# wireprotoframing.py - unified framing protocol for wire protocol

#

# 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.

# This file contains functionality to support the unified frame-based wire

# protocol. For details about the protocol, see

# `hg help internals.wireprotocol`.

from __future__ import absolute_import

import struct

from .i18n import _

from . import (

    error,

    util,

)

FRAME_HEADER_SIZE = 6

DEFAULT_MAX_FRAME_SIZE = 32768

FRAME_TYPE_COMMAND_NAME = 0x01

FRAME_TYPE_COMMAND_ARGUMENT = 0x02

FRAME_TYPE_COMMAND_DATA = 0x03

FRAME_TYPE_BYTES_RESPONSE = 0x04

FRAME_TYPE_ERROR_RESPONSE = 0x05

FRAME_TYPES = {

    b'command-name': FRAME_TYPE_COMMAND_NAME,

    b'command-argument': FRAME_TYPE_COMMAND_ARGUMENT,

    b'command-data': FRAME_TYPE_COMMAND_DATA,

    b'bytes-response': FRAME_TYPE_BYTES_RESPONSE,

    b'error-response': FRAME_TYPE_ERROR_RESPONSE,

}

FLAG_COMMAND_NAME_EOS = 0x01

FLAG_COMMAND_NAME_HAVE_ARGS = 0x02

FLAG_COMMAND_NAME_HAVE_DATA = 0x04

FLAGS_COMMAND = {

    b'eos': FLAG_COMMAND_NAME_EOS,

    b'have-args': FLAG_COMMAND_NAME_HAVE_ARGS,

    b'have-data': FLAG_COMMAND_NAME_HAVE_DATA,

}

FLAG_COMMAND_ARGUMENT_CONTINUATION = 0x01

FLAG_COMMAND_ARGUMENT_EOA = 0x02

FLAGS_COMMAND_ARGUMENT = {

    b'continuation': FLAG_COMMAND_ARGUMENT_CONTINUATION,

    b'eoa': FLAG_COMMAND_ARGUMENT_EOA,

}

FLAG_COMMAND_DATA_CONTINUATION = 0x01

FLAG_COMMAND_DATA_EOS = 0x02

FLAGS_COMMAND_DATA = {

    b'continuation': FLAG_COMMAND_DATA_CONTINUATION,

    b'eos': FLAG_COMMAND_DATA_EOS,

}

FLAG_BYTES_RESPONSE_CONTINUATION = 0x01

FLAG_BYTES_RESPONSE_EOS = 0x02

FLAGS_BYTES_RESPONSE = {

    b'continuation': FLAG_BYTES_RESPONSE_CONTINUATION,

    b'eos': FLAG_BYTES_RESPONSE_EOS,

}

FLAG_ERROR_RESPONSE_PROTOCOL = 0x01

FLAG_ERROR_RESPONSE_APPLICATION = 0x02

FLAGS_ERROR_RESPONSE = {

    b'protocol': FLAG_ERROR_RESPONSE_PROTOCOL,

    b'application': FLAG_ERROR_RESPONSE_APPLICATION,

}

# Maps frame types to their available flags.

FRAME_TYPE_FLAGS = {

    FRAME_TYPE_COMMAND_NAME: FLAGS_COMMAND,

    FRAME_TYPE_COMMAND_ARGUMENT: FLAGS_COMMAND_ARGUMENT,

    FRAME_TYPE_COMMAND_DATA: FLAGS_COMMAND_DATA,

    FRAME_TYPE_BYTES_RESPONSE: FLAGS_BYTES_RESPONSE,

    FRAME_TYPE_ERROR_RESPONSE: FLAGS_ERROR_RESPONSE,

}

ARGUMENT_FRAME_HEADER = struct.Struct(r'<HH')

def makeframe(requestid, frametype, frameflags, payload):

    """Assemble a frame into a byte array."""

    # TODO assert size of payload.

    frame = bytearray(FRAME_HEADER_SIZE + len(payload))

    # 24 bits length

    # 16 bits request id

    # 4 bits type

    # 4 bits flags

    l = struct.pack(r'<I', len(payload))

    frame[0:3] = l[0:3]

    struct.pack_into(r'<H', frame, 3, requestid)

    frame[5] = (frametype << 4) | frameflags

    frame[6:] = payload

    return frame

def makeframefromhumanstring(s):

    """Create a frame from a human readable string

    Strings have the form:

        <request-id> <type> <flags> <payload>

    This can be used by user-facing applications and tests for creating

    frames easily without having to type out a bunch of constants.

    Request ID is an integer.

    Frame type and flags can be specified by integer or named constant.

    Flags can be delimited by `|` to bitwise OR them together.

    """

    requestid, frametype, frameflags, payload = s.split(b' ', 3)

    requestid = int(requestid)

    if frametype in FRAME_TYPES:

        frametype = FRAME_TYPES[frametype]

    else:

        frametype = int(frametype)

    finalflags = 0

    validflags = FRAME_TYPE_FLAGS[frametype]

    for flag in frameflags.split(b'|'):

        if flag in validflags:

            finalflags |= validflags[flag]

        else:

            finalflags |= int(flag)

    payload = util.unescapestr(payload)

    return makeframe(requestid, frametype, finalflags, payload)

def parseheader(data):

    """Parse a unified framing protocol frame header from a buffer.

    The header is expected to be in the buffer at offset 0 and the

    buffer is expected to be large enough to hold a full header.

    """

    # 24 bits payload length (little endian)

    # 4 bits frame type

    # 4 bits frame flags

    # ... payload

    framelength = data[0] + 256 * data[1] + 16384 * data[2]

    requestid = struct.unpack_from(r'<H', data, 3)[0]

    typeflags = data[5]

    frametype = (typeflags & 0xf0) >> 4

    frameflags = typeflags & 0x0f

    return requestid, frametype, frameflags, framelength

def readframe(fh):

    """Read a unified framing protocol frame from a file object.

    Returns a 3-tuple of (type, flags, payload) for the decoded frame or

    None if no frame is available. May raise if a malformed frame is

    seen.

    """

    header = bytearray(FRAME_HEADER_SIZE)

    readcount = fh.readinto(header)

    if readcount == 0:

        return None

    if readcount != FRAME_HEADER_SIZE:

        raise error.Abort(_('received incomplete frame: got %d bytes: %s') %

                          (readcount, header))

    requestid, frametype, frameflags, framelength = parseheader(header)

    payload = fh.read(framelength)

    if len(payload) != framelength:

        raise error.Abort(_('frame length error: expected %d; got %d') %

                          (framelength, len(payload)))

    return requestid, frametype, frameflags, payload

def createcommandframes(requestid, cmd, args, datafh=None):

    """Create frames necessary to transmit a request to run a command.

    This is a generator of bytearrays. Each item represents a frame

    ready to be sent over the wire to a peer.

    """

    flags = 0

    if args:

        flags |= FLAG_COMMAND_NAME_HAVE_ARGS

    if datafh:

        flags |= FLAG_COMMAND_NAME_HAVE_DATA

    if not flags:

        flags |= FLAG_COMMAND_NAME_EOS

    yield makeframe(requestid, FRAME_TYPE_COMMAND_NAME, flags, cmd)

    for i, k in enumerate(sorted(args)):

        v = args[k]

        last = i == len(args) - 1

        # TODO handle splitting of argument values across frames.

        payload = bytearray(ARGUMENT_FRAME_HEADER.size + len(k) + len(v))

        offset = 0

        ARGUMENT_FRAME_HEADER.pack_into(payload, offset, len(k), len(v))

        offset += ARGUMENT_FRAME_HEADER.size

        payload[offset:offset + len(k)] = k

        offset += len(k)

        payload[offset:offset + len(v)] = v

        flags = FLAG_COMMAND_ARGUMENT_EOA if last else 0

        yield makeframe(requestid, FRAME_TYPE_COMMAND_ARGUMENT, flags, payload)

    if datafh:

        while True:

            data = datafh.read(DEFAULT_MAX_FRAME_SIZE)

            done = False

            if len(data) == DEFAULT_MAX_FRAME_SIZE:

                flags = FLAG_COMMAND_DATA_CONTINUATION

            else:

                flags = FLAG_COMMAND_DATA_EOS

                assert datafh.read(1) == b''

                done = True

            yield makeframe(requestid, FRAME_TYPE_COMMAND_DATA, flags, data)

            if done:

                break

def createbytesresponseframesfrombytes(requestid, data,

                                       maxframesize=DEFAULT_MAX_FRAME_SIZE):

    """Create a raw frame to send a bytes response from static bytes input.

    Returns a generator of bytearrays.

    """

    # Simple case of a single frame.

    if len(data) <= maxframesize:

        yield makeframe(requestid, FRAME_TYPE_BYTES_RESPONSE,

                        FLAG_BYTES_RESPONSE_EOS, data)

        return

    offset = 0

    while True:

        chunk = data[offset:offset + maxframesize]

        offset += len(chunk)

        done = offset == len(data)

        if done:

            flags = FLAG_BYTES_RESPONSE_EOS

        else:

            flags = FLAG_BYTES_RESPONSE_CONTINUATION

        yield makeframe(requestid, FRAME_TYPE_BYTES_RESPONSE, flags, chunk)

        if done:

            break

def createerrorframe(requestid, msg, protocol=False, application=False):

    # TODO properly handle frame size limits.

    assert len(msg) <= DEFAULT_MAX_FRAME_SIZE

    flags = 0

    if protocol:

        flags |= FLAG_ERROR_RESPONSE_PROTOCOL

    if application:

        flags |= FLAG_ERROR_RESPONSE_APPLICATION

    yield makeframe(requestid, FRAME_TYPE_ERROR_RESPONSE, flags, msg)

class serverreactor(object):

    """Holds state of a server handling frame-based protocol requests.

    This class is the "brain" of the unified frame-based protocol server

    component. While the protocol is stateless from the perspective of

    requests/commands, something needs to track which frames have been

    received, what frames to expect, etc. This class is that thing.

    Instances are modeled as a state machine of sorts. Instances are also

    reactionary to external events. The point of this class is to encapsulate

    the state of the connection and the exchange of frames, not to perform

    work. Instead, callers tell this class when something occurs, like a

    frame arriving. If that activity is worthy of a follow-up action (say

    *run a command*), the return value of that handler will say so.

    I/O and CPU intensive operations are purposefully delegated outside of

    this class.

    Consumers are expected to tell instances when events occur. They do so by

    calling the various ``on*`` methods. These methods return a 2-tuple

    describing any follow-up action(s) to take. The first element is the

    name of an action to perform. The second is a data structure (usually

    a dict) specific to that action that contains more information. e.g.

    if the server wants to send frames back to the client, the data structure

    will contain a reference to those frames.

    Valid actions that consumers can be instructed to take are:

    sendframes

       Indicates that frames should be sent to the client. The ``framegen``

       key contains a generator of frames that should be sent. The server

       assumes that all frames are sent to the client.

    error

       Indicates that an error occurred. Consumer should probably abort.

    runcommand

       Indicates that the consumer should run a wire protocol command. Details

       of the command to run are given in the data structure.

    wantframe

       Indicates that nothing of interest happened and the server is waiting on

       more frames from the client before anything interesting can be done.

    noop

       Indicates no additional action is required.

    Known Issues

    ------------

    There are no limits to the number of partially received commands or their

    size. A malicious client could stream command request data and exhaust the

    server's memory.

    Partially received commands are not acted upon when end of input is

    reached. Should the server error if it receives a partial request?

    Should the client send a message to abort a partially transmitted request

    to facilitate graceful shutdown?

    Active requests that haven't been responded to aren't tracked. This means

    that if we receive a command and instruct its dispatch, another command

    with its request ID can come in over the wire and there will be a race

    between who responds to what.

    """

    def __init__(self, deferoutput=False):

        """Construct a new server reactor.

        ``deferoutput`` can be used to indicate that no output frames should be

        instructed to be sent until input has been exhausted. In this mode,

        events that would normally generate output frames (such as a command

        response being ready) will instead defer instructing the consumer to

        send those frames. This is useful for half-duplex transports where the

        sender cannot receive until all data has been transmitted.

        """

        self._deferoutput = deferoutput

        self._state = 'idle'

        self._bufferedframegens = []

        # request id -> dict of commands that are actively being received.

        self._receivingcommands = {}

    def onframerecv(self, requestid, frametype, frameflags, payload):

        """Process a frame that has been received off the wire.

        Returns a dict with an ``action`` key that details what action,

        if any, the consumer should take next.

        """

        handlers = {

            'idle': self._onframeidle,

            'command-receiving': self._onframecommandreceiving,

            'errored': self._onframeerrored,

        }

        meth = handlers.get(self._state)

        if not meth:

            raise error.ProgrammingError('unhandled state: %s' % self._state)

        return meth(requestid, frametype, frameflags, payload)

    def onbytesresponseready(self, requestid, data):

        """Signal that a bytes response is ready to be sent to the client.

        The raw bytes response is passed as an argument.

        """

        framegen = createbytesresponseframesfrombytes(requestid, data)

        if self._deferoutput:

            self._bufferedframegens.append(framegen)

            return 'noop', {}

        else:

            return 'sendframes', {

                'framegen': framegen,

            }

    def oninputeof(self):

        """Signals that end of input has been received.

        No more frames will be received. All pending activity should be

        completed.

        """

        # TODO should we do anything about in-flight commands?

        if not self._deferoutput or not self._bufferedframegens:

            return 'noop', {}

        # If we buffered all our responses, emit those.

        def makegen():

            for gen in self._bufferedframegens:

                for frame in gen:

                    yield frame

        return 'sendframes', {

            'framegen': makegen(),

        }

    def onapplicationerror(self, requestid, msg):

        return 'sendframes', {

            'framegen': createerrorframe(requestid, msg, application=True),

        }

    def _makeerrorresult(self, msg):

        return 'error', {

            'message': msg,

        }