langchain[patch]: Allow headers to be passed in remote runnable reque…

…sts, docs (langchain-ai#4107)

* Allow headers to be passed in remote runnable requests, docs

* Fix broken link

docs/core_docs/docs/ecosystem/langserve.mdx

@@ -0,0 +1,40 @@
+# LangServe
+
+[LangServe](https://python.langchain.com/docs/langserve) is a Python framework that helps developers deploy LangChain [runnables and chains](/docs/expression_language/)
+as REST APIs.
+
+If you have a deployed LangServe route, you can use the [RemoteRunnable](https://api.js.langchain.com/classes/langchain_runnables_remote.RemoteRunnable.html) class to interact
+with it as if it were a local chain. This allows you to more easily call hosted LangServe instances from JavaScript environments (like in the browser on the frontend).
+
+You'll need to install or package LangChain into your frontend:
+
+```bash npm2yarn
+npm install langchain
+```
+
+## Usage
+
+Then, you can use any of the [supported LCEL interface methods](/docs/expression_language/interface).
+Here's an example of how this looks:
+
+import CodeBlock from "@theme/CodeBlock";
+import Example from "@examples/ecosystem/langsmith.ts";
+
+<CodeBlock language="typescript">{Example}</CodeBlock>
+
+[`streamLog`](/docs/expression_language/interface) is a lower level method for streaming chain intermediate steps as partial JSONPatch chunks.
+This method allows for a few extra options as well to only include or exclude certain named steps.
+
+`@langchain/core` also provides an `applyPatch` utility for aggregating these chunks into a full output:
+
+import StreamLogExample from "@examples/ecosystem/langsmith_stream_log.ts";
+
+<CodeBlock language="typescript">{StreamLogExample}</CodeBlock>
+
+### Configuration
+
+You can also pass in options for headers and timeouts into the constructor. These will be used when making incoming requests:
+
+import OptionsExample from "@examples/ecosystem/langsmith_options.ts";
+
+<CodeBlock language="typescript">{OptionsExample}</CodeBlock>

examples/src/ecosystem/langsmith.ts

@@ -0,0 +1,21 @@
+import { RemoteRunnable } from "langchain/runnables/remote";
+
+const remoteChain = new RemoteRunnable({
+  url: "https://your_hostname.com/path",
+});
+
+const result = await remoteChain.invoke({
+  param1: "param1",
+  param2: "param2",
+});
+
+console.log(result);
+
+const stream = await remoteChain.stream({
+  param1: "param1",
+  param2: "param2",
+});
+
+for await (const chunk of stream) {
+  console.log(chunk);
+}

examples/src/ecosystem/langsmith_options.ts

@@ -0,0 +1,18 @@
+import { RemoteRunnable } from "langchain/runnables/remote";
+
+const remoteChain = new RemoteRunnable({
+  url: "https://your_hostname.com/path",
+  options: {
+    timeout: 10000,
+    headers: {
+      Authorization: "Bearer YOUR_TOKEN",
+    },
+  },
+});
+
+const result = await remoteChain.invoke({
+  param1: "param1",
+  param2: "param2",
+});
+
+console.log(result);

examples/src/ecosystem/langsmith_stream_log.ts

@@ -0,0 +1,40 @@
+import { RemoteRunnable } from "langchain/runnables/remote";
+import { applyPatch } from "@langchain/core/utils/json_patch";
+
+const remoteChain = new RemoteRunnable({
+  url: "https://your_hostname.com/path",
+});
+
+const logStream = await remoteChain.streamLog(
+  {
+    param1: "param1",
+    param2: "param2",
+  },
+  // LangChain runnable config properties
+  {
+    configurable: {
+      llm: "some_property",
+    },
+    metadata: {
+      conversation_id: "other_metadata",
+    },
+  },
+  // Optional additional streamLog properties for filtering outputs
+  {
+    includeNames: [],
+    includeTags: [],
+    includeTypes: [],
+    excludeNames: [],
+    excludeTags: [],
+    excludeTypes: [],
+  }
+);
+
+let streamedResponse: Record<string, any> = {};
+
+for await (const chunk of logStream) {
+  console.log(chunk);
+  streamedResponse = applyPatch(streamedResponse, chunk.ops).newDocument;
+}
+
+console.log(streamedResponse);

langchain/src/runnables/remote.ts

@@ -43,6 +43,7 @@ import { IterableReadableStream } from "@langchain/core/utils/stream";
 
 type RemoteRunnableOptions = {
   timeout?: number;
+  headers?: Record<string, unknown>;
 };
 
 function isSuperset(set: Set<string>, subset: Set<string>) {
@@ -256,6 +257,7 @@ export class RemoteRunnable<
       body: JSON.stringify(body),
       headers: {
         "Content-Type": "application/json",
+        ...this.options?.headers,
       },
       signal: AbortSignal.timeout(this.options?.timeout ?? 60000),
     });