Support for outgoing HTTP trailing headers

doc/api.markdown

@@ -1894,6 +1894,24 @@ header information and the first body to the client. The second time
 data, and sends that separately. That is, the response is buffered up to the
 first chunk of body.
 
+### response.addTrailers(headers)
+
+This method adds HTTP trailing headers (a header but at the end of the
+message) to the response. 
+
+Trailers will **only** be emitted if chunked encoding is used for the 
+response; if it is not (e.g., if the request was HTTP/1.0), they will
+be silently discarded.
+
+Note that HTTP requires the `Trailer` header to be sent if you intend to
+emit trailers, with a list of the header fields in its value. E.g.,
+
+    response.writeHead(200, { 'Content-Type': 'text/plain',
+                              'Trailer': 'TraceInfo' });
+    response.write(fileData);
+    response.addTrailers({'Content-MD5': "7895bf4b8828b55ceaf47747b4bca667"});
+    response.end();
+
 
 ### response.end([data], [encoding])
 

lib/http.js

@@ -292,6 +292,7 @@ function OutgoingMessage (socket) {
   this.useChunkedEncodingByDefault = true;
 
   this._hasBody = true;
+  this._trailer = '';
 
   this.finished = false;
 }
@@ -484,6 +485,26 @@ OutgoingMessage.prototype.write = function (chunk, encoding) {
   return ret;
 };
 
+
+OutgoingMessage.prototype.addTrailers = function (headers) {
+  this._trailer = "";
+  var keys = Object.keys(headers);
+  var isArray = (Array.isArray(headers));
+  for (var i = 0, l = keys.length; i < l; i++) {
+    var key = keys[i];
+    if (isArray) {
+      field = headers[key][0];
+      value = headers[key][1];
+    } else {
+      field = key;
+      value = headers[key];
+    }
+
+    this._trailer += field + ": " + value + CRLF;
+  }
+};
+
+
 OutgoingMessage.prototype.finish = function () {
   throw new Error("finish() has been renamed to close().");
 };
@@ -520,7 +541,9 @@ OutgoingMessage.prototype.end = function (data, encoding) {
                                  + l
                                  + CRLF
                                  + data
-                                 + "\r\n0\r\n\r\n"
+                                 + "\r\n0\r\n"
+                                 + this._trailer
+                                 + "\r\n"
                                  , encoding
                                  );
     } else {
@@ -535,7 +558,7 @@ OutgoingMessage.prototype.end = function (data, encoding) {
 
   if (!hot) {
     if (this.chunkedEncoding) {
-      ret = this._send('0\r\n\r\n'); // Last chunk.
+      ret = this._send('0\r\n' + this._trailer + '\r\n'); // Last chunk.
     } else if (!data) {
       // Force a flush, HACK.
       ret = this._send('');

test/simple/test-http-set-trailers.js

@@ -0,0 +1,75 @@
+common = require("../common");
+assert = common.assert;
+http = require("http");
+net = require("net");
+
+outstanding_reqs = 0;
+
+var server = http.createServer(function(req, res) {
+  res.writeHead(200, [ ['content-type', 'text/plain'] ]);
+  res.addTrailers({"x-foo": "bar"});
+  res.end("stuff" + "\n");
+});
+server.listen(common.PORT);
+
+
+// first, we test an HTTP/1.0 request.
+server.addListener("listening", function() {
+  var c = net.createConnection(common.PORT);
+  var res_buffer = "";
+
+  c.setEncoding("utf8");
+
+  c.addListener("connect", function () {
+    outstanding_reqs++;
+    c.write( "GET / HTTP/1.0\r\n\r\n" );
+  });
+
+  c.addListener("data", function (chunk) {
+//    console.log(chunk);
+    res_buffer += chunk;
+  });
+
+  c.addListener("end", function () {
+    c.end();
+    assert.ok(! /x-foo/.test(res_buffer), "Trailer in HTTP/1.0 response.");
+    outstanding_reqs--;
+    if (outstanding_reqs == 0) {
+        server.close();
+        process.exit();
+    }
+  });
+});
+
+// now, we test an HTTP/1.1 request.
+server.addListener("listening", function() {
+  var c = net.createConnection(common.PORT);
+  var res_buffer = "";
+  var tid;
+
+  c.setEncoding("utf8");
+
+  c.addListener("connect", function () {
+    outstanding_reqs++;
+    c.write( "GET / HTTP/1.1\r\n\r\n" );
+    tid = setTimeout(assert.fail, 2000, "Couldn't find last chunk.");
+  });
+
+  c.addListener("data", function (chunk) {
+//    console.log(chunk);
+    res_buffer += chunk;
+    if (/0\r\n/.test(res_buffer)) { // got the end.
+        outstanding_reqs--;
+        clearTimeout(tid);
+        assert.ok(
+            /0\r\nx-foo: bar\r\n\r\n$/.test(res_buffer), 
+            "No trailer in HTTP/1.1 response."
+        );        
+        if (outstanding_reqs == 0) {
+            server.close();
+            process.exit();
+        }
+    }
+  });
+
+});