Express + Request Changing headers mid-stream

Question

I'm using express as my server and request to retrieve content from an up-stream box.

I've got this beautifully simple function to stream data from the up-stream to the client:

function(req, res){
  request("http://example.com").pipe(res);
}

The upstream box is returning a cache header Cache-Control: no-cache that I'd like to modify, so that Nginx (reverse proxy) can cache the response.

Where should I put the res.header('Cache-Control', 60);?

I've tried:

function(req, res){
  var retrieve = request("http://example.com");
  retrieve.on('data', function(chunk){
    if(res.get('Cache-Control') != 60)
      res.header('Cache-Control', 60);
  });
  retrieve.pipe(res);
}

But this throws a Error: Can't set headers after they are sent error.

Is there a listener that fires when the headers are sent, but before writeHeader() is called?

Have a look at http://stackoverflow.com/a/13032451/266795 and https://github.com/nodejitsu/node-http-proxy — Peter Lyons, Nov 01 '13 at 18:15
Perfect! Nice and simple. I'll add an answer once I'm allowed. — alexcline, Nov 01 '13 at 18:39

score 13 · Answer 1 · answered Jan 25 '15 at 22:42

13

It seems request has been updated since the accepted answer was submitted, making this process much easier. You can now do the following:

var resource = request('http://example.com');

resource.on('response', function(response) {
    response.headers['Cache-Control'] = 'max-age=60, public';
});

resource.pipe(res);

Much nicer!

answered Jan 25 '15 at 22:42

cbnz

656
1
9
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1

Take a look at the [request library](https://github.com/request/request). Basically, `request('http://example.com')` starts loading example.com and returns a [stream](https://nodejs.org/api/stream.html). Streams have an `.on()` method that allows you to listen for certain events, such as `'response'`, which is triggered when example.com has finished loading. When that happens, we set the cache control header. Finally, `resource.pipe(res)` takes the requst stream and redirects it back to `res`, which we can assume is what's being returned to the end user's browser. Does that make sense? – cbnz Aug 27 '15 at 03:09

score 8 · Accepted Answer · edited May 23 '17 at 12:09

8

Thanks to Peter Lyons, I was able to get this working using this code:

function(req, res){
  request("http://example.com").pipe(res);

  res.oldWriteHead = res.writeHead;
  res.writeHead = function(statusCode, reasonPhrase, headers){
    res.header('Cache-Control', 'max-age=60, public');
    res.oldWriteHead(statusCode, reasonPhrase, headers);
  }
}

edited May 23 '17 at 12:09

Community

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1

answered Nov 11 '13 at 17:34

alexcline

450
4
9

Express + Request Changing headers mid-stream

2 Answers2