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.

     1

#!/usr/bin/env python

     2

# Dump revlogs as raw data stream

     3

# $ find .hg/store/ -name "*.i" | xargs dumprevlog > repo.dump

     4

     5

from __future__ import absolute_import, print_function

     6

     7

import sys

     8

from mercurial import (

     9

    encoding,

    10

    node,

    11

    pycompat,

    12

    revlog,

    13

)

    14

from mercurial.utils import (

    15

    procutil,

    16

)

    17

    18

for fp in (sys.stdin, sys.stdout, sys.stderr):

    19

    procutil.setbinary(fp)

    20

    21

def binopen(path, mode=b'rb'):

    22

    if b'b' not in mode:

    23

        mode = mode + b'b'

    24

    return open(path, pycompat.sysstr(mode))

    25

    26

def printb(data, end=b'\n'):

    27

    sys.stdout.flush()

    28

    pycompat.stdout.write(data + end)

    29

    30

for f in sys.argv[1:]:

    31

    r = revlog.revlog(binopen, encoding.strtolocal(f))

    32

    print("file:", f)

    33

    for i in r:

    34

        n = r.node(i)

    35

        p = r.parents(n)

    36

        d = r.revision(n)

    37

        printb(b"node: %s" % node.hex(n))

    38

        printb(b"linkrev: %d" % r.linkrev(i))

    39

        printb(b"parents: %s %s" % (node.hex(p[0]), node.hex(p[1])))

    40

        printb(b"length: %d" % len(d))

    41

        printb(b"-start-")

    42

        printb(d)

    43

        printb(b"-end-")