Retry on WANT_WRITE & WANT_READ in sendall()

CHANGELOG.rst

@@ -225,6 +225,10 @@ Deprecations:
 Changes:
 ^^^^^^^^
 
+- Fixed the inability of ``OpenSSL.SSL.Connection.sendall()`` to
+  keep with sending data over the wire after ``SSL_ERROR_WANT_READ``
+  or ``SSL_ERROR_WANT_WRITE`` is returned by ``SSL_write()``.
+  `#176 <https://github.com/pyca/pyopenssl/pull/176>`_
 - Added a new optional ``chain`` parameter to ``OpenSSL.crypto.X509StoreContext()``
   where additional untrusted certificates can be specified to help chain building.
   `#948 <https://github.com/pyca/pyopenssl/pull/948>`_

src/OpenSSL/SSL.py

@@ -2053,7 +2053,14 @@
                 result = _lib.SSL_write(
                     self._ssl, data + total_sent, min(left_to_send, 2147483647)
                 )
-                self._raise_ssl_error(self._ssl, result)
+                try:
+                    self._raise_ssl_error(self._ssl, result)
+                except (WantReadError, WantWriteError):
+                    # NOTE: The use of SSL_MODE_ENABLE_PARTIAL_WRITE
+                    # NOTE: above guarantees that in case of failure
+                    # NOTE: no bytes have been written so we don't need
+                    # NOTE: to update the counters, just need to retry.
+                    continue
                 total_sent += result
                 left_to_send -= result