feat: SAF file picker, fd to jni code

app/src/main/cpp/PlaybackEngine.cpp

@@ -74,3 +74,11 @@ PlaybackEngine::~PlaybackEngine() {
 void PlaybackEngine::playBeat() {
     if(mPlayer) mPlayer->setStartBeat();
 }
+
+void PlaybackEngine::playMusic(int fd) {
+    //if(mPlayer) mPlayer->playMusic();
+    // TODO: fd is opened; dispose of fd when stopping or being discarded ...
+    LOGI("PlaybackEngine::playMusic(fd=%d)", fd);
+    close(fd); // for now, nothing is implemented. we just close it again.
+    // we will use mp3file_open_fd() later.
+}

app/src/main/cpp/PlaybackEngine.h

@@ -15,6 +15,7 @@ public:
     virtual ~PlaybackEngine();
     /** Play a beat sound. */
     virtual void playBeat();
+    void playMusic(int fd);
 private:
     MixingPlayer *mPlayer;
     std::string mFilesDir;

app/src/main/cpp/jni_lockstep.cpp

@@ -40,4 +40,13 @@ Java_at_lockstep_pb_PlaybackEngine_native_1setDefaultStreamValues(JNIEnv *env,
     oboe::DefaultStreamValues::FramesPerBurst = (int32_t) framesPerBurst;
 }
 
+JNIEXPORT void JNICALL
+Java_at_lockstep_pb_PlaybackEngine_native_1playMusic(JNIEnv *env,
+                                                                  jclass type,
+                                                     jlong engineHandle,
+                                                                  jint fd) {
+    auto engine = reinterpret_cast<PlaybackEngine *>(engineHandle);
+    engine->playMusic(fd);
+}
+
 } // extern "C"

app/src/main/cpp/mp3file.cpp

@@ -5,6 +5,7 @@
 #define LOG_TAG "mp3file"
 
 #include "mp3file.h"
+#include <unistd.h>
 #include <string.h>
 #include <cstdlib>
 #include "logging.h"
@@ -25,6 +26,7 @@ void mp3file_delete(MP3File *mp3file) {
         free(mp3file->buffer);
         mp3file->buffer = 0;
     }
+    if(mp3file->android_fd) close(mp3file->android_fd);
     free(mp3file);
 }
 
@@ -93,3 +95,70 @@ on_error:
 
 #undef handleError
 }
+
+MP3File* mp3file_open_fd(int fd, int forceEncoding) {
+    const char *errorText = "";
+#define handleError(text) \
+    do { \
+        errorText = text; \
+        goto on_error; \
+    } while(0)
+
+    int err = MPG123_OK;
+    mpg123_handle *mh = mpg123_new(NULL, &err);
+    if(err != MPG123_OK || mh == NULL) {
+        LOGE("mpg123_new() failed: %s", mpg123_plain_strerror(err));
+        return NULL;
+    }
+
+    MP3File* mp3 = mp3file_init(mh);
+    if(mp3 == NULL) handleError("malloc() failed");
+    err = mpg123_open_fd(mh, fd);
+    if(err != MPG123_OK) handleError("mpg123_open()");
+
+    int encoding;
+    err = mpg123_getformat(mh, &mp3->rate, &mp3->channels, &encoding);
+    if(err != MPG123_OK) handleError("mpg123_getformat()");
+    if(encoding != MPG123_ENC_SIGNED_16) handleError("unknown file encoding");
+
+    if(forceEncoding != 0) {
+        encoding = forceEncoding;
+    }
+
+    // Ensure that this output format will not change
+    // (it could, when we allow it).
+    mpg123_format_none(mh);
+    err = mpg123_format(mh, mp3->rate, mp3->channels, encoding);
+    if(err != MPG123_OK) handleError("could not set mpg123_format()");
+
+    mp3->buffer_size = mpg123_outblock(mh);
+    mp3->buffer = (unsigned char*) malloc(mp3->buffer_size);
+    if(mp3->buffer == NULL) handleError("malloc() failed");
+
+    mp3->num_samples = mpg123_length(mh);
+    mp3->samples_per_frame = mpg123_spf(mh);
+    mp3->secs_per_frame = mpg123_tpf(mh);
+
+    if (mp3->num_samples == MPG123_ERR || mp3->samples_per_frame < 0)
+        mp3->num_frames = 0;
+    else
+        mp3->num_frames = mp3->num_samples / mp3->samples_per_frame;
+
+    if (mp3->num_samples == MPG123_ERR || mp3->samples_per_frame < 0 || mp3->secs_per_frame < 0)
+        mp3->duration = 0;
+    else
+        mp3->duration = mp3->num_samples / mp3->samples_per_frame * mp3->secs_per_frame;
+
+    mp3->offset = 0;
+    mp3->remaining_samples = (int) mp3->num_samples;
+    LOGV("channels: %d rate: %ld num_samples: %ld", mp3->channels, mp3->rate, mp3->num_samples);
+    mp3->android_fd = fd;
+    return mp3;
+
+on_error:
+    LOGE("%s, err = %s", errorText, mpg123_plain_strerror(err));
+    mp3file_delete(mp3);
+    return NULL;
+
+#undef handleError
+}

app/src/main/cpp/mp3file.h

@@ -10,6 +10,7 @@
 struct MP3File
 {
     mpg123_handle* handle;
+    int android_fd;
     int channels;
     long rate;
     long num_samples;
@@ -26,5 +27,6 @@ struct MP3File
 MP3File* mp3file_init(mpg123_handle *handle);
 void mp3file_delete(MP3File *mp3file);
 MP3File* mp3file_open(const char *filename, int forceEncoding = 0);
+MP3File* mp3file_open_fd(int fd, int forceEncoding = 0);
 
 #endif //SAMPLES_MP3FILE_H