Parse GZip responses using volley

GZipRequest.java

import com.android.volley.NetworkResponse;
import com.android.volley.ParseError;
import com.android.volley.Response;
import com.android.volley.toolbox.HttpHeaderParser;
import com.android.volley.toolbox.StringRequest;

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.zip.GZIPInputStream;

public class GZipRequest extends StringRequest {

    public GZipRequest(int method, String url, Response.Listener<String> listener, Response.ErrorListener errorListener) {
        super(method, url, listener, errorListener);
    }

    public GZipRequest(String url, Response.Listener<String> listener, Response.ErrorListener errorListener) {
        super(url, listener, errorListener);
    }

    // parse the gzip response using a GZIPInputStream
    @Override
    protected Response<String> parseNetworkResponse(NetworkResponse response) {
        String output = ""; // note: better to use StringBuilder
        try {
            final GZIPInputStream gStream = new GZIPInputStream(new ByteArrayInputStream(response.data));
            final InputStreamReader reader = new InputStreamReader(gStream);
            final BufferedReader in = new BufferedReader(reader);
            String read;
            while ((read = in.readLine()) != null) {
                output += read;
            }
            reader.close();
            in.close();
            gStream.close();
        } catch (IOException e) {
            return Response.error(new ParseError());
        }
        return Response.success(output, HttpHeaderParser.parseCacheHeaders(response));
    }
}

hi FrancoSabadini, you mean you don't need to unzip manually? thanks.

FrancoSabadini is absolutely right. "Accept-Encoding gzip" is already set using Volley.

If is already set, how do you send/receive zipped requests/responses? How does the server know that I'm doing explicitly a GZIP request, so it have to send me a gzipped response? I'm trying to use this code, that seems quite good, but I always get a server error when I do a GET or a POST. For the POST, I'm overriding the getBody() method and converting the JSON params into a String and then into a byte array. Is this a good approach?

No, volley not set "Accept-Encoding" manually! Do that:

@Override
public Map<String, String> getHeaders() throws AuthFailureError {
    Map<String, String> params = new HashMap<>();
    params.putAll(super.getHeaders());
    params.put("Accept-Encoding", "gzip,deflate");
    return params;
}

to decompress, the best bet is proverbface' answer:

@Override
protected Response<String> parseNetworkResponse(NetworkResponse response) {
    StringBuilder output = new StringBuilder();
    try {
        GZIPInputStream gStream = new GZIPInputStream(new ByteArrayInputStream(response.data));
        InputStreamReader reader = new InputStreamReader(gStream);
        BufferedReader in = new BufferedReader(reader, 16384);

        String read;

        while ((read = in.readLine()) != null) {
            output.append(read).append("\n");
        }
        reader.close();
        in.close();
        gStream.close();
    } catch (IOException e) {
        return Response.error(new ParseError());
    }

    return Response.success(output.toString(), HttpHeaderParser.parseCacheHeaders(response));
}

I have new working code set

import com.android.volley.NetworkResponse;
import com.android.volley.Response;
import com.android.volley.toolbox.HttpHeaderParser;
import com.android.volley.toolbox.StringRequest;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.zip.InflaterInputStream;

/**

• Created by Amol on 03-08-2016.
  */
  public class GZipRequest extends StringRequest {

  public GZipRequest(int method, String url, Response.Listener listener, Response.ErrorListener errorListener) {
  super(method, url, listener, errorListener);
  }

  public GZipRequest(String url, Response.Listener listener, Response.ErrorListener errorListener) {
  super(url, listener, errorListener);
  }

  @OverRide
  protected Response parseNetworkResponse(NetworkResponse response) {
  return Response.success(unzipString(response.data), HttpHeaderParser.parseCacheHeaders(response));
  }

  public static String unzipString(byte[] zbytes) {
  String charsetName = "ISO-8859-1";
  String unzipped = null;
  try {
  // Add extra byte to array when Inflater is set to true
  byte[] input = new byte[zbytes.length + 1];
  System.arraycopy(zbytes, 0, input, 0, zbytes.length);
  input[zbytes.length] = 0;
  ByteArrayInputStream bin = new ByteArrayInputStream(input);
  InflaterInputStream in = new InflaterInputStream(bin);
  ByteArrayOutputStream bout = new ByteArrayOutputStream(512);
  int b;
  while ((b = in.read()) != -1) {
  bout.write(b);
  }
  bout.close();
  unzipped = bout.toString(charsetName);
  } catch (IOException e) {
  e.printStackTrace();
  }
  return unzipped;
  }

}

Dear @scottagarman,

I added something like this:

        String encoding = response.headers.get("Content-Encoding");
        if(encoding != null && encoding.equals("gzip")) {

I'm not sure if there is a better way to do this check somewhere else but my servers don't always gzip things.

Just my two cents, you could write also if("gzip".equals(response.headers.get("Content-Encoding"))) {
Saves you both the check on null and the additional String object.

BTW: you can find my implementation for a JsonArrayRequest here: GZipJsonArrayRequest.java