common/json_stream: add generic double-cr helper.

And make caller of json_stream_forward_change_id use it, since
we're going to reuse that.

Also call json_out_finished here, so next object doesn't have a ","
prepended.

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

common/json_stream.c

@@ -82,6 +82,31 @@ void json_stream_append(struct json_stream *js,
 	memcpy(dest, str, len);
 }
 
+/* We promise it will end in '\n\n' */
+void json_stream_double_cr(struct json_stream *js)
+{
+	const char *contents;
+	size_t len, cr_needed;
+
+	if (!js->jout)
+		return;
+
+	/* Must be well-formed at this point! */
+	json_out_finished(js->jout);
+
+	contents = json_out_contents(js->jout, &len);
+	/* It's an object (with an id!): definitely can't be less that "{}" */
+	assert(len >= 2);
+	if (contents[len-1] == '\n') {
+		if (contents[len-2] == '\n')
+			return;
+		cr_needed = 1;
+	} else
+		cr_needed = 2;
+
+	json_stream_append(js, "\n\n", cr_needed);
+}
+
 void json_stream_close(struct json_stream *js, struct command *writer)
 {
 	/* FIXME: We use writer == NULL for malformed: make writer a void *?
@@ -89,8 +114,7 @@ void json_stream_close(struct json_stream *js, struct command *writer)
 	assert(js->writer == writer);
 
 	/* Should be well-formed at this point! */
-	json_out_finished(js->jout);
-	json_stream_append(js, "\n\n", strlen("\n\n"));
+	json_stream_double_cr(js);
 	json_stream_flush(js);
 	js->writer = NULL;
 }

common/json_stream.h

@@ -160,6 +160,8 @@ struct io_plan *json_stream_output_(struct json_stream *js,
 							  void *arg),
 				    void *arg);
 
+/* Ensure there's a double \n after a JSON response. */
+void json_stream_double_cr(struct json_stream *js);
 void json_stream_flush(struct json_stream *js);
 
 #endif /* LIGHTNING_COMMON_JSON_STREAM_H */

lightningd/plugin.c

@@ -774,14 +774,6 @@ static void json_stream_forward_change_id(struct json_stream *stream,
 	json_stream_append(stream, new_id, strlen(new_id));
 	json_stream_append(stream, buffer + idtok->end + offset,
 			   toks->end - idtok->end - offset);
-
-	/* We promise it will end in '\n\n' */
-	/* It's an object (with an id!): definitely can't be less that "{}" */
-	assert(toks->end - toks->start >= 2);
-	if (buffer[toks->end-1] != '\n')
-		json_stream_append(stream, "\n\n", 2);
-	else if (buffer[toks->end-2] != '\n')
-		json_stream_append(stream, "\n", 1);
 }
 
 static void plugin_rpcmethod_cb(const char *buffer,
@@ -794,6 +786,7 @@ static void plugin_rpcmethod_cb(const char *buffer,
 
 	response = json_stream_raw_for_cmd(cmd);
 	json_stream_forward_change_id(response, buffer, toks, idtok, cmd->id);
+	json_stream_double_cr(response);
 	command_raw_complete(cmd, response);
 
 	list_del(&call->list);
@@ -851,6 +844,7 @@ static struct command_result *plugin_rpcmethod_dispatch(struct command *cmd,
 	snprintf(id, ARRAY_SIZE(id), "%"PRIu64, req->id);
 
 	json_stream_forward_change_id(req->stream, buffer, toks, idtok, id);
+	json_stream_double_cr(req->stream);
 	plugin_request_send(plugin, req);
 	req->stream = NULL;