implement BitmapFactory.decodeStream() using gdk_pixbuf_new_from_stream

The java InputStream is wrapped into a custom GInputStream
implementation

src/api-impl-jni/graphics/android_graphics_BitmapFactory.c

@@ -0,0 +1,60 @@
+#include <gtk/gtk.h>
+#include <string.h>
+
+#include "../defines.h"
+#include "../util.h"
+
+#include "../generated_headers/android_graphics_BitmapFactory.h"
+
+struct _JavaInputStream
+{
+	GInputStream parent_instance;
+
+	jobject is;
+	jbyteArray storage;
+	int storage_size;
+};
+
+G_DECLARE_FINAL_TYPE(JavaInputStream, java_input_stream, ATL, JAVA_INPUT_STREAM, GInputStream);
+
+static gssize java_input_stream_read(GInputStream *gstream, void *buffer, gsize count, GCancellable *cancellable, GError **error) {
+	JavaInputStream *stream = ATL_JAVA_INPUT_STREAM(gstream);
+	JNIEnv *env = get_jni_env();
+
+	count = MIN(count, stream->storage_size);
+
+	count = (*env)->CallIntMethod(env, stream->is, _METHOD(_CLASS(stream->is), "read", "([BII)I"), stream->storage, 0, count);
+	if (count == -1) {  // end of stream
+		return 0;
+	}
+	jbyte *storage_buf = (*env)->GetByteArrayElements(env, stream->storage, NULL);
+	memcpy(buffer, storage_buf, count);
+	(*env)->ReleaseByteArrayElements(env, stream->storage, storage_buf, 0);
+
+	return count;
+}
+
+static void java_input_stream_class_init(JavaInputStreamClass *klass) {
+	klass->parent_class.read_fn  = java_input_stream_read;
+}
+
+static void java_input_stream_init(JavaInputStream *self) {
+}
+
+G_DEFINE_TYPE(JavaInputStream, java_input_stream, G_TYPE_INPUT_STREAM)
+
+static GInputStream *java_input_stream_new(JNIEnv *env, jobject is, jbyteArray storage) {
+	JavaInputStream *stream = g_object_new(java_input_stream_get_type(), NULL);
+	stream->is = is;
+	stream->storage = storage;
+	stream->storage_size = (*env)->GetArrayLength(env, storage);
+	return &stream->parent_instance;
+}
+
+JNIEXPORT jlong JNICALL Java_android_graphics_BitmapFactory_nativeDecodeStream(JNIEnv *env, jclass, jobject is, jbyteArray storage, jobject outPadding, jobject opts) {
+	GInputStream *stream = java_input_stream_new(env, is, storage);
+
+	GdkPixbuf *pixbuf = gdk_pixbuf_new_from_stream(stream, NULL, NULL);
+	g_object_unref(stream);
+	return _INTPTR(pixbuf);
+}