Mercurial > hg
view mercurial/wireprototypes.py @ 37051:40206e227412
wireproto: define and implement protocol for issuing requests
The existing HTTP and SSH wire protocols suffer from a host of flaws
and shortcomings. I've been wanting to rewrite the protocol for a while
now. Supporting partial clone - which will require new wire protocol
commands and capabilities - and other advanced server functionality
will be much easier if we start from a clean slate and don't have
to be constrained by limitations of the existing wire protocol.
This commit starts to introduce a new data exchange format for
use over the wire protocol.
The new protocol is built on top of "frames," which are atomic
units of metadata + data. Frames will make it easier to implement
proxies and other mechanisms that want to inspect data without
having to maintain state. The existing frame metadata is very
minimal and it will evolve heavily. (We will eventually support
things like concurrent requests, out-of-order responses,
compression, side-channels for status updates, etc. Some of
these will require additions to the frame header.)
Another benefit of frames is that all reads are of a fixed size.
A reader works by consuming a frame header, extracting the payload
length, then reading that many bytes. No lookahead, buffering, or
memory reallocations are needed.
The new protocol attempts to be transport agnostic. I want all that's
required to use the new protocol to be a pair of unidirectional,
half-duplex pipes. (Yes, we will eventually make use of full-duplex
pipes, but that's for another commit.) Notably, when the SSH
transport switches to this new protocol, stderr will be unused.
This is by design: the lack of stderr on HTTP harms protocol
behavior there. By shoehorning everything into a pair of pipes,
we can have more consistent behavior across transports.
We currently only define the client side parts of the new protocol,
specifically the bits for requesting that a command run. This keeps
the new code and feature small and somewhat easy to review.
We add support to `hg debugwireproto` for writing frames into
HTTP request bodies. Our tests that issue commands to the new
HTTP endpoint have been updated to transmit frames. The server
bits haven't been touched to consume the frames yet. This will
occur in the next commit...
Astute readers may notice that the command name is transmitted in
both the HTTP request URL and the command request frame. This is
partially a kludge from me initially implementing the frame-based
protocol for SSH first. But it is also a feature: I intend to
eventually support issuing multiple commands per HTTP request. This
will allow us to replace the abomination that is the "batch" wire
protocol command with a protocol-level mechanism for performing
multi-dispatch. Because I want the frame-based protocol to be
as similar as possible across transports, I'd rather we (redundantly)
include the command name in the frame than differ behavior between
transports that have out-of-band routing information (like HTTP)
readily available.
Differential Revision: https://phab.mercurial-scm.org/D2851
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Mon, 19 Mar 2018 16:49:53 -0700 |
parents | 1cfef5693203 |
children | 27527d8cff5c |
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# Copyright 2018 Gregory Szorc <gregory.szorc@gmail.com> # # 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 abc # Names of the SSH protocol implementations. SSHV1 = 'ssh-v1' # These are advertised over the wire. Increment the counters at the end # to reflect BC breakages. SSHV2 = 'exp-ssh-v2-0001' HTTPV2 = 'exp-http-v2-0001' # All available wire protocol transports. TRANSPORTS = { SSHV1: { 'transport': 'ssh', 'version': 1, }, SSHV2: { 'transport': 'ssh', 'version': 2, }, 'http-v1': { 'transport': 'http', 'version': 1, }, HTTPV2: { 'transport': 'http', 'version': 2, } } class bytesresponse(object): """A wire protocol response consisting of raw bytes.""" def __init__(self, data): self.data = data class ooberror(object): """wireproto reply: failure of a batch of operation Something failed during a batch call. The error message is stored in `self.message`. """ def __init__(self, message): self.message = message class pushres(object): """wireproto reply: success with simple integer return The call was successful and returned an integer contained in `self.res`. """ def __init__(self, res, output): self.res = res self.output = output class pusherr(object): """wireproto reply: failure The call failed. The `self.res` attribute contains the error message. """ def __init__(self, res, output): self.res = res self.output = output class streamres(object): """wireproto reply: binary stream The call was successful and the result is a stream. Accepts a generator containing chunks of data to be sent to the client. ``prefer_uncompressed`` indicates that the data is expected to be uncompressable and that the stream should therefore use the ``none`` engine. """ def __init__(self, gen=None, prefer_uncompressed=False): self.gen = gen self.prefer_uncompressed = prefer_uncompressed class streamreslegacy(object): """wireproto reply: uncompressed binary stream The call was successful and the result is a stream. Accepts a generator containing chunks of data to be sent to the client. Like ``streamres``, but sends an uncompressed data for "version 1" clients using the application/mercurial-0.1 media type. """ def __init__(self, gen=None): self.gen = gen class baseprotocolhandler(object): """Abstract base class for wire protocol handlers. A wire protocol handler serves as an interface between protocol command handlers and the wire protocol transport layer. Protocol handlers provide methods to read command arguments, redirect stdio for the duration of the request, handle response types, etc. """ __metaclass__ = abc.ABCMeta @abc.abstractproperty def name(self): """The name of the protocol implementation. Used for uniquely identifying the transport type. """ @abc.abstractmethod def getargs(self, args): """return the value for arguments in <args> returns a list of values (same order as <args>)""" @abc.abstractmethod def forwardpayload(self, fp): """Read the raw payload and forward to a file. The payload is read in full before the function returns. """ @abc.abstractmethod def mayberedirectstdio(self): """Context manager to possibly redirect stdio. The context manager yields a file-object like object that receives stdout and stderr output when the context manager is active. Or it yields ``None`` if no I/O redirection occurs. The intent of this context manager is to capture stdio output so it may be sent in the response. Some transports support streaming stdio to the client in real time. For these transports, stdio output won't be captured. """ @abc.abstractmethod def client(self): """Returns a string representation of this client (as bytes).""" @abc.abstractmethod def addcapabilities(self, repo, caps): """Adds advertised capabilities specific to this protocol. Receives the list of capabilities collected so far. Returns a list of capabilities. The passed in argument can be returned. """ @abc.abstractmethod def checkperm(self, perm): """Validate that the client has permissions to perform a request. The argument is the permission required to proceed. If the client doesn't have that permission, the exception should raise or abort in a protocol specific manner. """