fix(discord,gateway): inbound WS buffer overflow and WebChat drop

src/channels/discord.c

@@ -142,6 +142,7 @@ struct discord_ctx {
 	char *rx_buf;
 	size_t rx_len;
 	size_t rx_cap;
+	int rx_skip;
 	int heartbeat_interval_ms;
 	uint64_t last_seq;
 	char *session_id;
@@ -180,25 +181,8 @@ static void discord_rx_reset(struct discord_ctx *dc)
 /** Appends one RX fragment; returns 0 ok, -1 overflow. */
 static int discord_rx_append(struct discord_ctx *dc, const void *in, size_t len)
 {
-	if (len > RX_MAX || dc->rx_len > RX_MAX - len)
-		return -1;
-	if (dc->rx_cap < dc->rx_len + len) {
-		size_t need = dc->rx_len + len + 1;
-		size_t ncap = dc->rx_cap ? dc->rx_cap * 2 : 4096;
-		while (ncap < need && ncap < RX_MAX)
-			ncap *= 2;
-		if (need > RX_MAX)
-			return -1;
-		char *p = realloc(dc->rx_buf, ncap);
-		if (!p)
-			return -1;
-		dc->rx_buf = p;
-		dc->rx_cap = ncap;
-	}
-	memcpy(dc->rx_buf + dc->rx_len, in, len);
-	dc->rx_len += len;
-	dc->rx_buf[dc->rx_len] = '\0';
-	return 0;
+	return discord_helpers_rx_append(&dc->rx_buf, &dc->rx_len, &dc->rx_cap, in, len,
+	                                 RX_MAX);
 }
 
 static int discord_send_json(struct lws *wsi, const char *json)
@@ -558,9 +542,15 @@ static int callback_discord(struct lws *wsi, enum lws_callback_reasons reason,
 		}
 		break;
 	case LWS_CALLBACK_CLIENT_RECEIVE:
+		if (dc->rx_skip) {
+			if (lws_is_final_fragment(wsi))
+				dc->rx_skip = 0;
+			break;
+		}
 		if (discord_rx_append(dc, in, len) != 0) {
 			fprintf(stderr, "shellclaw: discord: gateway payload too large\n");
 			discord_rx_reset(dc);
+			dc->rx_skip = !lws_is_final_fragment(wsi);
 			break;
 		}
 		if (lws_is_final_fragment(wsi)) {

src/channels/discord_helpers.c

@@ -6,6 +6,7 @@
 #include "channels/discord_helpers.h"
 #include "channels/channel.h"
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 const char *discord_lifecycle_str(discord_lifecycle_t lc)
@@ -139,3 +140,38 @@ int discord_helpers_send_backoff_ms(int attempt, double retry_after_sec, int jit
 		sleep_ms = cap_ms;
 	return sleep_ms;
 }
+
+int discord_helpers_rx_append(char **buf, size_t *len, size_t *cap, const void *in,
+                              size_t chunk_len, size_t max_cap)
+{
+	size_t need;
+	size_t ncap;
+	char *p;
+
+	if (!buf || !len || !cap || (!in && chunk_len != 0) || max_cap < 1)
+		return -1;
+	if (chunk_len > max_cap || *len > max_cap - chunk_len)
+		return -1;
+	need = *len + chunk_len + 1;
+	if (need > max_cap)
+		return -1;
+	if (*cap < need) {
+		ncap = *cap ? *cap * 2 : 4096;
+		while (ncap < need)
+			ncap *= 2;
+		if (ncap > max_cap)
+			ncap = max_cap;
+		if (ncap < need)
+			return -1;
+		p = realloc(*buf, ncap);
+		if (!p)
+			return -1;
+		*buf = p;
+		*cap = ncap;
+	}
+	if (chunk_len > 0)
+		memcpy(*buf + *len, in, chunk_len);
+	*len += chunk_len;
+	(*buf)[*len] = '\0';
+	return 0;
+}

src/channels/discord_helpers.h

@@ -1,7 +1,7 @@
 /**
  * @file discord_helpers.h
  * @brief Pure helpers shared by Discord channel and unit tests (allowlist, session id, mentions,
- *        REST 429 backoff calculation).
+ *        REST 429 backoff calculation, Gateway RX append).
  */
 
 #ifndef SHELLCLAW_DISCORD_HELPERS_H
@@ -53,6 +53,13 @@ int discord_helpers_route_message_create(const cJSON *payload, const char *const
                                          int allowed_count, const char *bot_user_id,
                                          char *session_out, size_t session_outsz);
 
+/**
+ * Append one Gateway RX fragment, growing so payload plus a trailing NUL always fit.
+ * @return 0 on success, -1 if the total would exceed @p max_cap or allocation failed.
+ */
+int discord_helpers_rx_append(char **buf, size_t *len, size_t *cap, const void *in,
+                              size_t chunk_len, size_t max_cap);
+
 #ifdef __cplusplus
 }
 #endif

src/gateway/http.c

@@ -37,7 +37,7 @@ static const struct lws_protocols protocols[] = {
 	{
 		.name = "ws",
 		.callback = ws_callback,
-		.rx_buffer_size = 256,
+		.rx_buffer_size = WS_RX_BUFFER_SIZE,
 	},
 	{ .name = NULL },
 };

src/gateway/http_lws.h

@@ -22,6 +22,8 @@ extern "C" {
 #define CONFIG_BODY_MAX 65536
 #define BODY_BUF_SIZE CONFIG_BODY_MAX
 #define ASAP_BODY_MAX (1024 * 1024)
+/** Per-callback WebChat RX. Must fit a full `{"type":"message","text":...}` frame (MSG_MAX). */
+#define WS_RX_BUFFER_SIZE 32768
 
 enum http_method {
 	HTTP_GET = 1,

tests/test_discord_helpers.c

@@ -7,6 +7,7 @@
 #include "channels/channel.h"
 #include "cJSON.h"
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 #define ASSERT(c) do { if (!(c)) { fprintf(stderr, "FAIL: %s:%d %s\n", __FILE__, __LINE__, #c); return 1; } } while (0)
@@ -99,6 +100,65 @@ static int test_route_message_create_fixture(void)
 	return 0;
 }
 
+/** Exact payload fill of a power-of-two cap must still reserve one byte for NUL. */
+static int test_rx_append_grows_for_nul(void)
+{
+	char *buf = NULL;
+	size_t len = 0;
+	size_t cap = 0;
+	char a[4095];
+	char one = 'Z';
+	char *big;
+	char *big2;
+
+	memset(a, 'A', sizeof(a));
+	ASSERT(discord_helpers_rx_append(&buf, &len, &cap, a, sizeof(a), 512 * 1024) == 0);
+	ASSERT(len == sizeof(a));
+	ASSERT(cap >= len + 1);
+	ASSERT(buf[len] == '\0');
+	ASSERT(discord_helpers_rx_append(&buf, &len, &cap, &one, 1, 512 * 1024) == 0);
+	ASSERT(len == 4096);
+	ASSERT(cap >= 4097);
+	ASSERT(buf[4096] == '\0');
+	ASSERT(buf[4095] == 'Z');
+
+	free(buf);
+	buf = NULL;
+	len = 0;
+	cap = 0;
+	big = malloc(65536);
+	big2 = malloc(65536);
+	ASSERT(big && big2);
+	memset(big, 'B', 65536);
+	memset(big2, 'C', 65536);
+	ASSERT(discord_helpers_rx_append(&buf, &len, &cap, big, 65536, 512 * 1024) == 0);
+	ASSERT(len == 65536);
+	ASSERT(cap == 131072);
+	ASSERT(discord_helpers_rx_append(&buf, &len, &cap, big2, 65536, 512 * 1024) == 0);
+	ASSERT(len == 131072);
+	ASSERT(cap >= 131073);
+	ASSERT(buf[131072] == '\0');
+	ASSERT(buf[0] == 'B' && buf[65535] == 'B');
+	ASSERT(buf[65536] == 'C' && buf[131071] == 'C');
+	free(big);
+	free(big2);
+	free(buf);
+	return 0;
+}
+
+static int test_rx_append_rejects_over_max(void)
+{
+	char *buf = NULL;
+	size_t len = 0;
+	size_t cap = 0;
+	char chunk[16];
+
+	memset(chunk, 'x', sizeof(chunk));
+	ASSERT(discord_helpers_rx_append(&buf, &len, &cap, chunk, sizeof(chunk), 8) != 0);
+	ASSERT(buf == NULL);
+	return 0;
+}
+
 int main(void)
 {
 	RUN(test_allow_entry_equals());
@@ -108,6 +168,8 @@ int main(void)
 	RUN(test_backoff_math());
 	RUN(test_lifecycle_str());
 	RUN(test_route_message_create_fixture());
+	RUN(test_rx_append_grows_for_nul());
+	RUN(test_rx_append_rejects_over_max());
 	printf("test_discord_helpers: all tests passed\n");
 	return 0;
 }