perf: Make time move a lot faster in fuzzing runs.

testing/fuzzing/BUILD.bazel

@@ -16,7 +16,7 @@ cc_library(
 )
 
 cc_fuzz_test(
-    name = "bootstrap_fuzzer",
+    name = "bootstrap_fuzz_test",
     srcs = ["bootstrap_harness.cc"],
     copts = ["-UNDEBUG"],
     corpus = ["//tools/toktok-fuzzer/corpus:bootstrap_fuzzer"],

testing/fuzzing/bootstrap_harness.cc

@@ -2,6 +2,7 @@
 #include <cstring>
 
 #include "../../toxcore/tox.h"
+#include "../../toxcore/tox_struct.h"
 #include "fuzz_adapter.h"
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
@@ -12,12 +13,18 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
     Tox_Err_New error_new;
     Tox *tox = tox_new(nullptr, &error_new);
 
+    uint64_t clock = 0;
+    mono_time_set_current_time_callback(
+        tox->mono_time,
+        [](Mono_Time *mono_time, void *user_data) { return *static_cast<uint64_t *>(user_data); },
+        &clock);
+
     assert(tox != nullptr);
     assert(error_new == TOX_ERR_NEW_OK);
 
     uint8_t pub_key[TOX_PUBLIC_KEY_SIZE] = {0};
 
-    bool success = tox_bootstrap(tox, "127.0.0.1", 12345, pub_key, nullptr);
+    const bool success = tox_bootstrap(tox, "127.0.0.1", 12345, pub_key, nullptr);
     assert(success);
 
     /*
@@ -26,8 +33,11 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
      * NOTE: This should be fine tuned after gathering some experience.
      */
 
-    for (uint32_t i = 0; i < 100; ++i) {
+    for (uint32_t i = 0; i < 50; ++i) {
         tox_iterate(tox, nullptr);
+        // Move the clock forward a decent amount so all the time-based checks
+        // trigger more quickly.
+        clock += 200;
     }
 
     tox_kill(tox);

testing/fuzzing/fuzz_adapter.c

@@ -1,8 +1,6 @@
 #include "fuzz_adapter.h"
 
 struct fuzz_buf {
-    /* Monotonic counter for time replacement */
-    uint64_t counter;
     /* Fuzz data buffer */
     const uint8_t *cur;
     const uint8_t *end;
@@ -17,7 +15,6 @@ static struct fuzz_buf data;
 
 void network_adapter_init(const uint8_t *buf, size_t length)
 {
-    data.counter = 0;
     data.cur = buf;
     data.end = buf + length;
 }
@@ -90,8 +87,3 @@ void fuzz_random_bytes(uint8_t *rnd, size_t length)
     memcpy(rnd, data.cur, bytes_read);
     data.cur += bytes_read;
 }
-
-uint64_t fuzz_get_count(void)
-{
-    return data.counter++;
-}

testing/fuzzing/fuzz_adapter.h

@@ -37,10 +37,6 @@ ssize_t fuzz_recv(int sockfd, void *buf, size_t len, int flags);
 /* The following functions intercept generation of random data */
 void fuzz_random_bytes(uint8_t *rnd, size_t length);
 
-/* The following function replaces all time bases with a monotonic counter */
-
-uint64_t fuzz_get_count(void);
-
 #ifdef __cplusplus
 }
 #endif

toxcore/mono_time.c

@@ -32,12 +32,6 @@
 
 #include "ccompat.h"
 
-//!TOKSTYLE-
-#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
-#include "../testing/fuzzing/fuzz_adapter.h"
-#endif
-//!TOKSTYLE+
-
 /** don't call into system billions of times for no reason */
 struct Mono_Time {
     uint64_t cur_time;
@@ -110,6 +104,11 @@ static uint64_t current_time_monotonic_default(Mono_Time *mono_time, void *user_
 non_null(1) nullable(2)
 static uint64_t current_time_monotonic_default(Mono_Time *mono_time, void *user_data)
 {
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+    // This assert should always fail. If it does, the fuzzing harness didn't
+    // override the mono time callback.
+    assert(mono_time == nullptr);
+#endif
     struct timespec clock_mono;
     clock_gettime(CLOCK_MONOTONIC, &clock_mono);
     return timespec_to_u64(clock_mono);
@@ -118,14 +117,6 @@ static uint64_t current_time_monotonic_default(Mono_Time *mono_time, void *user_
 #endif // !OS_WIN32
 
 
-#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
-non_null(1) nullable(2)
-static uint64_t current_time_monotonic_dummy(Mono_Time *mono_time, void *user_data)
-{
-    return fuzz_get_count();
-}
-#endif
-
 Mono_Time *mono_time_new(void)
 {
     Mono_Time *mono_time = (Mono_Time *)calloc(1, sizeof(Mono_Time));
@@ -147,11 +138,7 @@ Mono_Time *mono_time_new(void)
         return nullptr;
     }
 
-#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
-    mono_time->current_time_callback = current_time_monotonic_dummy;
-#else
     mono_time->current_time_callback = current_time_monotonic_default;
-#endif
     mono_time->user_data = nullptr;
 
 #ifdef OS_WIN32
@@ -169,12 +156,15 @@ Mono_Time *mono_time_new(void)
 
     mono_time->cur_time = 0;
 #ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
-    mono_time->base_time = 0; // Maximum reproducibility
+    // Maximum reproducibility and don't update mono_time before the harness has
+    // had a chance to set the callback.
+    // TODO(iphydf): Put mono time callback into Tox_Options with accessors only
+    // in tox_private.h.
+    mono_time->base_time = 0;
 #else
     mono_time->base_time = (uint64_t)time(nullptr) - (current_time_monotonic(mono_time) / 1000ULL);
-#endif
-
     mono_time_update(mono_time);
+#endif
 
     return mono_time;
 }