Support request gzip content.

Current CDN almost support auto gzip text base content mirrors.
e.g.: http://registry.qiniudn.com/npm
It can save ~650kb through gzip 700kb json content to 38kb.

lib/request.js

@@ -1,6 +1,7 @@
 module.exports = regRequest
 
 var url = require("url")
+  , zlib = require("zlib")
   , fs = require("graceful-fs")
   , rm = require("rimraf")
   , asyncMap = require("slide").asyncMap
@@ -128,6 +129,7 @@ function makeRequest (method, remote, where, what, etag, nofollow, cb_) {
   if (strict === undefined) strict = true
   var opts = { url: remote
              , method: method
+             , encoding: null // tell request let body be Buffer instance
              , ca: this.conf.get('ca')
              , localAddress: this.conf.get('local-address')
              , cert: this.conf.get('cert')
@@ -140,6 +142,7 @@ function makeRequest (method, remote, where, what, etag, nofollow, cb_) {
   }
 
   headers.accept = "application/json"
+  headers['accept-encoding'] = 'gzip'
 
   headers["user-agent"] = this.conf.get('user-agent') ||
                           'node/' + process.version
@@ -170,7 +173,7 @@ function makeRequest (method, remote, where, what, etag, nofollow, cb_) {
   this.log.http(method, remote.href || "/")
 
   var done = requestDone.call(this, method, where, cb)
-  var req = request(opts, done)
+  var req = request(opts, decodeResponseBody(done))
 
   req.on("error", cb)
   req.on("socket", function (s) {
@@ -182,6 +185,20 @@ function makeRequest (method, remote, where, what, etag, nofollow, cb_) {
   }
 }
 
+function decodeResponseBody(cb) {
+  return function (er, response, data) {
+    if (er) return cb(er, response, data)
+
+    if (response.headers['content-encoding'] !== 'gzip') return cb(er, response, data)
+
+    zlib.gunzip(data, function (er, buf) {
+      if (er) return cb(er, response, data)
+
+      cb(null, response, buf)
+    })
+  }
+}
+
 // cb(er, parsed, raw, response)
 function requestDone (method, where, cb) {
   return function (er, response, data) {

test/request-gzip-content.js

@@ -0,0 +1,47 @@
+var zlib = require('zlib')
+var tap = require('tap')
+var server = require('./fixtures/server.js')
+var RC = require('../')
+var pkg = {
+  _id: 'some-package-gzip@1.2.3',
+  name: 'some-package-gzip',
+  version: '1.2.3'
+}
+
+zlib.gzip(JSON.stringify(pkg), function (err, pkgGzip) {
+  var client = new RC({
+      cache: __dirname + '/fixtures/cache'
+    , 'fetch-retries': 1
+    , 'fetch-retry-mintimeout': 10
+    , 'fetch-retry-maxtimeout': 100
+    , registry: 'http://localhost:' + server.port })
+
+  tap.test('request gzip package content', function (t) {
+    server.expect('GET', '/some-package-gzip/1.2.3', function (req, res) {
+      res.statusCode = 200
+      res.setHeader('Content-Encoding', 'gzip');
+      res.setHeader('Content-Type', 'application/json');
+      res.end(pkgGzip)
+    })
+
+    client.get('/some-package-gzip/1.2.3', function (er, data, raw, res) {
+      if (er) throw er
+      t.deepEqual(data, pkg)
+      t.end()
+    })
+  })
+
+  tap.test('request wrong gzip package content', function (t) {
+    server.expect('GET', '/some-package-gzip-error/1.2.3', function (req, res) {
+      res.statusCode = 200
+      res.setHeader('Content-Encoding', 'gzip')
+      res.setHeader('Content-Type', 'application/json')
+      res.end(new Buffer('wrong gzip content'))
+    })
+
+    client.get('/some-package-gzip-error/1.2.3', function (er, data, raw, res) {
+      t.ok(er)
+      t.end()
+    })
+  })
+});