json: Add helper to decode sha256 hashes

common/json.c

@@ -225,6 +225,15 @@ bool json_to_bool(const char *buffer, const jsmntok_t *tok, bool *b)
 	return false;
 }
 
+bool json_to_sha256(const char *buffer, const jsmntok_t *tok, struct sha256 *dest)
+{
+	if (tok->type != JSMN_STRING)
+		return false;
+
+	return hex_decode(buffer + tok->start, tok->end - tok->start, dest,
+			  sizeof(struct sha256));
+}
+
 u8 *json_tok_bin_from_hex(const tal_t *ctx, const char *buffer, const jsmntok_t *tok)
 {
 	u8 *result;

common/json.h

@@ -1,6 +1,7 @@
 #ifndef LIGHTNING_COMMON_JSON_H
 #define LIGHTNING_COMMON_JSON_H
 #include "config.h"
+#include <ccan/crypto/sha256/sha256.h>
 #include <ccan/short_types/short_types.h>
 #include <ccan/tal/tal.h>
 #include <common/errcode.h>
@@ -50,6 +51,7 @@ bool json_to_u32(const char *buffer, const jsmntok_t *tok,
 bool json_to_u16(const char *buffer, const jsmntok_t *tok,
                  uint16_t *num);
 
+bool json_to_sha256(const char *buffer, const jsmntok_t *tok, struct sha256 *dest);
 /*
  * Extract a non-negative (either 0 or positive) floating-point number from this
  * (must be a number literal), multiply it by 1 million and return it as an