view hgeditor @ 36524:bfe38f787d5b

util: add a file object proxy that can notify observers

There are various places in Mercurial where we may want to
instrument low-level I/O. The use cases I can think of all
involve development-type activities like monitoring the raw
bytes passing through a file (for testing and debugging),
counting the number of I/O function calls (for performance
monitoring), and changing the behavior of I/O function calls
(e.g. simulating a failure) (to facilitate testing).

This commit invents a mechanism to wrap a file object so we
can observe activity on it. We have similar functionality in
badserverext.py. But that's a test-only extension and is pretty
specific to the HTTP server. I would like a mechanism in core
that is sufficiently generic so it can be used by multiple
consumers, including `hg debug*` commands.

The added code consists of a proxy type for file objects.
It is bound to an "observer," which receives callbacks whenever
I/O methods are called.

We also add an implementation of an observer that logs specific
I/O events. This observer will be used in an upcoming commit
to record low-level wire protocol activity.

A helper function to convert a file object into an observed
file object has also been implemented.

I don't anticipate any critical functionality in core using
these types. So I don't think explicit test coverage is
worth implementing.

Differential Revision: https://phab.mercurial-scm.org/D2462

#!/bin/sh
#
# This is an example of using HGEDITOR to create of diff to review the
# changes while committing.

# If you want to pass your favourite editor some other parameters
# only for Mercurial, modify this:
case "${EDITOR}" in
    "")
        EDITOR="vi"
        ;;
    emacs)
        EDITOR="$EDITOR -nw"
        ;;
    gvim|vim)
        EDITOR="$EDITOR -f -o"
        ;;
esac


HGTMP=""
cleanup_exit() {
    rm -rf "$HGTMP"
}

# Remove temporary files even if we get interrupted
trap "cleanup_exit" 0 # normal exit
trap "exit 255" HUP INT QUIT ABRT TERM

HGTMP=$(mktemp -d ${TMPDIR-/tmp}/hgeditor.XXXXXX)
[ x$HGTMP != x -a -d $HGTMP ] || {
  echo "Could not create temporary directory! Exiting." 1>&2
  exit 1
}

(
    grep '^HG: changed' "$1" | cut -b 13- | while read changed; do
        "$HG" diff "$changed" >> "$HGTMP/diff"
    done
)

cat "$1" > "$HGTMP/msg"

MD5=$(which md5sum 2>/dev/null) || \
    MD5=$(which md5 2>/dev/null)
[ -x "${MD5}" ] && CHECKSUM=`${MD5} "$HGTMP/msg"`
if [ -s "$HGTMP/diff" ]; then
    $EDITOR "$HGTMP/msg" "$HGTMP/diff" || exit $?
else
    $EDITOR "$HGTMP/msg" || exit $?
fi
[ -x "${MD5}" ] && (echo "$CHECKSUM" | ${MD5} -c >/dev/null 2>&1 && exit 13)

mv "$HGTMP/msg" "$1"

exit $?