@langchain/langgraph-sdk/dist/stream/projections/messages.cjs.map

Client library for interacting with the LangGraph API

{"version":3,"file":"messages.cjs","names":["namespaceKey","MessageAssembler","isRootNamespace","reconcileMessagesFromValues","ensureMessageInstances","shouldPreferValuesMessage","buildMessageIndex","assembledMessageToBaseMessage","openProjectionSubscription"],"sources":["../../../src/stream/projections/messages.ts"],"sourcesContent":["/**\n * Namespace-scoped `messages` projection.\n *\n * Opens `thread.subscribe({ channels: [\"messages\"], namespaces: [ns] })`\n * and folds each `messages` event through {@link MessageAssembler}.\n * Every update — start, block delta, block finish, message finish —\n * re-derives a `BaseMessage` class instance for the currently-active\n * message and updates its slot in the store.\n *\n * The projection emits `BaseMessage[]` (class instances from\n * `@langchain/core/messages`), never plain serialized objects.\n */\nimport type {\n  MessagesEvent,\n  MessageRole,\n  MessageStartData,\n  ValuesEvent,\n} from \"@langchain/protocol\";\nimport type { BaseMessage } from \"@langchain/core/messages\";\nimport { MessageAssembler } from \"../../client/stream/messages.js\";\nimport {\n  assembledMessageToBaseMessage,\n  type ExtendedMessageRole,\n} from \"../assembled-to-message.js\";\nimport type { Message } from \"../../types.messages.js\";\nimport type { ProjectionSpec, ProjectionRuntime } from \"../types.js\";\nimport { ensureMessageInstances } from \"../message-coercion.js\";\nimport { isRootNamespace, namespaceKey } from \"../namespace.js\";\nimport {\n  buildMessageIndex,\n  reconcileMessagesFromValues,\n  shouldPreferValuesMessage,\n} from \"../message-reconciliation.js\";\nimport { openProjectionSubscription } from \"./runtime.js\";\n\nexport function messagesProjection(\n  namespace: readonly string[]\n): ProjectionSpec<BaseMessage[]> {\n  const ns = [...namespace];\n  const key = `messages|${namespaceKey(ns)}`;\n\n  return {\n    key,\n    namespace: ns,\n    initial: [],\n    open({ thread, store, rootBus }): ProjectionRuntime {\n      const assembler = new MessageAssembler();\n      // Per-messageId state needed for BaseMessage projection:\n      //  - `role` is only in the `message-start` event; we cache it\n      //    so subsequent delta events still produce a typed message.\n      //  - `toolCallId` is pulled from message-start extras when role\n      //    is `tool` (a convention we keep compatible with serialized\n      //    v1 tool messages).\n      const roleByKey = new Map<\n        string,\n        { role: ExtendedMessageRole; toolCallId?: string }\n      >();\n      const indexById = new Map<string, number>();\n      // Ids this projection has observed via the `messages` channel\n      // (token-level deltas). Used by `applyValuesEvent` to prefer the\n      // stream-assembled version over the values-coerced shape while a\n      // turn is streaming, matching the root controller's policy.\n      const streamMessageIds = new Set<string>();\n      // Ids observed in the most recent `values.messages` snapshot.\n      // Messages that were present in a prior snapshot but are absent\n      // from this one are treated as explicit removals (server-side\n      // `RemoveMessage` reducer deltas). Stream-only messages (seen on\n      // the messages channel but never echoed in a values snapshot)\n      // are preserved — their enclosing superstep may simply not have\n      // committed yet.\n      let valuesMessageIds = new Set<string>();\n      // Same run-boundary rule as the root projection, driven by root\n      // lifecycle events: a terminal drops streamed, uncommitted messages\n      // that never finished; the next `running` drops the rest. Streamed\n      // events for a dropped id are ignored from then on, so a replayed\n      // `message-start` can't rebuild it.\n      const uncommittedIds = new Set<string>();\n      const finishedIds = new Set<string>();\n      const droppedIds = new Set<string>();\n\n      // Root-scoped projections whose channels are already covered by\n      // the controller's root pump attach to the shared fan-out\n      // instead of opening a second server subscription. The root\n      // pump runs at `{namespaces: [[]], depth: 1}`, which is exactly\n      // the scope a root-namespace `messagesProjection` wants.\n      const rootShortCircuit =\n        isRootNamespace(ns) && rootBus.channels.includes(\"messages\");\n\n      let disposed = false;\n\n      // Local mirror of the store contents. Every `applyEvent` /\n      // `applyValuesEvent` mutates this synchronously; a coalesced\n      // `scheduleFlush` copies it to `store` once per macrotask.\n      //\n      // Why the indirection? When a namespace-scoped projection\n      // (e.g. a subagent modal opened after the run finished) first\n      // subscribes, the server replays the entire history from\n      // `seq=0`. Dozens of `messages`-channel events can land in a\n      // single SSE parse — they drain through the `for await` loop\n      // as a long microtask chain. Microtasks run before any\n      // macrotask, so React's concurrent scheduler never gets a\n      // chance to commit between updates. Calling `store.setValue`\n      // per event in that burst overflows React's\n      // `nestedUpdateCount` guard and throws \"Maximum update depth\n      // exceeded\", permanently killing the projection and\n      // leaving the store stuck at its first few messages.\n      //\n      // Batching via `MessageChannel` (macrotask) coalesces the\n      // replay burst into one `setValue` call and lets React\n      // commit between flushes for live token streaming too.\n      const pendingMessages: BaseMessage[] = [];\n      let dirty = false;\n      let flushScheduled = false;\n      const flushChannel =\n        typeof MessageChannel !== \"undefined\" ? new MessageChannel() : null;\n\n      const flush = (): void => {\n        flushScheduled = false;\n        if (!dirty || disposed) return;\n        dirty = false;\n        // `.slice()` breaks identity so React's `Object.is` bail-out\n        // in `StreamStore.setValue` propagates the change.\n        store.setValue(pendingMessages.slice());\n      };\n      if (flushChannel != null) {\n        flushChannel.port1.onmessage = flush;\n      }\n\n      const scheduleFlush = (): void => {\n        dirty = true;\n        if (flushScheduled) return;\n        flushScheduled = true;\n        if (flushChannel != null) {\n          flushChannel.port2.postMessage(null);\n        } else {\n          setTimeout(flush, 0);\n        }\n      };\n\n      // Rebuild the store from `values.messages` snapshots.\n      //\n      // `values` events carry the full, committed state of the\n      // thread's `messages` channel at a checkpoint — they fire\n      // on node completion, AFTER every `messages`-channel delta\n      // for that turn has been emitted. They are the authoritative\n      // source of truth for ORDER and for non-streamed messages\n      // (human turns, serialised tool results, subagent echoes, …).\n      //\n      // Why rebuild rather than merge-by-id?\n      //\n      // In practice the server may emit the same logical message\n      // with DIFFERENT ids across successive `values` snapshots at\n      // the same namespace — e.g. a subagent first surfaces its\n      // seed prompt with a synthetic id like\n      // `subagent:<tool_call_id>:human`, then a later superstep\n      // echoes the same prompt back with a real UUID (or vice\n      // versa). A naive \"match-or-append by id\" strategy treats\n      // each fresh id as a new entry and the list grows\n      // monotonically, showing the same content twice (or more)\n      // in the UI.\n      //\n      // Policy (mirrors the root controller's `#applyValues`):\n      //\n      //  1. Walk `values.messages` in order. For each id, prefer\n      //     the stream-assembled entry if we have one for that id\n      //     (keeps in-progress token streaming visible); otherwise\n      //     take the values-coerced instance. Same-id values still\n      //     win when they carry data the stream lacks:\n      //       - tool messages arriving without `tool_call_id` on\n      //         the messages channel — the values snapshot always\n      //         carries it;\n      //       - AI messages whose finalized `tool_calls` didn't\n      //         fully land via the messages channel — the values\n      //         snapshot's AI message has them populated;\n      //       - metadata enrichment with unchanged content (e.g.\n      //         committed `additional_kwargs` on an echoed human).\n      //\n      //  2. Append any stream-only ids (seen on the messages\n      //     channel but never echoed in ANY values snapshot yet)\n      //     — their enclosing superstep hasn't committed yet, so\n      //     dropping them would flash the UI.\n      //\n      //  3. Ids that WERE in a prior values snapshot but are gone\n      //     from this one are treated as explicit removals\n      //     (`RemoveMessage` reducer deltas) and dropped.\n      //\n      // Unkeyed messages (no stable id) are passed through in\n      // their values order because we can't dedupe them safely.\n      const applyValuesEvent = (event: ValuesEvent): void => {\n        const data = event.params.data;\n        if (data == null || typeof data !== \"object\" || Array.isArray(data)) {\n          return;\n        }\n        const state = data as Record<string, unknown>;\n        const rawMessages = state.messages;\n        if (!Array.isArray(rawMessages) || rawMessages.length === 0) return;\n\n        const coerced = ensureMessageInstances(\n          rawMessages as (Message | BaseMessage)[]\n        );\n\n        const reconciliation = reconcileMessagesFromValues({\n          valueMessages: coerced,\n          currentMessages: pendingMessages,\n          currentIndexById: indexById,\n          previousValueMessageIds: valuesMessageIds,\n          streamedMessageIds: streamMessageIds,\n          preferValuesMessage: shouldPreferValuesMessage,\n        });\n        valuesMessageIds = reconciliation.valueMessageIds;\n        for (const id of valuesMessageIds) {\n          uncommittedIds.delete(id);\n          finishedIds.delete(id);\n        }\n        const reconciledMessages = [...reconciliation.messages];\n\n        pendingMessages.length = 0;\n        for (const message of reconciledMessages) pendingMessages.push(message);\n        indexById.clear();\n        for (const [id, idx] of buildMessageIndex(pendingMessages)) {\n          indexById.set(id, idx);\n        }\n        scheduleFlush();\n      };\n\n      const applyEvent = (event: MessagesEvent): void => {\n        const data = event.params.data;\n\n        if (data.event === \"message-start\") {\n          const startData = data as MessageStartData;\n          const role = (startData.role ?? \"ai\") as MessageRole;\n          // \"tool\" role is a v1 convention not represented in the\n          // protocol enum but common in practice — keep it working\n          // for graphs that emit it as an extensible field.\n          const extendedRole =\n            (startData as { role?: ExtendedMessageRole }).role ?? role;\n          const maybeToolCallId = (startData as { tool_call_id?: string })\n            .tool_call_id;\n          if (startData.id != null) {\n            roleByKey.set(startData.id, {\n              role: extendedRole,\n              toolCallId: maybeToolCallId,\n            });\n          }\n        }\n\n        const update = assembler.consume(event);\n        if (update == null) return;\n        const msg = update.message;\n        const id = msg.id;\n        if (id == null || droppedIds.has(id)) return;\n        if (!valuesMessageIds.has(id)) uncommittedIds.add(id);\n        if (update.kind === \"message-finish\") finishedIds.add(id);\n        const captured = roleByKey.get(id) ?? { role: \"ai\" as const };\n        const base = assembledMessageToBaseMessage(msg, captured.role, {\n          toolCallId: captured.toolCallId,\n        });\n\n        streamMessageIds.add(id);\n        const existingIdx = indexById.get(id);\n        if (existingIdx == null) {\n          indexById.set(id, pendingMessages.length);\n          pendingMessages.push(base);\n        } else {\n          pendingMessages[existingIdx] = base;\n        }\n        scheduleFlush();\n      };\n\n      const closeRun = (unfinishedOnly: boolean): void => {\n        assembler.abandonActive();\n        const dropped = new Set<string>();\n        for (const id of uncommittedIds) {\n          if (unfinishedOnly && finishedIds.has(id)) continue;\n          dropped.add(id);\n        }\n        if (dropped.size === 0) return;\n        for (const id of dropped) {\n          uncommittedIds.delete(id);\n          finishedIds.delete(id);\n          droppedIds.add(id);\n        }\n        const kept = pendingMessages.filter(\n          (m) => m.id == null || !dropped.has(m.id)\n        );\n        pendingMessages.length = 0;\n        pendingMessages.push(...kept);\n        indexById.clear();\n        for (const [id, idx] of buildMessageIndex(pendingMessages)) {\n          indexById.set(id, idx);\n        }\n        scheduleFlush();\n      };\n\n      // Root lifecycle arrives on the root pump, not this subscription.\n      // Defer a macrotask so events this subscription has already\n      // received from before the terminal are applied first.\n      const unsubscribeLifecycle = rootBus.subscribe((event) => {\n        if (event.method !== \"lifecycle\") return;\n        if (!isRootNamespace(event.params.namespace)) return;\n        const lifecycle = (event.params.data as { event?: string })?.event;\n        if (lifecycle === \"running\") {\n          setTimeout(() => !disposed && closeRun(false), 0);\n        } else if (\n          lifecycle === \"completed\" ||\n          lifecycle === \"interrupted\" ||\n          lifecycle === \"failed\"\n        ) {\n          setTimeout(() => !disposed && closeRun(true), 0);\n        }\n      });\n\n      let runtime: ProjectionRuntime | undefined;\n      const openSubscription = () => {\n        runtime = openProjectionSubscription({\n          thread,\n          // Subscribe to both `messages` (live token deltas that drive\n          // the in-flight assistant bubble) and `values` (periodic full-\n          // state snapshots). Consuming values lets late-mounted scoped\n          // projections backfill history after the run has finished.\n          channels: [\"messages\", \"values\"],\n          namespace: ns,\n          onEvent(event) {\n            if (event.method === \"messages\") {\n              applyEvent(event as MessagesEvent);\n            } else if (event.method === \"values\") {\n              applyValuesEvent(event as ValuesEvent);\n            }\n          },\n        });\n      };\n\n      if (rootShortCircuit) {\n        runtime = {\n          dispose: rootBus.subscribe((event) => {\n            if (!isRootNamespace(event.params.namespace)) return;\n            if (event.method === \"messages\") {\n              applyEvent(event as MessagesEvent);\n            } else if (event.method === \"values\") {\n              applyValuesEvent(event as ValuesEvent);\n            }\n          }),\n        };\n      } else {\n        void (async () => {\n          const seeded =\n            (await rootBus.trySeedFromHistory?.({\n              kind: \"messages\",\n              namespace: ns,\n              store,\n            })) === true;\n          if (!seeded && !disposed) openSubscription();\n        })();\n      }\n\n      return {\n        async dispose() {\n          disposed = true;\n          unsubscribeLifecycle();\n          if (flushChannel != null) {\n            flushChannel.port1.onmessage = null;\n            flushChannel.port1.close();\n            flushChannel.port2.close();\n          }\n          await runtime?.dispose();\n        },\n      };\n    },\n  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