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bundle2: ignore errors seeking a bundle after an exception (issue4784)...
bundle2: ignore errors seeking a bundle after an exception (issue4784) Many have seen a "stream ended unexpectedly" error. This message is raised from changegroup.readexactly() when a read(n) operation fails to return exactly N bytes. I believe most occurrences of this error in the wild stem from the code changed in this patch. Before, if bundle2's part applicator raised an Exception when processing/applying parts, the exception handler would attempt to iterate the remaining parts. If I/O during this iteration failed, it would likely raise the "stream ended unexpectedly" exception. The problem with this approach is that if we already encountered an I/O error iterating the bundle2 data during application, then any further I/O would almost certainly fail. If the original stream were closed, changegroup.readexactly() would obtain an empty string, triggering "stream ended unexpectedly" with "got 0." This is the error message that users would see. What's worse is that the original I/O related exception would be lost since a new exception would be raised. This made debugging the actual I/O failure effectively impossible. This patch changes the exception handler for bundle2 application to ignore errors when seeking the underlying stream. When the underlying error is I/O related, the seek should fail fast and the original exception will be re-raised. The output changes in test-http-bad-server.t demonstrate this. When the underlying error is not I/O related and the stream can be seeked, the old behavior is preserved.

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test-pager.t
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$ cat >> fakepager.py <<EOF
> import sys
> for line in sys.stdin:
> sys.stdout.write('paged! %r\n' % line)
> EOF
Enable ui.formatted because pager won't fire without it, and set up
pager and tell it to use our fake pager that lets us see when the
pager was running.
$ cat >> $HGRCPATH <<EOF
> [ui]
> formatted = yes
> [pager]
> pager = python $TESTTMP/fakepager.py
> EOF
$ hg init repo
$ cd repo
$ echo a >> a
$ hg add a
$ hg ci -m 'add a'
$ for x in `python $TESTDIR/seq.py 1 10`; do
> echo a $x >> a
> hg ci -m "modify a $x"
> done
By default diff and log are paged, but id is not:
$ hg diff -c 2 --pager=yes
paged! 'diff -r f4be7687d414 -r bce265549556 a\n'
paged! '--- a/a\tThu Jan 01 00:00:00 1970 +0000\n'
paged! '+++ b/a\tThu Jan 01 00:00:00 1970 +0000\n'
paged! '@@ -1,2 +1,3 @@\n'
paged! ' a\n'
paged! ' a 1\n'
paged! '+a 2\n'
$ hg log --limit 2
paged! 'changeset: 10:46106edeeb38\n'
paged! 'tag: tip\n'
paged! 'user: test\n'
paged! 'date: Thu Jan 01 00:00:00 1970 +0000\n'
paged! 'summary: modify a 10\n'
paged! '\n'
paged! 'changeset: 9:6dd8ea7dd621\n'
paged! 'user: test\n'
paged! 'date: Thu Jan 01 00:00:00 1970 +0000\n'
paged! 'summary: modify a 9\n'
paged! '\n'
$ hg id
46106edeeb38 tip
We can enable the pager on id:
BROKEN: should be paged
$ hg --config pager.attend-id=yes id
46106edeeb38 tip
Setting attend-$COMMAND to a false value works, even with pager in
core:
$ hg --config pager.attend-diff=no diff -c 2
diff -r f4be7687d414 -r bce265549556 a
--- a/a Thu Jan 01 00:00:00 1970 +0000
+++ b/a Thu Jan 01 00:00:00 1970 +0000
@@ -1,2 +1,3 @@
a
a 1
+a 2
If 'log' is in attend, then 'history' should also be paged:
$ hg history --limit 2 --config pager.attend=log
paged! 'changeset: 10:46106edeeb38\n'
paged! 'tag: tip\n'
paged! 'user: test\n'
paged! 'date: Thu Jan 01 00:00:00 1970 +0000\n'
paged! 'summary: modify a 10\n'
paged! '\n'
paged! 'changeset: 9:6dd8ea7dd621\n'
paged! 'user: test\n'
paged! 'date: Thu Jan 01 00:00:00 1970 +0000\n'
paged! 'summary: modify a 9\n'
paged! '\n'
Pager should not start if stdout is not a tty.
$ hg log -l1 -q --config ui.formatted=False
10:46106edeeb38
Pager should be disabled if pager.pager is empty (otherwise the output would
be silently lost.)
$ hg log -l1 -q --config pager.pager=
10:46106edeeb38
Pager with color enabled allows colors to come through by default,
even though stdout is no longer a tty.
$ cat >> $HGRCPATH <<EOF
> [extensions]
> color=
> [color]
> mode = ansi
> EOF
$ hg log --limit 3
paged! '\x1b[0;33mchangeset: 10:46106edeeb38\x1b[0m\n'
paged! 'tag: tip\n'
paged! 'user: test\n'
paged! 'date: Thu Jan 01 00:00:00 1970 +0000\n'
paged! 'summary: modify a 10\n'
paged! '\n'
paged! '\x1b[0;33mchangeset: 9:6dd8ea7dd621\x1b[0m\n'
paged! 'user: test\n'
paged! 'date: Thu Jan 01 00:00:00 1970 +0000\n'
paged! 'summary: modify a 9\n'
paged! '\n'
paged! '\x1b[0;33mchangeset: 8:cff05a6312fe\x1b[0m\n'
paged! 'user: test\n'
paged! 'date: Thu Jan 01 00:00:00 1970 +0000\n'
paged! 'summary: modify a 8\n'
paged! '\n'
An invalid pager command name is reported sensibly if we don't have to
use shell=True in the subprocess call:
$ hg log --limit 3 --config pager.pager=this-command-better-never-exist
missing pager command 'this-command-better-never-exist', skipping pager
\x1b[0;33mchangeset: 10:46106edeeb38\x1b[0m (esc)
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: modify a 10
\x1b[0;33mchangeset: 9:6dd8ea7dd621\x1b[0m (esc)
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: modify a 9
\x1b[0;33mchangeset: 8:cff05a6312fe\x1b[0m (esc)
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: modify a 8
A complicated pager command gets worse behavior. Bonus points if you can
improve this.
$ hg log --limit 3 \
> --config pager.pager='this-command-better-never-exist --seriously' \
> 2>/dev/null || true
Pager works with shell aliases.
$ cat >> $HGRCPATH <<EOF
> [alias]
> echoa = !echo a
> EOF
$ hg echoa
a
BROKEN: should be paged
$ hg --config pager.attend-echoa=yes echoa
a
Pager works with hg aliases including environment variables.
$ cat >> $HGRCPATH <<'EOF'
> [alias]
> printa = log -T "$A\n" -r 0
> EOF
$ A=1 hg --config pager.attend-printa=yes printa
paged! '1\n'
$ A=2 hg --config pager.attend-printa=yes printa
paged! '2\n'
Something that's explicitly attended is still not paginated if the
pager is globally set to off using a flag:
$ A=2 hg --config pager.attend-printa=yes printa --pager=no
2
Pager should not override the exit code of other commands
$ cat >> $TESTTMP/fortytwo.py <<'EOF'
> from mercurial import cmdutil, commands
> cmdtable = {}
> command = cmdutil.command(cmdtable)
> @command('fortytwo', [], 'fortytwo', norepo=True)
> def fortytwo(ui, *opts):
> ui.write('42\n')
> return 42
> EOF
$ cat >> $HGRCPATH <<'EOF'
> [extensions]
> fortytwo = $TESTTMP/fortytwo.py
> EOF
$ hg fortytwo --pager=on
paged! '42\n'
[42]
A command that asks for paging using ui.pager() directly works:
$ hg blame a
paged! ' 0: a\n'
paged! ' 1: a 1\n'
paged! ' 2: a 2\n'
paged! ' 3: a 3\n'
paged! ' 4: a 4\n'
paged! ' 5: a 5\n'
paged! ' 6: a 6\n'
paged! ' 7: a 7\n'
paged! ' 8: a 8\n'
paged! ' 9: a 9\n'
paged! '10: a 10\n'
but not with HGPLAIN
$ HGPLAIN=1 hg blame a
0: a
1: a 1
2: a 2
3: a 3
4: a 4
5: a 5
6: a 6
7: a 7
8: a 8
9: a 9
10: a 10
explicit flags work too:
$ hg blame --pager=no a
0: a
1: a 1
2: a 2
3: a 3
4: a 4
5: a 5
6: a 6
7: a 7
8: a 8
9: a 9
10: a 10
Put annotate in the ignore list for pager:
$ cat >> $HGRCPATH <<EOF
> [pager]
> ignore = annotate
> EOF
$ hg blame a
0: a
1: a 1
2: a 2
3: a 3
4: a 4
5: a 5
6: a 6
7: a 7
8: a 8
9: a 9
10: a 10
Environment variables like LESS and LV are set automatically:
$ cat > $TESTTMP/printlesslv.py <<EOF
> import os, sys
> sys.stdin.read()
> for name in ['LESS', 'LV']:
> sys.stdout.write(('%s=%s\n') % (name, os.environ.get(name, '-')))
> sys.stdout.flush()
> EOF
$ cat >> $HGRCPATH <<EOF
> [alias]
> noop = log -r 0 -T ''
> [ui]
> formatted=1
> [pager]
> pager = $PYTHON $TESTTMP/printlesslv.py
> EOF
$ unset LESS
$ unset LV
$ hg noop --pager=on
LESS=FRX
LV=-c
$ LESS=EFGH hg noop --pager=on
LESS=EFGH
LV=-c