changegroup: document deltaparent's choice of previous revision
As part of debugging low-level changegroup generation, I came across
what I initially thought was a weird behavior: changegroup v2 is
choosing the previous revision in the changegroup as a delta base
instead of p1. I was tempted to rewrite this to use p1, as p1
will delta better than prev in the common case. However, I realized
that taking p1 as the base would potentially require resolving a
revision fulltext and thus require more CPU for e.g. server-side
processing of getbundle requests.
This patch tweaks the code comment to note the choice of behavior.
It also notes there is room for a flag or config option to tweak
this behavior later: using p1 as the delta base would likely make
changegroups smaller at the expense of more CPU, which could be
beneficial for things like clone bundles.
A dummy certificate that will make OS X 10.6+ Python use the system CA
certificate store:
-----BEGIN CERTIFICATE-----
MIIBIzCBzgIJANjmj39sb3FmMA0GCSqGSIb3DQEBBQUAMBkxFzAVBgNVBAMTDmhn
LmV4YW1wbGUuY29tMB4XDTE0MDgzMDA4NDU1OVoXDTE0MDgyOTA4NDU1OVowGTEX
MBUGA1UEAxMOaGcuZXhhbXBsZS5jb20wXDANBgkqhkiG9w0BAQEFAANLADBIAkEA
mh/ZySGlcq0ALNLmA1gZqt61HruywPrRk6WyrLJRgt+X7OP9FFlEfl2tzHfzqvmK
CtSQoPINWOdAJMekBYFgKQIDAQABMA0GCSqGSIb3DQEBBQUAA0EAF9h49LkSqJ6a
IlpogZuUHtihXeKZBsiktVIDlDccYsNy0RSh9XxUfhk+XMLw8jBlYvcltSXdJ7We
aKdQRekuMQ==
-----END CERTIFICATE-----
This certificate was generated to be syntactically valid but never be usable;
it expired before it became valid.
Created as:
$ cat > cn.conf << EOT
> [req]
> distinguished_name = req_distinguished_name
> [req_distinguished_name]
> commonName = Common Name
> commonName_default = no.example.com
> EOT
$ openssl req -nodes -new -x509 -keyout /dev/null \
> -out dummycert.pem -days -1 -config cn.conf -subj '/CN=hg.example.com'
To verify the content of this certificate:
$ openssl x509 -in dummycert.pem -noout -text
Certificate:
Data:
Version: 1 (0x0)
Serial Number: 15629337334278746470 (0xd8e68f7f6c6f7166)
Signature Algorithm: sha1WithRSAEncryption
Issuer: CN=hg.example.com
Validity
Not Before: Aug 30 08:45:59 2014 GMT
Not After : Aug 29 08:45:59 2014 GMT
Subject: CN=hg.example.com
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
Public-Key: (512 bit)
Modulus:
00:9a:1f:d9:c9:21:a5:72:ad:00:2c:d2:e6:03:58:
19:aa:de:b5:1e:bb:b2:c0:fa:d1:93:a5:b2:ac:b2:
51:82:df:97:ec:e3:fd:14:59:44:7e:5d:ad:cc:77:
f3:aa:f9:8a:0a:d4:90:a0:f2:0d:58:e7:40:24:c7:
a4:05:81:60:29
Exponent: 65537 (0x10001)
Signature Algorithm: sha1WithRSAEncryption
17:d8:78:f4:b9:12:a8:9e:9a:22:5a:68:81:9b:94:1e:d8:a1:
5d:e2:99:06:c8:a4:b5:52:03:94:37:1c:62:c3:72:d1:14:a1:
f5:7c:54:7e:19:3e:5c:c2:f0:f2:30:65:62:f7:25:b5:25:dd:
27:b5:9e:68:a7:50:45:e9:2e:31