http: Add support for Expect:100-continue request header.

caucase/http_wsgibase.py

@@ -72,9 +72,24 @@ class ChunkedFile(ProxyFile):
     self._recv_buf = result[length:]
     return result[:length]
 
+class HookFirstReadFile(ProxyFile):
+  """
+  Trigger a callable on first read.
+  """
+  def __init__(self, actual_file, on_first_read):
+    super(HookFirstReadFile, self).__init__(actual_file)
+    self._on_first_read = on_first_read
+    self.read = self._read_hook
+
+  def _read_hook(self, *args, **kw):
+    self._on_first_read()
+    del self.read
+    return self.read(*args, **kw)
+
 class CleanServerHandler(ServerHandler):
   """
   - Handle chunked transfer encoding.
+  - Handle expect/continue protocol.
   - Do not include OS environment variables in each request's WSGI environment.
     Seriously, what the fsck, python ?
   """
@@ -97,3 +112,19 @@ class CleanServerHandler(ServerHandler):
         # We handle this, hide it from Application
         del environ['HTTP_TRANSFER_ENCODING']
         environ['wsgi.input'] = ChunkedFile(environ['wsgi.input'])
+      if environ.get('HTTP_EXPECT', '').lower() == '100-continue':
+        # We handle this, hide it from Application
+        del environ['HTTP_EXPECT']
+        environ['wsgi.input'] = HookFirstReadFile(
+          environ['wsgi.input'],
+          self._100_continue,
+        )
+
+  def _100_continue(self):
+    """
+    Emit "100 Continue" intermediate response.
+    """
+    self._write('HTTP/%s 100 Continue\r\n\r\n' % (
+      self.http_version,
+    ))
+    self._flush()