Add workaround for OSError raised by Popen.communicate()

Python 2.6 can raise OSError when too much data is
written to STDIN and the process died prematurely.

In the case of keystoneclient this happens during
the first cms_verify() call of a process. The calling
logic expects a useful error message in order to
refetch the CA or singing CERT, which is missing in the
case of an OSError. So just fake it instead.

Add basic unit tests to cover all of the public methods from
keystone.common.cms, raising test coverage to 77%. Add
unit test for this specific bug (test_cms_verify_token_no_oserror).

Closes-Bug: LP Bug#1235252

Change-Id: I6e650ab9494c605b4e41c78c87a9505e09d5fc29

1 files changed, 47 insertions, 4 deletions

diff --git a/keystoneclient/common/cms.py b/keystoneclient/common/cms.py
index da04029..0e6a5b7 100644
--- a/keystoneclient/common/cms.py
+++ b/keystoneclient/common/cms.py
@@ -21,6 +21,7 @@ If set_subprocess() is not called, this module will pick Python's subprocess
 or eventlet.green.subprocess based on if os module is patched by eventlet.
 """
 
+import errno
 import hashlib
 import logging
 
@@ -57,6 +58,46 @@ def set_subprocess(_subprocess=None):
     subprocess = _subprocess
 
 
+def _check_files_accessible(files):
+    err = None
+    try:
+        for try_file in files:
+            with open(try_file, 'r'):
+                pass
+    except IOError as e:
+        # Catching IOError means there is an issue with
+        # the given file.
+        err = ('Hit OSError in _process_communicate_handle_oserror()\n'
+               'Likely due to %s: %s') % (try_file, e.strerror)
+
+    return err
+
+
+def _process_communicate_handle_oserror(process, text, files):
+    """Wrapper around process.communicate that checks for OSError."""
+
+    try:
+        output, err = process.communicate(text)
+    except OSError as e:
+        if e.errno != errno.EPIPE:
+            raise
+        # OSError with EPIPE only occurs with Python 2.6.x/old 2.7.x
+        # http://bugs.python.org/issue10963
+
+        # The quick exit is typically caused by the openssl command not being
+        # able to read an input file, so check ourselves if can't read a file.
+        err = _check_files_accessible(files)
+        if process.stderr:
+            err += process.stderr.read()
+
+        output = ""
+        retcode = -1
+    else:
+        retcode = process.poll()
+
+    return output, err, retcode
+
+
 def cms_verify(formatted, signing_cert_file_name, ca_file_name):
     """Verifies the signature of the contents IAW CMS syntax.
 
@@ -73,8 +114,8 @@ def cms_verify(formatted, signing_cert_file_name, ca_file_name):
                                stdin=subprocess.PIPE,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE)
-    output, err = process.communicate(formatted)
-    retcode = process.poll()
+    output, err, retcode = _process_communicate_handle_oserror(
+        process, formatted, (signing_cert_file_name, ca_file_name))
 
     # Do not log errors, as some happen in the positive thread
     # instead, catch them in the calling code and log them there.
@@ -184,8 +225,10 @@ def cms_sign_text(text, signing_cert_file_name, signing_key_file_name):
                                stdin=subprocess.PIPE,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE)
-    output, err = process.communicate(text)
-    retcode = process.poll()
+
+    output, err, retcode = _process_communicate_handle_oserror(
+        process, text, (signing_cert_file_name, signing_key_file_name))
+
     if retcode or "Error" in err:
         LOG.error('Signing error: %s' % err)
         raise subprocess.CalledProcessError(retcode, "openssl")