Trying to Load a BufferedImage from a PNG through JNI

Question

Yes I realize that I can load it directly through Java and not go through JNI, but I need this to test correctly as my C code will aquire images without saving to Disk and I want Java code to manipulate the images without saving to disk. The image Im trying to load is a 800x600 PNG image.
So I have the code
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import javax.imageio.ImageIO;
import javax.swing.*;
import com.sun.media.jai.widget.DisplayJAI;
class ImageLoader{
     static{
          System.loadLibrary("LoadImage");
     private static native byte[] loadImage();
     public static void main(String[] args){
byte[] f = loadImage();
          InputStream s= new ByteArrayInputStream(f);
          BufferedImage bi;
          try {
               bi = ImageIO.read(s);
               displayBufferedImage(bi, "test");
          } catch (IOException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
      * Utility method for display a BufferedImage.<br>
      * @param  image input image
      * @param  title window title string
     public static void displayBufferedImage(BufferedImage image, String title)
          JFrame frame = new JFrame();
         frame.setTitle(title);
         //frame.getContentPane().add(new DisplayTwoSynchronizedImages(sourceImgBI, resultImgGray));
         frame.getContentPane().add(new JScrollPane(new DisplayJAI(image)));
         //frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         //frame.pack();
         frame.setSize(300,300);
         frame.setLocationRelativeTo( null );
         frame.setVisible(true); // show the frame.
     }and I have the JNI c code as
char* result;
JNIEXPORT jbyteArray JNICALL Java_ImageLoader_loadImage
  (JNIEnv * env, jclass jclassj){
               int fd = open("test.png",  O_RDWR, S_IRUSR|S_IWUSR );
               int size = (800*600*4);
               result = (char*)malloc(size);
               read(fd, result, size);
               jbyteArray return_result;
               return_result = env->NewByteArray(800*600);
               env->SetByteArrayRegion(return_result, 0, 800*600, (jbyte*)result);
               //free(result);
               return return_result;
     }but when I try to run the code I get the following error
javax.imageio.IIOException: Error reading PNG image data
     at com.sun.imageio.plugins.png.PNGImageReader.readImage(PNGImageReader.java:1287)
     at com.sun.imageio.plugins.png.PNGImageReader.read(PNGImageReader.java:1552)
     at javax.imageio.ImageIO.read(ImageIO.java:1438)
     at javax.imageio.ImageIO.read(ImageIO.java:1342)
     at ImageLoader.main(ImageLoader.java:31)
Caused by: java.io.EOFException: Unexpected end of ZLIB input stream
     at java.util.zip.InflaterInputStream.fill(InflaterInputStream.java:240)
     at java.util.zip.InflaterInputStream.read(InflaterInputStream.java:158)
     at java.io.BufferedInputStream.fill(BufferedInputStream.java:235)
     at java.io.BufferedInputStream.read1(BufferedInputStream.java:275)
     at java.io.BufferedInputStream.read(BufferedInputStream.java:334)
     at java.io.DataInputStream.readFully(DataInputStream.java:195)
     at com.sun.imageio.plugins.png.PNGImageReader.decodePass(PNGImageReader.java:1084)
     at com.sun.imageio.plugins.png.PNGImageReader.decodeImage(PNGImageReader.java:1188)
     at com.sun.imageio.plugins.png.PNGImageReader.readImage(PNGImageReader.java:1280)
     ... 4 moreI think that Im on the right track because Java is recognizing that this is a PNG image, but Im not sure whats wrong. I don't know much about the formats, so I know nothing about PNG's, maybe someone else can help me here.
Note: I ran the code
               BufferedImage bi2 = ImageIO.read(new File("test.png"));
               displayBufferedImage(bi2, "test2");and the image loads fine, so there is no issue with the image itself.

Answer 1

               int fd = open("test.png", O_RDWR, S_IRUSR|S_IWUSR );Why are you opening the image file read/write? Why not read-only?
               int size = (800*600*4);Here you're assuming the image is 800*600. Are you sure that's the case? Also you should write sizeof int here instead of 4.
               result = (char*)malloc(size);Here you aren't checking for the possibility that result is null.
               read(fd, result, size);Here you are ignoring the result returned by read(), so you are ignoring the possibilty that it was 0 or less than 'size'. Either are possible.
               jbyteArray return_result;
               return_result = env->NewByteArray(800*600);Here again you aren't testing for return_result == null.
               env->SetByteArrayRegion(return_result, 0, 800*600, (jbyte*)result);Here you should be checking for Java exceptions. Also you shouldn't be repeating the 800*600 here, make it a constant or a variable somewhere.
               //free(result);You need that free, otherwise you have a memory leak. If the image really is a constant 800*600 in size I would allocate 'result' on the stack so you don't need to housekeep it.
Also you are never closing the input file!
Caused by: java.io.EOFException: Unexpected end of ZLIB input streamSo clearly you didn't read all the image. That could be due to guessing wrong about 800*600 or getting a short read when reading the file.
I think that Im on the right track because Java is recognizing that this is a PNG imageI agree. It starts like a PNG image, so you read something, but it doesn't end like one, so you didn't read it all.> and the image loads fine, so there is no issue with the image itself.
Good test. Note that your Java code makes no assumption about the size of the image.