Reliable Sends in Python

Every send returns SendResult or raises a typed RepostError carrying the runtime’s best-known delivery state. The runtime keeps the request body and idempotency key stable across all attempts in one operation.

Idempotency and delivery outcomes

When you omit idempotency_key, the runtime generates one key and reuses it across that operation’s attempts. Pass your own business-stable key when a queue redelivery, process restart, or application retry may repeat the logical send.

`DeliveryState`	Meaning	What to do
`ACCEPTED`	Repost accepted the event.	The send returns `SendResult`.
`NOT_SENT`	The request definitely did not leave.	Retry with the same key when `retryable` is true.
`POSSIBLY_SENT`	Repost may have received the request.	Reconcile with the same key; do not mint a new one.
`REJECTED`	Repost definitively rejected the request.	Fix the request instead of retrying blindly.
`CANCELLED_UNKNOWN`	Cancellation happened after the request may have committed.	Reconcile with the same key.

from repost_client import DeliveryState, RepostError, is_retryable

try:
    result = client.webhooks.order.created(
        customer_id="customer_123",
        data=order,
        idempotency_key="order_123:created",
    )
except RepostError as error:
    if error.delivery_state in {
        DeliveryState.POSSIBLY_SENT,
        DeliveryState.CANCELLED_UNKNOWN,
    }:
        reconcile(error.idempotency_key)
    elif is_retryable(error):
        retry_later(order, error.idempotency_key)
    else:
        raise

Every RepostError has a stable code, delivery_state, retryable, operation_id, idempotency_key, attempt_count, and optional http_status and failure_reason. Error messages and metadata exclude credentials and payloads. The subclasses are RepostConfigurationError, RepostValidationError, RepostSerializationError, RepostTransportError, RepostPublishError, and RepostDescriptorVersionError. PublishError remains a deprecated compatibility base for transport and publish failures; prefer RepostTransportError and RepostPublishError.

Retry behavior

The runtime retries classified DNS, connection, I/O, and attempt-timeout failures; 409, 429, and 5xx responses; and malformed successful responses when reconciliation remains possible. TLS verification failures, proxy authentication failures, redirects, and ordinary 4xx rejections are terminal. The default is four total attempts. Backoff is exponential with full jitter. Both delta-seconds and HTTP-date Retry-After values are supported and capped by retry_max_delay_ms, which defaults to 60 seconds. operation_timeout_ms bounds connection work, attempts, and retry delays together. A custom Transport performs one attempt at a time. The runtime still owns retry classification, deadlines, idempotency, and response validation around it.

Cancellation

Python sends are synchronous. Pass a CancelToken when another thread or shutdown hook must cancel a blocking operation:

from repost_client import CancelToken

cancel = CancelToken()

# Another thread may call cancel.cancel().
client.webhooks.order.created(
    customer_id="customer_123",
    data=order,
    idempotency_key="order_123:created",
    cancel=cancel,
)

Cancellation is cooperative. A cancelled send raises RepostTransportError with ErrorCode.CANCELLED. Cancellation before commitment is NOT_SENT; cancellation after bytes may have left is CANCELLED_UNKNOWN. Cancelling one operation does not close the client or affect other sends.

Bounded admission

max_in_flight_operations is a hard bulkhead, not a queue. A send that cannot enter fails immediately with ErrorCode.OVERLOADED and NOT_SENT. max_buffered_bytes bounds aggregate retained request and response bytes. The runtime rejects new work or an oversized response instead of buffering without a limit. Apply backpressure in your queue or request handler, then retry with the same idempotency key.

Wire format

The runtime sends type, customerId, timestamp, and data in that order. Payload fields follow schema declaration order and their @map names. Absent optional values are omitted, defaults are injected only when a value is absent, and unknown dictionary properties are dropped. Datetimes are normalized to millisecond UTC form, enums use their wire values, and non-finite numbers are rejected before the network. The native pytest suite exercises this shape through the public generated client, real runtime, default HTTP transport, local HTTP server, and response parser.

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Observability

Watch in-flight work, retry lifecycles, failures, and dropped events.

Testing

Script attempts and assert on recorded requests without a network.

Delivery & retries

See what happens after Repost accepts a message.

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Reliable Sends in Python

Idempotency and delivery outcomes

Retry behavior

Cancellation

Bounded admission

Wire format

Continue

Observability

Testing

Delivery & retries

​Idempotency and delivery outcomes

​Retry behavior

​Cancellation

​Bounded admission

​Wire format

​Continue

Observability

Testing

Delivery & retries

Idempotency and delivery outcomes

Retry behavior

Cancellation

Bounded admission

Wire format

Continue