Lib/test/test_socket.py: skip testGetServBy if /etc/services is not found

[30ce6405-8009-45b0-95f2-ede633b46a57]

BPO	20868
Nosy	@vstinner, @tiran, @ned-deily, @iritkatriel
Files	skip_testGetServBy.patch

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GitHub fields: ```python assignee = None closed_at = created_at = labels = [] title = 'Lib/test/test_socket.py: skip testGetServBy if /etc/services is not found' updated_at = user = 'https://bugs.python.org/Steap' ``` bugs.python.org fields: ```python activity = actor = 'christian.heimes' assignee = 'none' closed = True closed_date = closer = 'christian.heimes' components = [] creation = creator = 'Steap' dependencies = [] files = ['34304'] hgrepos = [] issue_num = 20868 keywords = ['patch'] message_count = 6.0 messages = ['212910', '212912', '213016', '213635', '406598', '406599'] nosy_count = 5.0 nosy_names = ['vstinner', 'christian.heimes', 'ned.deily', 'Steap', 'iritkatriel'] pr_nums = [] priority = 'normal' resolution = 'rejected' stage = 'resolved' status = 'closed' superseder = None type = None url = 'https://bugs.python.org/issue20868' versions = [] ```

[30ce6405-8009-45b0-95f2-ede633b46a57]

In Lib/test/test_socket.py, testGetServBy calls socket.getservbyname(), which needs /etc/services (see "man getservbyname"). If this file is not found, the test fails instead of being skipped.

The attached patch was written against the latest revision of the Mercurial repository. It might be worth applying it for every currently supported version of Python.

[ned-deily]

Unfortunately, how getservbyname() and other similar network interface functions get their data is platform-dependent. /etc/services is a traditional file location but many modern systems use a database or shared database (e.g. NIS) and even allow the system administrator to dynamically change the source of the data. So, checking for /etc/services would cause the test to be skipped needlessly. I would think that most systems would not be very usable without a working getservbyname(). Under what circumstances is this causing a problem for you?

[vstinner]

I don't understand why /etc/services would miss. What is the current behaviour? What is the error message?

[30ce6405-8009-45b0-95f2-ede633b46a57]

I did not know that /etc/services is not always used :/

The main issue is that when you run the test suite in a chroot (to do "pure" builds) or in a network sandbox (for other functions). I get the following errors:

\====================================================================== ERROR: testGetServBy (test.test_socket.GeneralModuleTests) ----------------------------------------------------------------------

Traceback (most recent call last):
  File "/tmp/nix-build-python-3.3.4.drv-0/Python-3.3.4/Lib/test/test_socket.py", line 840, in testGetServBy
    raise socket.error
OSError

====================================================================== ERROR: testGetaddrinfo (test.test_socket.GeneralModuleTests) ----------------------------------------------------------------------

Traceback (most recent call last):
  File "/tmp/nix-build-python-3.3.4.drv-0/Python-3.3.4/Lib/test/test_socket.py", line 1126, in testGetaddrinfo
    socket.getaddrinfo(HOST, "http")
socket.gaierror: [Errno -8] Servname not supported for ai_socktype

====================================================================== ERROR: test_idna (test.test_socket.GeneralModuleTests) ----------------------------------------------------------------------

Traceback (most recent call last):
  File "/tmp/nix-build-python-3.3.4.drv-0/Python-3.3.4/Lib/test/test_socket.py", line 1186, in test_idna
    socket.gethostbyname('\u0438\u0441\u043f\u044b\u0442\u0430\u043d\u0438\u0435.python.org')
socket.gaierror: [Errno -2] Name or service not known

[iritkatriel]

when you run the test suite in a chroot (to do "pure" builds) or in a network sandbox (for other functions)

Do we support that?

[tiran]

Nope, we don't have to support this edge case.