db: Add a hexval helper to decode hex values from db into fields

This is going to be handy pretty soon. Channels are almost fully
blobs...

wallet/db.c

@@ -3,6 +3,7 @@
 #include "daemon/log.h"
 #include "lightningd/lightningd.h"
 
+#include <ccan/str/hex/hex.h>
 #include <ccan/tal/str/str.h>
 #include <ccan/tal/tal.h>
 #include <inttypes.h>
@@ -329,3 +330,12 @@ bool db_set_intvar(struct db *db, char *varname, s64 val)
 		    "');",
 		    varname, val);
 }
+
+bool sqlite3_column_hexval(sqlite3_stmt *s, int col, void *dest, size_t destlen)
+{
+	const char *source = sqlite3_column_blob(s, col);
+	size_t sourcelen = sqlite3_column_bytes(s, col);
+	if (sourcelen / 2 != destlen)
+		return false;
+	return hex_decode(source, sourcelen, dest, destlen);
+}

wallet/db.h

@@ -73,4 +73,10 @@ bool db_set_intvar(struct db *db, char *varname, s64 val);
  */
 s64 db_get_intvar(struct db *db, char *varname, s64 defval);
 
+/**
+ * sqlite3_column_hexval - Helper to populate a binary field from a hex value
+ */
+bool sqlite3_column_hexval(sqlite3_stmt *s, int col, void *dest,
+			   size_t destlen);
+
 #endif /* WALLET_DB_H */

wallet/wallet.c

@@ -335,9 +335,8 @@ bool wallet_shachain_load(struct wallet *wallet, u64 id,
 	while (sqlite3_step(stmt) == SQLITE_ROW) {
 		int pos = sqlite3_column_int(stmt, 2);
 		chain->chain.known[pos].index = sqlite3_column_int64(stmt, 0);
-		hex_decode(
+		sqlite3_column_hexval(stmt, 1, &chain->chain.known[pos].hash,
-		    sqlite3_column_blob(stmt, 1), sqlite3_column_bytes(stmt, 1),
+				      sizeof(struct sha256));
-		    &chain->chain.known[pos].hash, sizeof(struct sha256));
 	}
 	sqlite3_finalize(stmt);