sqlite3_column_arr: helper to allocate and read an array from a blob.

We use it on the secrets array for the moment, but it's also useful
for remote_shutdown_scriptpubkey, as used in the next patch.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

wallet/db.c

@@ -452,6 +452,24 @@ void db_set_intvar(struct db *db, char *varname, s64 val)
 		    varname, val);
 }
 
+void *sqlite3_column_arr_(const tal_t *ctx, sqlite3_stmt *stmt, int col,
+			  size_t bytes, const char *label, const char *caller)
+{
+	size_t sourcelen = sqlite3_column_bytes(stmt, col);
+	void *p;
+
+	if (sqlite3_column_type(stmt, col) == SQLITE_NULL)
+		return NULL;
+
+	if (sourcelen % bytes != 0)
+		fatal("%s: column size %zu not a multiple of %s (%zu)",
+		      caller, sourcelen, label, bytes);
+
+	p = tal_alloc_arr_(ctx, bytes, sourcelen / bytes, false, true, label);
+	memcpy(p, sqlite3_column_blob(stmt, col), sourcelen);
+	return p;
+}
+
 bool sqlite3_bind_short_channel_id(sqlite3_stmt *stmt, int col,
 				   const struct short_channel_id *id)
 {
@@ -646,15 +664,7 @@ bool sqlite3_column_sha256_double(sqlite3_stmt *stmt, int col,  struct sha256_do
 struct secret *sqlite3_column_secrets(const tal_t *ctx,
 				      sqlite3_stmt *stmt, int col)
 {
-	struct secret *secrets;
+	return sqlite3_column_arr(ctx, stmt, col, struct secret);
-	size_t n = sqlite3_column_bytes(stmt, col) / sizeof(*secrets);
-
-	/* Must fit exactly */
-	assert(n * sizeof(struct secret) == sqlite3_column_bytes(stmt, col));
-	if (n == 0)
-		return NULL;
-	secrets = tal_arr(ctx, struct secret, n);
-	return memcpy(secrets, sqlite3_column_blob(stmt, col), tal_len(secrets));
 }
 
 bool sqlite3_bind_sha256_double(sqlite3_stmt *stmt, int col, const struct sha256_double *p)

wallet/db.h

@@ -113,6 +113,13 @@ bool db_exec_prepared_mayfail_(const char *caller,
 			       struct db *db,
 			       sqlite3_stmt *stmt);
 
+#define sqlite3_column_arr(ctx, stmt, col, type)			\
+	((type *)sqlite3_column_arr_((ctx), (stmt), (col),		\
+				     sizeof(type), TAL_LABEL(type, "[]"), \
+				     __func__))
+void *sqlite3_column_arr_(const tal_t *ctx, sqlite3_stmt *stmt, int col,
+			  size_t bytes, const char *label, const char *caller);
+
 bool sqlite3_bind_short_channel_id(sqlite3_stmt *stmt, int col,
 				   const struct short_channel_id *id);
 bool sqlite3_column_short_channel_id(sqlite3_stmt *stmt, int col,