var zlib = require('zlib');
var concatStream = require('concat-stream');
/**
* Modify the response of json
* @param res {Response} The http response
* @param contentEncoding {String} The http header content-encoding: gzip/deflate
* @param callback {Function} Custom modified logic
*/
module.exports = function modifyResponse(res, contentEncoding, callback) {
var unzip, zip;
// Now only deal with the gzip and deflate content-encoding.
if (contentEncoding === 'gzip') {
unzip = zlib.Gunzip();
zip = zlib.Gzip();
} else if (contentEncoding === 'deflate') {
unzip = zlib.Inflate();
zip = zlib.Deflate();
}
// The cache response method can be called after the modification.
var _write = res.write;
var _end = res.end;
if (unzip) {
unzip.on('error', function (e) {
console.log('Unzip error: ', e);
_end.call(res);
});
} else {
console.log('Not supported content-encoding: ' + contentEncoding);
return;
}
// The rewrite response method is replaced by unzip stream.
res.write = function (data) {
unzip.write(data);
};
res.end = function (data) {
unzip.end(data);
};
// Concat the unzip stream.
var concatWrite = concatStream(function (data) {
var body;
try {
body = JSON.parse(data.toString());
} catch (e) {
body = data.toString();
console.log('JSON.parse error:', e);
}
// Custom modified logic
if (typeof callback === 'function') {
body = callback(body);
}
// Converts the JSON to buffer.
body = new Buffer(JSON.stringify(body));
// Call the response method and recover the content-encoding.
zip.on('data', function (chunk) {
_write.call(res, chunk);
});
zip.on('end', function () {
_end.call(res);
});
zip.write(body);
zip.end();
});
unzip.pipe(concatWrite);
};