lfs: add support for serving blob files

lfs: add server side support for the Batch API

lfs: add basic routing for the server side wire protocol processing The recent hgweb refactoring yielded a clean point to wrap a function that could handle this, so I moved the routing for this out of the core. While not an hg wire protocol, this seems logically close enough. For now, these handlers do nothing other than check permissions. The protocol requires support for PUT requests, so that has been added to the core, and funnels into the same handler as GET and POST. The permission checking code was assuming that anything not checking 'pull' or None ops should be using POST. But that breaks the upload check if it checks 'push'. So I invented a new 'upload' permission, and used it to avoid the mandate to POST. A function wrap point could be added, but security code should probably stay grouped together. Given that anything not 'pull' or None was requiring POST, the comment on hgweb.common.permhooks is probably wrong- there is no 'read'. The rationale for the URIs is that the spec for the Batch API[1] defines the URL as the LFS server url + '/objects/batch'. The default git URLs are: Git remote: https://git-server.com/foo/bar LFS server: https://git-server.com/foo/bar.git/info/lfs Batch API: https://git-server.com/foo/bar.git/info/lfs/objects/batch '.git/' seems like it's not something a user would normally track. If we adhere to how git defines the URLs, then the hg-git extension should be able to talk to a git based server without any additional work. The URI for the transfer requests starts with '.hg/' to ensure that there are no conflicts with tracked files. Since these are handed out by the Batch API, we can change this at any point in the future. (Specifically, it might be a good idea to use something under the proposed /api/ namespace.) In any case, no files are stored at these locations in the repository directory. I started a new module for this because it seems like a good idea to keep all of the security sensitive server side code together. There's also an issue with `hg verify` in that it will want to download *all* blobs in order to run. Sadly, there's no way in the protocol to ask the server to verify the content of a blob it may have. (The verify action is for storing files on a 3rd party server, and then informing the LFS server when that completes.) So we may end up implementing a custom transfer adapter that simply indicates if the blobs are valid, and fall back to basic transfers for non-hg servers. In other words, this code is likely to get bigger before this is made non-experimental. [1] https://github.com/git-lfs/git-lfs/blob/master/docs/api/batch.md

test-lfs: drop trailing ', ' item separators from debug JSON output The trailing space looks weird when conditionalizing the line. The commas shouldn't be necessary because of the indenting. The `lfs-test-server` isn't sending all of the same items (notably, the "transfer" attribute is missing), so having the commas means more lines need to be conditionalized.

lfs: add a blob verification method to the local store A corrupt blob can be signaled through the Batch API response, without actually transferring the file. A true/false indicator is slightly easier than immediately catching an exception.

tests: conditionalize printed environment variable output in test-alias

debugsetparents: avoid using "r1/r2" variable names for nodeids Differential Revision: https://phab.mercurial-scm.org/D2963

tag: avoid using "r" variable name for nodeid Differential Revision: https://phab.mercurial-scm.org/D2962

locate: avoid using "rev" variable name for nodeid Also, drop silly "ctx = repo[ctx.node()]". Differential Revision: https://phab.mercurial-scm.org/D2961

py3: bytes/unicode dance on __doc__ of cmdalias