feat: introduce the OpenlayerHandler, which implements the LangChain callback handler interface

Author: gustavocidornelas

src/lib/integrations/langchainCallback.ts

@@ -0,0 +1,141 @@
+import { BaseCallbackHandler } from '@langchain/core/callbacks/base';
+import { LLMResult } from '@langchain/core/dist/outputs';
+import type { Serialized } from '@langchain/core/load/serializable';
+import { AIMessage, BaseMessage, SystemMessage } from '@langchain/core/messages';
+import { addChatCompletionStepToTrace } from '../tracing/tracer';
+
+const LANGCHAIN_TO_OPENLAYER_PROVIDER_MAP: Record<string, string> = {
+  openai: 'OpenAI',
+  'openai-chat': 'OpenAI',
+  'chat-ollama': 'Ollama',
+  vertexai: 'Google',
+};
+const PROVIDER_TO_STEP_NAME: Record<string, string> = {
+  OpenAI: 'OpenAI Chat Completion',
+  Ollama: 'Ollama Chat Completion',
+  Google: 'Google Vertex AI Chat Completion',
+};
+
+export class OpenlayerHandler extends BaseCallbackHandler {
+  name = 'OpenlayerHandler';
+  startTime: number | null = null;
+  endTime: number | null = null;
+  prompt: Array<{ role: string; content: string }> | null = null;
+  latency: number = 0;
+  provider: string | undefined;
+  model: string | null = null;
+  modelParameters: Record<string, any> | null = null;
+  promptTokens: number | null = 0;
+  completionTokens: number | null = 0;
+  totalTokens: number | null = 0;
+  output: string = '';
+  metadata: Record<string, any>;
+
+  constructor(kwargs: Record<string, any> = {}) {
+    super();
+    this.metadata = kwargs;
+  }
+  override async handleChatModelStart(
+    llm: Serialized,
+    messages: BaseMessage[][],
+    runId: string,
+    parentRunId?: string | undefined,
+    extraParams?: Record<string, unknown> | undefined,
+    tags?: string[] | undefined,
+    metadata?: Record<string, unknown> | undefined,
+    name?: string,
+  ): Promise<void> {
+    this.initializeRun(extraParams || {}, metadata || {});
+    this.prompt = this.langchainMassagesToPrompt(messages);
+    this.startTime = performance.now();
+  }
+
+  private initializeRun(extraParams: Record<string, any>, metadata: Record<string, unknown>): void {
+    this.modelParameters = extraParams['invocation_params'] || {};
+
+    const provider = metadata?.['ls_provider'] as string;
+    if (provider && LANGCHAIN_TO_OPENLAYER_PROVIDER_MAP[provider]) {
+      this.provider = LANGCHAIN_TO_OPENLAYER_PROVIDER_MAP[provider];
+    }
+    this.model = (this.modelParameters?.['model'] as string) || (metadata['ls_model_name'] as string) || null;
+    this.output = '';
+  }
+
+  private langchainMassagesToPrompt(messages: BaseMessage[][]): Array<{ role: string; content: string }> {
+    let prompt: Array<{ role: string; content: string }> = [];
+    for (const message of messages) {
+      for (const m of message) {
+        if (m instanceof AIMessage) {
+          prompt.push({ role: 'assistant', content: m.content as string });
+        } else if (m instanceof SystemMessage) {
+          prompt.push({ role: 'system', content: m.content as string });
+        } else {
+          prompt.push({ role: 'user', content: m.content as string });
+        }
+      }
+    }
+    return prompt;
+  }
+
+  override async handleLLMStart(
+    llm: Serialized,
+    prompts: string[],
+    runId: string,
+    parentRunId?: string,
+    extraParams?: Record<string, unknown>,
+    tags?: string[],
+    metadata?: Record<string, unknown>,
+    runName?: string,
+  ) {
+    this.initializeRun(extraParams || {}, metadata || {});
+    this.prompt = prompts.map((p) => ({ role: 'user', content: p }));
+    this.startTime = performance.now();
+  }
+
+  override async handleLLMEnd(output: LLMResult, runId: string, parentRunId?: string, tags?: string[]) {
+    this.endTime = performance.now();
+    this.latency = this.endTime - this.startTime!;
+    this.extractTokenInformation(output);
+    this.extractOutput(output);
+    this.addToTrace();
+  }
+
+  private extractTokenInformation(output: LLMResult) {
+    if (this.provider === 'OpenAI') {
+      this.openaiTokenInformation(output);
+    }
+  }
+
+  private openaiTokenInformation(output: LLMResult) {
+    if (output.llmOutput && 'tokenUsage' in output.llmOutput) {
+      this.promptTokens = output.llmOutput?.['tokenUsage']?.promptTokens ?? 0;
+      this.completionTokens = output.llmOutput?.['tokenUsage']?.completionTokens ?? 0;
+      this.totalTokens = output.llmOutput?.['tokenUsage']?.totalTokens ?? 0;
+    }
+  }
+
+  private extractOutput(output: LLMResult) {
+    const lastResponse = output?.generations?.at(-1)?.at(-1) ?? undefined;
+    this.output += lastResponse?.text ?? '';
+  }
+
+  private addToTrace() {
+    let name = 'Chat Completion Model';
+    if (this.provider && this.provider in PROVIDER_TO_STEP_NAME) {
+      name = PROVIDER_TO_STEP_NAME[this.provider] ?? 'Chat Completion Model';
+    }
+    addChatCompletionStepToTrace({
+      name: name,
+      inputs: { prompt: this.prompt },
+      output: this.output,
+      latency: this.latency,
+      tokens: this.totalTokens,
+      promptTokens: this.promptTokens,
+      completionTokens: this.completionTokens,
+      model: this.model,
+      modelParameters: this.modelParameters,
+      metadata: this.metadata,
+      provider: this.provider ?? '',
+    });
+  }
+}