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
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Ama
adding a
$ hg qnew a.patch
$ echo a >> a
$ hg qrefresh
$ hg qnew b.patch
$ echo b > b
$ hg add b
$ hg qrefresh
$ hg qnew c.patch
$ echo c > c
$ hg add c
$ hg qrefresh
$ hg qgoto a.patch
popping c.patch
popping b.patch
now at: a.patch
$ hg qgoto c.patch
applying b.patch
applying c.patch
now at: c.patch
$ hg qgoto b.patch
popping c.patch
now at: b.patch
Using index:
$ hg qgoto 0
popping b.patch
now at: a.patch
$ hg qgoto 2
applying b.patch
applying c.patch
now at: c.patch
No warnings when using index ... and update from non-qtip and with pending
changes in unrelated files:
$ hg qnew bug314159
$ echo d >> c
$ hg qrefresh
$ hg qnew bug141421
$ echo e >> b
$ hg qrefresh
$ hg up -r bug314159
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo f >> a
$ echo f >> b
$ echo f >> c
$ hg qgoto 1
abort: local changes found, qrefresh first
[255]
$ hg qgoto 1 -f
popping bug141421
popping bug314159
popping c.patch
now at: b.patch
$ hg st
M a
M b
? c.orig
$ hg up -qCr.
$ hg qgoto 3
applying c.patch
applying bug314159
now at: bug314159
Detect ambiguous non-index:
$ hg qgoto 14
patch name "14" is ambiguous:
bug314159
bug141421
abort: patch 14 not in series
[255]
$ cd ..