deal gracefully with invalid file descriptors - don't capture the particular stream

--HG--
branch : trunk

py/_io/capture.py

@@ -175,7 +175,8 @@ class Capture(object):
 class StdCaptureFD(Capture): 
     """ This class allows to capture writes to FD1 and FD2 
         and may connect a NULL file to FD0 (and prevent
-        reads from sys.stdin)
+        reads from sys.stdin).  If any of the 0,1,2 file descriptors 
+        is invalid it will not be captured. 
     """
     def __init__(self, out=True, err=True, mixed=False, 
         in_=True, patchsys=True, now=True):
@@ -192,13 +193,19 @@ class StdCaptureFD(Capture):
         mixed = self._options['mixed']
         self.in_ = in_
         if in_:
+            try:
                 self._oldin = (sys.stdin, os.dup(0))
+            except OSError:
+                pass 
         if out:
             tmpfile = None
             if hasattr(out, 'write'):
                 tmpfile = out
-            self.out = py.io.FDCapture(1, tmpfile=tmpfile, now=False)
+            try:
+                self.out = FDCapture(1, tmpfile=tmpfile, now=False)
                 self._options['out'] = self.out.tmpfile
+            except OSError:
+                pass 
         if err:
             if out and mixed:
                 tmpfile = self.out.tmpfile 
@@ -206,8 +213,11 @@ class StdCaptureFD(Capture):
                 tmpfile = err
             else:
                 tmpfile = None
-            self.err = py.io.FDCapture(2, tmpfile=tmpfile, now=False) 
+            try:
+                self.err = FDCapture(2, tmpfile=tmpfile, now=False) 
                 self._options['err'] = self.err.tmpfile
+            except OSError:
+                pass 
 
     def startall(self):
         if self.in_:

testing/io_/test_capture.py

@@ -360,6 +360,28 @@ def test_stdcapture_fd_tmpfile(tmpfile):
     outf, errf = capfd.done()
     assert outf == tmpfile
 
+class TestStdCaptureFDinvalidFD:
+    pytestmark = needsdup
+    def test_stdcapture_fd_invalid_fd(self, testdir):
+        testdir.makepyfile("""
+            import py, os
+            def test_stdout():
+                os.close(1)
+                cap = py.io.StdCaptureFD(out=True, err=False, in_=False)
+                cap.done()
+            def test_stderr():
+                os.close(2)
+                cap = py.io.StdCaptureFD(out=False, err=True, in_=False)
+                cap.done()
+            def test_stdin():
+                os.close(0)
+                cap = py.io.StdCaptureFD(out=False, err=False, in_=True)
+                cap.done()
+        """)
+        result = testdir.runpytest("--capture=fd")
+        assert result.ret == 0
+        assert result.parseoutcomes()['passed'] == 3
+
 def test_capture_not_started_but_reset(): 
     capsys = py.io.StdCapture(now=False)
     capsys.done()