copilotkit__copilotkit/packages/bot-slack/src/sanitizing-http-agent.ts

import { HttpAgent, parseSSEStream, runHttpRequest } from "@ag-ui/client";
import type { BaseEvent, RunAgentInput } from "@ag-ui/core";
import { map } from "rxjs";
import type { Observable } from "rxjs";

/**
 * An `HttpAgent` that tolerates the AG-UI event streams real agents emit.
 *
 * `@ag-ui/client`'s stock transform re-validates every streamed event
 * against a strict Zod schema. Some events that `@ag-ui/langgraph`
 * legitimately emits fail it — notably a `TOOL_CALL_START` whose
 * `parentMessageId` is `null` ("Expected string, received null") — and a
 * single rejected event aborts the entire run. That breaks LangGraph
 * interrupts / human-in-the-loop in Slack, where the tool call that
 * triggers the interrupt carries exactly that shape.
 *
 * The bridge talks to a trusted runtime, so rather than re-validate its
 * output we use the same SSE parse the stock path wraps
 * (`parseSSEStream`) and coerce the known nullable-string fields. Note
 * this deliberately drops the stock transform's *entire* strict Zod
 * re-validation step (not just the offending field) — acceptable only
 * because the runtime is trusted and `runHttpRequest` still throws on
 * transport/HTTP errors. The first coercion logs a one-time breadcrumb so
 * the workaround is visible in production. Revert to the stock transform
 * (`transformHttpEventStream`) once upstream makes these fields nullable.
 */
export class SanitizingHttpAgent extends HttpAgent {
  run(input: RunAgentInput): Observable<BaseEvent> {
    return parseSSEStream(
      runHttpRequest(() => this.fetch(this.url, this.requestInit(input))),
      this.debugLogger,
    ).pipe(map((event: unknown) => coerceNullStrings(event) as BaseEvent));
  }
}

/** One-time breadcrumb so the workaround's use is visible in production. */
let coercionWarned = false;

/**
 * Coerce known nullable-string event fields to `""`. Targeted on purpose:
 * we only touch fields where a `null` is known to come through from
 * `@ag-ui/langgraph` and would otherwise trip a downstream string check.
 */
function coerceNullStrings(event: unknown): unknown {
  if (!event || typeof event !== "object") return event;
  const e = event as Record<string, unknown>;
  if (e["parentMessageId"] === null) {
    e["parentMessageId"] = "";
    if (!coercionWarned) {
      coercionWarned = true;
      console.warn(
        '[SanitizingHttpAgent] coerced a null `parentMessageId` to "" and ' +
          "bypassed @ag-ui/client strict event re-validation for this stream " +
          "(known @ag-ui/langgraph quirk). Remove this agent once upstream " +
          "makes the field nullable.",
      );
    }
  }
  return e;
}