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
Set up a repo
$ cat <<EOF >> $HGRCPATH
> [ui]
> interactive = true
> [extensions]
> record =
> EOF
$ hg init a
$ cd a
Record help
$ hg record -h
hg record [OPTION]... [FILE]...
interactively select changes to commit
If a list of files is omitted, all changes reported by 'hg status' will be
candidates for recording.
See 'hg help dates' for a list of formats valid for -d/--date.
If using the text interface (see 'hg help config'), you will be prompted
for whether to record changes to each modified file, and for files with
multiple changes, for each change to use. For each query, the following
responses are possible:
y - record this change
n - skip this change
e - edit this change manually
s - skip remaining changes to this file
f - record remaining changes to this file
d - done, skip remaining changes and files
a - record all changes to all remaining files
q - quit, recording no changes
? - display help
This command is not available when committing a merge.
(use 'hg help -e record' to show help for the record extension)
options ([+] can be repeated):
-A --addremove mark new/missing files as added/removed before
committing
--close-branch mark a branch head as closed
--amend amend the parent of the working directory
-s --secret use the secret phase for committing
-e --edit invoke editor on commit messages
-I --include PATTERN [+] include names matching the given patterns
-X --exclude PATTERN [+] exclude names matching the given patterns
-m --message TEXT use text as commit message
-l --logfile FILE read commit message from file
-d --date DATE record the specified date as commit date
-u --user USER record the specified user as committer
-S --subrepos recurse into subrepositories
-w --ignore-all-space ignore white space when comparing lines
-b --ignore-space-change ignore changes in the amount of white space
-B --ignore-blank-lines ignore changes whose lines are all blank
-Z --ignore-space-at-eol ignore changes in whitespace at EOL
(some details hidden, use --verbose to show complete help)
Select no files
$ touch empty-rw
$ hg add empty-rw
$ hg record empty-rw<<EOF
> n
> EOF
diff --git a/empty-rw b/empty-rw
new file mode 100644
examine changes to 'empty-rw'? [Ynesfdaq?] n
no changes to record
[1]
$ hg tip -p
changeset: -1:000000000000
tag: tip
user:
date: Thu Jan 01 00:00:00 1970 +0000