Add pycurl-specific hack to Iteratorizer

Inside the pycurl callback, we can't raise exceptions, because the
pycurl extension module will unconditionally print the exception
itself, and not pass it up to the caller.  Instead, we have the
callback return a value that tells curl to abort.  (-1 would be best,
in case we were given 0 bytes, but the extension doesn't support
that either).

This resolves the 'Exception("should die")' problem when interrupting
a streaming generator like stream_extract.

nilmdb/httpclient.py

@@ -119,7 +119,7 @@ class HTTPClient(object):
             self.curl.setopt(pycurl.WRITEFUNCTION, callback)
             self.curl.perform()
         try:
-            with nilmdb.utils.Iteratorizer(func) as it:
+            with nilmdb.utils.Iteratorizer(func, curl_hack = True) as it:
                 for i in it:
                     if self._status == 200:
                         # If we had a 200 response, yield the data to caller.

nilmdb/utils/iteratorizer.py

@@ -10,7 +10,7 @@ import contextlib
 # Based partially on http://stackoverflow.com/questions/9968592/
 
 class IteratorizerThread(threading.Thread):
-    def __init__(self, queue, function):
+    def __init__(self, queue, function, curl_hack):
         """
         function: function to execute, which takes the
         callback (provided by this class) as an argument
@@ -19,11 +19,24 @@ class IteratorizerThread(threading.Thread):
         self.function = function
         self.queue = queue
         self.die = False
+        self.curl_hack = curl_hack
 
     def callback(self, data):
-        if self.die:
-            raise Exception() # trigger termination
-        self.queue.put((1, data))
+        try:
+            if self.die:
+                raise Exception() # trigger termination
+            self.queue.put((1, data))
+        except:
+            if self.curl_hack:
+                # We can't raise exceptions, because the pycurl
+                # extension module will unconditionally print the
+                # exception itself, and not pass it up to the caller.
+                # Instead, just return a value that tells curl to
+                # abort.  (-1 would be best, in case we were given 0
+                # bytes, but the extension doesn't support that).
+                self.queue.put((2, sys.exc_info()))
+                return 0
+            raise
 
     def run(self):
         try:
@@ -34,7 +47,7 @@ class IteratorizerThread(threading.Thread):
             self.queue.put((0, result))
 
 @contextlib.contextmanager
-def Iteratorizer(function):
+def Iteratorizer(function, curl_hack = False):
     """
     Context manager that takes a function expecting a callback,
     and provides an iterable that yields the values passed to that
@@ -49,7 +62,7 @@ def Iteratorizer(function):
         print 'function returned:', it.retval
     """
     queue = Queue.Queue(maxsize = 1)
-    thread = IteratorizerThread(queue, function)
+    thread = IteratorizerThread(queue, function, curl_hack)
     thread.daemon = True
     thread.start()
 

tests/test_iteratorizer.py

@@ -52,3 +52,10 @@ class TestIteratorizer(object):
                 it.next()
         foo()
         eq_(it.retval, None)
+
+        # Do the same thing when the curl hack is applied
+        def foo():
+            with nilmdb.utils.Iteratorizer(f, curl_hack = True) as it:
+                it.next()
+        foo()
+        eq_(it.retval, None)