core[minor]: Stream events v2 (#5539)

* Start stream events v2

* More progress

* Fixes

* Docs

* Docs

* Fix build

docs/core_docs/docs/versions/v0_2.mdx → docs/core_docs/docs/versions/v0_2/index.mdx

@@ -7,6 +7,12 @@ sidebar_label: v0.2
 
 LangChain v0.2 was released in May 2024. This release includes a number of breaking changes and deprecations. This document contains a guide on upgrading to 0.2.x, as well as a list of deprecations and breaking changes.
 
+:::note Reference
+
+- [Migrating to Astream Events v2](/docs/versions/v0_2/migrating_astream_events)
+
+:::
+
 ## Migration
 
 This documentation will help you upgrade your code to LangChain `0.2.x.`. To prepare for migration, we first recommend you take the following steps:

docs/core_docs/docs/versions/v0_2/migrating_astream_events.mdx

@@ -0,0 +1,125 @@
+---
+sidebar_position: 2
+sidebar_label: streamEvents v2
+---
+
+# Migrating to streamEvents v2
+
+:::danger
+
+This migration guide is a work in progress and is not complete.
+
+:::
+
+We've added a `v2` of the [`streamEvents`](/docs/how_to/streaming#using-stream-events) API with the release of `0.2.0`. You can see this [PR](https://github.com/langchain-ai/langchainjs/pull/5539/) for more details.
+
+The `v2` version is a re-write of the `v1` version, and should be more efficient, with more consistent output for the events. The `v1` version of the API will be deprecated in favor of the `v2` version and will be removed in `0.4.0`.
+
+Below is a list of changes between the `v1` and `v2` versions of the API.
+
+### output for `on_chat_model_end`
+
+In `v1`, the outputs associated with `on_chat_model_end` changed depending on whether the
+chat model was run as a root level runnable or as part of a chain.
+
+As a root level runnable the output was:
+
+```ts
+{
+  data: {
+    output: AIMessageChunk((content = "hello world!"), (id = "some id"));
+  }
+}
+```
+
+As part of a chain the output was:
+
+```
+{
+  data: {
+    output: {
+      generations: [
+        [
+          {
+            generation_info: None,
+            message: AIMessageChunk(
+                content="hello world!", id="some id"
+            ),
+            text: "hello world!",
+          }
+        ]
+      ],
+    }
+  },
+}
+```
+
+As of `v2`, the output will always be the simpler representation:
+
+```ts
+{
+  data: {
+    output: AIMessageChunk((content = "hello world!"), (id = "some id"));
+  }
+}
+```
+
+:::note
+Non chat models (i.e., regular LLMs) will be consistently associated with the more verbose format for now.
+:::
+
+### output for `on_retriever_end`
+
+`on_retriever_end` output will always return a list of `Documents`.
+
+This was the output in `v1`:
+
+```ts
+{
+  data: {
+    output: {
+      documents: [
+        Document(...),
+        Document(...),
+        ...
+      ]
+    }
+  }
+}
+```
+
+And here is the new output for `v2`:
+
+```ts
+{
+  data: {
+    output: [
+      Document(...),
+      Document(...),
+      ...
+    ]
+  }
+}
+```
+
+### Removed `on_retriever_stream`
+
+The `on_retriever_stream` event was an artifact of the implementation and has been removed.
+
+Full information associated with the event is already available in the `on_retriever_end` event.
+
+Please use `on_retriever_end` instead.
+
+### Removed `on_tool_stream`
+
+The `on_tool_stream` event was an artifact of the implementation and has been removed.
+
+Full information associated with the event is already available in the `on_tool_end` event.
+
+Please use `on_tool_end` instead.
+
+### Propagating Names
+
+Names of runnables have been updated to be more consistent.
+
+If you're filtering by event names, check if you need to update your filters.

langchain-core/.eslintrc.cjs

@@ -37,6 +37,7 @@ module.exports = {
     "@typescript-eslint/no-unused-vars": ["warn", { args: "none" }],
     "@typescript-eslint/no-floating-promises": "error",
     "@typescript-eslint/no-misused-promises": "error",
+    "@typescript-eslint/no-this-alias": 0,
     camelcase: 0,
     "class-methods-use-this": 0,
     "import/extensions": [2, "ignorePackages"],

langchain-core/src/runnables/remote.ts

@@ -535,7 +535,7 @@ export class RemoteRunnable<
 
   _streamEvents(
     input: RunInput,
-    options: Partial<CallOptions> & { version: "v1" },
+    options: Partial<CallOptions> & { version: "v1" | "v2" },
     streamOptions?: Omit<LogStreamCallbackHandlerInput, "autoClose"> | undefined
   ): AsyncGenerator<StreamEvent> {
     // eslint-disable-next-line @typescript-eslint/no-this-alias
@@ -611,14 +611,14 @@ export class RemoteRunnable<
 
   streamEvents(
     input: RunInput,
-    options: Partial<CallOptions> & { version: "v1" },
+    options: Partial<CallOptions> & { version: "v1" | "v2" },
     streamOptions?: Omit<LogStreamCallbackHandlerInput, "autoClose">
   ): IterableReadableStream<StreamEvent>;
 
   streamEvents(
     input: RunInput,
     options: Partial<CallOptions> & {
-      version: "v1";
+      version: "v1" | "v2";
       encoding: "text/event-stream";
     },
     streamOptions?: Omit<LogStreamCallbackHandlerInput, "autoClose">
@@ -627,14 +627,14 @@ export class RemoteRunnable<
   streamEvents(
     input: RunInput,
     options: Partial<CallOptions> & {
-      version: "v1";
+      version: "v1" | "v2";
       encoding?: "text/event-stream" | undefined;
     },
     streamOptions?: Omit<LogStreamCallbackHandlerInput, "autoClose">
   ): IterableReadableStream<StreamEvent | Uint8Array> {
-    if (options?.version !== "v1") {
+    if (options.version !== "v1" && options.version !== "v2") {
       throw new Error(
-        `Only version "v1" of the events schema is currently supported.`
+        `Only versions "v1" and "v2" of the events schema is currently supported.`
       );
     }
     if (options.encoding !== undefined) {