add a way to set a log consumer

this is a private API to capture filament's logs.

libs/utils/include/utils/ostream.h

@@ -69,6 +69,13 @@ public:
     ostream& dec() noexcept;
     ostream& hex() noexcept;
 
+    /*! @cond PRIVATE */
+    // Sets a consumer of the log. The consumer is invoked on flush() and replaces the default.
+    // Thread safe and reentrant.
+    using ConsumerCallback = void(*)(void*, char const*);
+    void setConsumer(ConsumerCallback consumer, void* user) noexcept;
+    /*! @endcond */
+
 protected:
     ostream& print(const char* format, ...) noexcept;
 

libs/utils/src/Log.cpp

@@ -31,6 +31,8 @@
 #include <emscripten/console.h>
 #endif
 
+#include <mutex>
+
 namespace utils {
 namespace io {
 
@@ -52,6 +54,12 @@ private:
 ostream& LogStream::flush() noexcept {
     std::lock_guard const lock(mImpl->mLock);
     Buffer& buf = getBuffer();
+    char const* const str = buf.get();
+    if (UTILS_UNLIKELY(!str)) {
+        // this can happen if the log hasn't been written ever
+        return *this;
+    }
+
 #ifdef __ANDROID__
     int prio = ANDROID_LOG_UNKNOWN;
     switch (mPriority) {
@@ -61,20 +69,20 @@ ostream& LogStream::flush() noexcept {
         case LOG_INFO:      prio = ANDROID_LOG_INFO;    break;
         case LOG_VERBOSE:   prio = ANDROID_LOG_VERBOSE; break;
     }
-    __android_log_write(prio, UTILS_LOG_TAG, buf.get());
+    __android_log_write(prio, UTILS_LOG_TAG, str);
 #elif defined(__EMSCRIPTEN__)
     switch (mPriority) {
         case LOG_DEBUG:
         case LOG_WARNING:
         case LOG_INFO:
-            _emscripten_out(buf.get());
+            _emscripten_out(str);
             break;
         case LOG_ERROR:
-            _emscripten_err(buf.get());
+            _emscripten_err(str);
             break;
         case LOG_VERBOSE:
 #ifndef NFIL_DEBUG
-            _emscripten_out(buf.get());
+            _emscripten_out(str);
 #endif
             break;
     }
@@ -83,14 +91,14 @@ ostream& LogStream::flush() noexcept {
         case LOG_DEBUG:
         case LOG_WARNING:
         case LOG_INFO:
-            fprintf(stdout, "%s", buf.get());
+            fprintf(stdout, "%s", str);
             break;
         case LOG_ERROR:
-            fprintf(stderr, "%s", buf.get());
+            fprintf(stderr, "%s", str);
             break;
         case LOG_VERBOSE:
 #ifndef NDEBUG
-            fprintf(stdout, "%s", buf.get());
+            fprintf(stdout, "%s", str);
 #endif
             break;
     }

libs/utils/src/ostream.cpp

@@ -24,9 +24,12 @@
 #include <utils/PrivateImplementation-impl.h>
 
 #include <algorithm>
+#include <mutex>
 #include <string>
 #include <string_view>
+#include <utility>
 
+#include <stdlib.h>
 #include <stdarg.h>
 
 template class utils::PrivateImplementation<utils::io::ostream_>;
@@ -35,7 +38,31 @@ namespace utils::io {
 
 ostream::~ostream() = default;
 
+void ostream::setConsumer(ConsumerCallback consumer, void* user) noexcept {
+    auto* const pImpl = mImpl;
+    std::lock_guard const lock(pImpl->mLock);
+    pImpl->mConsumer = { consumer, user };
+}
+
 ostream& flush(ostream& s) noexcept {
+    auto* const pImpl = s.mImpl;
+    pImpl->mLock.lock();
+    auto const callback = pImpl->mConsumer;
+    if (UTILS_UNLIKELY(callback.first)) {
+        auto& buf = s.getBuffer();
+        char const* const data = buf.get();
+        if (UTILS_LIKELY(data)) {
+            char* const str = strdup(data);
+            buf.reset();
+            pImpl->mLock.unlock();
+            // call ConsumerCallback without lock held
+            callback.first(callback.second, str);
+            ::free(str);
+            return s;
+        }
+    }
+    pImpl->mLock.unlock();
+
     return s.flush();
 }
 

libs/utils/src/ostream_.h

@@ -25,6 +25,7 @@ namespace utils::io {
 struct ostream_ {
     std::mutex mLock;
     ostream::Buffer mData;
+    std::pair<ostream::ConsumerCallback, void*> mConsumer{};
     bool mShowHex = false;
 };
 

libs/utils/test/test_sstream.cpp

@@ -18,8 +18,33 @@
 
 #include <utils/sstream.h>
 
+#include <utils/Log.h>
+
+using namespace utils;
 using namespace utils::io;
 
+TEST(ostream, setConsumer) {
+    slog.d.setConsumer(+[](void*, char const*) {
+        GTEST_FAIL();
+    }, nullptr);
+    // we test that we don't crash if the log is empty and that we don't call the consumer.
+    flush(slog.d);
+
+    slog.d.setConsumer(nullptr, nullptr);
+    slog.d << "hello world";
+    // we test that after resetting the consumer, it's not called on flush.
+    flush(slog.d);
+
+    const char* str = "hello world!";
+    slog.d.setConsumer(+[](void* user, char const* str) {
+        ASSERT_STREQ(str, (const char*)user);
+    }, (void*)str);
+    slog.d << str;
+    // we test that the comsumer is called with the right string
+    flush(slog.d);
+    slog.d.setConsumer(nullptr, nullptr);
+}
+
 TEST(sstream, EmptyString) {
     sstream ss;
     EXPECT_STREQ("", ss.c_str());