hgext/lfs/wireprotolfsserver.py

lfs: add server side support for the Batch API

# wireprotolfsserver.py - lfs protocol server side implementation
#
# Copyright 2018 Matt Harbison <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import datetime
import errno
import json

from mercurial.hgweb import (
    common as hgwebcommon,
)

from mercurial import (
    pycompat,
)

HTTP_OK = hgwebcommon.HTTP_OK
HTTP_BAD_REQUEST = hgwebcommon.HTTP_BAD_REQUEST

def handlewsgirequest(orig, rctx, req, res, checkperm):
    """Wrap wireprotoserver.handlewsgirequest() to possibly process an LFS
    request if it is left unprocessed by the wrapped method.
    """
    if orig(rctx, req, res, checkperm):
        return True

    if not req.dispatchpath:
        return False

    try:
        if req.dispatchpath == b'.git/info/lfs/objects/batch':
            checkperm(rctx, req, 'pull')
            return _processbatchrequest(rctx.repo, req, res)
        # TODO: reserve and use a path in the proposed http wireprotocol /api/
        #       namespace?
        elif req.dispatchpath.startswith(b'.hg/lfs/objects'):
            return _processbasictransfer(rctx.repo, req, res,
                                         lambda perm:
                                                checkperm(rctx, req, perm))
        return False
    except hgwebcommon.ErrorResponse as e:
        # XXX: copied from the handler surrounding wireprotoserver._callhttp()
        #      in the wrapped function.  Should this be moved back to hgweb to
        #      be a common handler?
        for k, v in e.headers:
            res.headers[k] = v
        res.status = hgwebcommon.statusmessage(e.code, pycompat.bytestr(e))
        res.setbodybytes(b'0\n%s\n' % pycompat.bytestr(e))
        return True

def _sethttperror(res, code, message=None):
    res.status = hgwebcommon.statusmessage(code, message=message)
    res.headers[b'Content-Type'] = b'text/plain; charset=utf-8'
    res.setbodybytes(b'')

def _processbatchrequest(repo, req, res):
    """Handle a request for the Batch API, which is the gateway to granting file
    access.

    https://github.com/git-lfs/git-lfs/blob/master/docs/api/batch.md
    """

    # Mercurial client request:
    #
    #   HOST: localhost:$HGPORT
    #   ACCEPT: application/vnd.git-lfs+json
    #   ACCEPT-ENCODING: identity
    #   USER-AGENT: git-lfs/2.3.4 (Mercurial 4.5.2+1114-f48b9754f04c+20180316)
    #   Content-Length: 125
    #   Content-Type: application/vnd.git-lfs+json
    #
    #   {
    #     "objects": [
    #       {
    #         "oid": "31cf...8e5b"
    #         "size": 12
    #       }
    #     ]
    #     "operation": "upload"
    #  }

    if (req.method != b'POST'
        or req.headers[b'Content-Type'] != b'application/vnd.git-lfs+json'
        or req.headers[b'Accept'] != b'application/vnd.git-lfs+json'):
        # TODO: figure out what the proper handling for a bad request to the
        #       Batch API is.
        _sethttperror(res, HTTP_BAD_REQUEST, b'Invalid Batch API request')
        return True

    # XXX: specify an encoding?
    lfsreq = json.loads(req.bodyfh.read())

    # If no transfer handlers are explicitly requested, 'basic' is assumed.
    if 'basic' not in lfsreq.get('transfers', ['basic']):
        _sethttperror(res, HTTP_BAD_REQUEST,
                      b'Only the basic LFS transfer handler is supported')
        return True

    operation = lfsreq.get('operation')
    if operation not in ('upload', 'download'):
        _sethttperror(res, HTTP_BAD_REQUEST,
                      b'Unsupported LFS transfer operation: %s' % operation)
        return True

    localstore = repo.svfs.lfslocalblobstore

    objects = [p for p in _batchresponseobjects(req, lfsreq.get('objects', []),
                                                operation, localstore)]

    rsp = {
        'transfer': 'basic',
        'objects': objects,
    }

    res.status = hgwebcommon.statusmessage(HTTP_OK)
    res.headers[b'Content-Type'] = b'application/vnd.git-lfs+json'
    res.setbodybytes(pycompat.bytestr(json.dumps(rsp)))

    return True

def _batchresponseobjects(req, objects, action, store):
    """Yield one dictionary of attributes for the Batch API response for each
    object in the list.

    req: The parsedrequest for the Batch API request
    objects: The list of objects in the Batch API object request list
    action: 'upload' or 'download'
    store: The local blob store for servicing requests"""

    # Successful lfs-test-server response to solict an upload:
    # {
    #    u'objects': [{
    #       u'size': 12,
    #       u'oid': u'31cf...8e5b',
    #       u'actions': {
    #           u'upload': {
    #               u'href': u'http://localhost:$HGPORT/objects/31cf...8e5b',
    #               u'expires_at': u'0001-01-01T00:00:00Z',
    #               u'header': {
    #                   u'Accept': u'application/vnd.git-lfs'
    #               }
    #           }
    #       }
    #    }]
    # }

    # TODO: Sort out the expires_at/expires_in/authenticated keys.

    for obj in objects:
        # Convert unicode to ASCII to create a filesystem path
        oid = obj.get('oid').encode('ascii')
        rsp = {
            'oid': oid,
            'size': obj.get('size'),  # XXX: should this check the local size?
            #'authenticated': True,
        }

        exists = True
        verifies = False

        # Verify an existing file on the upload request, so that the client is
        # solicited to re-upload if it corrupt locally.  Download requests are
        # also verified, so the error can be flagged in the Batch API response.
        # (Maybe we can use this to short circuit the download for `hg verify`,
        # IFF the client can assert that the remote end is an hg server.)
        # Otherwise, it's potentially overkill on download, since it is also
        # verified as the file is streamed to the caller.
        try:
            verifies = store.verify(oid)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                rsp['error'] = {
                    'code': 500,
                    'message': inst.strerror or 'Internal Server Server'
                }
                yield rsp
                continue

            exists = False

        # Items are always listed for downloads.  They are dropped for uploads
        # IFF they already exist locally.
        if action == 'download':
            if not exists:
                rsp['error'] = {
                    'code': 404,
                    'message': "The object does not exist"
                }
                yield rsp
                continue

            elif not verifies:
                rsp['error'] = {
                    'code': 422,   # XXX: is this the right code?
                    'message': "The object is corrupt"
                }
                yield rsp
                continue

        elif verifies:
            yield rsp  # Skip 'actions': already uploaded
            continue

        expiresat = datetime.datetime.now() + datetime.timedelta(minutes=10)

        rsp['actions'] = {
            '%s' % action: {
                # TODO: Account for the --prefix, if any.
                'href': '%s/.hg/lfs/objects/%s' % (req.baseurl, oid),
                # datetime.isoformat() doesn't include the 'Z' suffix
                "expires_at": expiresat.strftime('%Y-%m-%dT%H:%M:%SZ'),
                'header': {
                    # The spec doesn't mention the Accept header here, but avoid
                    # a gratuitous deviation from lfs-test-server in the test
                    # output.
                    'Accept': 'application/vnd.git-lfs'
                }
            }
        }

        yield rsp

def _processbasictransfer(repo, req, res, checkperm):
    """Handle a single file upload (PUT) or download (GET) action for the Basic
    Transfer Adapter.

    After determining if the request is for an upload or download, the access
    must be checked by calling ``checkperm()`` with either 'pull' or 'upload'
    before accessing the files.

    https://github.com/git-lfs/git-lfs/blob/master/docs/api/basic-transfers.md
    """

    method = req.method

    if method == b'PUT':
        checkperm('upload')
    elif method == b'GET':
        checkperm('pull')

    return False