json: Add a helper to decode a hex-encoded value from JSON

Signed-off-by: Christian Decker <decker.christian@gmail.com>

common/json.c

@@ -128,6 +128,26 @@ bool json_to_bool(const char *buffer, const jsmntok_t *tok, bool *b)
 	return false;
 }
 
+u8 *json_tok_bin_from_hex(const tal_t *ctx, const char *buffer, const jsmntok_t *tok)
+{
+	u8 *result;
+	size_t hexlen, rawlen;
+	hexlen = tok->end - tok->start;
+	rawlen = hex_data_size(hexlen);
+
+	result = tal_arr(ctx, u8, rawlen);
+	if (!hex_decode(buffer + tok->start, hexlen, result, rawlen))
+		return tal_free(result);
+
+	return result;
+}
+
+bool json_to_preimage(const char *buffer, const jsmntok_t *tok, struct preimage *preimage)
+{
+	size_t hexlen = tok->end - tok->start;
+	return hex_decode(buffer + tok->start, hexlen, preimage->r, sizeof(preimage->r));
+}
+
 bool json_tok_is_num(const char *buffer, const jsmntok_t *tok)
 {
 	if (tok->type != JSMN_PRIMITIVE)

common/json.h

@@ -1,6 +1,7 @@
 #ifndef LIGHTNING_COMMON_JSON_H
 #define LIGHTNING_COMMON_JSON_H
 #include "config.h"
+#include <bitcoin/preimage.h>
 #include <ccan/tal/tal.h>
 #include <stdbool.h>
 #include <stdint.h>
@@ -21,6 +22,12 @@ bool json_tok_streq(const char *buffer, const jsmntok_t *tok, const char *str);
 /* Allocate a tal string copy */
 char *json_strdup(const tal_t *ctx, const char *buffer, const jsmntok_t *tok);
 
+/* Decode a hex-encoded binary */
+u8 *json_tok_bin_from_hex(const tal_t *ctx, const char *buffer, const jsmntok_t *tok);
+
+/* Decode a hex-encoded payment preimage */
+bool json_to_preimage(const char *buffer, const jsmntok_t *tok, struct preimage *preimage);
+
 /* Extract number from this (may be a string, or a number literal) */
 bool json_to_number(const char *buffer, const jsmntok_t *tok,
 		    unsigned int *num);