wireproto: define and implement HTTP handshake to upgrade protocol
When clients connect to repositories over HTTP, they issue a request
to the well-known URL "?cmd=capabilities" to fetch the repository
capabilities. This is the handshake portion of the HTTP protocol.
This commit defines a mechanism to use that HTTP request to return
information about modern server features.
If a client sends an X-HgUpgrade-* header containing a list of
client-supported API names, the server responds with a response
containing information about available services. This includes
the normal capabilities string. So if the server doesn't support
any newer services, the client can easily fall back.
By advertising supported services from clients, server operators
can see and log what client support exists in the wild. This will
also help with debugging.
The response contains the base path to API services. We know there
are potential issues with the <repo>/api/ URL space conflicting with
hgwebdir and subrepos. By making the API URL dynamic from the
perspective of the client, the URL for APIs is not subject to backwards
compatibility concerns - at least as long as a ?cmd=capabilities request
is made.
We've also defined the ``cbor`` client capability for the X-HgProto-*
header. This MUST be sent in order to get the modern response from
"?cmd=capabilities". During implementation, I initially always sent
an application/mercurial-cbor response. However, the handshake
mechanism will be more future compatible if the client is in charge
of which formats to request. We already perform content negotiation
from X-HgProto-*, so keying off this for the capabilities response
feels appropriate.
In addition, I initially used application/cbor. However, it is
conceivable that a non-Mercurial server could serve application/cbor.
To rule out this possibility, I've invented a new media type that
is Mercurial specific and can't be confused for generic CBOR.
Differential Revision: https://phab.mercurial-scm.org/D3242
https://bz.mercurial-scm.org/1175
$ hg init
$ touch a
$ hg ci -Am0
adding a
$ hg mv a a1
$ hg ci -m1
$ hg co 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg mv a a2
$ hg up
note: possible conflict - a was renamed multiple times to:
a2
a1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg ci -m2
$ touch a
$ hg ci -Am3
adding a
$ hg mv a b
$ hg ci -Am4 a
$ hg ci --debug --traceback -Am5 b
committing files:
b
warning: can't find ancestor for 'b' copied from 'a'!
committing manifest
committing changelog
updating the branch cache
committed changeset 5:83a687e8a97c80992ba385bbfd766be181bfb1d1
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
4 files, 6 changesets, 4 total revisions
$ hg export --git tip
# HG changeset patch
# User test
# Date 0 0
# Thu Jan 01 00:00:00 1970 +0000
# Node ID 83a687e8a97c80992ba385bbfd766be181bfb1d1
# Parent 1d1625283f71954f21d14c3d44d0ad3c019c597f
5
diff --git a/b b/b
new file mode 100644
https://bz.mercurial-scm.org/show_bug.cgi?id=4476
$ hg init foo
$ cd foo
$ touch a && hg ci -Aqm a
$ hg mv a b
$ echo b1 >> b
$ hg ci -Aqm b1
$ hg up 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg mv a b
$ echo b2 >> b
$ hg ci -Aqm b2
$ hg graft 1
grafting 1:5974126fad84 "b1"
merging b
warning: conflicts while merging b! (edit, then use 'hg resolve --mark')
abort: unresolved conflicts, can't continue
(use 'hg resolve' and 'hg graft --continue')
[255]
$ echo a > b
$ echo b3 >> b
$ hg resolve --mark b
(no more unresolved files)
continue: hg graft --continue
$ hg graft --continue
grafting 1:5974126fad84 "b1"
warning: can't find ancestor for 'b' copied from 'a'!
$ hg log -f b -T 'changeset: {rev}:{node|short}\nsummary: {desc}\n\n'
changeset: 3:376d30ccffc0
summary: b1
changeset: 2:416baaa2e5e4
summary: b2
changeset: 0:3903775176ed
summary: a