sql: rewrite scid string literals to use scid() for index support

When users query with WHERE in_channel='735095x480x1', the string
literal is compared directly against the integer SCID column, forcing
SQLite to perform a full table scan even when an index exists.

Automatically rewrite scid string literals (matching NNNxNNNxNNN format)
to use the scid() function before passing the query to SQLite, so
'735095x480x1' becomes scid('735095x480x1'). This allows SQLite to
use indexes on SCID columns transparently.

Queries already using scid() explicitly are detected and left unchanged.

Changelog-Fixed: sql plugin now automatically translates short_channel_id string literals to integers for efficient index usage.
Fixes: #8941

Author: vincenzopalazzo

plugins/sql.c

@@ -1322,6 +1322,63 @@ static struct command_result *refresh_tables(struct command *cmd,
 	return td->refresh(cmd, dbq->tables[0], dbq);
 }
 
+/* Check if a string is a valid short_channel_id (NNNxNNNxNNN format) */
+static bool looks_like_scid(const char *str, size_t len)
+{
+	struct short_channel_id scid;
+
+	return short_channel_id_from_str(str, len, &scid);
+}
+
+/* Rewrite SQL query to wrap scid string literals with scid() function.
+ * This transforms '735095x480x1' into scid('735095x480x1') so that
+ * SQLite can use indexes on integer SCID columns. */
+static const char *rewrite_scid_literals(const tal_t *ctx, const char *query)
+{
+	char *result = tal_strdup(ctx, "");
+	const char *p = query;
+
+	while (*p) {
+		/* Look for single-quoted string literals */
+		if (*p == '\'') {
+			const char *start = p + 1;
+			const char *end = strchr(start, '\'');
+
+			if (!end) {
+				/* Unterminated quote, just copy rest */
+				tal_append_fmt(&result, "%s", p);
+				break;
+			}
+
+			if (looks_like_scid(start, end - start)) {
+				/* Check if already wrapped in scid() by looking
+				 * back for "scid(" before the quote */
+				bool already_wrapped = false;
+				if (p - query >= 5) {
+					const char *before = p - 5;
+					if (strncmp(before, "scid(", 5) == 0)
+						already_wrapped = true;
+				}
+				if (!already_wrapped) {
+					tal_append_fmt(&result, "scid('%.*s')",
+						       (int)(end - start), start);
+					p = end + 1;
+					continue;
+				}
+			}
+			/* Not a scid or already wrapped: copy quote and content */
+			tal_append_fmt(&result, "%.*s",
+				       (int)(end - p + 1), p);
+			p = end + 1;
+		} else {
+			tal_append_fmt(&result, "%c", *p);
+			p++;
+		}
+	}
+
+	return result;
+}
+
 static struct command_result *json_sql(struct command *cmd,
 				       const char *buffer,
 				       const jsmntok_t *params)
@@ -1336,6 +1393,10 @@ static struct command_result *json_sql(struct command *cmd,
 		   NULL))
 		return command_param_failed();
 
+	/* Rewrite scid string literals to use scid() function so
+	 * SQLite can use indexes on integer SCID columns. */
+	query = rewrite_scid_literals(tmpctx, query);
+
 	dbq->tables = tal_arr(dbq, struct table_desc *, 0);
 	dbq->authfail = NULL;
 	dbq->cmd = cmd;