fuzz-tests: add a test for handle_peer_error_or_warning()

Changelog-None: `handle_peer_error_or_warning()` in
`common/read_peer_message.{c, h}` is responsible for parsing any
incoming `error` or `warning` messages as defined in BOLT #1.

Add a test for it.

Author: Chandra Pratap

tests/fuzz/Makefile

@@ -72,5 +72,11 @@ FUZZ_COMMON_OBJS := \
 $(FUZZ_TARGETS_OBJS): $(COMMON_HEADERS) $(WIRE_HEADERS) $(COMMON_SRC)
 $(FUZZ_TARGETS_BIN): $(LIBFUZZ_OBJS) $(FUZZ_COMMON_OBJS) $(BITCOIN_OBJS)
 
+tests/fuzz/fuzz-error-warning:	common/peer_billboard.o		\
+				common/wire_error.o		\
+				common/peer_io.o		\
+				common/read_peer_msg.o		\
+				common/peer_status_wiregen.o
+
 ALL_C_SOURCES += $(FUZZ_TARGETS_SRC) $(LIBFUZZ_SRC)
 ALL_FUZZ_TARGETS += $(FUZZ_TARGETS_BIN)

tests/fuzz/fuzz-error-warning.c

@@ -0,0 +1,42 @@
+#include "config.h"
+#include <stdio.h>
+#include <fcntl.h>
+#include <setjmp.h>
+#include <common/per_peer_state.h>
+#include <common/peer_failed.h>
+#include <common/read_peer_msg.h>
+#include <common/status.h>
+#include <common/utils.h>
+#include <tests/fuzz/libfuzz.h>
+
+static jmp_buf exit_jmp;
+
+/* MOCKS START */
+/* Stub for peer_failed_connection_lost */
+void peer_failed_connection_lost(void)
+{ fprintf(stderr, "peer_failed_connection_lost called!\n"); abort(); }
+/* Stub for peer_failed_received_errmsg */
+void peer_failed_received_errmsg(struct per_peer_state *pps UNNEEDED,
+				 bool disconnect UNNEEDED,
+				 const char *desc)
+
+{ longjmp(exit_jmp, 1); }
+/* MOCKS END */
+
+void init(int *argc, char ***argv)
+{
+	int devnull = open("/dev/null", O_WRONLY);
+	status_setup_sync(devnull);
+}
+
+void run(const u8 *data, size_t size)
+{
+	if (setjmp(exit_jmp) != 0)
+		return;
+
+	u8 *msg = tal_dup_arr(tmpctx, u8, data, size, 0);
+	struct per_peer_state pps = { .peer_fd = -1 };
+	handle_peer_error_or_warning(&pps, msg);
+
+	clean_tmpctx();
+}