POST request to tracd with multipart 1.0.0 is stuck

[Jun Omae]

The form-data parser in multipart module attempts to read data from a Request instance more than Content-Length bytes. It is intent that an empty bytes is received if EOF reached, however, it is stuck when tracd is used.

[Jun Omae]

Workaround:

trac/web/wsgi.py

@@ -243 +243 @@
             self.rfile = None
 
 
+class WSGIInput(object):
+
+    __slots__ = ('rfile', 'remaining')
+
+    def __init__(self, rfile, environ):
+        length = environ.get('CONTENT_LENGTH')
+        if length and length.isdigit():
+            try:
+                length = int(length)
+            except:
+                length = None
+        else:
+            length = None
+        self.rfile = rfile
+        self.remaining = length
+
+    def __repr__(self):
+        return '<{} rfile={!r} remaining={!r}>'.format(self.__class__.__name__,
+                                                       self.rfile,
+                                                       self.remaining)
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        return self.readline()
+
+    def read(self, size=-1):
+        if self.remaining is None:
+            data = self.rfile.read(size)
+        else:
+            if size < 0:
+                size = self.remaining
+            elif size > self.remaining:
+                size = self.remaining
+            data = self.rfile.read(size)
+            self.remaining -= len(data)
+        return data
+
+    def readline(self, size=-1):
+        if size < 0:
+            size = self.remaining
+        elif size > self.remaining:
+            size = self.remaining
+        line = self.rfile.readline(size)
+        self.remaining -= len(line)
+        return line
+
+    def readlines(self, hint=-1):
+        raise NotImplementedError
+
+
 class WSGIServerGateway(WSGIGateway):
 
     def __init__(self, handler, environ):
-        WSGIGateway.__init__(self, environ, handler.rfile,
+        wsgi_input = WSGIInput(handler, environ)
+        WSGIGateway.__init__(self, environ, wsgi_input,
                              _ErrorsWrapper(lambda x: handler.log_error('%s', x)))
         self.handler = handler
 

[Jun Omae]

Replying to Jun Omae:

Workaround:

WSGI specification, ​PEP 3333 – Python Web Server Gateway Interface v1.0.1 | peps.python.org, says:

The server is not required to read past the client’s specified Content-Length, and should simulate an end-of-file condition if the application attempts to read past that point. The application should not attempt to read more data than is specified by the CONTENT_LENGTH variable.

So that, we should provide WSGIInput class in the workaround to simulate EOF condition.