jsonrpc: make sure even errors are valid json.

We often quote their msg in our reply; sanitize it!

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

lightningd/jsonrpc.c

@@ -480,13 +480,13 @@ struct json_stream *json_stream_fail_nodata(struct command *cmd,
 					    const char *errmsg)
 {
 	struct json_stream *r = json_start(cmd);
+	struct json_escaped *e = json_partial_escape(tmpctx, errmsg);
 
 	assert(code);
-	assert(errmsg);
 
 	json_stream_append_fmt(r, " \"error\" : "
 			  "{ \"code\" : %d,"
-			  " \"message\" : \"%s\"", code, errmsg);
+			  " \"message\" : \"%s\"", code, e->s);
 	return r;
 }
 

tests/test_misc.py

@@ -1060,3 +1060,13 @@ def test_configfile_before_chdir(node_factory):
     assert l1.rpc.listconfigs()['always-use-proxy']
     assert l1.rpc.listconfigs()['proxy'] == '127.0.0.1:100'
     os.chdir(olddir)
+
+
+def test_json_error(node_factory):
+    """Must return valid json even if it quotes our weirdness"""
+    l1 = node_factory.get_node()
+    with pytest.raises(RpcError, match=r'Given id is not a channel ID or short channel ID'):
+        l1.rpc.close({"tx": "020000000001011490f737edd2ea2175a032b58ea7cd426dfc244c339cd044792096da3349b18a0100000000ffffffff021c900300000000001600140e64868e2f752314bc82a154c8c5bf32f3691bb74da00b00000000002200205b8cd3b914cf67cdd8fa6273c930353dd36476734fbd962102c2df53b90880cd0247304402202b2e3195a35dc694bbbc58942dc9ba59cc01d71ba55c9b0ad0610ccd6a65633702201a849254453d160205accc00843efb0ad1fe0e186efa6a7cee1fb6a1d36c736a012103d745445c9362665f22e0d96e9e766f273f3260dea39c8a76bfa05dd2684ddccf00000000", "txid": "2128c10f0355354479514f4a23eaa880d94e099406d419bbb0d800143accddbb", "channel_id": "bbddcc3a1400d8b0bb19d40694094ed980a8ea234a4f5179443555030fc12820"})
+
+    # Should not corrupt following RPC
+    l1.rpc.getinfo()