Module: MCPClient::HttpTransportBase::CacheSupport

Includes:

RequestAuthorization

Included in:

MCPClient::HttpTransportBase

Defined in:

lib/mcp_client/http_transport_base/cache_support.rb

Overview

MCP 2026-07-28 caching support shared by the HTTP transports: serving a stale list on transient re-fetch failures, and keeping privately scoped cache entries within their authorization context.

Defined Under Namespace

Classes: AuthorizationRecorder, HeaderProbe

Constant Summary

NOOP_APP =

Stand-in app for instantiating middleware whose request hook is run without a request (the freshness probe).

->(_env) {}

UNKNOWN_CONTEXT =

Context that matches no cached entry: the credentials the next request would carry cannot be determined without sending it.

:unknown

PROBE_AUTHORIZATION_NEUTRAL_MIDDLEWARE =

Framework middleware that never puts an Authorization header on a request, whatever literal configuration it was installed with: the probe steps over it instead of running it (some of it overrides call and could not be run without sending anyway). A handler that was also handed a host callback is unknown all the same (#probe_host_callback_free? is checked first).

Faraday::FollowRedirects::Middleware is on the list because the gem itself depends on it and a host that installs it should keep its private cache hits: it has no request phase, and the only header it ever touches is the Authorization it deletes on a cross-host redirect -- which can cost a hit, never leak one.

%w[
  Faraday::Retry::Middleware
  Faraday::Request::Retry
  Faraday::Request::Json
  Faraday::Request::UrlEncoded
  Faraday::Request::Multipart
  Faraday::Response::Json
  Faraday::Response::Logger
  Faraday::FollowRedirects::Middleware
].freeze

PROBE_PURE_MIDDLEWARE =

The only middleware the probe runs: Faraday's own Authorization middleware, whose header is a pure function of the arguments it was installed with -- and only when those arguments are literal configuration it can do nothing with but read (#probe_static_value?). Host middleware is never run.

[Faraday::Request::Authorization].freeze

PROBE_STATIC_CLASSES =

Configuration a middleware can only read: a literal, or a plain container of literals. Anything else (a proc that vends a fresh token, an object that answers call, a holder something else can rotate) may hand a different credential to every request.

[NilClass, TrueClass, FalseClass, Numeric, Symbol, String].freeze

PROBE_STATIC_DEPTH =

How deep a container of configuration is looked into; beyond it the configuration counts as something the probe cannot read.

4

PROBE_DEFAULT_INITIALIZE_OWNERS =

Constructors that build a middleware instance and nothing else. A class with a constructor of its own can give its instances an on_request hook (define_singleton_method, an extended module), which a test of the class would never see -- so a class-level "no request phase" verdict only holds when Faraday's own constructor is the one that builds the instance.

[Faraday::Middleware, Object, Kernel, BasicObject].freeze

SENT_AUTHORIZATION_KEY =

Faraday env keys the AuthorizationRecorder files one exchange's record under. Both belong to that exchange and to no other, which a thread-local cannot express: a request the host's response phase nests inside this one runs on this very thread and would overwrite whatever this exchange left there.

:mcp_client_sent_authorization

RESPONSE_RECEIVED_AT_KEY =

:mcp_client_response_received_at

Constants included from RequestAuthorization

RequestAuthorization::ANONYMOUS_AUTHORIZATION, RequestAuthorization::UNRECORDED_AUTHORIZATION