json: Add two param functions to parse string arrs and outpoint arrs

In a couple of places we accept arrays of strings and don't validate
them. If we forward them, e.g., call a JSON-RPC method from the
plugin, we end up embedding the unverified string in the JSON-RPC
call without escaping, which then leads to invalid JSON being passed
on.

This at least partially causes ElementsProject#4238

bitcoin/tx.h

@@ -21,6 +21,12 @@ struct wally_psbt;
 struct bitcoin_txid {
 	struct sha256_double shad;
 };
+
+struct bitcoin_outpoint {
+	struct bitcoin_txid txid;
+	u16 n;
+};
+
 /* Define bitcoin_txid_eq */
 STRUCTEQ_DEF(bitcoin_txid, 0, shad.sha.u);
 

common/json_helpers.c

@@ -93,6 +93,31 @@ bool json_to_txid(const char *buffer, const jsmntok_t *tok,
 				     tok->end - tok->start, txid);
 }
 
+bool json_to_outpoint(const char *buffer, const jsmntok_t *tok,
+		      struct bitcoin_outpoint *op)
+{
+	size_t len = tok->end - tok->start;
+	char str[len + 1];
+
+	if (len < 66)
+		return NULL;
+
+	memcpy(str, buffer+tok->start, len);
+	str[len] = 0x00;
+
+	if (str[64] != ':')
+		return NULL;
+
+	if (!bitcoin_txid_from_hex(str, 64, &op->txid))
+		return false;
+
+	op->n = atoi(str + 65);
+	if (op->n < 0)
+		return false;
+
+	return true;
+}
+
 bool json_to_channel_id(const char *buffer, const jsmntok_t *tok,
 			struct channel_id *cid)
 {

common/json_helpers.h

@@ -62,6 +62,10 @@ bool json_to_msat(const char *buffer, const jsmntok_t *tok,
 bool json_to_txid(const char *buffer, const jsmntok_t *tok,
 		  struct bitcoin_txid *txid);
 
+/* Extract a bitcoin outpoint from this */
+bool json_to_outpoint(const char *buffer, const jsmntok_t *tok,
+		      struct bitcoin_outpoint *op);
+
 /* Extract a channel id from this */
 bool json_to_channel_id(const char *buffer, const jsmntok_t *tok,
 			struct channel_id *cid);

common/json_tok.c

@@ -501,3 +501,32 @@ struct command_result *param_psbt(struct command *cmd,
 	return command_fail_badparam(cmd, name, buffer, tok,
 				     "Expected a PSBT");
 }
+
+struct command_result *param_outpoint_arr(struct command *cmd,
+					  const char *name,
+					  const char *buffer,
+					  const jsmntok_t *tok,
+					  struct bitcoin_outpoint **outpoints)
+{
+	size_t i;
+	const jsmntok_t *curr;
+	if (tok->type != JSMN_ARRAY) {
+		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+				    "Could not decode the outpoint array for %s: "
+				    "\"%s\" is not a valid outpoint array.",
+				    name, json_strdup(tmpctx, buffer, tok));
+	}
+
+	*outpoints = tal_arr(cmd, struct bitcoin_outpoint, tok->size);
+
+	json_for_each_arr(i, curr, tok) {
+		struct bitcoin_outpoint op;
+		if (!json_to_outpoint(buffer, curr, &op))
+			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+					    "Could not decode outpoint \"%.*s\", "
+					    "expected format: txid:output",
+					    json_tok_full_len(curr), json_tok_full(buffer, curr));
+		(*outpoints)[i] = op;
+	}
+	return NULL;
+}

common/json_tok.h

@@ -11,6 +11,7 @@
 struct amount_msat;
 struct amount_sat;
 struct bitcoin_txid;
+struct bitcoin_outpoint;
 struct channel_id;
 struct command;
 struct command_result;
@@ -172,4 +173,13 @@ struct command_result *param_psbt(struct command *cmd,
 				  const char *buffer,
 				  const jsmntok_t *tok,
 				  struct wally_psbt **psbt);
+
+/**
+ * Parse a list of `txid:output` outpoints.
+ */
+struct command_result *param_outpoint_arr(struct command *cmd,
+					  const char *name,
+					  const char *buffer,
+					  const jsmntok_t *tok,
+					  struct bitcoin_outpoint **outpoints);
 #endif /* LIGHTNING_COMMON_JSON_TOK_H */

common/test/run-param.c

@@ -52,6 +52,10 @@ bool json_to_channel_id(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEED
 bool json_to_node_id(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
 			       struct node_id *id UNNEEDED)
 { fprintf(stderr, "json_to_node_id called!\n"); abort(); }
+/* Generated stub for json_to_outpoint */
+bool json_to_outpoint(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
+		      struct bitcoin_outpoint *op UNNEEDED)
+{ fprintf(stderr, "json_to_outpoint called!\n"); abort(); }
 /* Generated stub for json_to_pubkey */
 bool json_to_pubkey(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
 		    struct pubkey *pubkey UNNEEDED)