libplugin: use jsonrpc_io for reading replies to our async commands.
What the developer wrote
Authored by Rusty Russell
libplugin: use jsonrpc_io for reading replies to our async commands.
This will also be more efficient than doing memmove every time.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
What changed, and why it matters
This commit refactors how plugin code reads JSON-RPC replies from Core Lightning. It replaces a custom buffer-and-memmove parser with a shared helper called jsonrpc_io. The stated reason is efficiency and code reuse. There is no direct evidence in the commit that this fixes a security bug, but any change to network-facing JSON parsing can affect reliability and potentially security if the old code mishandled malformed input.
Review the jsonrpc_io implementation to confirm it preserves or improves bounds checking, malformed-input handling, and memory growth limits compared to the removed manual parser. Treat as routine defensive review unless additional context shows the old parser had a known flaw.
Security signals we found
Refactor of JSON-RPC input parsing in plugin RPC path
Removal of manual buffer compaction and jsmn parsing
Adoption of shared jsonrpc_io helper whose security properties are not shown in this diff
No explicit security framing, CVE, or vulnerability description in commit message
Evidence from the diff
The change removes plugin-local RPC buffering logic (rpc_buffer, rpc_used, rpc_len_read, rpc_read_offset, rpc_parser, rpc_toks) and instead uses common/jsonrpc_io.h’s jsonrpc_io_new, jsonrpc_io_read, jsonrpc_io_parse, and jsonrpc_io_parse_done. The old loop read partial data, grew a buffer, parsed with jsmn, compacted via memmove, and dispatched replies. The new loop calls jsonrpc_io_parse repeatedly to consume complete objects and jsonrpc_io_read for further I/O. The commit message frames this as an efficiency/cleanup, not a security fix.
Changed components
plugins/libplugin.cPlugin RPC read path (async commands)Inspect captured patch +25 / −71
diff --git a/plugins/libplugin.c b/plugins/libplugin.c
index 836e1768..96b2fc63 100644
--- a/plugins/libplugin.c
+++ b/plugins/libplugin.c
@@ -11,6 +11,7 @@
#include <common/json_filter.h>
#include <common/json_param.h>
#include <common/json_stream.h>
+#include <common/jsonrpc_io.h>
#include <common/memleak.h>
#include <common/plugin.h>
#include <common/route.h>
@@ -98,10 +99,8 @@ struct plugin {
/* Asynchronous RPC interaction */
struct io_conn *io_rpc_conn;
struct list_head rpc_js_list;
- char *rpc_buffer;
- size_t rpc_used, rpc_len_read, rpc_read_offset;
- jsmn_parser rpc_parser;
- jsmntok_t *rpc_toks;
+ struct jsonrpc_io *jsonrpc_in;
+
/* Tracking async RPC requests */
STRMAP(struct out_req *) out_reqs;
u64 next_outreq_id;
@@ -1365,73 +1364,33 @@ static void rpc_conn_finished(struct io_conn *conn,
plugin_err(plugin, "Lost connection to the RPC socket.");
}
-static bool rpc_read_response_one(struct plugin *plugin)
-{
- const jsmntok_t *jrtok;
- bool complete;
-
- if (!json_parse_input(&plugin->rpc_parser, &plugin->rpc_toks,
- plugin->rpc_buffer + plugin->rpc_read_offset,
- plugin->rpc_used - plugin->rpc_read_offset,
- &complete)) {
- plugin_err(plugin, "Failed to parse RPC JSON response '%.*s'",
- (int)(plugin->rpc_used - plugin->rpc_read_offset),
- plugin->rpc_buffer + plugin->rpc_read_offset);
- }
-
- if (!complete) {
- /* We need more. */
- goto compact;
- }
-
- /* Empty buffer? (eg. just whitespace). */
- if (tal_count(plugin->rpc_toks) == 1) {
- jsmn_init(&plugin->rpc_parser);
- toks_reset(plugin->rpc_toks);
- goto compact;
- }
-
- jrtok = json_get_member(plugin->rpc_buffer + plugin->rpc_read_offset,
- plugin->rpc_toks, "jsonrpc");
- if (!jrtok) {
- plugin_err(plugin, "JSON-RPC message does not contain \"jsonrpc\" field: '%.*s'",
- (int)(plugin->rpc_used - plugin->rpc_read_offset),
- plugin->rpc_buffer + plugin->rpc_read_offset);
- }
-
- handle_rpc_reply(plugin, plugin->rpc_buffer + plugin->rpc_read_offset, plugin->rpc_toks);
-
- /* Move this object out of the buffer */
- plugin->rpc_read_offset += plugin->rpc_toks[0].end;
- jsmn_init(&plugin->rpc_parser);
- toks_reset(plugin->rpc_toks);
- return true;
-
-compact:
- memmove(plugin->rpc_buffer, plugin->rpc_buffer + plugin->rpc_read_offset,
- plugin->rpc_used - plugin->rpc_read_offset);
- plugin->rpc_used -= plugin->rpc_read_offset;
- plugin->rpc_read_offset = 0;
- return false;
-}
static struct io_plan *rpc_conn_read_response(struct io_conn *conn,
struct plugin *plugin)
{
- plugin->rpc_used += plugin->rpc_len_read;
- if (plugin->rpc_used == tal_count(plugin->rpc_buffer))
- tal_resize(&plugin->rpc_buffer, plugin->rpc_used * 2);
+ /* Gather an parse any new bytes */
+ for (;;) {
+ const jsmntok_t *toks;
+ const char *buf;
+ const char *err;
- /* Read and process all messages from the connection */
- while (rpc_read_response_one(plugin))
- ;
+ err = jsonrpc_io_parse(tmpctx,
+ plugin->jsonrpc_in,
+ &toks, &buf);
+ if (err)
+ plugin_err(plugin, "%s", err);
+
+ if (!toks)
+ break;
+
+ handle_rpc_reply(plugin, buf, toks);
+ jsonrpc_io_parse_done(plugin->jsonrpc_in);
+ }
- /* Read more, if there is. */
- return io_read_partial(plugin->io_rpc_conn,
- plugin->rpc_buffer + plugin->rpc_used,
- tal_bytelen(plugin->rpc_buffer) - plugin->rpc_used,
- &plugin->rpc_len_read,
- rpc_conn_read_response, plugin);
+ /* Read more */
+ return jsonrpc_io_read(conn, plugin->jsonrpc_in,
+ rpc_conn_read_response,
+ plugin);
}
static struct io_plan *rpc_conn_write_request(struct io_conn *conn,
@@ -2416,14 +2375,9 @@ static struct plugin *new_plugin(const tal_t *ctx,
jsmn_init(&p->parser);
p->toks = toks_alloc(p);
/* Async RPC */
- p->rpc_buffer = tal_arr(p, char, 64);
+ p->jsonrpc_in = jsonrpc_io_new(p);
list_head_init(&p->rpc_js_list);
p->io_rpc_conn = NULL;
- p->rpc_used = 0;
- p->rpc_read_offset = 0;
- p->rpc_len_read = 0;
- jsmn_init(&p->rpc_parser);
- p->rpc_toks = toks_alloc(p);
p->next_outreq_id = 0;
strmap_init(&p->out_reqs);
p->beglist = NULL;
Why this scored 26/100
Community notes
Notes can correct, qualify, or add evidence to the AI analysis. Every note shown here has been validated by a human moderator.
The AI analysis stands alone for now. Submit a note if you can add evidence or important context.