int streamIteratorGetID(streamIterator *si, streamID *id, int64_t *numfields) {
    while(1) { /* Will stop when element > stop_key or end of radix tree. */
        /* If the current listpack is set to NULL, this is the start of the
         * iteration or the previous listpack was completely iterated.
         * Go to the next node. */
        if (si->lp == NULL || si->lp_ele == NULL) {
            if (!si->rev && !raxNext(&si->ri)) return 0;
            else if (si->rev && !raxPrev(&si->ri)) return 0;
            serverAssert(si->ri.key_len == sizeof(streamID));
            /* Get the master ID. */
            streamDecodeID(si->ri.key,&si->master_id);
            /* Get the master fields count. */
            si->lp = si->ri.data;
            si->lp_ele = lpFirst(si->lp);           /* Seek items count */
            si->lp_ele = lpNext(si->lp,si->lp_ele); /* Seek deleted count. */
            si->lp_ele = lpNext(si->lp,si->lp_ele); /* Seek num fields. */
            si->master_fields_count = lpGetInteger(si->lp_ele);
            si->lp_ele = lpNext(si->lp,si->lp_ele); /* Seek first field. */
            si->master_fields_start = si->lp_ele;
            /* We are now pointing to the first field of the master entry.
             * We need to seek either the first or the last entry depending
             * on the direction of the iteration. */
            if (!si->rev) {
                /* If we are iterating in normal order, skip the master fields
                 * to seek the first actual entry. */
                for (uint64_t i = 0; i < si->master_fields_count; i++)
                    si->lp_ele = lpNext(si->lp,si->lp_ele);
            } else {
                /* If we are iterating in reverse direction, just seek the
                 * last part of the last entry in the listpack (that is, the
                 * fields count). */
                si->lp_ele = lpLast(si->lp);
            }
        } else if (si->rev) {
            /* If we are iterating in the reverse order, and this is not
             * the first entry emitted for this listpack, then we already
             * emitted the current entry, and have to go back to the previous
             * one. */
            int lp_count = lpGetInteger(si->lp_ele);
            while(lp_count--) si->lp_ele = lpPrev(si->lp,si->lp_ele);
            /* Seek lp-count of prev entry. */
            si->lp_ele = lpPrev(si->lp,si->lp_ele);
        }

        /* For every radix tree node, iterate the corresponding listpack,
         * returning elements when they are within range. */
        while(1) {
            if (!si->rev) {
                /* If we are going forward, skip the previous entry
                 * lp-count field (or in case of the master entry, the zero
                 * term field) */
                si->lp_ele = lpNext(si->lp,si->lp_ele);
                if (si->lp_ele == NULL) break;
            } else {
                /* If we are going backward, read the number of elements this
                 * entry is composed of, and jump backward N times to seek
                 * its start. */
                int64_t lp_count = lpGetInteger(si->lp_ele);
                if (lp_count == 0) { /* We reached the master entry. */
                    si->lp = NULL;
                    si->lp_ele = NULL;
                    break;
                }
                while(lp_count--) si->lp_ele = lpPrev(si->lp,si->lp_ele);
            }

            /* Get the flags entry. */
            si->lp_flags = si->lp_ele;
            int flags = lpGetInteger(si->lp_ele);
            si->lp_ele = lpNext(si->lp,si->lp_ele); /* Seek ID. */

            /* Get the ID: it is encoded as difference between the master
             * ID and this entry ID. */
            *id = si->master_id;
            id->ms += lpGetInteger(si->lp_ele);
            si->lp_ele = lpNext(si->lp,si->lp_ele);
            id->seq += lpGetInteger(si->lp_ele);
            si->lp_ele = lpNext(si->lp,si->lp_ele);
            unsigned char buf[sizeof(streamID)];
            streamEncodeID(buf,id);

            /* The number of entries is here or not depending on the
             * flags. */
            if (flags & STREAM_ITEM_FLAG_SAMEFIELDS) {
                *numfields = si->master_fields_count;
            } else {
                *numfields = lpGetInteger(si->lp_ele);
                si->lp_ele = lpNext(si->lp,si->lp_ele);
            }

            /* If current >= start, and the entry is not marked as
             * deleted, emit it. */
            if (!si->rev) {
                if (memcmp(buf,si->start_key,sizeof(streamID)) >= 0 &&
                    !(flags & STREAM_ITEM_FLAG_DELETED))
                {
                    if (memcmp(buf,si->end_key,sizeof(streamID)) > 0)
                        return 0; /* We are already out of range. */
                    si->entry_flags = flags;
                    if (flags & STREAM_ITEM_FLAG_SAMEFIELDS)
                        si->master_fields_ptr = si->master_fields_start;
                    return 1; /* Valid item returned. */
                }
            } else {
                if (memcmp(buf,si->end_key,sizeof(streamID)) <= 0 &&
                    !(flags & STREAM_ITEM_FLAG_DELETED))
                {
                    if (memcmp(buf,si->start_key,sizeof(streamID)) < 0)
                        return 0; /* We are already out of range. */
                    si->entry_flags = flags;
                    if (flags & STREAM_ITEM_FLAG_SAMEFIELDS)
                        si->master_fields_ptr = si->master_fields_start;
                    return 1; /* Valid item returned. */
                }
            }

            /* If we do not emit, we have to discard if we are going
             * forward, or seek the previous entry if we are going
             * backward. */
            if (!si->rev) {
                int64_t to_discard = (flags & STREAM_ITEM_FLAG_SAMEFIELDS) ?
                                      *numfields : *numfields*2;
                for (int64_t i = 0; i < to_discard; i++)
                    si->lp_ele = lpNext(si->lp,si->lp_ele);
            } else {
                int64_t prev_times = 4; /* flag + id ms + id seq + one more to
                                           go back to the previous entry "count"
                                           field. */
                /* If the entry was not flagged SAMEFIELD we also read the
                 * number of fields, so go back one more. */
                if (!(flags & STREAM_ITEM_FLAG_SAMEFIELDS)) prev_times++;
                while(prev_times--) si->lp_ele = lpPrev(si->lp,si->lp_ele);
            }
        }

        /* End of listpack reached. Try the next/prev radix tree node. */
    }
}