From patchwork Sun Jun  4 23:59:24 2017
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Subject: [12,of,22] obsstore: let read marker API take a range of offsets
From: Jun Wu <quark@fb.com>
X-Patchwork-Id: 21190
Message-Id: <985b38cca3131ca81a96.1496620764@x1c>
To: <mercurial-devel@mercurial-scm.org>
Date: Sun, 4 Jun 2017 16:59:24 -0700

# HG changeset patch
# User Jun Wu <quark@fb.com>
# Date 1496595729 25200
#      Sun Jun 04 10:02:09 2017 -0700
# Node ID 985b38cca3131ca81a961ba4ab2006a3ef23ebb0
# Parent  69870e8f6bc97775c47d363efc5c58bce33239c0
# Available At https://bitbucket.org/quark-zju/hg-draft
#              hg pull https://bitbucket.org/quark-zju/hg-draft -r 985b38cca313
obsstore: let read marker API take a range of offsets

This allows us to read a customized range of markers, instead of loading all
of them.

The condition of stop is made consistent across C and Python implementation
so we will still read marker when offset=a, stop=a+1.

diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
--- a/mercurial/obsolete.py
+++ b/mercurial/obsolete.py
@@ -179,8 +179,7 @@ usingsha256 = 2
 _fm0fnodesize = _calcsize(_fm0node)
 
-def _fm0readmarkers(data, off):
+def _fm0readmarkers(data, off, stop):
     # Loop on markers
-    l = len(data)
-    while off + _fm0fsize <= l:
+    while off < stop:
         # read fixed part
         cur = data[off:off + _fm0fsize]
@@ -318,5 +317,5 @@ def _fm0decodemeta(data):
 _fm1metapairsize = _calcsize('BB')
 
-def _fm1purereadmarkers(data, off):
+def _fm1purereadmarkers(data, off, stop):
     # make some global constants local for performance
     noneflag = _fm1parentnone
@@ -332,8 +331,7 @@ def _fm1purereadmarkers(data, off):
 
     # Loop on markers
-    stop = len(data) - _fm1fsize
     ufixed = struct.Struct(_fm1fixed).unpack
 
-    while off <= stop:
+    while off < stop:
         # read fixed part
         o1 = off + fsize
@@ -429,9 +427,8 @@ def _fm1encodeonemarker(marker):
     return ''.join(data)
 
-def _fm1readmarkers(data, off):
+def _fm1readmarkers(data, off, stop):
     native = getattr(parsers, 'fm1readmarkers', None)
     if not native:
-        return _fm1purereadmarkers(data, off)
-    stop = len(data) - _fm1fsize
+        return _fm1purereadmarkers(data, off, stop)
     return native(data, off, stop)
 
@@ -445,12 +442,15 @@ def _readmarkerversion(data):
 
 @util.nogc
-def _readmarkers(data):
+def _readmarkers(data, off=None, stop=None):
     """Read and enumerate markers from raw data"""
     diskversion = _readmarkerversion(data)
-    off = 1
+    if not off:
+        off = 1  # skip 1 byte version number
+    if stop is None:
+        stop = len(data)
     if diskversion not in formats:
         msg = _('parsing obsolete marker: unknown version %r') % diskversion
         raise error.UnknownVersion(msg, version=diskversion)
-    return diskversion, formats[diskversion][0](data, off)
+    return diskversion, formats[diskversion][0](data, off, stop)
 
 def encodeheader(version=_fm0version):