view tests/test-githelp.t @ 40022:33eb670e2834

wireprotov2: define semantics for content redirects

When I implemented the clonebundles feature and deployed it on
hg.mozilla.org using Amazon S3 as a content server, server-side CPU
and bandwidth usage dropped off a cliff and a ton of server scaling
headaches went away pretty much the instant clients with support for
clonebundles were rolled out to Firefox CI.

An obvious takeaway from that experience was that offloading server
load to scalable file servers - potentially backed by a CDN - is a
really good idea. Another takeaway was that Mercurial's wire protocol
wasn't in a good position to support data offload generally.

In wire protocol version 1, there isn't a mechanism in the protocol to
say "grab the data from over here instead." For HTTP, we could teach
the client to follow HTTP redirects. Or we could invent a media type
that encoded redirects inline. But for SSH, we were pretty much out of
luck because that protocol wasn't very flexible.

Wire protocol version 2 offers the opportunity to do something better.

The recent generic server-side content caching layer in the wire
protocol version 2 server demonstrated that it is possible to have
drop-in caching of responses to command requests. This by itself
adds tons of value and already makes the built-in server much more
scalable. But I don't want to stop there.

The existing server-side caching implementation has a big weakness:
it requires the server to send data to the client. This means that
the Mercurial server is potentially sending gigabytes of data to
thousands of clients. This is problematic because compared to scaling
static file servers, scaling dynamic servers is *hard*.

A solution to this is to "offload" serving of content to something
that isn't the Mercurial server. By offloading content serving, you
turn the Mercurial server from a centralized monolithic service to
a distributed mostly-indexing service. Assuming high rates of content
offload, this should drastically reduce the total work performed by
the Mercurial server, both in terms of CPU and data transfer. This
will make Mercurial servers vastly easier to scale.

This commit defines the semantics for "content redirects" in wire
protocol version 2. Essentially:

* Servers advertise the set of locations a response could be served
  from.
* When making requests, clients advertise the set of locations they
  are willing to fetch content from.
* Servers can then replace the inline response with one that says
  "get the response from over here instead."

This feature - when fully implemented - will allow extending the
server-side caching layer to facilitate such things as integrating
your server-side cache with a scalable blob store (such as S3 or
a CDN) and offloading most data transfer to that external service.

This feature could also be leveraged for load balancing. e.g.
requests could come into a central server and then get redirected
to an available mirror depending on server availability or locality.
There's tons of potential :)

Differential Revision: https://phab.mercurial-scm.org/D4774

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > githelp =
  > EOF

  $ hg init repo
  $ cd repo
  $ echo foo > test_file
  $ mkdir dir
  $ echo foo > dir/file
  $ echo foo > removed_file
  $ echo foo > deleted_file
  $ hg add -q .
  $ hg commit -m 'bar'
  $ hg bookmark both
  $ touch both
  $ touch untracked_file
  $ hg remove removed_file
  $ rm deleted_file

githelp on a single command should succeed
  $ hg githelp -- commit
  hg commit
  $ hg githelp -- git commit
  hg commit

githelp should fail nicely if we don't give it arguments
  $ hg githelp
  abort: missing git command - usage: hg githelp -- <git command>
  [255]
  $ hg githelp -- git
  abort: missing git command - usage: hg githelp -- <git command>
  [255]

githelp on a command with options should succeed
  $ hg githelp -- commit -pm "abc"
  hg commit --interactive -m 'abc'

githelp on a command with standalone unrecognized option should succeed with warning
  $ hg githelp -- commit -p -v
  ignoring unknown option -v
  hg commit --interactive

githelp on a command with unrecognized option packed with other options should fail with error
  $ hg githelp -- commit -pv
  abort: unknown option 'v' packed with other options
  (please try passing the option as its own flag: -v)
  [255]

githelp for git rebase --skip
  $ hg githelp -- git rebase --skip
  hg revert --all -r .
  hg rebase --continue

githelp for git commit --amend (hg commit --amend pulls up an editor)
  $ hg githelp -- commit --amend
  hg commit --amend

githelp for git commit --amend --no-edit (hg amend does not pull up an editor)
  $ hg githelp -- commit --amend --no-edit
  hg amend

githelp for git checkout -- . (checking out a directory)
  $ hg githelp -- checkout -- .
  note: use --no-backup to avoid creating .orig files
  
  hg revert .

githelp for git checkout "HEAD^" (should still work to pass a rev)
  $ hg githelp -- checkout "HEAD^"
  hg update .^

githelp checkout: args after -- should be treated as paths no matter what
  $ hg githelp -- checkout -- HEAD
  note: use --no-backup to avoid creating .orig files
  
  hg revert HEAD

githelp for git checkout with rev and path
  $ hg githelp -- checkout "HEAD^" -- file.txt
  note: use --no-backup to avoid creating .orig files
  
  hg revert -r .^ file.txt

githelp for git with rev and path, without separator
  $ hg githelp -- checkout "HEAD^" file.txt
  note: use --no-backup to avoid creating .orig files
  
  hg revert -r .^ file.txt

githelp for checkout with a file as first argument
  $ hg githelp -- checkout test_file
  note: use --no-backup to avoid creating .orig files
  
  hg revert test_file

githelp for checkout with a removed file as first argument
  $ hg githelp -- checkout removed_file
  note: use --no-backup to avoid creating .orig files
  
  hg revert removed_file

githelp for checkout with a deleted file as first argument
  $ hg githelp -- checkout deleted_file
  note: use --no-backup to avoid creating .orig files
  
  hg revert deleted_file

githelp for checkout with a untracked file as first argument
  $ hg githelp -- checkout untracked_file
  note: use --no-backup to avoid creating .orig files
  
  hg revert untracked_file

githelp for checkout with a directory as first argument
  $ hg githelp -- checkout dir
  note: use --no-backup to avoid creating .orig files
  
  hg revert dir

githelp for checkout when not in repo root
  $ cd dir
  $ hg githelp -- checkout file
  note: use --no-backup to avoid creating .orig files
  
  hg revert file

  $ cd ..

githelp for checkout with an argument that is both a file and a revision
  $ hg githelp -- checkout both
  hg update both

githelp for checkout with the -p option
  $ hg githelp -- git checkout -p xyz
  hg revert -i -r xyz

  $ hg githelp -- git checkout -p xyz -- abc
  note: use --no-backup to avoid creating .orig files
  
  hg revert -i -r xyz abc

githelp for checkout with the -f option and a rev
  $ hg githelp -- git checkout -f xyz
  hg update -C xyz
  $ hg githelp -- git checkout --force xyz
  hg update -C xyz

githelp for checkout with the -f option without an arg
  $ hg githelp -- git checkout -f
  hg revert --all
  $ hg githelp -- git checkout --force
  hg revert --all

githelp for grep with pattern and path
  $ hg githelp -- grep shrubbery flib/intern/
  hg grep shrubbery flib/intern/

githelp for reset, checking ~ in git becomes ~1 in mercurial
  $ hg githelp -- reset HEAD~
  hg update .~1
  $ hg githelp -- reset "HEAD^"
  hg update .^
  $ hg githelp -- reset HEAD~3
  hg update .~3

  $ hg githelp -- reset --mixed HEAD
  note: --mixed has no meaning since Mercurial has no staging area
  
  hg update .
  $ hg githelp -- reset --soft HEAD
  note: --soft has no meaning since Mercurial has no staging area
  
  hg update .
  $ hg githelp -- reset --hard HEAD
  hg update --clean .

githelp for git show --name-status
  $ hg githelp -- git show --name-status
  hg log --style status -r .

githelp for git show --pretty=format: --name-status
  $ hg githelp -- git show --pretty=format: --name-status
  hg status --change .

githelp for show with no arguments
  $ hg githelp -- show
  hg export

githelp for show with a path
  $ hg githelp -- show test_file
  hg cat test_file

githelp for show with not a path:
  $ hg githelp -- show rev
  hg export rev

githelp for show with many arguments
  $ hg githelp -- show argone argtwo
  hg export argone argtwo
  $ hg githelp -- show test_file argone argtwo
  hg cat test_file argone argtwo

githelp for show with --unified options
  $ hg githelp -- show --unified=10
  hg export --config diff.unified=10
  $ hg githelp -- show -U100
  hg export --config diff.unified=100

githelp for show with a path and --unified
  $ hg githelp -- show -U20 test_file
  hg cat test_file --config diff.unified=20

githelp for stash drop without name
  $ hg githelp -- git stash drop
  hg shelve -d <shelve name>

githelp for stash drop with name
  $ hg githelp -- git stash drop xyz
  hg shelve -d xyz

githelp for whatchanged should show deprecated message
  $ hg githelp -- whatchanged -p
  this command has been deprecated in the git project, thus isn't supported by this tool
  

githelp for git branch -m renaming
  $ hg githelp -- git branch -m old new
  hg bookmark -m old new

When the old name is omitted, git branch -m new renames the current branch.
  $ hg githelp -- git branch -m new
  hg bookmark -m `hg log -T"{activebookmark}" -r .` new

Branch deletion in git strips commits
  $ hg githelp -- git branch -d
  hg strip -B
  $ hg githelp -- git branch -d feature
  hg strip -B feature -B
  $ hg githelp -- git branch --delete experiment1 experiment2
  hg strip -B experiment1 -B experiment2 -B

githelp for reuse message using the shorthand
  $ hg githelp -- git commit -C deadbeef
  hg commit -M deadbeef

githelp for reuse message using the the long version
  $ hg githelp -- git commit --reuse-message deadbeef
  hg commit -M deadbeef

githelp for apply with no options
  $ hg githelp -- apply
  hg import --no-commit

githelp for apply with directory strip custom
  $ hg githelp -- apply -p 5
  hg import --no-commit -p 5

git merge-base
  $ hg githelp -- git merge-base --is-ancestor
  ignoring unknown option --is-ancestor
  note: ancestors() is part of the revset language
  (learn more about revsets with 'hg help revsets')
  
  hg log -T '{node}\n' -r 'ancestor(A,B)'

githelp for git blame
  $ hg githelp -- git blame
  hg annotate -udl

githelp for add

  $ hg githelp -- git add
  hg add

  $ hg githelp -- git add -p
  note: Mercurial will commit when complete, as there is no staging area in Mercurial
  
  hg commit --interactive

  $ hg githelp -- git add --all
  note: use hg addremove to remove files that have been deleted
  
  hg add

githelp for reflog

  $ hg githelp -- git reflog
  hg journal
  
  note: in hg commits can be deleted from repo but we always have backups

  $ hg githelp -- git reflog --all
  hg journal --all
  
  note: in hg commits can be deleted from repo but we always have backups