stream

Maps a protocol event method to its subscription Channel.

Returns undefined for unrecognized methods so that new server-side channels (e.g. from extension transformers) don't break existing subscribers. The custom method resolves to the named custom:<name> channel when the payload carries a name, otherwise the bare custom channel. Both "input" and the wire-level "input.requested" map to the input channel.

Whether namespace starts with prefix.

Segments are compared literally first; if the prefix segment itself contains no :, the candidate segment is also compared after its dynamic suffix is stripped (see normalizeNamespaceSegment). This mirrors is_prefix_match in api/langgraph_api/protocol/namespace.py so server-side filtering and client-side per-subscription narrowing stay consistent.

@langchain/langgraph/stream — backend toolkit for the v2 streaming protocol.

This entrypoint collects the primitives needed to build a custom transport or server on top of the Agent Streaming Protocol:

• StreamChannel — an append-only, buffered event log with independent replay cursors, for buffering events and fanning them out to multiple subscribers.
• convertToProtocolEvent — turns raw streamEvents (v3) payloads into canonical ProtocolEvents.
• inferChannel / matchesSubscription — map an event to its Channel and decide whether a buffered event should be delivered for a given subscription filter (with optional since replay cursor).
• SUPPORTED_CHANNELS / isSupportedChannel — the recognized channel set and a guard for validating subscription requests.

These are intentionally transport-agnostic: pair them with SSE, WebSocket, or any custom framing to expose a graph over the protocol.

Whether value names a protocol subscription channel — either a base channel ("messages", "values", …) or a named custom channel ("custom:<name>"). Unknown/future method names return false, mirroring inferChannel.

Returns whether an event should be delivered for a subscription definition.

When the definition carries a since replay cursor, events at or before that sequence number are excluded — letting the same predicate drive both live fan-out and buffered replay over a StreamChannel.

Strip dynamic suffixes (after :) from a namespace segment.

Server-emitted namespaces contain runtime-generated suffixes like "fetcher:abc-uuid", while user-supplied subscription filters are typically static names ("fetcher"). Mirrors normalize_namespace_segment in api/langgraph_api/protocol/namespace.py.

True when payload is a lightweight checkpoint envelope (not a full-state Pregel checkpoints debug payload).

A projection channel for StreamTransformers.

Implements AsyncIterable<T> so it can be iterated directly by in-process consumers via run.extensions.<key>. Channels created with StreamChannel.remote or new StreamChannel(name) are also auto-forwarded to remote clients.

A projection channel for StreamTransformers.

Implements AsyncIterable<T> so it can be iterated directly by in-process consumers via run.extensions.<key>. Channels created with StreamChannel.remote or new StreamChannel(name) are also auto-forwarded to remote clients.

Minimal protocol-event shape consumed by inferChannel and matchesSubscription.

Both the core ProtocolEvent and the wire-level Event from @langchain/protocol structurally satisfy this contract, so the same predicates can drive in-process fan-out, buffered replay, and server-side (SSE / WebSocket) event-sink filtering without coupling to a single event type.

Single envelope for a streaming protocol emission: sequence, channel (method), and payload (params).

Channels that can appear on a protocol event. Beyond the raw StreamMode channels emitted by the Pregel stream, the v2 protocol layer synthesizes additional channels (e.g. lifecycle, input) via built-in StreamTransformers and exposes user-defined channels created with StreamChannel.

Hierarchical path identifying a position in the agent tree.

Each element is one segment; longer arrays mean deeper nesting (e.g. subgraph or multi-agent scopes).