Android: Access APK files using AssetFileDescriptor

include/SDL_rwops.h

@@ -94,8 +94,11 @@ typedef struct SDL_RWops
             void *inputStreamRef;
             void *readableByteChannelRef;
             void *readMethod;
+            void *assetFileDescriptorRef;
             long position;
-            int size;
+            long size;
+            long offset;
+            int fd;
         } androidio;
 #elif defined(__WIN32__)
         struct

src/core/android/SDL_android.cpp

@@ -37,6 +37,8 @@ extern "C" {
 
 #include <android/log.h>
 #include <pthread.h>
+#include <sys/types.h>
+#include <unistd.h>
 #define LOG_TAG "SDL_android"
 //#define LOGI(...)  __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)
 //#define LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)
@@ -559,6 +561,9 @@ static int Android_JNI_FileOpen(SDL_RWops* ctx)
     jclass channels;
     jobject readableByteChannel;
     jstring fileNameJString;
+    jobject fd;
+    jclass fdCls;
+    jfieldID descriptor;
 
     JNIEnv *mEnv = Android_JNI_GetEnv();
     if (!refs.init(mEnv)) {
@@ -566,21 +571,58 @@ static int Android_JNI_FileOpen(SDL_RWops* ctx)
     }
 
     fileNameJString = (jstring)ctx->hidden.androidio.fileNameRef;
+    ctx->hidden.androidio.position = 0;
 
     // context = SDLActivity.getContext();
     mid = mEnv->GetStaticMethodID(mActivityClass,
             "getContext","()Landroid/content/Context;");
     context = mEnv->CallStaticObjectMethod(mActivityClass, mid);
     
+
     // assetManager = context.getAssets();
     mid = mEnv->GetMethodID(mEnv->GetObjectClass(context),
             "getAssets", "()Landroid/content/res/AssetManager;");
     assetManager = mEnv->CallObjectMethod(context, mid);
 
+    /* First let's try opening the file to obtain an AssetFileDescriptor.
+    * This method reads the files directly from the APKs using standard *nix calls
+    */
+    mid = mEnv->GetMethodID(mEnv->GetObjectClass(assetManager), "openFd", "(Ljava/lang/String;)Landroid/content/res/AssetFileDescriptor;");
+    inputStream = mEnv->CallObjectMethod(assetManager, mid, fileNameJString);
+    if (Android_JNI_ExceptionOccurred()) {
+        goto fallback;
+    }
+
+    ctx->hidden.androidio.assetFileDescriptorRef = mEnv->NewGlobalRef(inputStream);
+    mid = mEnv->GetMethodID(mEnv->GetObjectClass(inputStream), "getStartOffset", "()J");
+    ctx->hidden.androidio.offset = mEnv->CallLongMethod(inputStream, mid);
+    if (Android_JNI_ExceptionOccurred()) {
+        goto fallback;
+    }
+
+    mid = mEnv->GetMethodID(mEnv->GetObjectClass(inputStream), "getDeclaredLength", "()J");
+    ctx->hidden.androidio.size = mEnv->CallLongMethod(inputStream, mid);
+    
+    if (Android_JNI_ExceptionOccurred()) {
+        goto fallback;
+    }
+
+    mid = mEnv->GetMethodID(mEnv->GetObjectClass(inputStream), "getFileDescriptor", "()Ljava/io/FileDescriptor;");
+    fd = mEnv->CallObjectMethod(inputStream, mid);
+    fdCls = mEnv->GetObjectClass(fd);
+    descriptor = mEnv->GetFieldID(fdCls, "descriptor", "I");
+    ctx->hidden.androidio.fd = mEnv->GetIntField(fd, descriptor);
+
+    if (false) {
+fallback:
+        __android_log_print(ANDROID_LOG_DEBUG, "SDL", "Falling back to legacy InputStream method for opening file");
+        /* Try the old method using InputStream */
+        ctx->hidden.androidio.assetFileDescriptorRef = NULL;
+
         // inputStream = assetManager.open(<filename>);
         mid = mEnv->GetMethodID(mEnv->GetObjectClass(assetManager),
-            "open", "(Ljava/lang/String;)Ljava/io/InputStream;");
+                "open", "(Ljava/lang/String;I)Ljava/io/InputStream;");
-    inputStream = mEnv->CallObjectMethod(assetManager, mid, fileNameJString);
+        inputStream = mEnv->CallObjectMethod(assetManager, mid, fileNameJString, 1 /*ACCESS_RANDOM*/);
         if (Android_JNI_ExceptionOccurred()) {
             goto failure;
         }
@@ -596,7 +638,7 @@ static int Android_JNI_FileOpen(SDL_RWops* ctx)
         // size = inputStream.available();
         mid = mEnv->GetMethodID(mEnv->GetObjectClass(inputStream),
                 "available", "()I");
-    ctx->hidden.androidio.size = mEnv->CallIntMethod(inputStream, mid);
+        ctx->hidden.androidio.size = (long)mEnv->CallIntMethod(inputStream, mid);
         if (Android_JNI_ExceptionOccurred()) {
             goto failure;
         }
@@ -619,8 +661,7 @@ static int Android_JNI_FileOpen(SDL_RWops* ctx)
         mid = mEnv->GetMethodID(mEnv->GetObjectClass(readableByteChannel),
                 "read", "(Ljava/nio/ByteBuffer;)I");
         ctx->hidden.androidio.readMethod = mid;
-
+    }
-    ctx->hidden.androidio.position = 0;
 
     if (false) {
 failure:
@@ -636,6 +677,10 @@ failure:
             mEnv->DeleteGlobalRef((jobject)ctx->hidden.androidio.readableByteChannelRef);
         }
 
+        if(ctx->hidden.androidio.assetFileDescriptorRef != NULL) {
+            mEnv->DeleteGlobalRef((jobject)ctx->hidden.androidio.assetFileDescriptorRef);
+        }
+
     }
 
     return result;
@@ -660,6 +705,7 @@ extern "C" int Android_JNI_FileOpen(SDL_RWops* ctx,
     ctx->hidden.androidio.inputStreamRef = NULL;
     ctx->hidden.androidio.readableByteChannelRef = NULL;
     ctx->hidden.androidio.readMethod = NULL;
+    ctx->hidden.androidio.assetFileDescriptorRef = NULL;
 
     return Android_JNI_FileOpen(ctx);
 }
@@ -668,6 +714,19 @@ extern "C" size_t Android_JNI_FileRead(SDL_RWops* ctx, void* buffer,
         size_t size, size_t maxnum)
 {
     LocalReferenceHolder refs(__FUNCTION__);
+
+    if (ctx->hidden.androidio.assetFileDescriptorRef) {
+        size_t bytesMax = size * maxnum;
+        if (ctx->hidden.androidio.size != -1 /*UNKNOWN_LENGTH*/ && ctx->hidden.androidio.position + bytesMax > ctx->hidden.androidio.size) {
+            bytesMax = ctx->hidden.androidio.size - ctx->hidden.androidio.position;
+        }
+        size_t result = read(ctx->hidden.androidio.fd, buffer, bytesMax );
+        if (result > 0) {
+            ctx->hidden.androidio.position += result;
+            return result / size;
+        }
+        return 0;
+    } else {
         jlong bytesRemaining = (jlong) (size * maxnum);
         jlong bytesMax = (jlong) (ctx->hidden.androidio.size -  ctx->hidden.androidio.position);
         int bytesRead = 0;
@@ -700,9 +759,9 @@ extern "C" size_t Android_JNI_FileRead(SDL_RWops* ctx, void* buffer,
             bytesRead += result;
             ctx->hidden.androidio.position += result;
         }
-
         return bytesRead / size;
     }    
+}
 
 extern "C" size_t Android_JNI_FileWrite(SDL_RWops* ctx, const void* buffer,
         size_t size, size_t num)
@@ -727,6 +786,17 @@ static int Android_JNI_FileClose(SDL_RWops* ctx, bool release)
             mEnv->DeleteGlobalRef((jobject)ctx->hidden.androidio.fileNameRef);
         }
 
+        if (ctx->hidden.androidio.assetFileDescriptorRef) {
+            jobject inputStream = (jobject)ctx->hidden.androidio.assetFileDescriptorRef;
+            jmethodID mid = mEnv->GetMethodID(mEnv->GetObjectClass(inputStream),
+                    "close", "()V");
+            mEnv->CallVoidMethod(inputStream, mid);
+            mEnv->DeleteGlobalRef((jobject)ctx->hidden.androidio.assetFileDescriptorRef);
+            if (Android_JNI_ExceptionOccurred()) {
+                result = -1;
+            }
+        }
+        else {
             jobject inputStream = (jobject)ctx->hidden.androidio.inputStreamRef;
 
             // inputStream.close();
@@ -738,6 +808,7 @@ static int Android_JNI_FileClose(SDL_RWops* ctx, bool release)
             if (Android_JNI_ExceptionOccurred()) {
                 result = -1;
             }
+        }
 
         if (release) {
             SDL_FreeRW(ctx);
@@ -755,6 +826,30 @@ extern "C" Sint64 Android_JNI_FileSize(SDL_RWops* ctx)
 
 extern "C" Sint64 Android_JNI_FileSeek(SDL_RWops* ctx, Sint64 offset, int whence)
 {
+    if (ctx->hidden.androidio.assetFileDescriptorRef) {
+        switch (whence) {
+            case RW_SEEK_SET:
+                if (ctx->hidden.androidio.size != -1 /*UNKNOWN_LENGTH*/ && offset > ctx->hidden.androidio.size) offset = ctx->hidden.androidio.size;
+                offset += ctx->hidden.androidio.offset;
+                break;
+            case RW_SEEK_CUR:
+                offset += ctx->hidden.androidio.position;
+                if (ctx->hidden.androidio.size != -1 /*UNKNOWN_LENGTH*/ && offset > ctx->hidden.androidio.size) offset = ctx->hidden.androidio.size;
+                offset += ctx->hidden.androidio.offset;
+                break;
+            case RW_SEEK_END:
+                offset = ctx->hidden.androidio.offset + ctx->hidden.androidio.size + offset;
+                break;
+            default:
+                SDL_SetError("Unknown value for 'whence'");
+                return -1;
+        }
+        whence = SEEK_SET;
+
+        off_t ret = lseek(ctx->hidden.androidio.fd, (off_t)offset, SEEK_SET);
+        if (ret == -1) return -1;
+        ctx->hidden.androidio.position = ret - ctx->hidden.androidio.offset;
+    } else {
         Sint64 newPosition;
 
         switch (whence) {
@@ -807,8 +902,10 @@ extern "C" Sint64 Android_JNI_FileSeek(SDL_RWops* ctx, Sint64 offset, int whence
             Android_JNI_FileOpen(ctx);
             Android_JNI_FileSeek(ctx, newPosition, RW_SEEK_SET);
         }
+    }
 
     return ctx->hidden.androidio.position;
+    
 }
 
 extern "C" int Android_JNI_FileClose(SDL_RWops* ctx)