add pipe example. Closes #9

examples/streams-pipe.js

@@ -0,0 +1,74 @@
+
+var zlib = require('zlib');
+var koa = require('..');
+var fs = require('fs');
+var app = koa();
+
+// ignore favicons
+
+app.use(function(next){
+  return function *(){
+    if ('/favicon.ico' == this.path) this.status = 404;
+    yield next;
+  }
+});
+
+// logger
+
+app.use(function(next){
+  return function *(){
+    console.log('%s %s', this.method, this.url);
+    yield next;
+  }
+});
+
+// stream a file
+
+app.use(function(next){
+  return function *(){
+    var path = __dirname + this.path;
+    var exists = yield isFile(path);
+
+    if (!exists) return yield next;
+
+    this.body = fs.createReadStream(path);
+    yield next;
+  }
+});
+
+// gzip the response
+
+app.use(function(next){
+  return function *(){
+    if (!this.hasContent) return yield next;
+
+    // TODO: fix ...
+    if (!this.body) return yield next;
+
+    if (this.body.readable) {
+      var body = this.body;
+      var gzip = zlib.createGzip();
+      this.set('Content-Encoding', 'gzip');
+      this.body = gzip;
+      body.pipe(gzip);
+    }
+
+    yield next;
+  }
+});
+
+app.listen(3000);
+
+/**
+ * Stat regular file helper.
+ */
+
+function isFile(file) {
+  return function(done){
+    fs.stat(file, function(err, stat){
+      if (err && 'ENOENT' == err.code) return done(null, false);
+      if (err) return done(err);
+      done(null, stat.isFile());
+    });
+  }
+}