Event and Webhook Delivery Semantics
draft-mayankpanke-event-delivery-semantics-00

Network Working Group                                           M. Panke
Internet-Draft                                    Independent Researcher
Intended status: Informational                             December 2025
Expires: 28 June 2026

                  Event and Webhook Delivery Semantics
             draft-mayankpanke-event-delivery-semantics-00

Abstract

   Event- and webhook-based integrations are a common application-layer
   mechanism for interoperability across Internet services, yet they
   lack a shared delivery semantics contract.  Existing implementations
   vary widely in retry behavior, acknowledgment signaling, failure
   classification, idempotency identifiers, and replay handling,
   resulting in fragile integrations and ambiguous operational
   expectations.

   This document defines a minimal, application-layer delivery semantics
   profile for event and webhook delivery over existing transports, most
   commonly HTTP.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Interoperability Failures Observed in Practice  . . . . .   3
     2.2.  Limitations of Existing Transport Semantics . . . . . . .   3
     2.3.  Non-Goals . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Architecture Overview . . . . . . . . . . . . . . . . . . . .   4
   6.  Delivery Semantics Model  . . . . . . . . . . . . . . . . . .   4
     6.1.  Delivery Attempt  . . . . . . . . . . . . . . . . . . . .   4
     6.2.  Sender-Observed Outcomes  . . . . . . . . . . . . . . . .   5
     6.3.  Retry Signaling . . . . . . . . . . . . . . . . . . . . .   5
   7.  Idempotency and Deduplication Signaling . . . . . . . . . . .   5
     7.1.  Idempotency Identifier  . . . . . . . . . . . . . . . . .   5
     7.2.  Deduplication Expectations  . . . . . . . . . . . . . . .   5
   8.  Failure Classification  . . . . . . . . . . . . . . . . . . .   5
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   11. Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Event- and webhook-based delivery is widely used to notify external
   systems of state changes or occurrences across administrative
   boundaries.  These integrations are typically implemented over HTTP
   and are expected to operate in the presence of partial failure,
   independent failure domains, and variable network conditions.

   Despite their ubiquity, there is no common, interoperable delivery
   semantics model that defines how delivery attempts, retries,
   acknowledgments, or failures are signaled and interpreted.  This
   document addresses that gap by defining a minimal, application-layer
   semantics profile focused on sender-observable behavior.

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2.  Problem Statement

   Event- and webhook-based delivery is a widely deployed application-
   layer integration pattern used to notify external systems of state
   changes or occurrences.  Such delivery is commonly implemented over
   existing transports, most frequently HTTP, and is typically expected
   to operate in the presence of partial failure, network interruption,
   and independent administrative control of endpoints.

   Despite widespread deployment, there is no common, interoperable
   delivery semantics contract governing how event producers, consumers,
   and intermediaries signal delivery attempts, retries, acknowledgment,
   or failure.  As a result, independently developed implementations
   rely on implicit assumptions, vendor-specific conventions, or
   informal documentation, leading to fragile integrations and
   inconsistent operational behavior.

2.1.  Interoperability Failures Observed in Practice

   The absence of a shared delivery semantics model results in recurring
   issues including ambiguous retry behavior and retry exhaustion
   signaling, inconsistent acknowledgment semantics, non-standard
   idempotency and deduplication signaling, unclear classification of
   delivery failures, and increased exposure to replay and abuse
   attacks.

   These issues arise from missing application-layer semantics rather
   than deficiencies in underlying transport protocols.

2.2.  Limitations of Existing Transport Semantics

   Transport protocols such as HTTP provide generic delivery and error
   signaling mechanisms but intentionally do not define application-
   specific semantics such as retry interpretation, acknowledgment
   meaning, or deduplication scope.  Correct use of transport semantics
   alone is therefore insufficient to ensure interoperable event
   delivery behavior.

2.3.  Non-Goals

   This document does not attempt to define or guarantee end-to-end
   delivery or processing correctness; provide exactly-once, at-most-
   once, or effectively-once guarantees; impose receiver-side storage or
   execution requirements; redefine or replace existing transport
   protocols; or standardize event payload formats or business
   semantics.  All guarantees are limited to sender-observable behavior
   and signaling.

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3.  Goals

   The goals of this specification are to define a common vocabulary for
   event delivery semantics, standardize observable signaling for
   delivery attempts and retries, enable interoperable idempotency and
   deduplication signaling, improve security posture through consistent
   guidance, and reduce ambiguity without constraining implementation
   choices.

4.  Terminology

   The key words "MUST", "MUST NOT", "SHOULD", and "MAY" are to be
   interpreted as described in RFC 2119.

   Delivery Attempt  A single effort by a producer or intermediary to
      deliver an event to a consumer endpoint.

   Acknowledgment  A signal indicating receipt of a delivery attempt,
      without implying processing success or durability.

   Idempotency Identifier  A producer-supplied identifier intended to
      correlate multiple delivery attempts for the same logical event.

5.  Architecture Overview

   This specification considers three primary roles: Event Producer,
   Event Consumer, and an optional Intermediary.  The delivery semantics
   defined in this document apply to interactions between these roles at
   the application layer.

6.  Delivery Semantics Model

   This specification defines a sender-observable delivery semantics
   model for event and webhook delivery.  The model applies to each
   delivery attempt independently and does not infer receiver-side
   processing behavior beyond what is explicitly signaled.

6.1.  Delivery Attempt

   A Delivery Attempt represents a single, discrete effort by an Event
   Producer or Intermediary to deliver an event to a Consumer endpoint.
   Each Delivery Attempt MUST be treated as best-effort, MUST NOT imply
   receipt, durability, or processing, and MAY be retried according to
   sender policy when sender-observed outcomes indicate a non-terminal
   condition.

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6.2.  Sender-Observed Outcomes

   This specification defines sender-observed outcomes for a Delivery
   Attempt, including Accepted, Transient Failure, and Terminal Failure.
   Senders MUST base retry behavior solely on these outcomes and MUST
   NOT infer receiver-side state beyond what is explicitly signaled.

6.3.  Retry Signaling

   Retry behavior is sender-driven and policy-dependent.  This
   specification standardizes only retry signaling, not retry
   guarantees.  Consumers MAY provide retry guidance, and senders MAY
   honor such guidance.

7.  Idempotency and Deduplication Signaling

   Idempotency and deduplication are addressed through explicit
   signaling mechanisms only.  This specification does not require or
   assume receiver-side deduplication behavior.

7.1.  Idempotency Identifier

   An Idempotency Identifier is a producer-supplied identifier intended
   to correlate multiple Delivery Attempts representing the same logical
   event.  When present, the identifier MUST remain stable across
   retries and MUST be scoped to the producer-consumer context.

7.2.  Deduplication Expectations

   Consumers MAY choose to perform deduplication based on the
   Idempotency Identifier and local policy.  Senders MUST tolerate
   duplicate delivery in all cases.  Deduplication remains an
   optimization, not a correctness requirement.

8.  Failure Classification

   Failure classification in this specification is minimal and sender-
   centric.  Failures are classified as transport-level failures or
   application-level rejections and are used solely to inform sender
   behavior such as retry decisions, alternate delivery paths, or
   operator intervention.

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9.  Security Considerations

   Event delivery mechanisms are susceptible to spoofing, replay, and
   abuse.  This document profiles existing security mechanisms and
   provides guidance on authentication, authorization, integrity
   protection, and replay mitigation.  No new cryptographic mechanisms
   are defined.

10.  IANA Considerations

   This document makes no request of IANA.

11.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

Author's Address

   Mayank Panke
   Independent Researcher
   Email: panke.mayank@gmail.com

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