PipeStream: A Recursive Entity Streaming Protocol for Distributed Processing over QUIC

1.1. Problem Statement

Distributed processing pipelines face significant challenges when handling large, complex inputs that require multiple stages of transformation, analysis, and enrichment. Traditional batch processing approaches require entire inputs to be loaded into memory, processed sequentially, and transmitted in their entirety between processing stages. This methodology introduces substantial latency, excessive memory consumption, and poor utilization of distributed computing resources.¶

Modern distributed processing workflows increasingly demand the ability to:¶

• Process inputs incrementally as data becomes available¶

• Distribute processing load across heterogeneous worker nodes¶

• Maintain consistency guarantees across parallel processing paths¶

• Handle inputs of arbitrary size without memory constraints¶

• Support recursive decomposition where constituent parts may themselves be decomposed¶

• Scale from single inputs to collections of millions of entries¶

Current approaches based on batch processing and store-and-forward architectures are inefficient for large inputs and fail to exploit the inherent parallelism available in distributed processing environments. Furthermore, existing streaming protocols do not provide the consistency semantics required for hierarchical processing where the integrity of the rehydrated output depends on the successful processing of all constituent parts.¶

These pipelines also increasingly span organizational and vendor boundaries: a processing stage operated by one party must interoperate with stages operated by others. Today that interoperability is achieved through per-vendor SDKs and bespoke coordination logic, because no standardized wire protocol expresses the decomposition, tracking, and reassembly semantics these systems share. PipeStream specifies that wire protocol.¶

1.2. Applicability

PipeStream is a domain-neutral recursive streaming protocol. Its design has been validated against distributed document processing, but it is equally applicable to any workload that can be modeled as hierarchical decomposition of a root entity into sub-entities, parallel processing of those sub-entities, and deterministic reassembly of results. Example domains include:¶

• Distributed document processing and content enrichment pipelines¶

• Hierarchical video transcoding and rendering (scene decomposition)¶

• Federated computation pipelines such as distributed machine learning¶

• Genomic sequencing and assembly workflows¶

PipeStream uniquely bridges true streaming and request-response processing models. Layer 0 streaming is optimal when processing nodes have low-latency interconnects and can process entities incrementally. Layer 2 yield/resume and claim checks handle workflows that require external service calls, rate limiting, human approval gates, or cross-session resumption. This dual nature allows a single protocol to serve both real-time streaming pipelines and complex multi-stage workflows with heterogeneous latency characteristics.¶

1.3. PipeStream Overview

PipeStream addresses these challenges by defining a streaming protocol that enables incremental processing with strong consistency guarantees. The protocol is built upon QUIC [RFC9000] transport, leveraging its native support for multiplexed streams, low-latency connection establishment, and reliable delivery semantics.¶

The fundamental innovation of PipeStream is its treatment of inputs as recursive compositions of entities. A root entity MAY be decomposed into multiple sub-entities, each of which MAY itself be further decomposed, creating a tree structure of processing tasks. This recursive decomposition enables fine-grained parallelism while the protocol's control stream mechanism ensures that all branches of the decomposition tree are tracked and synchronized.¶

PipeStream employs a dual-stream design:¶

1. Data Stream: Carries entity payloads through the processing pipeline. Entities flow through this stream with minimal buffering, enabling low-latency incremental processing.¶

2. Control Stream: Carries control information tracking the status of entity decomposition and rehydration. The control stream ensures that all parts of a dehydrated entity are accounted for before rehydration proceeds.¶

1.4. Design Philosophy

PipeStream implements a recursive scatter-gather pattern [scatter-gather] over QUIC streams. An input entity is "dehydrated" (scattered) at the source into constituent sub-entities, these sub-entities are transmitted and processed in parallel across distributed pipeline stages, and finally the results are "rehydrated" (gathered) at the destination to reconstitute the complete processed output. The checkpoint blocking mechanism (Section 9.3) provides barrier synchronization semantics analogous to the barrier pattern in parallel computing.¶

This approach provides several advantages:¶

• Incremental Processing: Processing nodes MAY begin work on early entities before the complete input has been transmitted.¶

• Parallelism: Independent entities MAY be processed concurrently across multiple worker nodes.¶

• Memory Efficiency: No single node is required to hold the complete input in memory.¶

• Fault Isolation: Failures in processing individual entities can be detected, reported, and potentially retried without affecting other entities.¶

• Consistency: The checkpoint blocking mechanism ensures that rehydration operations proceed only when all constituent parts have been successfully processed.¶

1.5. Protocol Layering

PipeStream is organized into three protocol layers to accommodate varying deployment requirements:¶

Implementations MUST support Layer 0. Support for Layers 1 and 2 is OPTIONAL and negotiated during connection establishment.¶

1.6. Scope

This document specifies the PipeStream protocol including message formats, state machines, error handling, and the interaction between data and control streams. The document defines the transport-level layer field and recursive processing semantics but leaves concrete payload meaning to application profile specifications.¶

2.1. Protocol Entities

Entity

The fundamental unit of data flowing through a PipeStream pipeline. An Entity represents either a complete input or a constituent part of a decomposed input. Each Entity possesses a unique identifier within its processing scope and carries payload data tagged with a transport-level layer value. Entities are immutable once created; transformations produce new Entities rather than modifying existing ones. An input enters the pipeline as a single root Entity and MAY be decomposed into multiple Entities during processing; it is considered complete when its root Entity (or the rehydrated result of its decomposition) exits the pipeline.¶

Scope

A hierarchical namespace for Entity IDs. Each scope maintains its own Entity ID space, cursor, and Assembly Manifest. Scopes enable root entities to contain parts, and parts to contain sub-tasks, each with independent ID management. (Protocol Layer 1)¶

2.2. Dehydration and Rehydration

Scatter-Gather

The distributed processing pattern implemented by PipeStream. A single input is "scattered" (dehydrated) into multiple parts for parallel processing, and the results are "gathered" (rehydrated) back into a single output. PipeStream extends classical scatter-gather with recursive nesting: any scattered part may itself be scattered further.¶

Dehydrate (Scatter)

The operation of decomposing an Entity into multiple constituent Entities for parallel or distributed processing. When an Entity is dehydrated, the originating node MUST create an Assembly Manifest entry recording the identifiers of all resulting sub-entities. The dehydration operation is recursive; a sub-entity produced by dehydration MAY itself be dehydrated, creating a tree of decomposition. Dehydration transitions data from a solid state (a single complete unit) to a fluid state (multiple in-flight entities).¶

Rehydrate (Gather)

The operation of reassembling multiple Entities back into a single composite Entity. A rehydrate operation MUST NOT proceed until all constituent Entities listed in the corresponding Assembly Manifest entry have been received and processed (or handled according to the Completion Policy). Rehydration transitions data from a fluid state back to a solid state.¶

Solid State

An Entity that exists as a complete, stored unit or as a single root Entity entering or exiting a pipeline. Contrast with "fluid state".¶

Fluid State

An input that has been decomposed into multiple in-flight Entities being processed in parallel across distributed nodes. An input is in the fluid state between dehydration and rehydration. Contrast with "solid state".¶

2.3. Consistency Mechanisms

Checkpoint

A synchronization point in the processing pipeline where all in-flight Entities MUST reach a consistent state before processing may continue. A checkpoint is considered "satisfied" when all Assembly Manifest entries created before the checkpoint have been resolved.¶

Barrier

A synchronization point scoped to a specific subtree. Unlike checkpoints which are global, barriers block only entities dependent on a specific parent's descendants. (Protocol Layer 1)¶

Control Stream

The control stream that tracks Entity completion status throughout the processing pipeline. The Control Stream is transmitted on a dedicated QUIC stream parallel to the data streams.¶

Assembly Manifest

A data structure within the Control Stream that tracks the relationship between a composite Entity and its constituent sub-entities produced by dehydration.¶

Cursor

A pointer to the lowest unresolved Entity ID within a scope. Entity IDs behind the cursor are considered resolved and MAY be recycled. The cursor enables efficient ID space management without global coordination.¶

2.4. Resilience Mechanisms (Protocol Layer 2)

Yield

A temporary pause in Entity processing, typically due to external dependencies (API calls, rate limiting, human approval). A yielded Entity carries a continuation token enabling resumption without reprocessing.¶

Claim Check

A detached reference to a deferred Entity that can be queried or resumed independently, potentially in a different session. Claim checks enable asynchronous processing patterns and retry queues.¶

Completion Policy

A configuration specifying how to handle partial failures during dehydration. Policies include STRICT (all must succeed), LENIENT (continue with partial results), BEST_EFFORT (complete with whatever succeeds), and QUORUM (require minimum success ratio).¶

2.5. Data Representation

Data Layer

A transport-level 2-bit field carried in the Entity Header that identifies the payload representation. The concrete meaning of each layer value is defined by an application profile rather than by the core protocol.¶

2.6. Additional Terms

Pipeline

A configured sequence of processing stages through which Entities flow.¶

Processor

A node in the mesh that performs operations on entities (e.g., transformation, dehydration, or rehydration).¶

Sink

A terminal stage in a pipeline where rehydrated entities or terminal entities are persisted or delivered to an external system.¶

Stage

A single processing step within a Pipeline.¶

Scope Digest

A cryptographic summary (Merkle root) of all Entity statuses within a completed scope, propagated to parent scopes for efficient verification. (Protocol Layer 1)¶

3.1. Layer 0: Core Protocol

Layer 0 provides the fundamental streaming capabilities:¶

• Unified Control Frame (UCF) header (1-octet type + 4-octet length prefix)¶

• Status frame (16-octet base bit-packed frame)¶

• Entity frame (header + payload)¶

• Status codes: PENDING, PROCESSING, COMPLETE, FAILED, CHECKPOINT¶

• Assembly Manifest for parent-child tracking¶

• Cursor-based Entity ID recycling¶

• Single-level dehydrate/rehydrate¶

• Checkpoint blocking¶

All implementations MUST support Layer 0.¶

3.2. Layer 1: Recursive Extension

Layer 1 adds hierarchical processing capabilities:¶

• Scoped Entity ID namespaces (root -> component -> sub-task -> leaf)¶

• Explicit Depth tracking in status frames¶

• SCOPE_DIGEST for Merkle-based subtree completion¶

• BARRIER for subtree-scoped synchronization¶

• Nested dehydration with depth tracking¶

Layer 1 is OPTIONAL. Implementations advertise Layer 1 support during capability negotiation.¶

3.3. Layer 2: Resilience Extension

Layer 2 adds fault tolerance and async processing:¶

• YIELDED status with continuation tokens¶

• DEFERRED status with claim checks¶

• RETRYING, SKIPPED, ABANDONED statuses¶

• Completion policies (STRICT, LENIENT, BEST_EFFORT, QUORUM)¶

• Claim check extensions and deferred processing tokens¶

• Stopping point validation¶

Layer 2 is OPTIONAL and requires Layer 1. Implementations advertise Layer 2 support during capability negotiation.¶

3.4. Capability Negotiation

PipeStream uses a two-tier negotiation model. The ALPN identifier (Section 11.1) identifies the base PipeStream transport mapping, while the capabilities structure handles dynamic resource limits and optional layer support that may vary based on endpoint configuration or real-time load.¶

During CONNECT, endpoints exchange supported capabilities using the capabilities structure. This message MUST be encoded using the default CBOR format for both the client's initiation and the server's response (Section 3.4.2).¶

serialization-format = uint .le 255
                       ; Value from the PipeStream Serialization
                       ; Formats registry (Section 11.5).
                       ; This document defines only CBOR (0).

capabilities = {
  layer0-core: bool,               ; MUST be true
  layer1-recursive: bool,          ; Scoped IDs, digests
  layer2-resilience: bool,         ; Yield, claim checks
  ? max-scope-depth: uint .le 7,   ; Default: 7 (8 levels, 0-7)
  ? max-entities-per-scope: uint,  ; Default: 4,294,967,292
                                   ; (Section 9.1)
  ? max-window-size: uint,         ; Default: 2,147,483,646
                                   ; (Max in-flight entities;
                                   ; see Section 9.1)
  ? serialization-format: serialization-format, ; Default: CBOR
  ? keepalive-timeout-ms: uint,    ; Default: 30000 (30s)
}

Peers negotiate down to common capabilities. If Layer 2 is requested but Layer 1 is not supported, Layer 2 MUST be disabled.¶

The layer0-core field MUST be true; an endpoint that receives a Capabilities message with layer0-core set to false MUST close the connection with PIPESTREAM_LAYER_UNSUPPORTED (0x0C). The max-entities-per-scope and max-window-size values are bounded by the Entity ID space constraints defined in Section 9.1; an endpoint MUST NOT advertise values exceeding those bounds.¶

4.1. Design Goals

This section is descriptive; the normative requirements that realize these goals appear in Sections 5 through 9.¶

4.2. Architecture Summary

PipeStream uses a dual-plane architecture within a single QUIC connection. The endpoint that initiates the QUIC connection is the client. Either endpoint MAY originate entities (Section 5.2); in many deployments the client acts as producer and the server as consumer, but the protocol does not require this asymmetry after connection establishment.¶

4.3. Connection Lifecycle

A PipeStream connection follows this lifecycle:¶

1. Establishment: Client initiates QUIC connection with ALPN identifier "pipestream/1"¶

2. Capability Exchange: Client and server exchange supported protocol layers and limits¶

3. Control Stream Initialization: Client opens Stream 0 as bidirectional Control Stream¶

4. Entity Streaming: Entities are transmitted per Sections 5 and 6¶

5. Termination: Connection closes via GOAWAY-initiated graceful shutdown (Section 6.5) or QUIC CONNECTION_CLOSE¶

5.1. Control Stream (Stream 0)

The Control Stream provides the control plane for PipeStream operations.¶

5.2. Entity Streams

Entity Streams carry entity payload data using the Entity Frame format defined in Section 6.8.¶

5.3. Prohibition of 0-RTT Early Data

QUIC permits applications to send data in 0-RTT early data before the TLS handshake completes; such data is replayable by an attacker. PipeStream capability negotiation establishes per-connection state whose replay could alter negotiated limits or serialization formats.¶

Endpoints MUST NOT send PipeStream frames in 0-RTT early data, and a server MUST NOT process PipeStream frames received in early data before the QUIC handshake is confirmed. A future extension may define 0-RTT semantics along with the required replay protections.¶

5.4. Performance Considerations

5.5. Transport Error Mapping

PipeStream error signaling on Stream 0 and QUIC transport signals are complementary. Endpoints SHOULD bridge them so peers receive both transport-level and protocol-level context. An implementation MAY omit bridging when operating as a simple pass-through proxy that does not inspect entity status.¶

1. If an Entity Stream is aborted with RESET_STREAM or STOP_SENDING, the endpoint SHOULD emit a corresponding status (FAILED when terminal, ABANDONED, or policy-driven equivalent) for that entity on Stream 0. The endpoint MAY omit the status frame only if the connection itself is being closed immediately.¶

2. If PipeStream determines a terminal entity error first (for example, checksum failure or invalid frame), the endpoint SHOULD abort the affected Entity Stream with an appropriate QUIC error and emit the corresponding PipeStream status/error context on Stream 0. Aborting the stream MAY be deferred if the entity payload is still needed for diagnostic purposes.¶

3. If Stream 0 is reset or becomes unusable, endpoints SHOULD treat this as a control-plane failure and close the connection with PIPESTREAM_CONTROL_RESET (0x03). An endpoint that can recover control-plane state through an application-layer mechanism MAY attempt reconnection before closing.¶

4. On QUIC connection termination (CONNECTION_CLOSE), entities without a previously observed terminal status MUST be handled by local failure policy, typically by marking them FAILED or ABANDONED.¶

6.1. Control Stream Framing (Stream 0)

To ensure forward compatibility and consistent parsing, all messages on the Control Stream use a Unified Control Frame (UCF) structure with an explicit length prefix.¶

6.2. Status Frames (Layer 0)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Ver(4) |Stat(4)|E|C|D(3) |           Flags (19 bits)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Entity ID (32 bits)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Scope ID (32 bits)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Reserved (32 bits)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  New Cursor Value (32 bits)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.3. Scope Digest Frame (0x54)

When Protocol Layer 1 is negotiated, a scope completion is summarized:¶

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Flags (8)      |        Reserved (24)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Scope ID (32 bits)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                   Entities Processed (64 bits)                |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                   Entities Succeeded (64 bits)                |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                    Entities Failed (64 bits)                  |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                    Entities Deferred (64 bits)                |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                    Merkle Root (256 bits)                     |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Flags (8 bits):

Reserved for future use. MUST be zero when sent and MUST be ignored by receivers.¶

Scope ID (32 bits):

Identifier of the scope being summarized.¶

Entities Processed (64 bits):

The total number of entities that were processed within the scope.¶

Entities Succeeded (64 bits):

The number of entities that reached a terminal success state.¶

Entities Failed (64 bits):

The number of entities that reached a terminal failure state.¶

Entities Deferred (64 bits):

The number of entities that were deferred via claim checks.¶

Merkle Root (256 bits):

The SHA-256 Merkle root covering all entity statuses in the scope (see Section 9.5).¶

The SCOPE_DIGEST payload is 72 octets (77 octets on the wire including the UCF header). The Scope ID MUST match the 32-bit identifier defined in Section 6.2.1.¶

6.4. Barrier Frame (0x55)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S|  Reserved (31 bits)                                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Scope ID (32 bits)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Parent Entity ID (32 bits)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

S (1 bit):

Status (0 = waiting, 1 = released).¶

Reserved (31 bits):

Reserved for future use. MUST be zero when sent and MUST be ignored by receivers.¶

Scope ID (32 bits):

Identifier for the scope to which this barrier applies.¶

Parent Entity ID (32 bits):

The identifier of the parent entity whose sub-tree is blocked by this barrier.¶

The BARRIER payload is 12 octets (17 octets on the wire including the UCF header).¶

6.5. GOAWAY Frame (0x56)

The GOAWAY frame signals that the sender will not accept new entities beyond a specified Entity ID. It enables graceful shutdown: in-flight entities with IDs at or below the Last Entity ID are processed to completion, while the peer refrains from opening new Entity Streams.¶

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Reserved (32 bits)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Last Entity ID (32 bits)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Reserved (32 bits):

Reserved for future use. MUST be zero when sent and MUST be ignored by receivers.¶

Last Entity ID (32 bits):

The highest Entity ID that the sender will process. Entities with IDs greater than this value (per the circular ordering defined in Section 9.1) MUST NOT be sent by the peer after receiving this frame.¶

The GOAWAY payload is 8 octets (13 octets on the wire including the UCF header).¶

6.6. Yield and Claim Check Extensions (Layer 2)

When E=1 in a status frame, an Extension Header MUST follow.¶

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Extension Length (32 bits)                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Yield Reason  |           Token Length (24 bits)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                  Yield Token (variable)                       |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                    Claim Check ID (64 bits)                   |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                Expiry Timestamp (64 bits, Unix micros)        |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.7. Serialized Message Frames (0x80-0xFF)

These frame types use the common UCF header defined in Section 6.1. The payload body is encoded using the serialization format negotiated during capability exchange (Section 3.4.2). If no format was negotiated, CBOR [RFC8949] is the default.¶

6.8. Entity Frames

Entity frames carry the actual entity payload data on Entity Streams.¶

   +---------------------------+
   |    Header Length (4)      |   4 octets, big-endian uint32
   +---------------------------+
   |                           |
   |    Header (serialized)    |   Variable length
   |                           |
   +---------------------------+
   |                           |
   |    Payload                |   Variable length (per header)
   |                           |
   +---------------------------+

entity-header = {
  entity-id: uint,               ; 32-bit on wire (STATUS frame)
  ? parent-id: uint,             ; 32-bit scope-local
  ? scope-id: uint,              ; 32-bit (Section 6.2.1)
  layer: uint .le 3,             ; Data layer 0-3
  ? content-type: tstr,          ; MIME type
  ? payload-length: uint,        ; Octet count of the payload
                                 ; carried in this frame; SHOULD be
                                 ; present. Omitted only when the
                                 ; final length is unknown at
                                 ; header-emission time (the stream
                                 ; FIN delimits the payload).
  ? checksum: bstr .size 32,     ; SHA-256; SHOULD be present
  ? metadata: { * tstr => tstr },
  ? chunk-info: chunk-info,
  ? completion-policy: completion-policy, ; Layer 2
}

chunk-info = {
  total-chunks: uint,
  chunk-index: uint,
  chunk-offset: uint,
}

yield-token = {
  reason: yield-reason,            ; See Appendix C for enum values
  ? continuation-state: bstr,
  ? validation: stopping-point-validation,
}

claim-check = {
  claim-id: uint,
  entity-id: uint,
  ? scope-id: uint,
  expiry-timestamp: uint,        ; Unix epoch microseconds
  ? validation: stopping-point-validation,
}

; entity-status enumerates the status codes of Section 6.2.2;
; the full definition appears in Appendix C.

stopping-point-validation = {
  ? state-checksum: bstr,        ; Hash of processing state
  ? bytes-processed: uint,       ; Progress marker
  ? children-complete: uint,
  ? children-total: uint,
  ? is-resumable: bool,
  ? checkpoint-ref: tstr,
}

7.1. Entity Header

The normative wire-level Entity Header is defined in Section 6.8.2. It provides transport-level identification and routing metadata, including entity-id, parent-id, scope-id, layer, payload-length, and optional integrity metadata. The core protocol interprets these fields for stream processing, flow control, and recursive coordination, but it does not define application-specific payload structure.¶

7.2. Data Layers

PipeStream defines a 2-bit Data Layer field (values 0-3) in the Entity Header that identifies the payload encoding class. The semantics of each layer value are defined by Application Profile specifications. The core protocol does not assign meaning to specific layer values; it ensures that the layer field is faithfully transmitted and that receivers can route entities to appropriate handlers based on layer.¶

Application Profiles SHOULD define at most four data layers. Common patterns include:¶

This layering enables pipeline stages to progressively transform entities from raw input to structured output while maintaining type distinction through the layer field.¶

7.3. Application-Level Envelope

The Entity Header (Section 6.8.2) provides transport-level identification (entity-id, scope-id, and layer). Applications that require additional identification, such as a stable input identifier that persists across pipeline runs, multi-tenancy context, or domain-specific metadata, SHOULD define an application-level envelope message carried within the entity payload.¶

If an application-level envelope carries its own entity identifier, that identifier MUST match the entity-id in the enclosing Entity Header. The definition of application-level envelopes is outside the scope of this specification. See [PIPESTREAM-DOCPROC] for an example companion profile that defines such an envelope for document-processing workloads.¶

7.4. Common Storage References

PipeStream defines a common storage reference type for entities that refer to externally stored data. Application Profiles are not required to use this type but SHOULD prefer it over ad hoc storage reference formats to improve interoperability between pipeline stages from different implementations.¶

file-storage-reference = {
  provider: tstr,                ; Storage provider identifier
  bucket: tstr,                  ; Bucket/container name
  key: tstr,                     ; Object key/path
  ? region: tstr,                ; Optional region hint
  ? attrs: { * tstr => tstr },   ; Provider-specific attributes
  ? encryption: encryption-metadata,
}

encryption-metadata = {
  algorithm: tstr,               ; "AES-256-GCM", "AES-256-CBC"
  ? key-provider: tstr,          ; "aws-kms", "azure-keyvault",
                                 ; "gcp-kms", "vault"
  ? key-id: tstr,                ; Key ARN/URI/ID
  ? wrapped-key: bstr,           ; Client-side encrypted DEK
  ? iv: bstr,                    ; Initialization vector
  ? context: { * tstr => tstr }, ; Encryption context
}

8.1. Overview

A PipeStream session proceeds through four sequential actions:¶

                +---------------------------------------------+
                |           PipeStream Action Flow            |
                +---------------------------------------------+
                                     |
                                     v
                +---------------------------------------------+
                |                  CONNECT                    |
                |    (Session + Capability Negotiation)       |
                +---------------------------------------------+
                                     |
                                     v
                +---------------------------------------------+
                |                   PARSE                     |
                |        (Dehydration: 1:N possible)         |
                +---------------------------------------------+
                                     |
                       +-------------+-------------+
                       v             v             v
                +-----------+ +-----------+ +-----------+
                |  PROCESS  | |  PROCESS  | |  PROCESS  |
                |   (1:1)   | |   (1:1)   | |   (N:1)   |
                +-----------+ +-----------+ +-----------+
                       |             |             |
                       +-------------+-------------+
                                     |
                                     v
                +---------------------------------------------+
                |                   SINK                      |
                |          (Terminal Consumption)             |
                +---------------------------------------------+

8.2. CONNECT Action

The CONNECT action establishes the session with capability negotiation.¶

8.3. PARSE Action

The PARSE action performs decomposition by dehydrating an input entity into one or more sub-entities. When Layer 2 is negotiated, the sender MAY attach a completion policy that governs how partial success, timeouts, or retries are handled during recursive processing.¶

completion-policy = {
  ? mode: completion-mode,
  ? max-retries: uint,           ; Default: 3
  ? retry-delay-ms: uint,        ; Default: 1000
  ? timeout-ms: uint,            ; Default: 300000 (5 min)
  ? min-success-ratio: float32,  ; For QUORUM mode
  ? on-timeout: failure-action,
  ? on-failure: failure-action,
}

completion-mode = &(
  unspecified: 0,                ; Default; treat as STRICT
  strict: 1,                    ; All children MUST complete
  lenient: 2,                   ; Continue with partial results
  best-effort: 3,               ; Complete with whatever succeeds
  quorum: 4,                    ; Need min-success-ratio
)

failure-action = &(
  unspecified: 0,                ; Default; treat as FAIL
  fail: 1,                      ; Propagate failure up
  skip: 2,                      ; Skip, continue with siblings
  retry: 3,                     ; Retry up to max-retries
  defer: 4,                     ; Create claim check, continue
)

8.4. PROCESS Action

8.5. SINK Action

The SINK action represents terminal consumption of processed entities. Sink implementations are application-specific and are defined by Application Profile specifications. Common sink patterns include persistent storage, search engine indexing, event notification, and downstream service delivery.¶

9.1. Entity ID Lifecycle and Cursor

Entity IDs are managed using a cursor-based circular recycling scheme within the 32-bit ID space. All circular arithmetic in this document is performed modulo 0xFFFFFFFD; this modulus excludes the reserved values at the top of the 32-bit space from circulation. The following Entity ID values are reserved and MUST NOT be assigned to entities:¶

Assignable Entity IDs therefore range from 0x00000001 to 0xFFFFFFFC, yielding 4,294,967,292 usable identifiers per scope.¶

The ID space is divided into three logical regions relative to the current cursor and last_assigned pointers:¶

The window size is computed as (last_assigned - cursor) mod 0xFFFFFFFD. If window_size >= max_window, the sender MUST apply backpressure and stop assigning new IDs until the cursor advances.¶

The max_window value MUST NOT exceed 2,147,483,646 (the largest value strictly less than 0xFFFFFFFD / 2). This bound guarantees that the circular comparison function is_before (Section 9.3) is unambiguous for any pair of in-flight Entity IDs. The default max-window-size advertised in the capabilities exchange (Section 3.4) is 2,147,483,646.¶

Rules:¶

1. new_id = (last_assigned + 1) % 0xFFFFFFFD¶

2. If new_id == 0, new_id = 1 (skip reserved NULL_ENTITY)¶

3. If (new_id - cursor) % 0xFFFFFFFD >= max_window -> STOP, apply backpressure¶

4. On reaching a terminal state (COMPLETE, SKIPPED, ABANDONED, or FAILED with no remaining retries): mark resolved; if entity_id == cursor, advance cursor past all contiguous resolved IDs¶

5. IDs behind cursor are implicitly recyclable¶

An entity in the FAILED state that may still transition to RETRYING (see the state transition table in Section 6.2) MUST NOT be marked resolved. Only when retries are exhausted or no completion policy permits retries does FAILED become terminal for cursor purposes.¶

9.2. Assembly Manifest

The Assembly Manifest is a local data structure maintained by each endpoint to track the parent-child relationships created during dehydration. It is not transmitted on the wire; rather, each endpoint constructs its own manifest from the parent-id fields in received EntityHeaders and from status updates observed on the Control Stream. The CDDL below defines the logical structure of each entry; implementations MAY use any internal representation that preserves the required semantics.¶

Each Assembly Manifest entry tracks:¶

assembly-manifest-entry = {
  parent-id: uint,
  ? scope-id: uint,              ; Layer 1
  children-ids: [* uint],
  ? children-status: [* entity-status],
  ? policy: completion-policy,   ; Layer 2
  ? created-at: uint,
  ? state: resolution-state,
}

resolution-state = &(
  unspecified: 0,
  active: 1,
  resolved: 2,
  partial: 3,                   ; Some children failed/skipped
  failed: 4,
)

9.3. Checkpoint Blocking

A checkpoint is satisfied when:¶

1. All entities in the checkpoint scope with IDs less than checkpoint_entity_id (considering circular wrap) have reached terminal state.¶

2. All Assembly Manifest entries within the checkpoint scope have been resolved.¶

3. All nested checkpoints within the checkpoint scope have been satisfied.¶

CheckpointFrame (Section 6.7 / Appendix C) carries both:¶

checkpoint-frame = {
  checkpoint-id: tstr,
  sequence-number: uint,
  checkpoint-entity-id: uint,
  ? scope-id: uint,
  ? flags: uint,
  ? timeout-ms: uint,
}

• checkpoint_id: an opaque identifier for logging and correlation.¶

• checkpoint_entity_id: the numeric ordering key used for barrier evaluation.¶

Implementations MUST use checkpoint_entity_id (not checkpoint_id) when evaluating Condition 1.¶

For circular comparison in Condition 1, implementations MUST use the same modulo ordering as cursor management. Define MAX = 0xFFFFFFFD and:¶

is_before(a, b) = ((b - a + MAX) % MAX) < (MAX / 2)¶

An entity ID a is considered "less than checkpoint_entity_id b" iff is_before(a, b) is true.¶

9.4. Scope ID Allocation (Layer 1)

When Layer 1 is negotiated, Scope IDs are 32-bit unsigned integers assigned by the endpoint that initiates the dehydration. The allocation scheme is as follows:¶

1. Scope ID 0 is the root scope and MUST NOT be used for child scopes.¶

2. The dehydrating endpoint assigns a unique Scope ID to each new child scope created during dehydration. The Scope ID MUST be unique within the connection for the lifetime of that scope (i.e., until the scope's SCOPE_DIGEST frame has been sent and all entities in the scope have reached terminal state).¶

3. Scope IDs MAY be allocated sequentially or randomly; the protocol does not require any particular ordering. Sequential allocation is RECOMMENDED for simplicity and debuggability.¶

4. Once a scope has been closed (its SCOPE_DIGEST has been sent and all entities within the scope have reached terminal state), the Scope ID MAY be reused for a new scope. Implementations MUST ensure that no in-flight status frames reference a recycled Scope ID before reuse.¶

9.5. Scope Digest Propagation (Layer 1)

When a scope completes, the endpoint MUST compute a Scope Digest and propagate it to the parent scope via a SCOPE_DIGEST frame (Section 6.3).¶

The Merkle root in the Scope Digest is computed as follows:¶

1. For each entity in the scope, ordered by ascending numeric Entity ID value, construct a 5-octet leaf value by concatenating:¶

   • The 4-octet big-endian Entity ID.¶

   • A 1-octet status field where the lower 4 bits contain the entity's terminal Stat code (Section 6.2.2) and the upper 4 bits are zero.¶

2. Compute each leaf hash as SHA-256(0x00 || leaf), where leaf is the 5-octet value from step 1.¶

3. Build a binary Merkle tree by repeatedly hashing pairs of sibling nodes: SHA-256(0x01 || left || right). If the number of nodes at any level is odd, the last node is promoted to the next level without hashing.¶

4. The root of this tree is the merkle_root value in the SCOPE_DIGEST frame.¶

The 0x00 and 0x01 domain-separation prefixes distinguish leaf hashes from interior-node hashes, preventing second-preimage attacks in which an interior node is presented as a leaf (or vice versa). This construction follows the approach used for Merkle Tree Hashes in Certificate Transparency.¶

This construction is deterministic: any two implementations processing the same set of entity statuses MUST produce the same Merkle root.¶

Because each Entity ID contributes exactly one leaf, an implementation MUST NOT recycle an Entity ID within a scope whose SCOPE_DIGEST has not yet been computed. Cursor-based recycling (Section 9.1) already guarantees this when scopes complete before the ID space wraps; implementations whose scopes approach the ID-space capacity MUST close and digest the scope before reusing any of its Entity IDs.¶

9.6. Rehydration Readiness Tracking

Implementations MUST track Assembly Manifest resolution order using a local data structure that can efficiently identify the next parent entity eligible for rehydration as child statuses arrive out of order.¶

The specific algorithm and internal representation are implementation choices and are outside the scope of this specification.¶

9.7. Stopping Point Validation (Layer 2)

When yielding or deferring, include validation:¶

stopping-point-validation = {
  ? state-checksum: bstr,        ; Hash of processing state
  ? bytes-processed: uint,       ; Progress marker
  ? children-complete: uint,
  ? children-total: uint,
  ? is-resumable: bool,
  ? checkpoint-ref: tstr,
}

10.1. Transport Security

PipeStream inherits security from QUIC [RFC9000] and TLS 1.3 [RFC8446]. All connections MUST use TLS 1.3 or later. Implementations MUST NOT provide mechanisms to disable encryption.¶

PipeStream frames MUST NOT be sent or processed in 0-RTT early data (Section 5.3), which removes the replay exposure that early data would otherwise introduce for capability negotiation and status frames.¶

10.2. Entity Payload Integrity

Each Entity SHOULD include a SHA-256 [FIPS-180-4] checksum in its EntityHeader (the checksum field defined in Section 6.8.2). The checksum is OPTIONAL in the wire format to accommodate zero-length entities, streamed entities whose final length is unknown at header-emission time, and scenarios where application-layer integrity mechanisms provide equivalent guarantees. When a checksum is present, it MUST be exactly 32 octets containing the SHA-256 digest computed over the raw payload bytes (the octet sequence following the EntityHeader on the Entity Stream). The checksum does not cover the EntityHeader itself.¶

For chunked entities (where chunk-info is present in the EntityHeader), each chunk MAY carry its own per-chunk checksum. The checksum in the first chunk's EntityHeader, if present, MUST cover only that chunk's payload bytes. An implementation that requires whole-entity integrity verification MUST either compute a rolling digest across all chunks or require the sender to transmit a final summary entity containing the whole-payload checksum.¶

To support true streaming of large entities, implementations MAY begin processing an entity payload before the complete payload has been received and verified. However, the final rehydration or terminal SINK operation MUST NOT be committed until the complete payload checksum has been verified.¶

If a checksum verification fails, the implementation MUST:¶

1. Reject the entity with PIPESTREAM_INTEGRITY_ERROR (0x04).¶

2. Discard any partial results or temporary state associated with the entity.¶

3. Propagate the failure according to the Completion Policy (Section 8.3).¶

Implementations that require immediate consistency SHOULD buffer the entire entity and verify the checksum before initiating processing.¶

10.3. Resource Exhaustion

Implementations MUST enforce all resource limits listed above. Exceeding any limit MUST result in the corresponding error code (see Section 11.4). Implementations SHOULD allow operators to configure stricter limits than the defaults shown here.¶

To prevent memory-exhaustion attacks, implementations MUST NOT pre-allocate memory for variable-length payloads based solely on the 32-bit Length field in the UCF header (Section 6.1.1). Memory MUST be allocated incrementally as octets are received, or capped at a smaller initial buffer until the message type and context are verified.¶

10.4. Amplification Attacks

A single dehydration operation can produce an arbitrary number of child entities from a small input, creating a potential amplification vector. To mitigate this:¶

1. Implementations MUST enforce the max_entities_per_scope limit negotiated during capability exchange (Section 3.4). Any dehydration that would exceed this limit MUST be rejected.¶

2. Implementations MUST enforce the max_scope_depth limit. A dehydration chain deeper than this limit MUST be rejected with PIPESTREAM_DEPTH_EXCEEDED (0x07).¶

3. Implementations SHOULD enforce a configurable ratio between input entity size and total child entity count. A recommended default is no more than 1,000 children per megabyte of parent payload.¶

4. The backpressure mechanism (Section 9.1) provides a natural throttle: when the in-flight window fills, no new Entity IDs can be assigned until existing entities complete and the cursor advances. Implementations MUST NOT bypass backpressure for dehydration-generated entities.¶

10.5. Privacy Considerations

PipeStream entity headers and control stream frames carry metadata that may reveal information about the entities being processed, even when payloads are encrypted at the application layer:¶

1. Entity structure leakage: The number of child entities produced by dehydration, the scope depth, and the Entity ID assignment pattern may reveal the structure of the input being processed (e.g., an entity that dehydrates into 50 children is likely a multi-part input). Implementations that require structural privacy SHOULD pad dehydration counts or use fixed decomposition granularity. Deployments that do not handle privacy-sensitive data MAY omit this padding.¶

2. Metadata in headers: The content_type, metadata map, and payload_length fields in EntityHeader (Section 6.8.2) are transmitted in cleartext within the QUIC-encrypted stream. Implementations that require metadata confidentiality beyond transport encryption SHOULD encrypt EntityHeader fields at the application layer and use an opaque content_type such as application/octet-stream. This overhead is unnecessary when the deployment operates within a trusted network.¶

3. Traffic analysis: The timing and size of status frames on the Control Stream may correlate with processing patterns. Implementations operating in privacy-sensitive environments SHOULD send status frames at fixed intervals with padding to obscure processing timing. Deployments in trusted environments MAY omit traffic padding to reduce bandwidth overhead.¶

4. Identifiers: Application-level input identifiers and filenames carried inside profile-defined payload envelopes are not interpreted by PipeStream Core but may still be logged by intermediate processing nodes. Implementations SHOULD provide mechanisms to redact or pseudonymize such identifiers at pipeline boundaries. This recommendation may be relaxed when all nodes in the pipeline are operated by the same administrative entity.¶

10.6. Replay and Token Reuse

10.7. Encryption Key Management

When using FileStorageReference with encryption:¶

1. Key IDs MUST reference keys in approved providers.¶

2. Wrapped keys MUST use approved envelope encryption.¶

3. Key rotation MUST be supported via key_id versioning.¶

4. Implementations MUST NOT log key material.¶

5. Implementations MUST NOT include unwrapped data encryption keys in EntityHeader metadata or Control Stream frames.¶

11.1. ALPN Identifier Registration

This document registers the following ALPN [RFC7301] protocol identifier:¶

Protocol:

PipeStream Version 1¶

Identification Sequence:

0x70 0x69 0x70 0x65 0x73 0x74 0x72 0x65 0x61 0x6D 0x2F 0x31 ("pipestream/1")¶

Specification:

This document¶

11.2. PipeStream Frame Type Registry

IANA is requested to create the "PipeStream Frame Types" registry. All frames on Stream 0 MUST use a 4-octet length prefix following the 1-octet Type. The registry is partitioned into three ranges that determine both the registration policy and the framing class of the payload:¶

Each registration consists of a value, a frame type name, the minimum protocol layer, a short description, and a reference to a specification. The initial contents are:¶

11.3. PipeStream Status Code Registry

IANA is requested to create the "PipeStream Status Codes" registry. Status codes are 4-bit values (0x0-0xF). Values 0xD-0xE are reserved for Expert Review. Value 0xF is reserved for private use.¶

11.4. PipeStream Error Code Registry

IANA is requested to create the "PipeStream Error Codes" registry. Values in the range 0x00-0x3F are assigned by Expert Review. Values in the range 0x40-0xFF are reserved for private use.¶

PipeStream error codes are used as QUIC application error codes in CONNECTION_CLOSE and RESET_STREAM frames. When terminating a connection or aborting a stream due to a protocol-level error, the endpoint MUST use the corresponding PipeStream error code value as the QUIC Application Error Code.¶

11.5. PipeStream Serialization Format Registry

IANA is requested to create the "PipeStream Serialization Formats" registry. New entries require Expert Review [RFC8126]. A registration request MUST include a reference to a specification that normatively defines the encoding of every serialized PipeStream message (Section 3.4.2).¶

11.6. URI Scheme Registration

This section registers the "pipestream" URI scheme per [RFC7595]. The URI scheme identifies application context for detached or resumable resources (for example, Layer 2 yield/claim-check flows). PipeStream Layer 0 streaming semantics do not depend on this URI scheme.¶

Scheme name:

pipestream¶

Status:

Permanent¶

Applications/protocols that use this scheme:

PipeStream protocol (this document)¶

Scheme syntax:

See Section 11.6.1.¶

Scheme semantics:

A pipestream URI identifies an application-level session context within a PipeStream deployment and, optionally, a scope path and an entity reference within that context. It is used to locate detached or resumable resources, such as Layer 2 claim checks, potentially across transport connections. The authority component identifies the endpoint that issued the resource.¶

Encoding considerations:

All components other than the authority are restricted to a subset of unreserved ASCII characters by the ABNF in Section 11.6.1. Percent-encoding is neither required nor permitted in those components. The authority component follows the syntax and encoding rules of [RFC3986], Section 3.2.¶

Interoperability considerations:

None beyond those described in this document.¶

Security considerations:

See Section 10 of this document. A pipestream URI may embed session and claim identifiers that function as bearer capabilities; such URIs SHOULD be treated as sensitive and MUST NOT be exposed in logs or referral contexts where they could enable claim redemption by unauthorized parties.¶

Contact:

Kristian Rickert (kristian.rickert@pipestream.ai)¶

Change controller:

IETF¶

References:

This document¶

pipestream-URI = "pipestream://" authority "/" session-id
                 [ "/" scope-path ] [ "/" entity-ref ]

session-id     = 1*( ALPHA / DIGIT / "-" )
scope-path     = scope-id *( "." scope-id )
scope-id       = 1*DIGIT
entity-ref     = 1*( ALPHA / DIGIT )
authority      = <authority, see RFC 3986, Section 3.2>

11.7. Guidance for Designated Experts

For all registries defined in this section, the designated experts are advised to apply the following criteria when evaluating requests:¶

1. A permanent, readily available public specification of the proposed value is required and needs to define the value's semantics precisely enough for independent interoperable implementations.¶

2. The proposed value must not conflict with, duplicate, or create ambiguity with existing registrations, including the framing class of frame types (fixed bit-packed versus serialized payload; Section 11.2).¶

3. Requests should be evaluated for their effect on existing deployments; extensions that require behavior changes from unmodified endpoints are inappropriate for these registries and instead require a new protocol version (Section 3.4.1).¶

4. Assignments from scarce code spaces (in particular the 4-bit status code space) should be granted conservatively; the expert may require demonstrated deployment interest before assigning values from a scarce space.¶

12.1. Normative References

[FIPS-180-4]

National Institute of Standards and Technology, "Secure Hash Standard (SHS)", FIPS PUB 180-4, August 2015.

[RFC2119]

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/rfc/rfc2119>.

[RFC3986]

Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, <https://www.rfc-editor.org/rfc/rfc3986>.

[RFC5234]

Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, <https://www.rfc-editor.org/rfc/rfc5234>.

[RFC7301]

Friedl, S., Popov, A., Langley, A., and E. Stephan, "Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.

[RFC7595]

Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines and Registration Procedures for URI Schemes", BCP 35, RFC 7595, DOI 10.17487/RFC7595, June 2015, <https://www.rfc-editor.org/rfc/rfc7595>.

[RFC8126]

Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/rfc/rfc8126>.

[RFC8174]

Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

[RFC8446]

Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/rfc/rfc8446>.

[RFC8610]

Birkholz, H., Vigano, C., and C. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, June 2019, <https://www.rfc-editor.org/rfc/rfc8610>.

[RFC8949]

Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, December 2020, <https://www.rfc-editor.org/rfc/rfc8949>.

[RFC9000]

Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, <https://www.rfc-editor.org/rfc/rfc9000>.

12.2. Informative References

[MOQT]

Nandakumar, S., Vasiliev, V., Swett, I., and A. Frindell, "Media over QUIC Transport", Work in Progress, Internet-Draft, draft-ietf-moq-transport-19, 6 July 2026, <https://datatracker.ietf.org/doc/html/draft-ietf-moq-transport-19>.

[PIPESTREAM-DOCPROC]

Rickert, K., "PipeStream Document Processing Profile", March 2026, <https://github.com/ai-pipestream/pipestream-quic-protocol-rfc/tree/main/docproc>.

[RFC7574]

Bakker, A., Petrocco, R., and V. Grishchenko, "Peer-to-Peer Streaming Peer Protocol (PPSPP)", RFC 7574, DOI 10.17487/RFC7574, July 2015, <https://www.rfc-editor.org/rfc/rfc7574>.

[RFC7696]

Housley, R., "Guidelines for Cryptographic Algorithm Agility and Selecting Mandatory-to-Implement Algorithms", BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, <https://www.rfc-editor.org/rfc/rfc7696>.

[RFC7942]

Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, July 2016, <https://www.rfc-editor.org/rfc/rfc7942>.

[RFC9114]

Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114, June 2022, <https://www.rfc-editor.org/rfc/rfc9114>.

[RFC9250]

Huitema, C., Dickinson, S., and A. Mankin, "DNS over Dedicated QUIC Connections", RFC 9250, DOI 10.17487/RFC9250, May 2022, <https://www.rfc-editor.org/rfc/rfc9250>.

[RFC9260]

Stewart, R., Tuexen, M., and K. Nielsen, "Stream Control Transmission Protocol", RFC 9260, June 2022, <https://www.rfc-editor.org/rfc/rfc9260>.

[RFC9297]

Schinazi, D. and L. Pardue, "HTTP Datagrams and the Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, August 2022, <https://www.rfc-editor.org/rfc/rfc9297>.

[RFC9308]

Kuehlewind, M. and B. Trammell, "Applicability of the QUIC Transport Protocol", RFC 9308, September 2022, <https://www.rfc-editor.org/rfc/rfc9308>.

[scatter-gather]

Lea, D., "The Scatter-Gather Design Pattern", DOI 10.1007/978-1-4612-1260-6, 1996, <https://doi.org/10.1007/978-1-4612-1260-6>.

B.1. QUIC as Application Transport

RFC 9308 [RFC9308] provides guidance for designers of application protocol mappings to QUIC. PipeStream follows this guidance: stream semantics are mapped to the protocol's data model (Section 4), flow control operates at both the stream and connection level, and an ALPN token is registered for protocol identification (Section 11).¶

The precedent for application protocols that bypass HTTP and map directly onto QUIC is well established. DNS over Dedicated QUIC Connections [RFC9250] adopts a direct mapping on the grounds that HTTP framing introduces unnecessary overhead when the application has its own message semantics. The Media over QUIC Transport protocol [MOQT] similarly defines its own framing and control messages over QUIC streams, with HTTP/3 as an optional encapsulation rather than a requirement.¶

PipeStream's requirements align with these precedents. The protocol's dual-stream architecture (Section 4), bit-packed control frames (Section 6), and recursive entity lifecycle (Section 9) have no counterpart in HTTP semantics, and mapping them onto request-response pairs would add complexity without benefit.¶

B.2. Efficiency Considerations

The decision to implement PipeStream as a standalone protocol over QUIC is driven by the following efficiency requirements:¶

B.3. HTTP/3

HTTP/3 [RFC9114] provides multiplexed request-response exchanges over QUIC. Its stream model binds each client-initiated request to a server response on the same stream. PipeStream requires bidirectional, peer-initiated entity streams where either endpoint may open new streams to transmit sub-entities arising from recursive decomposition. The request-response constraint precludes this.¶

PipeStream also requires a persistent control stream carrying compact, fixed-size status frames at high frequency. HTTP/3 does define unidirectional control streams, but their framing is specific to HTTP semantics (SETTINGS, GOAWAY, MAX_PUSH_ID) and cannot be repurposed for application-level status coordination without introducing a parallel signaling mechanism that duplicates much of what QUIC already provides.¶

B.4. gRPC

gRPC defines a remote procedure call framework over HTTP/2, with experimental support for HTTP/3. Bidirectional streaming in gRPC is scoped to a single RPC method: one request stream and one response stream per call. PipeStream requires an arbitrary number of concurrent entity streams with independent flow control, plus a dedicated control stream, all within a single connection. Achieving this over gRPC would require either multiplexing all entities onto a single bidirectional RPC (sacrificing per-stream flow control and head-of-line independence) or opening a separate RPC per entity (sacrificing session-level coordination and incurring per-call overhead).¶

Beyond the stream model mismatch, gRPC does not provide protocol-level primitives for recursive entity decomposition, checkpoint-based consistency across parallel processing paths, or hierarchical scope management with digest propagation. Building equivalent semantics on top of gRPC requires application-layer coordination logic that PipeStream provides natively as part of the protocol specification.¶

gRPC further mandates a 5-octet length-prefixed framing envelope for every message. PipeStream's fixed-size control frames are bit-packed at the wire level with zero serialization overhead, which is material at the status update frequencies the protocol is designed to sustain.¶

PipeStream complements rather than replaces gRPC: a PipeStream pipeline stage MAY internally use gRPC to communicate with processing services while relying on PipeStream for inter-stage coordination and consistency.¶

B.5. WebTransport

WebTransport [RFC9297] provides bidirectional streams and unreliable datagrams over HTTP/3, and is the closest existing protocol to the transport abstraction PipeStream requires. However, several properties make it unsuitable as a substrate:¶

WebTransport sessions are established via an HTTP/3 CONNECT request, inheriting the client-server asymmetry of HTTP. In PipeStream, both endpoints participate symmetrically in capability negotiation and may initiate entity streams; the protocol does not distinguish a "client" role from a "server" role after the handshake.¶

WebTransport is designed for environments constrained by the web security model (origin-based isolation, CORS). PipeStream targets server-to-server processing pipelines where these constraints are inapplicable.¶

WebTransport provides raw byte streams with no built-in coordination semantics. PipeStream would need to implement its own framing, status state machine, checkpoint barriers, and scope hierarchy on top of WebTransport streams. At that point, the HTTP/3 session layer introduces an additional round trip during establishment and per-stream framing overhead, with no corresponding benefit.¶

B.6. Media over QUIC Transport

The Media over QUIC Transport protocol [MOQT] is architecturally the closest existing QUIC-native protocol to PipeStream: both use a bidirectional control stream for session coordination alongside unidirectional streams carrying independent data objects, following the application-mapping guidance of [RFC9308].¶

The two protocols nevertheless solve different problems. MOQT is a publish/subscribe media delivery protocol optimized for fan-out through relays: objects within a track are delivered to a dynamic set of subscribers, delivery of any individual object may be abandoned when it ceases to be useful (for example, after a latency deadline passes), and no participant tracks whether the totality of published objects reached any subscriber. PipeStream is a scatter-gather processing protocol with the opposite requirements: the set of child entities produced by a decomposition is determinate, every entity MUST be driven to a terminal status, and reassembly is gated on cryptographically verifiable completion of the entire set (Section 9). MOQT has no counterpart to hierarchical scopes, scope digests, barrier synchronization, or completion policies, and PipeStream has no counterpart to tracks, subscriptions, or relay-based fan-out.¶

Extending MOQT with completion tracking would require adding precisely the control-plane machinery this document defines, while inheriting subscription semantics that have no role in pipeline processing.¶

B.7. Broker-Based Pipeline Architectures

Many production processing pipelines are built not on RPC frameworks but on message brokers and distributed commit logs, with stages communicating through persistent intermediary queues or topics. These architectures provide durable decoupling and replay, and PipeStream is not a replacement for them where store-and-forward durability between organizationally separate stages is the primary requirement.¶

However, broker-based architectures externalize the semantics that PipeStream provides natively. Completion of a hierarchically decomposed job must be tracked in a coordination store outside the message path; end-to-end integrity of a reassembled output must be verified by application logic; and backpressure operates per queue rather than end-to-end across a pipeline. Each stage boundary additionally imposes a full persist-and-forward cycle, which defeats incremental streaming of large entities. The broker itself is also an interoperability boundary: no standardized wire protocol expresses scatter-gather semantics across brokers from different vendors, so multi-organization pipelines are coupled through vendor-specific client libraries.¶

A PipeStream deployment MAY use a broker behind an individual processing stage (as it may use gRPC; see above) while relying on PipeStream for inter-stage transport, completion tracking, and integrity verification.¶

B.8. Summary

PipeStream occupies a design point not addressed by existing protocols: a QUIC-native application protocol combining multiplexed entity streaming, recursive decomposition with hierarchical scopes, Merkle-based integrity propagation, and barrier-synchronized reassembly. While existing protocols like SCTP [RFC9260] and PPSPP [RFC7574] address subsets of these requirements, none provide the integrated lifecycle and coordination semantics that PipeStream defines.¶

D.1. Reference Implementation

Organization:

PipeStream AI¶

Description:

Reference implementation of the PipeStream protocol.¶

Maturity:

Under development; not yet publicly released.¶

Coverage:

To be updated as development progresses.¶

Licensing:

To be determined.¶

Contact:

Kristian Rickert (kristian.rickert@pipestream.ai)¶

The authors welcome reports of additional implementations for inclusion in future revisions of this appendix.¶