posix: always seek to EOF when opening a file in append mode
Python 3 already does this, so skip it there.
Consider the program:
#include <stdio.h>
int main() {
FILE *f = fopen("narf", "w");
fprintf(f, "narf\n");
fclose(f);
f = fopen("narf", "a");
printf("%ld\n", ftell(f));
fprintf(f, "troz\n");
printf("%ld\n", ftell(f));
return 0;
}
on macOS, FreeBSD, and Linux with glibc, this program prints
5
10
but on musl libc (Alpine Linux and probably others) this prints
0
10
By my reading of
https://pubs.opengroup.org/onlinepubs/009695399/functions/fopen.html
this is technically correct, specifically:
> Opening a file with append mode (a as the first character in the
> mode argument) shall cause all subsequent writes to the file to be
> forced to the then current end-of-file, regardless of intervening
> calls to fseek().
in other words, the file position doesn't really matter in append-mode
files, and we can't depend on it being at all meaningful unless we
perform a seek() before tell() after open(..., 'a'). Experimentally
after a .write() we can do a .tell() and it'll always be reasonable,
but I'm unclear from reading the specification if that's a smart thing
to rely on. This matches what we do on Windows and what Python 3 does
for free, so let's just be consistent. Thanks to Yuya for the idea.
from __future__ import absolute_import, print_function
import unittest
class TestResult(unittest._TextTestResult):
def __init__(self, options, *args, **kwargs):
super(TestResult, self).__init__(*args, **kwargs)
self._options = options
# unittest.TestResult didn't have skipped until 2.7. We need to
# polyfill it.
self.skipped = []
# We have a custom "ignored" result that isn't present in any Python
# unittest implementation. It is very similar to skipped. It may make
# sense to map it into skip some day.
self.ignored = []
self.times = []
self._firststarttime = None
# Data stored for the benefit of generating xunit reports.
self.successes = []
self.faildata = {}
def addFailure(self, test, reason):
print("FAILURE!", test, reason)
def addSuccess(self, test):
print("SUCCESS!", test)
def addError(self, test, err):
print("ERR!", test, err)
# Polyfill.
def addSkip(self, test, reason):
print("SKIP!", test, reason)
def addIgnore(self, test, reason):
print("IGNORE!", test, reason)
def onStart(self, test):
print("ON_START!", test)
def onEnd(self):
print("ON_END!")
def addOutputMismatch(self, test, ret, got, expected):
return False
def stopTest(self, test, interrupted=False):
super(TestResult, self).stopTest(test)