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Diffstat (limited to 'venv/lib/python3.11/site-packages/h11/_state.py')
| -rw-r--r-- | venv/lib/python3.11/site-packages/h11/_state.py | 367 |
1 files changed, 367 insertions, 0 deletions
diff --git a/venv/lib/python3.11/site-packages/h11/_state.py b/venv/lib/python3.11/site-packages/h11/_state.py new file mode 100644 index 0000000..3593430 --- /dev/null +++ b/venv/lib/python3.11/site-packages/h11/_state.py @@ -0,0 +1,367 @@ +################################################################ +# The core state machine +################################################################ +# +# Rule 1: everything that affects the state machine and state transitions must +# live here in this file. As much as possible goes into the table-based +# representation, but for the bits that don't quite fit, the actual code and +# state must nonetheless live here. +# +# Rule 2: this file does not know about what role we're playing; it only knows +# about HTTP request/response cycles in the abstract. This ensures that we +# don't cheat and apply different rules to local and remote parties. +# +# +# Theory of operation +# =================== +# +# Possibly the simplest way to think about this is that we actually have 5 +# different state machines here. Yes, 5. These are: +# +# 1) The client state, with its complicated automaton (see the docs) +# 2) The server state, with its complicated automaton (see the docs) +# 3) The keep-alive state, with possible states {True, False} +# 4) The SWITCH_CONNECT state, with possible states {False, True} +# 5) The SWITCH_UPGRADE state, with possible states {False, True} +# +# For (3)-(5), the first state listed is the initial state. +# +# (1)-(3) are stored explicitly in member variables. The last +# two are stored implicitly in the pending_switch_proposals set as: +# (state of 4) == (_SWITCH_CONNECT in pending_switch_proposals) +# (state of 5) == (_SWITCH_UPGRADE in pending_switch_proposals) +# +# And each of these machines has two different kinds of transitions: +# +# a) Event-triggered +# b) State-triggered +# +# Event triggered is the obvious thing that you'd think it is: some event +# happens, and if it's the right event at the right time then a transition +# happens. But there are somewhat complicated rules for which machines can +# "see" which events. (As a rule of thumb, if a machine "sees" an event, this +# means two things: the event can affect the machine, and if the machine is +# not in a state where it expects that event then it's an error.) These rules +# are: +# +# 1) The client machine sees all h11.events objects emitted by the client. +# +# 2) The server machine sees all h11.events objects emitted by the server. +# +# It also sees the client's Request event. +# +# And sometimes, server events are annotated with a _SWITCH_* event. For +# example, we can have a (Response, _SWITCH_CONNECT) event, which is +# different from a regular Response event. +# +# 3) The keep-alive machine sees the process_keep_alive_disabled() event +# (which is derived from Request/Response events), and this event +# transitions it from True -> False, or from False -> False. There's no way +# to transition back. +# +# 4&5) The _SWITCH_* machines transition from False->True when we get a +# Request that proposes the relevant type of switch (via +# process_client_switch_proposals), and they go from True->False when we +# get a Response that has no _SWITCH_* annotation. +# +# So that's event-triggered transitions. +# +# State-triggered transitions are less standard. What they do here is couple +# the machines together. The way this works is, when certain *joint* +# configurations of states are achieved, then we automatically transition to a +# new *joint* state. So, for example, if we're ever in a joint state with +# +# client: DONE +# keep-alive: False +# +# then the client state immediately transitions to: +# +# client: MUST_CLOSE +# +# This is fundamentally different from an event-based transition, because it +# doesn't matter how we arrived at the {client: DONE, keep-alive: False} state +# -- maybe the client transitioned SEND_BODY -> DONE, or keep-alive +# transitioned True -> False. Either way, once this precondition is satisfied, +# this transition is immediately triggered. +# +# What if two conflicting state-based transitions get enabled at the same +# time? In practice there's only one case where this arises (client DONE -> +# MIGHT_SWITCH_PROTOCOL versus DONE -> MUST_CLOSE), and we resolve it by +# explicitly prioritizing the DONE -> MIGHT_SWITCH_PROTOCOL transition. +# +# Implementation +# -------------- +# +# The event-triggered transitions for the server and client machines are all +# stored explicitly in a table. Ditto for the state-triggered transitions that +# involve just the server and client state. +# +# The transitions for the other machines, and the state-triggered transitions +# that involve the other machines, are written out as explicit Python code. +# +# It'd be nice if there were some cleaner way to do all this. This isn't +# *too* terrible, but I feel like it could probably be better. +# +# WARNING +# ------- +# +# The script that generates the state machine diagrams for the docs knows how +# to read out the EVENT_TRIGGERED_TRANSITIONS and STATE_TRIGGERED_TRANSITIONS +# tables. But it can't automatically read the transitions that are written +# directly in Python code. So if you touch those, you need to also update the +# script to keep it in sync! +from typing import cast, Dict, Optional, Set, Tuple, Type, Union + +from ._events import * +from ._util import LocalProtocolError, Sentinel + +# Everything in __all__ gets re-exported as part of the h11 public API. +__all__ = [ + "CLIENT", + "SERVER", + "IDLE", + "SEND_RESPONSE", + "SEND_BODY", + "DONE", + "MUST_CLOSE", + "CLOSED", + "MIGHT_SWITCH_PROTOCOL", + "SWITCHED_PROTOCOL", + "ERROR", +] + + +class CLIENT(Sentinel, metaclass=Sentinel): + pass + + +class SERVER(Sentinel, metaclass=Sentinel): + pass + + +# States +class IDLE(Sentinel, metaclass=Sentinel): + pass + + +class SEND_RESPONSE(Sentinel, metaclass=Sentinel): + pass + + +class SEND_BODY(Sentinel, metaclass=Sentinel): + pass + + +class DONE(Sentinel, metaclass=Sentinel): + pass + + +class MUST_CLOSE(Sentinel, metaclass=Sentinel): + pass + + +class CLOSED(Sentinel, metaclass=Sentinel): + pass + + +class ERROR(Sentinel, metaclass=Sentinel): + pass + + +# Switch types +class MIGHT_SWITCH_PROTOCOL(Sentinel, metaclass=Sentinel): + pass + + +class SWITCHED_PROTOCOL(Sentinel, metaclass=Sentinel): + pass + + +class _SWITCH_UPGRADE(Sentinel, metaclass=Sentinel): + pass + + +class _SWITCH_CONNECT(Sentinel, metaclass=Sentinel): + pass + + +EventTransitionType = Dict[ + Type[Sentinel], + Dict[ + Type[Sentinel], + Dict[Union[Type[Event], Tuple[Type[Event], Type[Sentinel]]], Type[Sentinel]], + ], +] + +EVENT_TRIGGERED_TRANSITIONS: EventTransitionType = { + CLIENT: { + IDLE: {Request: SEND_BODY, ConnectionClosed: CLOSED}, + SEND_BODY: {Data: SEND_BODY, EndOfMessage: DONE}, + DONE: {ConnectionClosed: CLOSED}, + MUST_CLOSE: {ConnectionClosed: CLOSED}, + CLOSED: {ConnectionClosed: CLOSED}, + MIGHT_SWITCH_PROTOCOL: {}, + SWITCHED_PROTOCOL: {}, + ERROR: {}, + }, + SERVER: { + IDLE: { + ConnectionClosed: CLOSED, + Response: SEND_BODY, + # Special case: server sees client Request events, in this form + (Request, CLIENT): SEND_RESPONSE, + }, + SEND_RESPONSE: { + InformationalResponse: SEND_RESPONSE, + Response: SEND_BODY, + (InformationalResponse, _SWITCH_UPGRADE): SWITCHED_PROTOCOL, + (Response, _SWITCH_CONNECT): SWITCHED_PROTOCOL, + }, + SEND_BODY: {Data: SEND_BODY, EndOfMessage: DONE}, + DONE: {ConnectionClosed: CLOSED}, + MUST_CLOSE: {ConnectionClosed: CLOSED}, + CLOSED: {ConnectionClosed: CLOSED}, + SWITCHED_PROTOCOL: {}, + ERROR: {}, + }, +} + +StateTransitionType = Dict[ + Tuple[Type[Sentinel], Type[Sentinel]], Dict[Type[Sentinel], Type[Sentinel]] +] + +# NB: there are also some special-case state-triggered transitions hard-coded +# into _fire_state_triggered_transitions below. +STATE_TRIGGERED_TRANSITIONS: StateTransitionType = { + # (Client state, Server state) -> new states + # Protocol negotiation + (MIGHT_SWITCH_PROTOCOL, SWITCHED_PROTOCOL): {CLIENT: SWITCHED_PROTOCOL}, + # Socket shutdown + (CLOSED, DONE): {SERVER: MUST_CLOSE}, + (CLOSED, IDLE): {SERVER: MUST_CLOSE}, + (ERROR, DONE): {SERVER: MUST_CLOSE}, + (DONE, CLOSED): {CLIENT: MUST_CLOSE}, + (IDLE, CLOSED): {CLIENT: MUST_CLOSE}, + (DONE, ERROR): {CLIENT: MUST_CLOSE}, +} + + +class ConnectionState: + def __init__(self) -> None: + # Extra bits of state that don't quite fit into the state model. + + # If this is False then it enables the automatic DONE -> MUST_CLOSE + # transition. Don't set this directly; call .keep_alive_disabled() + self.keep_alive = True + + # This is a subset of {UPGRADE, CONNECT}, containing the proposals + # made by the client for switching protocols. + self.pending_switch_proposals: Set[Type[Sentinel]] = set() + + self.states: Dict[Type[Sentinel], Type[Sentinel]] = {CLIENT: IDLE, SERVER: IDLE} + + def process_error(self, role: Type[Sentinel]) -> None: + self.states[role] = ERROR + self._fire_state_triggered_transitions() + + def process_keep_alive_disabled(self) -> None: + self.keep_alive = False + self._fire_state_triggered_transitions() + + def process_client_switch_proposal(self, switch_event: Type[Sentinel]) -> None: + self.pending_switch_proposals.add(switch_event) + self._fire_state_triggered_transitions() + + def process_event( + self, + role: Type[Sentinel], + event_type: Type[Event], + server_switch_event: Optional[Type[Sentinel]] = None, + ) -> None: + _event_type: Union[Type[Event], Tuple[Type[Event], Type[Sentinel]]] = event_type + if server_switch_event is not None: + assert role is SERVER + if server_switch_event not in self.pending_switch_proposals: + raise LocalProtocolError( + "Received server {} event without a pending proposal".format( + server_switch_event + ) + ) + _event_type = (event_type, server_switch_event) + if server_switch_event is None and _event_type is Response: + self.pending_switch_proposals = set() + self._fire_event_triggered_transitions(role, _event_type) + # Special case: the server state does get to see Request + # events. + if _event_type is Request: + assert role is CLIENT + self._fire_event_triggered_transitions(SERVER, (Request, CLIENT)) + self._fire_state_triggered_transitions() + + def _fire_event_triggered_transitions( + self, + role: Type[Sentinel], + event_type: Union[Type[Event], Tuple[Type[Event], Type[Sentinel]]], + ) -> None: + state = self.states[role] + try: + new_state = EVENT_TRIGGERED_TRANSITIONS[role][state][event_type] + except KeyError: + event_type = cast(Type[Event], event_type) + raise LocalProtocolError( + "can't handle event type {} when role={} and state={}".format( + event_type.__name__, role, self.states[role] + ) + ) from None + self.states[role] = new_state + + def _fire_state_triggered_transitions(self) -> None: + # We apply these rules repeatedly until converging on a fixed point + while True: + start_states = dict(self.states) + + # It could happen that both these special-case transitions are + # enabled at the same time: + # + # DONE -> MIGHT_SWITCH_PROTOCOL + # DONE -> MUST_CLOSE + # + # For example, this will always be true of a HTTP/1.0 client + # requesting CONNECT. If this happens, the protocol switch takes + # priority. From there the client will either go to + # SWITCHED_PROTOCOL, in which case it's none of our business when + # they close the connection, or else the server will deny the + # request, in which case the client will go back to DONE and then + # from there to MUST_CLOSE. + if self.pending_switch_proposals: + if self.states[CLIENT] is DONE: + self.states[CLIENT] = MIGHT_SWITCH_PROTOCOL + + if not self.pending_switch_proposals: + if self.states[CLIENT] is MIGHT_SWITCH_PROTOCOL: + self.states[CLIENT] = DONE + + if not self.keep_alive: + for role in (CLIENT, SERVER): + if self.states[role] is DONE: + self.states[role] = MUST_CLOSE + + # Tabular state-triggered transitions + joint_state = (self.states[CLIENT], self.states[SERVER]) + changes = STATE_TRIGGERED_TRANSITIONS.get(joint_state, {}) + self.states.update(changes) + + if self.states == start_states: + # Fixed point reached + return + + def start_next_cycle(self) -> None: + if self.states != {CLIENT: DONE, SERVER: DONE}: + raise LocalProtocolError( + "not in a reusable state. self.states={}".format(self.states) + ) + # Can't reach DONE/DONE with any of these active, but still, let's be + # sure. + assert self.keep_alive + assert not self.pending_switch_proposals + self.states = {CLIENT: IDLE, SERVER: IDLE} |