARDED_EVENTS:
        adjust_status = adjust_discarded_events_message(
            lttng_live_msg_iter->self_msg_iter, stream_iter->stream, late_msg, &adjusted_message,
            stream_iter->last_inactivity_ts.value);
        break;
    case BT_MESSAGE_TYPE_DISCARDED_PACKETS:
        adjust_status = adjust_discarded_packets_message(
            lttng_live_msg_iter->self_msg_iter, stream_iter->stream, late_msg, &adjusted_message,
            stream_iter->last_inactivity_ts.value);
        break;
    default:
        bt_common_abort();
    }

    if (adjust_status != LTTNG_LIVE_ITERATOR_STATUS_OK) {
        stream_iter_status = adjust_status;
        goto end;
    }

    BT_ASSERT_DBG(adjusted_message);
    stream_iter->current_msg = adjusted_message;
    stream_iter->current_msg_ts_ns = last_inactivity_ts_ns;
    bt_message_put_ref(late_msg);

end:
    return stream_iter_status;
}

static enum lttng_live_iterator_status
next_stream_iterator_for_trace(struct lttng_live_msg_iter *lttng_live_msg_iter,
                               struct lttng_live_trace *live_trace,
                               struct lttng_live_stream_iterator **youngest_trace_stream_iter)
{
    struct lttng_live_stream_iterator *youngest_candidate_stream_iter = NULL;
    enum lttng_live_iterator_status stream_iter_status;
    int64_t youngest_candidate_msg_ts = INT64_MAX;
    uint64_t stream_iter_idx;

    BT_ASSERT_DBG(live_trace);
    BT_ASSERT_DBG(live_trace->stream_iterators);

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Finding the next stream iterator for trace: "
                    "trace-id={}",
                    live_trace->id);
    /*
     * Update the current message of every stream iterators of this trace.
     * The current msg of every stream must have a timestamp equal or
     * larger than the last message returned by this iterator. We must
     * ensure monotonicity.
     */
    stream_iter_idx = 0;
    while (stream_iter_idx < live_trace->stream_iterators->len) {
        bool stream_iter_is_ended = false;
        struct lttng_live_stream_iterator *stream_iter =
            (lttng_live_stream_iterator *) g_ptr_array_index(live_trace->stream_iterators,
                                                             stream_iter_idx);

        /*
         * If there is no current message for this stream, go fetch
         * one.
         */
        while (!stream_iter->current_msg) {
            const bt_message *msg = NULL;
            int64_t curr_msg_ts_ns = INT64_MAX;

            stream_iter_status =
                lttng_live_iterator_next_msg_on_stream(lttng_live_msg_iter, stream_iter, &msg);

            if (stream_iter_status == LTTNG_LIVE_ITERATOR_STATUS_END) {
                stream_iter_is_ended = true;
                break;
            }

            if (stream_iter_status != LTTNG_LIVE_ITERATOR_STATUS_OK) {
                goto end;
            }

            BT_ASSERT_DBG(msg);

            BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                            "Live stream iterator returned message: msg-type={}, "
                            "stream-name=\"{}\", viewer-stream-id={}",
                            static_cast<bt2::MessageType>(bt_message_get_type(msg)),
                            stream_iter->name->str, stream_iter->viewer_stream_id);

            /*
             * Get the timestamp in nanoseconds from origin of this
             * message.
             */
            live_get_msg_ts_ns(lttng_live_msg_iter, msg, lttng_live_msg_iter->last_msg_ts_ns,
                               &curr_msg_ts_ns);

            /*
             * Check if the message of the current live stream
             * iterator occurred at the exact same time or after the
             * last message returned by this component's message
             * iterator. If not, we need to handle it with care.
             */
            if (curr_msg_ts_ns >= lttng_live_msg_iter->last_msg_ts_ns) {
                stream_iter->current_msg = msg;
                stream_iter->current_msg_ts_ns = curr_msg_ts_ns;
            } else {
                /*
                 * We received a message from the past. This
                 * may be fixable but it can also be an error.
                 */
                stream_iter_status =
                    handle_late_message(lttng_live_msg_iter, stream_iter, curr_msg_ts_ns, msg);
                if (stream_iter_status != LTTNG_LIVE_ITERATOR_STATUS_OK) {
                    BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                                 "Late message could not be handled correctly: "
                                                 "lttng-live-msg-iter-addr={}, "
                                                 "stream-name=\"{}\", "
                                                 "curr-msg-ts={}, last-msg-ts={}",
                                                 fmt::ptr(lttng_live_msg_iter),
                                                 stream_iter->name->str, curr_msg_ts_ns,
                                                 lttng_live_msg_iter->last_msg_ts_ns);
                    stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_ERROR;
                    goto end;
                }
            }
        }

        BT_ASSERT_DBG(stream_iter != youngest_candidate_stream_iter);

        if (!stream_iter_is_ended) {
            if (G_UNLIKELY(youngest_candidate_stream_iter == NULL) ||
                stream_iter->current_msg_ts_ns < youngest_candidate_msg_ts) {
                /*
                 * Update the current best candidate message
                 * for the stream iterator of this live trace
                 * to be forwarded downstream.
                 */
                youngest_candidate_msg_ts = stream_iter->current_msg_ts_ns;
                youngest_candidate_stream_iter = stream_iter;
            } else if (stream_iter->current_msg_ts_ns == youngest_candidate_msg_ts) {
                /*
                 * Order the messages in an arbitrary but
                 * deterministic way.
                 */
                BT_ASSERT_DBG(stream_iter != youngest_candidate_stream_iter);
                int ret = common_muxing_compare_messages(
                    stream_iter->current_msg, youngest_candidate_stream_iter->current_msg);
                if (ret < 0) {
                    /*
                     * The `youngest_candidate_stream_iter->current_msg`
                     * should go first. Update the next
                     * iterator and the current timestamp.
                     */
                    youngest_candidate_msg_ts = stream_iter->current_msg_ts_ns;
                    youngest_candidate_stream_iter = stream_iter;
                } else if (ret == 0) {
                    /*
                     * Unable to pick which one should go
                     * first.
                     */
                    BT_CPPLOGW_SPEC(
                        lttng_live_msg_iter->logger,
                        "Cannot deterministically pick next live stream message iterator because they have identical next messages: "
                        "stream-iter-addr={}"
                        "stream-iter-addr={}",
                        fmt::ptr(stream_iter), fmt::ptr(youngest_candidate_stream_iter));
                }
            }

            stream_iter_idx++;
        } else {
            /*
             * The live stream iterator has ended. That
             * iterator is removed from the array, but
             * there is no need to increment
             * stream_iter_idx as
             * g_ptr_array_remove_index_fast replaces the
             * removed element with the array's last
             * element.
             */
            g_ptr_array_remove_index_fast(live_trace->stream_iterators, stream_iter_idx);
        }
    }

    if (youngest_candidate_stream_iter) {
        *youngest_trace_stream_iter = youngest_candidate_stream_iter;
        stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_OK;
    } else {
        /*
         * The only case where we don't have a candidate for this trace
         * is if we reached the end of all the iterators.
         */
        BT_ASSERT(live_trace->stream_iterators->len == 0);
        stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_END;
    }

end:
    return stream_iter_status;
}

static enum lttng_live_iterator_status
next_stream_iterator_for_session(struct lttng_live_msg_iter *lttng_live_msg_iter,
                                 struct lttng_live_session *session,
                                 struct lttng_live_stream_iterator **youngest_session_stream_iter)
{
    enum lttng_live_iterator_status stream_iter_status;
    uint64_t trace_idx = 0;
    int64_t youngest_candidate_msg_ts = INT64_MAX;
    struct lttng_live_stream_iterator *youngest_candidate_stream_iter = NULL;

    BT_CPPLOGD_SPEC(lttng_live_msg_iter->logger,
                    "Finding the next stream iterator for session: "
                    "session-id={}",
                    session->id);
    /*
     * Make sure we are attached to the session and look for new streams
     * and metadata.
     */
    stream_iter_status = lttng_live_get_session(lttng_live_msg_iter, session);
    if (stream_iter_status != LTTNG_LIVE_ITERATOR_STATUS_OK &&
        stream_iter_status != LTTNG_LIVE_ITERATOR_STATUS_CONTINUE &&
        stream_iter_status != LTTNG_LIVE_ITERATOR_STATUS_END) {
        goto end;
    }

    BT_ASSERT_DBG(session->traces);

    while (trace_idx < session->traces->len) {
        bool trace_is_ended = false;
        struct lttng_live_stream_iterator *stream_iter;
        struct lttng_live_trace *trace =
            (lttng_live_trace *) g_ptr_array_index(session->traces, trace_idx);

        stream_iter_status =
            next_stream_iterator_for_trace(lttng_live_msg_iter, trace, &stream_iter);
        if (stream_iter_status == LTTNG_LIVE_ITERATOR_STATUS_END) {
            /*
             * All the live stream iterators for this trace are
             * ENDed. Remove the trace from this session.
             */
            trace_is_ended = true;
        } else if (stream_iter_status != LTTNG_LIVE_ITERATOR_STATUS_OK) {
            goto end;
        }

        if (!trace_is_ended) {
            BT_ASSERT_DBG(stream_iter);

            if (G_UNLIKELY(youngest_candidate_stream_iter == NULL) ||
                stream_iter->current_msg_ts_ns < youngest_candidate_msg_ts) {
                youngest_candidate_msg_ts = stream_iter->current_msg_ts_ns;
                youngest_candidate_stream_iter = stream_iter;
            } else if (stream_iter->current_msg_ts_ns == youngest_candidate_msg_ts) {
                /*
                 * Order the messages in an arbitrary but
                 * deterministic way.
                 */
                int ret = common_muxing_compare_messages(
                    stream_iter->current_msg, youngest_candidate_stream_iter->current_msg);
                if (ret < 0) {
                    /*
                     * The `youngest_candidate_stream_iter->current_msg`
                     * should go first. Update the next iterator
                     * and the current timestamp.
                     */
                    youngest_candidate_msg_ts = stream_iter->current_msg_ts_ns;
                    youngest_candidate_stream_iter = stream_iter;
                } else if (ret == 0) {
                    /* Unable to pick which one should go first. */
                    BT_CPPLOGW_SPEC(
                        lttng_live_msg_iter->logger,
                        "Cannot deterministically pick next live stream message iterator because they have identical next messages: "
                        "stream-iter-addr={}"
                        "youngest-candidate-stream-iter-addr={}",
                        fmt::ptr(stream_iter), fmt::ptr(youngest_candidate_stream_iter));
                }
            }
            trace_idx++;
        } else {
            /*
             * trace_idx is not incremented since
             * g_ptr_array_remove_index_fast replaces the
             * element at trace_idx with the array's last element.
             */
            g_ptr_array_remove_index_fast(session->traces, trace_idx);
        }
    }
    if (youngest_candidate_stream_iter) {
        *youngest_session_stream_iter = youngest_candidate_stream_iter;
        stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_OK;
    } else {
        /*
         * The only cases where we don't have a candidate for this
         * trace is:
         *  1. if we reached the end of all the iterators of all the
         *  traces of this session,
         *  2. if we never had live stream iterator in the first place.
         *
         * In either cases, we return END.
         */
        BT_ASSERT(session->traces->len == 0);
        stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_END;
    }
end:
    return stream_iter_status;
}

static inline void put_messages(bt_message_array_const msgs, uint64_t count)
{
    uint64_t i;

    for (i = 0; i < count; i++) {
        BT_MESSAGE_PUT_REF_AND_RESET(msgs[i]);
    }
}

bt_message_iterator_class_next_method_status
lttng_live_msg_iter_next(bt_self_message_iterator *self_msg_it, bt_message_array_const msgs,
                         uint64_t capacity, uint64_t *count)
{
    bt_message_iterator_class_next_method_status status;
    enum lttng_live_viewer_status viewer_status;
    struct lttng_live_msg_iter *lttng_live_msg_iter =
        (struct lttng_live_msg_iter *) bt_self_message_iterator_get_data(self_msg_it);
    struct lttng_live_component *lttng_live = lttng_live_msg_iter->lttng_live_comp;
    enum lttng_live_iterator_status stream_iter_status;
    uint64_t session_idx;

    *count = 0;

    BT_ASSERT_DBG(lttng_live_msg_iter);

    if (G_UNLIKELY(lttng_live_msg_iter->was_interrupted)) {
        /*
         * The iterator was interrupted in a previous call to the
         * `_next()` method. We currently do not support generating
         * messages after such event. The babeltrace2 CLI should never
         * be running the graph after being interrupted. So this check
         * is to prevent other graph users from using this live
         * iterator in an messed up internal state.
         */
        status = BT_MESSAGE_ITERATOR_CLASS_NEXT_METHOD_STATUS_ERROR;
        BT_CPPLOGE_APPEND_CAUSE_SPEC(
            lttng_live_msg_iter->logger,
            "Message iterator was interrupted during a previous call to the `next()` and currently does not support continuing after such event.");
        goto end;
    }

    /*
     * Clear all the invalid message reference that might be left over in
     * the output array.
     */
    memset(msgs, 0, capacity * sizeof(*msgs));

    /*
     * If no session are exposed on the relay found at the url provided by
     * the user, session count will be 0. In this case, we return status
     * end to return gracefully.
     */
    if (lttng_live_msg_iter->sessions->len == 0) {
        if (lttng_live->params.sess_not_found_act != SESSION_NOT_FOUND_ACTION_CONTINUE) {
            status = BT_MESSAGE_ITERATOR_CLASS_NEXT_METHOD_STATUS_END;
            goto end;
        } else {
            /*
             * The are no more active session for this session
             * name. Retry to create a viewer session for the
             * requested session name.
             */
            viewer_status = lttng_live_create_viewer_session(lttng_live_msg_iter);
            if (viewer_status != LTTNG_LIVE_VIEWER_STATUS_OK) {
                if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_ERROR) {
                    status = BT_MESSAGE_ITERATOR_CLASS_NEXT_METHOD_STATUS_ERROR;
                    BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                                 "Error creating LTTng live viewer session");
                } else if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_INTERRUPTED) {
                    status = BT_MESSAGE_ITERATOR_CLASS_NEXT_METHOD_STATUS_AGAIN;
                } else {
                    bt_common_abort();
                }
                goto end;
            }
        }
    }

    if (lttng_live_msg_iter->active_stream_iter == 0) {
        lttng_live_force_new_streams_and_metadata(lttng_live_msg_iter);
    }

    /*
     * Here the muxing of message is done.
     *
     * We need to iterate over all the streams of all the traces of all the
     * viewer sessions in order to get the message with the smallest
     * timestamp. In this case, a session is a viewer session and there is
     * one viewer session per consumer daemon. (UST 32bit, UST 64bit and/or
     * kernel). Each viewer session can have multiple traces, for example,
     * 64bit UST viewer sessions could have multiple per-pid traces.
     *
     * We iterate over the streams of each traces to update and see what is
     * their next message's timestamp. From those timestamps, we select the
     * message with the smallest timestamp as the best candidate message
     * for that trace and do the same thing across all the sessions.
     *
     * We then compare the timestamp of best candidate message of all the
     * sessions to pick the message with the smallest timestamp and we
     * return it.
     */
    while (*count < capacity) {
        struct lttng_live_stream_iterator *youngest_stream_iter = NULL,
                                          *candidate_stream_iter = NULL;
        int64_t youngest_msg_ts_ns = INT64_MAX;

        BT_ASSERT_DBG(lttng_live_msg_iter->sessions);
        session_idx = 0;
        while (session_idx < lttng_live_msg_iter->sessions->len) {
            struct lttng_live_session *session = (lttng_live_session *) g_ptr_array_index(
                lttng_live_msg_iter->sessions, session_idx);

            /* Find the best candidate message to send downstream. */
            stream_iter_status = next_stream_iterator_for_session(lttng_live_msg_iter, session,
                                                                  &candidate_stream_iter);

            /* If we receive an END status, it means that either:
             * - Those traces never had active streams (UST with no
             *   data produced yet),
             * - All live stream iterators have ENDed.*/
            if (stream_iter_status == LTTNG_LIVE_ITERATOR_STATUS_END) {
                if (session->closed && session->traces->len == 0) {
                    /*
                     * Remove the session from the list.
                     * session_idx is not modified since
                     * g_ptr_array_remove_index_fast
                     * replaces the the removed element with
                     * the array's last element.
                     */
                    g_ptr_array_remove_index_fast(lttng_live_msg_iter->sessions, session_idx);
                } else {
                    session_idx++;
                }
                continue;
            }

            if (stream_iter_status != LTTNG_LIVE_ITERATOR_STATUS_OK) {
                goto return_status;
            }

            if (G_UNLIKELY(youngest_stream_iter == NULL) ||
                candidate_stream_iter->current_msg_ts_ns < youngest_msg_ts_ns) {
                youngest_msg_ts_ns = candidate_stream_iter->current_msg_ts_ns;
                youngest_stream_iter = candidate_stream_iter;
            } else if (candidate_stream_iter->current_msg_ts_ns == youngest_msg_ts_ns) {
                /*
                 * The currently selected message to be sent
                 * downstream next has the exact same timestamp
                 * that of the current candidate message. We
                 * must break the tie in a predictable manner.
                 */
                BT_CPPLOGD_STR_SPEC(
                    lttng_live_msg_iter->logger,
                    "Two of the next message candidates have the same timestamps, pick one deterministically.");
                /*
                 * Order the messages in an arbitrary but
                 * deterministic way.
                 */
                int ret = common_muxing_compare_messages(candidate_stream_iter->current_msg,
                                                         youngest_stream_iter->current_msg);
                if (ret < 0) {
                    /*
                     * The `candidate_stream_iter->current_msg`
                     * should go first. Update the next
                     * iterator and the current timestamp.
                     */
                    youngest_msg_ts_ns = candidate_stream_iter->current_msg_ts_ns;
                    youngest_stream_iter = candidate_stream_iter;
                } else if (ret == 0) {
                    /* Unable to pick which one should go first. */
                    BT_CPPLOGW_SPEC(
                        lttng_live_msg_iter->logger,
                        "Cannot deterministically pick next live stream message iterator because they have identical next messages: "
                        "next-stream-iter-addr={}"
                        "candidate-stream-iter-addr={}",
                        fmt::ptr(youngest_stream_iter), fmt::ptr(candidate_stream_iter));
                }
            }

            session_idx++;
        }

        if (!youngest_stream_iter) {
            stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_AGAIN;
            goto return_status;
        }

        BT_ASSERT_DBG(youngest_stream_iter->current_msg);
        /* Ensure monotonicity. */
        BT_ASSERT_DBG(lttng_live_msg_iter->last_msg_ts_ns <=
                      youngest_stream_iter->current_msg_ts_ns);

        /*
         * Insert the next message to the message batch. This will set
         * stream iterator current message to NULL so that next time
         * we fetch the next message of that stream iterator
         */
        BT_MESSAGE_MOVE_REF(msgs[*count], youngest_stream_iter->current_msg);
        (*count)++;

        /* Update the last timestamp in nanoseconds sent downstream. */
        lttng_live_msg_iter->last_msg_ts_ns = youngest_msg_ts_ns;
        youngest_stream_iter->current_msg_ts_ns = INT64_MAX;

        stream_iter_status = LTTNG_LIVE_ITERATOR_STATUS_OK;
    }

return_status:
    switch (stream_iter_status) {
    case LTTNG_LIVE_ITERATOR_STATUS_OK:
    case LTTNG_LIVE_ITERATOR_STATUS_AGAIN:
        /*
         * If we gathered messages, return _OK even if the graph was
         * interrupted. This allows for the components downstream to at
         * least get the those messages. If the graph was indeed
         * interrupted there should not be another _next() call as the
         * application will tear down the graph. This component class
         * doesn't support restarting after an interruption.
         */
        if (*count > 0) {
            status = BT_MESSAGE_ITERATOR_CLASS_NEXT_METHOD_STATUS_OK;
        } else {
            status = BT_MESSAGE_ITERATOR_CLASS_NEXT_METHOD_STATUS_AGAIN;
        }
        break;
    case LTTNG_LIVE_ITERATOR_STATUS_END:
        status = BT_MESSAGE_ITERATOR_CLASS_NEXT_METHOD_STATUS_END;
        break;
    case LTTNG_LIVE_ITERATOR_STATUS_NOMEM:
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Memory error preparing the next batch of messages: "
                                     "live-iter-status={}",
                                     stream_iter_status);
        status = BT_MESSAGE_ITERATOR_CLASS_NEXT_METHOD_STATUS_MEMORY_ERROR;
        break;
    case LTTNG_LIVE_ITERATOR_STATUS_ERROR:
    case LTTNG_LIVE_ITERATOR_STATUS_INVAL:
    case LTTNG_LIVE_ITERATOR_STATUS_UNSUPPORTED:
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                     "Error preparing the next batch of messages: "
                                     "live-iter-status={}",
                                     stream_iter_status);

        status = BT_MESSAGE_ITERATOR_CLASS_NEXT_METHOD_STATUS_ERROR;
        /* Put all existing messages on error. */
        put_messages(msgs, *count);
        break;
    default:
        bt_common_abort();
    }

end:
    return status;
}

static struct lttng_live_msg_iter *
lttng_live_msg_iter_create(struct lttng_live_component *lttng_live_comp,
                           bt_self_message_iterator *self_msg_it)
{
    lttng_live_msg_iter *msg_iter = new lttng_live_msg_iter {lttng_live_comp->logger};
    msg_iter->self_comp = lttng_live_comp->self_comp;
    msg_iter->lttng_live_comp = lttng_live_comp;
    msg_iter->self_msg_iter = self_msg_it;

    msg_iter->active_stream_iter = 0;
    msg_iter->last_msg_ts_ns = INT64_MIN;
    msg_iter->was_interrupted = false;

    msg_iter->sessions =
        g_ptr_array_new_with_free_func((GDestroyNotify) lttng_live_destroy_session);
    BT_ASSERT(msg_iter->sessions);

    return msg_iter;
}

bt_message_iterator_class_initialize_method_status
lttng_live_msg_iter_init(bt_self_message_iterator *self_msg_it,
                         bt_self_message_iterator_configuration *, bt_self_component_port_output *)
{
    bt_message_iterator_class_initialize_method_status status;
    struct lttng_live_component *lttng_live;
    struct lttng_live_msg_iter *lttng_live_msg_iter;
    enum lttng_live_viewer_status viewer_status;
    bt_self_component *self_comp = bt_self_message_iterator_borrow_component(self_msg_it);

    lttng_live = (lttng_live_component *) bt_self_component_get_data(self_comp);

    /* There can be only one downstream iterator at the same time. */
    BT_ASSERT(!lttng_live->has_msg_iter);
    lttng_live->has_msg_iter = true;

    lttng_live_msg_iter = lttng_live_msg_iter_create(lttng_live, self_msg_it);
    if (!lttng_live_msg_iter) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live->logger, "Failed to create lttng_live_msg_iter");
        status = BT_MESSAGE_ITERATOR_CLASS_INITIALIZE_METHOD_STATUS_MEMORY_ERROR;
        goto error;
    }

    viewer_status = live_viewer_connection_create(lttng_live->params.url->str, false,
                                                  lttng_live_msg_iter, lttng_live_msg_iter->logger,
                                                  &lttng_live_msg_iter->viewer_connection);
    if (viewer_status != LTTNG_LIVE_VIEWER_STATUS_OK) {
        if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_ERROR) {
            BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                         "Failed to create viewer connection");
        } else if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_INTERRUPTED) {
            /*
             * Interruption in the _iter_init() method is not
             * supported. Return an error.
             */
            BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                         "Interrupted while creating viewer connection");
        }

        status = BT_MESSAGE_ITERATOR_CLASS_INITIALIZE_METHOD_STATUS_ERROR;
        goto error;
    }

    viewer_status = lttng_live_create_viewer_session(lttng_live_msg_iter);
    if (viewer_status != LTTNG_LIVE_VIEWER_STATUS_OK) {
        if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_ERROR) {
            BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                         "Failed to create viewer session");
        } else if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_INTERRUPTED) {
            /*
             * Interruption in the _iter_init() method is not
             * supported. Return an error.
             */
            BT_CPPLOGE_APPEND_CAUSE_SPEC(lttng_live_msg_iter->logger,
                                         "Interrupted when creating viewer session");
        }

        status = BT_MESSAGE_ITERATOR_CLASS_INITIALIZE_METHOD_STATUS_ERROR;
        goto error;
    }

    if (lttng_live_msg_iter->sessions->len == 0) {
        switch (lttng_live->params.sess_not_found_act) {
        case SESSION_NOT_FOUND_ACTION_CONTINUE:
            BT_CPPLOGI_SPEC(
                lttng_live_msg_iter->logger,
                "Unable to connect to the requested live viewer session. Keep "
                "trying to connect because of {}=\"{}\" component parameter: url=\"{}\"",
                SESS_NOT_FOUND_ACTION_PARAM, SESS_NOT_FOUND_ACTION_CONTINUE_STR,
                lttng_live->params.url->str);
            break;
        case SESSION_NOT_FOUND_ACTION_FAIL:
            BT_CPPLOGE_APPEND_CAUSE_SPEC(
                lttng_live_msg_iter->logger,
                "Unable to connect to the requested live viewer session. Fail "
                "the message iterator initialization because of {}=\"{}\" "
                "component parameter: url =\"{}\"",
                SESS_NOT_FOUND_ACTION_PARAM, SESS_NOT_FOUND_ACTION_FAIL_STR,
                lttng_live->params.url->str);
            status = BT_MESSAGE_ITERATOR_CLASS_INITIALIZE_METHOD_STATUS_ERROR;
            goto error;
        case SESSION_NOT_FOUND_ACTION_END:
            BT_CPPLOGI_SPEC(
                lttng_live_msg_iter->logger,
                "Unable to connect to the requested live viewer session. End gracefully at the first _next() "
                "call because of {}=\"{}\" component parameter: "
                "url=\"{}\"",
                SESS_NOT_FOUND_ACTION_PARAM, SESS_NOT_FOUND_ACTION_END_STR,
                lttng_live->params.url->str);
            break;
        default:
            bt_common_abort();
        }
    }

    bt_self_message_iterator_set_data(self_msg_it, lttng_live_msg_iter);
    status = BT_MESSAGE_ITERATOR_CLASS_INITIALIZE_METHOD_STATUS_OK;
    goto end;

error:
    lttng_live_msg_iter_destroy(lttng_live_msg_iter);
end:
    return status;
}

static struct bt_param_validation_map_value_entry_descr list_sessions_params[] = {
    {URL_PARAM, BT_PARAM_VALIDATION_MAP_VALUE_ENTRY_MANDATORY,
     bt_param_validation_value_descr::makeString()},
    BT_PARAM_VALIDATION_MAP_VALUE_ENTRY_END};

static bt_component_class_query_method_status
lttng_live_query_list_sessions(const bt_value *params, const bt_value **result,
                               const bt2c::Logger& logger)
{
    bt_component_class_query_method_status status;
    const bt_value *url_value = NULL;
    const char *url;
    struct live_viewer_connection *viewer_connection = NULL;
    enum lttng_live_viewer_status viewer_status;
    enum bt_param_validation_status validation_status;
    gchar *validate_error = NULL;

    validation_status = bt_param_validation_validate(params, list_sessions_params, &validate_error);
    if (validation_status == BT_PARAM_VALIDATION_STATUS_MEMORY_ERROR) {
        status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_MEMORY_ERROR;
        goto error;
    } else if (validation_status == BT_PARAM_VALIDATION_STATUS_VALIDATION_ERROR) {
        status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_ERROR;
        BT_CPPLOGE_APPEND_CAUSE_SPEC(logger, "{}", validate_error);
        goto error;
    }

    url_value = bt_value_map_borrow_entry_value_const(params, URL_PARAM);
    url = bt_value_string_get(url_value);

    viewer_status = live_viewer_connection_create(url, true, NULL, logger, &viewer_connection);
    if (viewer_status != LTTNG_LIVE_VIEWER_STATUS_OK) {
        if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_ERROR) {
            BT_CPPLOGE_APPEND_CAUSE_SPEC(logger, "Failed to create viewer connection");
            status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_ERROR;
        } else if (viewer_status == LTTNG_LIVE_VIEWER_STATUS_INTERRUPTED) {
            status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_AGAIN;
        } else {
            bt_common_abort();
        }
        goto error;
    }

    status = live_viewer_connection_list_sessions(viewer_connection, result);
    if (status != BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_OK) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(logger, "Failed to list viewer sessions");
        goto error;
    }

    goto end;

error:
    BT_VALUE_PUT_REF_AND_RESET(*result);

    if (status >= 0) {
        status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_ERROR;
    }

end:
    if (viewer_connection) {
        live_viewer_connection_destroy(viewer_connection);
    }

    g_free(validate_error);

    return status;
}

static bt_component_class_query_method_status
lttng_live_query_support_info(const bt_value *params, const bt_value **result,
                              const bt2c::Logger& logger)
{
    bt_component_class_query_method_status status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_OK;
    const bt_value *input_type_value;
    const bt_value *input_value;
    double weight = 0;
    struct bt_common_lttng_live_url_parts parts = {};

    /* Used by the logging macros */
    __attribute__((unused)) bt_self_component *self_comp = NULL;

    *result = NULL;
    input_type_value = bt_value_map_borrow_entry_value_const(params, "type");
    if (!input_type_value) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(logger, "Missing expected `type` parameter.");
        goto error;
    }

    if (!bt_value_is_string(input_type_value)) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(logger, "`type` parameter is not a string value.");
        goto error;
    }

    if (strcmp(bt_value_string_get(input_type_value), "string") != 0) {
        /* We don't handle file system paths */
        goto create_result;
    }

    input_value = bt_value_map_borrow_entry_value_const(params, "input");
    if (!input_value) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(logger, "Missing expected `input` parameter.");
        goto error;
    }

    if (!bt_value_is_string(input_value)) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(logger, "`input` parameter is not a string value.");
        goto error;
    }

    parts = bt_common_parse_lttng_live_url(bt_value_string_get(input_value), NULL, 0);
    if (parts.session_name) {
        /*
         * Looks pretty much like an LTTng live URL: we got the
         * session name part, which forms a complete URL.
         */
        weight = .75;
    }

create_result:
    *result = bt_value_real_create_init(weight);
    if (!*result) {
        status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_MEMORY_ERROR;
        goto error;
    }

    goto end;

error:
    if (status >= 0) {
        status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_ERROR;
    }

    BT_ASSERT(!*result);

end:
    bt_common_destroy_lttng_live_url_parts(&parts);
    return status;
}

bt_component_class_query_method_status lttng_live_query(bt_self_component_class_source *comp_class,
                                                        bt_private_query_executor *priv_query_exec,
                                                        const char *object, const bt_value *params,
                                                        __attribute__((unused)) void *method_data,
                                                        const bt_value **result)
{
    bt_component_class_query_method_status status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_OK;
    bt2c::Logger logger {bt2::SelfComponentClass {comp_class},
                         bt2::PrivateQueryExecutor {priv_query_exec},
                         "PLUGIN/SRC.CTF.LTTNG-LIVE/QUERY"};

    if (strcmp(object, "sessions") == 0) {
        status = lttng_live_query_list_sessions(params, result, logger);
    } else if (strcmp(object, "babeltrace.support-info") == 0) {
        status = lttng_live_query_support_info(params, result, logger);
    } else {
        BT_CPPLOGI_SPEC(logger, "Unknown query object `{}`", object);
        status = BT_COMPONENT_CLASS_QUERY_METHOD_STATUS_UNKNOWN_OBJECT;
        goto end;
    }

end:
    return status;
}

static void lttng_live_component_destroy_data(struct lttng_live_component *lttng_live)
{
    if (!lttng_live) {
        return;
    }

    if (lttng_live->params.url) {
        g_string_free(lttng_live->params.url, TRUE);
    }

    delete lttng_live;
}

void lttng_live_component_finalize(bt_self_component_source *component)
{
    lttng_live_component *data = (lttng_live_component *) bt_self_component_get_data(
        bt_self_component_source_as_self_component(component));

    if (!data) {
        return;
    }
    lttng_live_component_destroy_data(data);
}

static enum session_not_found_action
parse_session_not_found_action_param(const bt_value *no_session_param)
{
    enum session_not_found_action action;
    const char *no_session_act_str = bt_value_string_get(no_session_param);

    if (strcmp(no_session_act_str, SESS_NOT_FOUND_ACTION_CONTINUE_STR) == 0) {
        action = SESSION_NOT_FOUND_ACTION_CONTINUE;
    } else if (strcmp(no_session_act_str, SESS_NOT_FOUND_ACTION_FAIL_STR) == 0) {
        action = SESSION_NOT_FOUND_ACTION_FAIL;
    } else {
        BT_ASSERT(strcmp(no_session_act_str, SESS_NOT_FOUND_ACTION_END_STR) == 0);
        action = SESSION_NOT_FOUND_ACTION_END;
    }

    return action;
}

static bt_param_validation_value_descr inputs_elem_descr =
    bt_param_validation_value_descr::makeString();

static const char *sess_not_found_action_choices[] = {
    SESS_NOT_FOUND_ACTION_CONTINUE_STR,
    SESS_NOT_FOUND_ACTION_FAIL_STR,
    SESS_NOT_FOUND_ACTION_END_STR,
};

static struct bt_param_validation_map_value_entry_descr params_descr[] = {
    {INPUTS_PARAM, BT_PARAM_VALIDATION_MAP_VALUE_ENTRY_MANDATORY,
     bt_param_validation_value_descr::makeArray(1, 1, inputs_elem_descr)},
    {SESS_NOT_FOUND_ACTION_PARAM, BT_PARAM_VALIDATION_MAP_VALUE_ENTRY_OPTIONAL,
     bt_param_validation_value_descr::makeString(sess_not_found_action_choices)},
    BT_PARAM_VALIDATION_MAP_VALUE_ENTRY_END};

static bt_component_class_initialize_method_status
lttng_live_component_create(const bt_value *params, bt_self_component_source *self_comp,
                            struct lttng_live_component **component)
{
    struct lttng_live_component *lttng_live = NULL;
    const bt_value *inputs_value;
    const bt_value *url_value;
    const bt_value *value;
    const char *url;
    enum bt_param_validation_status validation_status;
    gchar *validation_error = NULL;
    bt_component_class_initialize_method_status status;
    bt2c::Logger logger {bt2::SelfSourceComponent {self_comp}, "PLUGIN/SRC.CTF.LTTNG-LIVE/COMP"};

    validation_status = bt_param_validation_validate(params, params_descr, &validation_error);
    if (validation_status == BT_PARAM_VALIDATION_STATUS_MEMORY_ERROR) {
        status = BT_COMPONENT_CLASS_INITIALIZE_METHOD_STATUS_MEMORY_ERROR;
        goto error;
    } else if (validation_status == BT_PARAM_VALIDATION_STATUS_VALIDATION_ERROR) {
        BT_CPPLOGE_APPEND_CAUSE_SPEC(logger, "{}", validation_error);
        status = BT_COMPONENT_CLASS_INITIALIZE_METHOD_STATUS_ERROR;
        goto error;
    }

    lttng_live = new lttng_live_component {std::move(logger)};
    lttng_live->self_comp = bt_self_component_source_as_self_component(self_comp);
    lttng_live->max_query_size = MAX_QUERY_SIZE;
    lttng_live->has_msg_iter = false;

    inputs_value = bt_value_map_borrow_entry_value_const(params, INPUTS_PARAM);
    url_value = bt_value_array_borrow_element_by_index_const(inputs_value, 0);
    url = bt_value_string_get(url_value);

    lttng_live->params.url = g_string_new(url);
    if (!lttng_live->params.url) {
        status = BT_COMPONENT_CLASS_INITIALIZE_METHOD_STATUS_MEMORY_ERROR;
        goto error;
    }

    value = bt_value_map_borrow_entry_value_const(params, SESS_NOT_FOUND_ACTION_PARAM);
    if (value) {
        lttng_live->params.sess_not_found_act = parse_session_not_found_action_param(value);
    } else {
        BT_CPPLOGI_SPEC(lttng_live->logger,
                        "Optional `{}` parameter is missing: defaulting to `{}`.",
                        SESS_NOT_FOUND_ACTION_PARAM, SESS_NOT_FOUND_ACTION_CONTINUE_STR);
        lttng_live->params.sess_not_found_act = SESSION_NOT_FOUND_ACTION_CONTINUE;
    }

    status = BT_COMPONENT_CLASS_INITIALIZE_METHOD_STATUS_OK;
    goto end;

error:
    lttng_live_component_destroy_data(lttng_live);
    lttng_live = NULL;
end:
    g_free(validation_error);

    *component = lttng_live;
    return status;
}

bt_component_class_initialize_method_status
lttng_live_component_init(bt_self_component_source *self_comp_src,
                          bt_self_component_source_configuration *, const bt_value *params, void *)
{
    struct lttng_live_component *lttng_live;
    bt_component_class_initialize_method_status ret;
    bt_self_component *self_comp = bt_self_component_source_as_self_component(self_comp_src);
    bt_self_component_add_port_status add_port_status;

    ret = lttng_live_component_create(params, self_comp_src, &lttng_live);
    if (ret != BT_COMPONENT_CLASS_INITIALIZE_METHOD_STATUS_OK) {
        goto error;
    }

    add_port_status = bt_self_component_source_add_output_port(self_comp_src, "out", NULL, NULL);
    if (add_port_status != BT_SELF_COMPONENT_ADD_PORT_STATUS_OK) {
        ret = (bt_component_class_initialize_method_status) add_port_status;
        goto end;
    }

    bt_self_component_set_data(self_comp, lttng_live);
    goto end;

error:
    lttng_live_component_destroy_data(lttng_live);
    lttng_live = NULL;
end:
    return ret;
}