function findBoundary(header) {
    for (var i = 0; i < header.length; i++) {
        if (header[i].substr(0,2) === '--') {
            return header[i];
        }
    }

    return undefined;
}

function findContentType(header) {
    for (var i = 0; i < header.length; i++) {
        if (header[i].substr(0,13) === 'Content-Type:') {
            return header[i].substr(13).trim();
        }
    }

    return undefined;
}

DICOMWeb.getImageFrame = function(uri, mediaType) {
    mediaType = mediaType || 'application/octet-stream';

    return new Promise(function(resolve, reject) {
        var xhr = new XMLHttpRequest();
        xhr.responseType = 'arraybuffer';
        xhr.open('get', uri, true);
        xhr.setRequestHeader('Accept', 'multipart/related;type=' + mediaType);
        xhr.onreadystatechange = function(oEvent) {
            // TODO: consider sending out progress messages here as we receive the pixel data
            if (xhr.readyState === 4) {
                if (xhr.status === 200) {
                    // request succeeded, Parse the multi-part mime response
                    var imageFrameAsArrayBuffer = xhr.response;
                    var response = new Uint8Array(xhr.response);
                    // First look for the multipart mime header
                    var tokenIndex = findIndexOfString(response, '\n\r\n');
                    if (tokenIndex === -1) {
                        reject('invalid response - no multipart mime header');
                    }

                    var header = uint8ArrayToString(response, 0, tokenIndex);
                    // Now find the boundary  marker
                    var split = header.split('\r\n');
                    var boundary = findBoundary(split);
                    if (!boundary) {
                        reject('invalid response - no boundary marker');
                    }

                    var offset = tokenIndex + 4; // skip over the \n\r\n

                    // find the terminal boundary marker
                    var endIndex = findIndexOfString(response, boundary, offset);
                    if (endIndex === -1) {
                        reject('invalid response - terminating boundary not found');
                    }
                    // return the info for this pixel data
                    var length = endIndex - offset - 1;
                    resolve({
                        contentType: findContentType(split),
                        arrayBuffer: imageFrameAsArrayBuffer,
                        offset: offset,
                        length: length
                    });
                } else {
                    // request failed, reject the deferred
                    reject(xhr.response);
                }
            }
        };

        xhr.send();
    });
};