Crate restate_email 

Restate-backed worker contracts for outbound email delivery.

This crate exposes the serializable email worker contract and an optional Restate service adapter. Provider-specific send options cross the queue boundary through the registry-driven SendRequestSeed, using the provider-keyed wire representation owned by email-transport.

The Restate service adapter is available as Service with the service feature. The caller-side ingress transport lives in the email-transport-restate crate, which submits this contract through Restate ingress without depending on restate-sdk.

Quick start

use restate_email::{Service, StaticTransportRegistry};
use restate_sdk::{endpoint::Endpoint, service::IntoServiceDefinition};

let registry = StaticTransportRegistry::new();
let service = Service::new(registry).into_service_definition();
let _endpoint = Endpoint::builder().bind(service).build();

Securing the worker

Restate signs every request it makes to an SDK endpoint when the runtime is configured with a request identity key. Verify those signatures by registering the corresponding public keys on the endpoint builder; once at least one key is registered, unsigned requests are rejected. Registering several keys keeps both the old and the new key valid during rotation:

let _endpoint = Endpoint::builder()
    .bind(service)
    .identity_key("publickeyv1_w7YHemBctH5Ck2nQRQ47iBBqhNHy4FV7t2Usbye2A6f")?
    .identity_key("publickeyv1_ChjENKeMvCtRnqG2mrBK1HmPKufgFUc98K8B3ononQvp")?
    .build();

Identity keys authenticate the Restate runtime to the worker; callers authenticate to Restate ingress separately (see email-transport-restate).

Features

The default feature set enables service for backwards-compatible worker builds. Disable default features to consume only the SDK-free wire contract.

• service: Restate worker service adapter and transport registry.
• transport-resend: registers Resend provider options and enables the Resend worker example.
• schemars: JSON Schema implementations and examples for queue contracts.
• rfc5322-string-compat: accepts the legacy RFC 5322 string address shape supported by email-message.

Platform support

This crate targets native Restate workers. Transport implementations may support additional platforms, but Service depends on Restate’s native endpoint/runtime integration.

Examples

• restate_email_worker builds a worker with a custom transport and optional identity-key verification.
• restate_resend_worker wires email_kit::transport::resend::ResendTransport into the service; it requires the transport-resend feature.

Re-exports

pub use transport::CatchAllTransportResolver;

pub use transport::StaticTransportRegistry;

pub use transport::TransportLookupError;

pub use transport::TransportResolver;

Modules

transport

Transport resolution helpers for restate-email workers.

Structs

CorrelationId

Correlation identifier carried end-to-end from queue to transport.

IdempotencyKey

Provider idempotency token for safe retries.

RestateSendOptions

Restate-specific options for a single send attempt.

SendOptions

Per-send controls shared by structured and raw transport sends.

SendRequest

Queue payload consumed by Email.send.

SendRequestSeed

Registry-driven deserializer for SendRequest.

SendResponse

Wire-stable response shape returned by the Restate Email.send handler.

Service

Concrete Restate service implementation over a transport resolver.

ServiceClient

Client to invoke the Service service from another handler.

TransportKey

Configured transport key (e.g. "primary", "fallback").

TransportOptionRegistry

Registry of queue/wire codecs for concrete TransportOption types.

TransportOptions

Per-send transport options.

TransportOptionsSeed

DeserializeSeed for TransportOptions.

Enums

InvocationMode

How far a Restate-backed send is followed before it returns.

StringNewtypeError

Reasons a string value cannot be promoted into a validated string newtype defined via the crate::string_newtype! macro.

TransportOptionRegistryError

Failure to register a provider-option codec.

Constants

STRING_NEWTYPE_MAX_BYTES

Maximum byte length of a string-newtype value.

Traits

RuntimeBound

Re-export of email_transport::RuntimeBound.

TransportOption

Marker for typed provider-specific send options.