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nostrdb/query: extract ndb_cursor_start

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This is useful for positioning LMDB cursors at the start of a query. We
will be re-using this in the upcoming query code

Signed-off-by: William Casarin <jb55@jb55.com>
This commit is contained in:
William Casarin
2024-01-04 13:44:57 -08:00
committed by Daniel D’Aquino
parent 6dbf3416b9
commit 942e47a720
1 changed files with 23 additions and 11 deletions
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34
nostrdb/src/nostrdb.c
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@@ -1493,6 +1493,27 @@ int ndb_write_last_profile_fetch(struct ndb *ndb, const unsigned char *pubkey,
return ndb_writer_queue_msg(&ndb->writer, &msg);
}
// When doing cursor scans from greatest to lowest, this function positions the
// cursor at the first element before descending. MDB_SET_RANGE puts us right
// after the first element, so we have to go back one.
static int ndb_cursor_start(MDB_cursor *cur, MDB_val *k, MDB_val *v)
{
// Position cursor at the next key greater than or equal to the specified key
if (mdb_cursor_get(cur, k, v, MDB_SET_RANGE)) {
// Failed :(. It could be the last element?
if (mdb_cursor_get(cur, k, v, MDB_LAST))
return 0;
} else {
// if set range worked and our key exists, it should be
// the one right before this one
if (mdb_cursor_get(cur, k, v, MDB_PREV))
return 0;
}
return 1;
}
// get some value based on a clustered id key
int ndb_get_tsid(struct ndb_txn *txn, enum ndb_dbs db, const unsigned char *id,
MDB_val *val)
@@ -1513,17 +1534,8 @@ int ndb_get_tsid(struct ndb_txn *txn, enum ndb_dbs db, const unsigned char *id,
return 0;
}
// Position cursor at the next key greater than or equal to the specified key
if (mdb_cursor_get(cur, &k, &v, MDB_SET_RANGE)) {
// Failed :(. It could be the last element?
if (mdb_cursor_get(cur, &k, &v, MDB_LAST))
goto cleanup;
} else {
// if set range worked and our key exists, it should be
// the one right before this one
if (mdb_cursor_get(cur, &k, &v, MDB_PREV))
goto cleanup;
}
if (!ndb_cursor_start(cur, &k, &v))
goto cleanup;
if (memcmp(k.mv_data, id, 32) == 0) {
*val = v;