Azik Azik - 2 months ago 21
Node.js Question

How to send an image from Android client to Node.js server via HttpUrlConnection?

I am trying to send an image to the server using HttpUrlConnection, because it's recommended by Google. I decided to convert the image into Base64 string and send it to the server where I decoded it into .jpg file. But this method is only feasible with small-sized thumbnails and I cannot send a full-sized images.

Here is the android client code:

public static void postData(Bitmap imageToSend) {



try

{
URL url = new URL("http://");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("POST");

conn.setDoInput(true);
conn.setDoOutput(true);

conn.setRequestProperty("Connection", "Keep-Alive");
conn.setRequestProperty("Cache-Control", "no-cache");

conn.setReadTimeout(35000);
conn.setConnectTimeout(35000);


ByteArrayOutputStream bos = new ByteArrayOutputStream();

// writes a compress version of Bitmap to a specified outputstream
imageToSend.compress(Bitmap.CompressFormat.JPEG, 100, bos);

byte[] byteArray = bos.toByteArray();
String imageEncoded = Base64.encodeToString(byteArray, Base64.DEFAULT);

List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("image", imageEncoded));


OutputStream os = conn.getOutputStream();
BufferedWriter writer = new BufferedWriter(
new OutputStreamWriter(os, "UTF-8"));

// getQuery is function for creating a URL encoded string
writer.write(getQuery(params));

System.out.println("Response Code: " + conn.getResponseCode());

InputStream in = new BufferedInputStream(conn.getInputStream());
Log.d("sdfs", "sfsd");
BufferedReader responseStreamReader = new BufferedReader(new InputStreamReader(in));
String line = "";
StringBuilder stringBuilder = new StringBuilder();
while ((line = responseStreamReader.readLine()) != null)
stringBuilder.append(line).append("\n");
responseStreamReader.close();

String response = stringBuilder.toString();
System.out.println(response);

bos.flush();
bos.close();
in.close();
conn.disconnect();

}

catch(MalformedURLException e) {
e.printStackTrace();
}

catch(IOException e) {
e.printStackTrace();
}


}


Node.js server code:



function base64_decode(base64str,file) {
var bitmap = new Buffer(base64str,'base64');
//writing into an image file
fs.writeFile(file, bitmap);
//write a text file
console.log('File created from base64 encoded string');
}

app.post("/", function (req,res,next) {
//requesting the value of the image key which is urlencoded base 64 string
var image = req.body.image;
console.log(req.body.image);
base64_decode(image,'newImage.jpg');

res.writeHead(200, {'Content-Type':'text/plain'});
res.write('the image is saved');
res.end();
if (req.url != "/")
next();





I cannot use the same method for the full-sized images, because of the BufferedWriter size limits - the base64 encoded string is too long for it.

Another method is using HttpPost and MultipartEntity, but both are deprecated in API22, and I did not know how to handle request on the server side. In the other examples some wrappers were used, like two hyphens, boundaries, crlf, but I could not find why.

I need an example with HttpUrlConnection

Any help is appreciated, because I'm newbie to Android and node.js

Answer

I'd recommend uploading binary data. You could place image meta-data (like name, type, user-id, ...) as url parameters or custom http-headers (X-...).

Android client code (not tested!):

 public static void postData(Bitmap imageToSend) {
        try
        {
            URL url = new URL("http://myserver/myapp/upload-image");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");

            conn.setDoInput(true);
            conn.setDoOutput(true);

            conn.setRequestProperty("Connection", "Keep-Alive");
            conn.setRequestProperty("Cache-Control", "no-cache");

            conn.setReadTimeout(35000);
            conn.setConnectTimeout(35000);

            // directly let .compress write binary image data
            // to the output-stream
            OutputStream os = conn.getOutputStream();
            imageToSend.compress(Bitmap.CompressFormat.JPEG, 100, os);
            os.flush();
            os.close();

            System.out.println("Response Code: " + conn.getResponseCode());

            InputStream in = new BufferedInputStream(conn.getInputStream());
            Log.d("sdfs", "sfsd");
            BufferedReader responseStreamReader = new BufferedReader(new InputStreamReader(in));
            String line = "";
            StringBuilder stringBuilder = new StringBuilder();
            while ((line = responseStreamReader.readLine()) != null)
                stringBuilder.append(line).append("\n");
            responseStreamReader.close();

            String response = stringBuilder.toString();
            System.out.println(response);

            conn.disconnect();
        }
        catch(MalformedURLException e) {
            e.printStackTrace();
        }
        catch(IOException e) {
            e.printStackTrace();
        }
}

Node.js, Express code:

function rawBody(req, res, next) {
    var chunks = [];

    req.on('data', function(chunk) {
        chunks.push(chunk);
    });

    req.on('end', function() {
        var buffer = Buffer.concat(chunks);

        req.bodyLength = buffer.length;
        req.rawBody = buffer;
        next();
    });

    req.on('error', function (err) {
        console.log(err);
        res.status(500);
    });
}

app.post('/upload-image', rawBody, function (req, res) {

    if (req.rawBody && req.bodyLength > 0) {

        // TODO save image (req.rawBody) somewhere

        // send some content as JSON
        res.send(200, {status: 'OK'});
    } else {
        res.send(500);
    }

});

I'll try to explain the node.js part: The function rawBody acts as Express middleware. When a POST request is made, this function gets called with the request object. It registers listeners for data, end and error events. The data events append all incoming chunks of data to a buffer. When end fires, the property rawBody is created in the request object and contains the binary data (your image blob). rawBody() then transfers control to the next handler which can now save the blob to your database or filesystem.

When dealing with really big data blobs, this kind of processing is not the best way. It would be better to stream the data to a file or to the database to save memory.