Crate mcp_usage_tower 

Tower hot path for MCP authentication, caching, and terminal-delivery billing.

Request metadata is classified from the mandatory MCP headers. Bodies are deserialized only for cache keys, durable-task attribution, and the terminal response decision. Response bodies remain streaming: the wrapper observes frames as the client consumes them and records usage only after a terminal JSON-RPC response reaches end-of-stream.

Structs

ClassifiedCall

Validated identity shared by pricing and metering.

DeferredCompletions

Queue of terminal accounting waiting for somewhere to await.

EdgeConfig

Runtime configuration shared by every cloned metering service.

EdgeMetrics

Process-local edge counters.

InMemoryTaskStore

Process-local task attribution for an embedded server.

InMemoryTenantStore

Mutable in-memory tenant table for development and embedded deployments.

MeterLayer

Tower layer that installs MeterService.

MeterService

Service produced by MeterLayer.

MetricsSnapshot

Point-in-time metric values.

OpenTelemetryMetrics

Registration guard for the OpenTelemetry observable instruments.

ProtocolHeaders

Trusted protocol metadata lifted from request headers.

TaskAttribution

Pre-priced durable-task attribution without the original name or URI.

Tenant

Authenticated tenant configuration used by the edge.

Enums

Classification

The outcome of looking at the request headers alone.

ClassificationError

Why mandatory MCP request metadata could not be trusted.

CredentialError

Missing or ambiguous tenant credentials.

EdgeConfigError

Invalid edge configuration.

TaskOriginKind

Non-identifying method category retained for a durable task.

TaskStoreError

A sanitized durable-task store failure.

UnaccountedReason

Why a response the edge observed produced no accounting at all.

WeakApiKey

Why an API key was refused as too weak to be safe.

Constants

API_KEY_HEADER

API-key header accepted in addition to Authorization: Bearer.

METHOD_HEADER

Mirrored JSON-RPC method request header.

MIN_API_KEY_BYTES

Shortest API key accepted by validate_api_key_strength.

NAME_HEADER

Mirrored tool, prompt, or resource name request header.

PROTOCOL_VERSION_HEADER

Standard protocol-version request header.

Traits

TaskAttributionStore

Persists pre-priced, non-identifying attribution under a durable task ID.

TenantStore

Resolves a presented high-entropy API key without retaining its plaintext.

Functions

classify_protocol_headers

Validate and classify raw MCP header values.

classify_request_headers

Validate unique protocol headers before authenticating or reading a body.

extract_api_key

Extract exactly one API key or Bearer credential.

hash_api_key

SHA-256 lookup hash for an API key.

install_opentelemetry

Register low-cardinality observable counters with an application-owned meter.

validate_api_key_strength

Reject API keys that are obviously too weak to be compared by digest.

Type Aliases

MeterBody

Response body returned by MeterService.

TaskStoreFuture

Boxed future returned by object-safe task stores.