Added simple yield server demonstrating streaming content to multiple…

… clients.

cookbook/streaming_large_files.md

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+---
+layout: default
+title: How to Stream Large Files
+---
+
+# How to Stream Large Files
+
+This is an example of how you can use web.py to stream large files.  You'll find it DOES work as advertised, but there are some protocol changes you may have to make to stream files of certain types to certain clients.  
+
+You need the content type and chunked header to make things show up correctly on a typical web browser.  
+
+Simple Example
+import web
+import time
+
+urls = (
+    "/",    "count_holder",
+    "/(.*)",  "count_down",
+    )
+app = web.application(urls, globals())
+
+
+class count_down:
+    def GET(self,count):
+        web.header('Content-type','text/html')
+        web.header('Transfer-Encoding','chunked')        
+        yield '<h2>Prepare for Launch!</h2>'
+        j = '<li>Liftoff in %s...</li>'
+        yield '<ul>'
+        count = int(count)
+        for i in range(count,0,-1):
+            out = j % i
+            time.sleep(1)
+            yield out
+        yield '</ul>'
+        time.sleep(1)
+        yield '<h1>Lift off</h1>'
+
+class count_holder:
+    def GET(self):
+        web.header('Content-type','text/html')
+        web.header('Transfer-Encoding','chunked')        
+        boxes = 4
+        delay = 3
+        countdown = 10
+        for i in range(boxes):
+            output = '<iframe src="/%d" width="200" height="500"></iframe>' % (countdown - i)
+            yield output
+            time.sleep(delay)
+
+if __name__ == "__main__":
+    app.run()