Merge pull request #1247 from tahoe-lafs/3960-misleading-ENOSPC-on-Windows

Attempt to workaround for failing Windows builds

Fixes ticket:3960

.github/workflows/ci.yml

@@ -86,8 +86,20 @@ jobs:
         run: python misc/build_helpers/show-tool-versions.py
 
       - name: Run tox for corresponding Python version
+        if: ${{ !contains(matrix.os, 'windows') }}
         run: python -m tox
 
+      # On Windows, a non-blocking pipe might respond (when emulating Unix-y
+      # API) with ENOSPC to indicate buffer full. Trial doesn't handle this
+      # well, so it breaks test runs. To attempt to solve this, we pipe the
+      # output through passthrough.py that will hopefully be able to do the right
+      # thing by using Windows APIs.
+      - name: Run tox for corresponding Python version
+        if: ${{ contains(matrix.os, 'windows') }}
+        run: |
+          pip install twisted pywin32
+          python -m tox | python misc/windows-enospc/passthrough.py
+
       - name: Upload eliot.log
         uses: actions/upload-artifact@v3
         with:

misc/windows-enospc/passthrough.py

@@ -0,0 +1,36 @@
+"""
+Writing to non-blocking pipe can result in ENOSPC when using Unix APIs on
+Windows.  So, this program passes through data from stdin to stdout, using
+Windows APIs instead of Unix-y APIs.
+"""
+
+from twisted.internet.stdio import StandardIO
+from twisted.internet import reactor
+from twisted.internet.protocol import Protocol
+from twisted.internet.interfaces import IHalfCloseableProtocol
+from twisted.internet.error import ReactorNotRunning
+from zope.interface import implementer
+
+@implementer(IHalfCloseableProtocol)
+class Passthrough(Protocol):
+    def readConnectionLost(self):
+        self.transport.loseConnection()
+
+    def writeConnectionLost(self):
+        try:
+            reactor.stop()
+        except ReactorNotRunning:
+            pass
+
+    def dataReceived(self, data):
+        self.transport.write(data)
+
+    def connectionLost(self, reason):
+        try:
+            reactor.stop()
+        except ReactorNotRunning:
+            pass
+
+
+std = StandardIO(Passthrough())
+reactor.run()