Add random message generator to help with fuzz testing

tests/fuzztest/SConscript

@@ -36,4 +36,8 @@ fuzzstub = malloc_env.Program(["fuzzstub.c",
                     "$COMMON/pb_common_with_malloc.o",
                     "$COMMON/malloc_wrappers.o"])
 
+generate_message = malloc_env.Program(["generate_message.c",
+                    "alltypes_static.pb.c",
+                    "$COMMON/pb_encode.o",
+                    "$COMMON/pb_common.o"])
 

tests/fuzztest/generate_message.c

+/* Generates a random, valid protobuf message. Useful to seed
+ * external fuzzers such as afl-fuzz.
+ */
+
+#include <pb_encode.h>
+#include <pb_common.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <time.h>
+#include "alltypes_static.pb.h"
+
+static uint64_t random_seed;
+
+/* Uses xorshift64 here instead of rand() for both speed and
+ * reproducibility across platforms. */
+static uint32_t rand_word()
+{
+    random_seed ^= random_seed >> 12;
+    random_seed ^= random_seed << 25;
+    random_seed ^= random_seed >> 27;
+    return random_seed * 2685821657736338717ULL;
+}
+
+/* Fills a buffer with random data. */
+static void rand_fill(uint8_t *buf, size_t count)
+{
+    while (count--)
+    {
+        *buf++ = rand_word() & 0xff;
+    }
+}
+
+/* Check that size/count fields do not exceed their max size.
+ * Otherwise we would have to loop pretty long in generate_message().
+ * Note that there may still be a few encoding errors from submessages.
+ */
+static void limit_sizes(alltypes_static_AllTypes *msg)
+{
+    pb_field_iter_t iter;
+    pb_field_iter_begin(&iter, alltypes_static_AllTypes_fields, msg);
+    while (pb_field_iter_next(&iter))
+    {
+        if (PB_LTYPE(iter.pos->type) == PB_LTYPE_BYTES)
+        {
+            ((pb_bytes_array_t*)iter.pData)->size %= iter.pos->data_size - PB_BYTES_ARRAY_T_ALLOCSIZE(0);
+        }
+        
+        if (PB_HTYPE(iter.pos->type) == PB_HTYPE_REPEATED)
+        {
+            *((pb_size_t*)iter.pSize) %= iter.pos->array_size;
+        }
+        
+        if (PB_HTYPE(iter.pos->type) == PB_HTYPE_ONEOF)
+        {
+            /* Set the oneof to this message type with 50% chance. */
+            if (rand_word() & 1)
+            {
+                *((pb_size_t*)iter.pSize) = iter.pos->tag;
+            }
+        }
+    }
+}
+
+static void generate_message()
+{
+    alltypes_static_AllTypes msg;
+    uint8_t buf[8192];
+    pb_ostream_t stream = {0};
+    
+    do {
+        if (stream.errmsg)
+            fprintf(stderr, "Encoder error: %s\n", stream.errmsg);
+        
+        stream = pb_ostream_from_buffer(buf, sizeof(buf));
+        rand_fill((void*)&msg, sizeof(msg));
+        limit_sizes(&msg);
+    } while (!pb_encode(&stream, alltypes_static_AllTypes_fields, &msg));
+    
+    fwrite(buf, 1, stream.bytes_written, stdout);
+}
+
+int main(int argc, char **argv)
+{
+    if (argc > 1)
+    {
+        random_seed = atol(argv[1]);
+    }
+    else
+    {
+        random_seed = time(NULL);
+    }
+    
+    fprintf(stderr, "Random seed: %llu\n", (long long unsigned)random_seed);
+    
+    generate_message();
+    
+    return 0;
+}
+