common: increase jsonrpc_io buffer size temporarily to aggrevate perf issues.
What the developer wrote
Authored by Rusty Russell
common: increase jsonrpc_io buffer size temporarily to aggrevate perf issues.
A client can do this by sending a large request, so this allows us to see what
happens if they do that, even though 1MB (2MB buffer) is more than we need.
This drives our performance through the floor: see next patch which gets
us back on track.
tests/test_coinmoves.py::test_generate_coinmoves (2,000,000, sqlite3):
Time (from start to end of l2 node): 271 seconds **WAS 135**
Worst latency: 105 seconds **WAS 12.1**
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
What changed, and why it matters
This commit is a temporary debugging change that increases an internal buffer size from 2 KB to 1 MB. The author explicitly states it is meant to expose and measure performance problems caused by large JSON-RPC requests, not to fix a security bug. By itself, it makes the node slower when handling big requests, but it does not introduce a clear vulnerability such as a crash or memory corruption.
Treat this commit as a temporary instrumentation change rather than a security patch. Review the follow-up commit referenced in the message to confirm performance and resource-usage regressions are resolved before any release. If this commit were to remain in a release branch, consider adding request-size limits or backpressure to prevent unbounded memory growth from many concurrent large JSON-RPC requests.
Security signals we found
Large buffer increase in network-facing JSON-RPC I/O path
Author acknowledges performance degradation under large client requests
No bounds checking, quota, or rate-limit changes accompany the buffer increase
Commit is explicitly described as temporary and diagnostic
Evidence from the diff
The single-line change raises READ_CHUNKSIZE in common/jsonrpc_io.c from 2048 bytes to 1024*1024 bytes. The commit message says this is a deliberate temporary step to ‘aggrevate [aggravate] perf issues’ that a client can already trigger by sending a large request. The author includes benchmark numbers showing a roughly 2x slowdown and a large latency spike, and points to a follow-up patch that restores performance. The diff does not alter parsing logic, allocation limits, or authentication checks.
Changed components
common/jsonrpc_io.cJSON-RPC I/O read bufferInspect captured patch +1 / −1
diff --git a/common/jsonrpc_io.c b/common/jsonrpc_io.c
index ab7255a9..e302434e 100644
--- a/common/jsonrpc_io.c
+++ b/common/jsonrpc_io.c
@@ -8,7 +8,7 @@
#include <errno.h>
#include <unistd.h>
-#define READ_CHUNKSIZE 2048
+#define READ_CHUNKSIZE (1024*1024)
struct jsonrpc_io {
MEMBUF(char) membuf;
Why this scored 21/100
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