Calling Perplexity on Bun

Two endpoints backed by the Perplexity API — answers with their sources attached

Overview

Perplexity answers from a live search rather than from training data alone, so every reply arrives with a list of the pages it was built from. That is the whole reason to reach for it, and it is what this example carries through to the caller: both endpoints return the text and the sources.

The client is the OpenAI SDK. Perplexity implements the Chat Completions API, so pointing baseURL at it is the entire integration:

const client = new OpenAI({
  apiKey: process.env.PERPLEXITY_API_KEY,
  baseURL: "https://api.perplexity.ai",
});

Everything after that line is the same code as the OpenAI example — same method, same streaming chunks, same error classes. What this page is actually about is the part the OpenAI SDK does not know: the sources, which arrive on a field its types do not declare.

Objectives

To gain familiarity with:

• pointing an OpenAI-compatible client at a third-party endpoint;
• reading provider fields that sit outside a typed SDK’s surface;
• carrying structured extras alongside a streamed answer; and
• reading a secret once, at startup, and sharing one client.

Steps

Folder Structure End State

• my-project
  • app.ts

bun add @drashland/drash openai
export PERPLEXITY_API_KEY="pplx-..."

import OpenAI from "openai";
import {
  Application,
  HTTPError,
  Resource,
} from "@drashland/drash/modules/http.polyfill.js";
import { Status } from "@drashland/drash/core/http/response/Status.js";
 
const MODEL = "sonar";                                 // `sonar-pro` searches harder
                                                       // and costs more per call.
const client = new OpenAI({
  apiKey: process.env.PERPLEXITY_API_KEY,
  baseURL: "https://api.perplexity.ai",                // The entire integration.
});
 
type Source = { title?: string; url: string };
 
// Perplexity attaches the pages it answered from. The field is not in the
// OpenAI SDK's types — it is a provider extension — so read it off the raw
// object, and accept either of the two shapes the API has used.
function readSources(payload: unknown): Source[] {
  const raw = payload as {
    search_results?: { title?: string; url?: string }[];
    citations?: string[];
  };
 
  if (Array.isArray(raw?.search_results)) {
    return raw.search_results
      .filter((result): result is Source => typeof result.url === "string")
      .map((result) => ({ title: result.title, url: result.url }));
  }
 
  if (Array.isArray(raw?.citations)) {
    return raw.citations.map((url) => ({ url }));
  }
 
  return [];                                           // Some models answer without
}                                                      // searching. Not an error.
 
// Both resources start here. A `Request` parses its own body, and this throws
// rather than returning an error, which is how a resource reports anything the
// caller got wrong.
async function readPrompt(request: Request): Promise<string> {
  let body: { prompt?: unknown };
 
  try {
    body = await request.json();
  } catch {
    throw new HTTPError(Status.BadRequest, "Body must be JSON");
  }
 
  if (typeof body.prompt !== "string" || body.prompt === "") {
    throw new HTTPError(Status.BadRequest, "Body must have a `prompt` string");
  }
 
  return body.prompt;
}
 
// These are the SDK's classes, not Perplexity's. They are chosen by HTTP
// status, so they sort an OpenAI-compatible provider's failures just as well.
// Order matters — the specific classes come before `APIError`, their parent.
function apiErrorToHTTPError(error: unknown): unknown {
  if (error instanceof OpenAI.AuthenticationError) {
    return new HTTPError(Status.InternalServerError);  // Your key is wrong.
  }
 
  if (error instanceof OpenAI.RateLimitError) {
    return new HTTPError(Status.TooManyRequests);      // Pass the limit on.
  }
 
  if (error instanceof OpenAI.BadRequestError) {
    return new HTTPError(Status.BadRequest);           // Usually the prompt.
  }
 
  if (error instanceof OpenAI.APIError) {
    return new HTTPError(Status.BadGateway);           // Upstream is down.
  }
 
  return error;                                        // Not ours. Leave it.
}
 
class Chat extends Resource {                          // Answers with the whole reply.
  public paths = ["/chat"];
 
  public async POST(request: Request) {
    const prompt = await readPrompt(request);
 
    let completion;
 
    try {
      completion = await client.chat.completions.create({
        model: MODEL,
        messages: [{ role: "user", content: prompt }],
      });
    } catch (error) {
      throw apiErrorToHTTPError(error);
    }
 
    const text = completion.choices[0]?.message.content ?? "";
    const sources = readSources(completion);
 
    return Response.json({ text, sources });
  }
}
 
class ChatStream extends Resource {                    // Answers a piece at a time.
  public paths = ["/chat/stream"];
 
  public async POST(request: Request) {
    const prompt = await readPrompt(request);          // Throws before the `Response`
                                                       // exists — that matters.
    let stream;
 
    try {
      stream = await client.chat.completions.create({
        model: MODEL,
        messages: [{ role: "user", content: prompt }],
        stream: true,
      });
    } catch (error) {
      throw apiErrorToHTTPError(error);
    }
 
    const encoder = new TextEncoder();
 
    const body = new ReadableStream({
      async start(controller) {
        const send = (frame: string) =>
          controller.enqueue(encoder.encode(frame));
 
        let sources: Source[] = [];
 
        try {
          for await (const chunk of stream) {
            const found = readSources(chunk);
 
            if (found.length > 0) {
              sources = found;
            }
 
            const text = chunk.choices[0]?.delta.content;
 
            if (text) {
              send(`data: ${JSON.stringify({ text })}\n\n`);
            }
          }
 
          send(`event: sources\ndata: ${JSON.stringify({ sources })}\n\n`);
          send("event: done\ndata: {}\n\n");
        } catch (error) {                              // Too late for a status code.
          send(                                        // Say so in the stream instead.
            `event: error\ndata: ${
              JSON.stringify({ message: "upstream failed" })
            }\n\n`,
          );
          console.error(error);
        } finally {
          controller.close();
        }
      },
    });
 
    return new Response(body, {
      headers: {
        "content-type": "text/event-stream",
        "cache-control": "no-store",
      },
    });
  }
}
 
const app = Application
  .builder()
  .resources(Chat, ChatStream)
  .build();
 
const hostname = "localhost";
const port = 1447;
 
Bun.serve({
  hostname,
  port,
  fetch(request: Request): Promise<Response> {
    return app
      .handle<Response>(request)
      .catch((error) => {
        // `name` is checked before `instanceof` because `instanceof` fails when
        // two copies of Drash end up in one bundle.
        if (error.name === "HTTPError") {
          return new Response(error.message, {
            status: error.status_code,
            statusText: error.status_code_description,
          });
        }
 
        console.error(error);
 
        return new Response("The server could not generate a response", {
          status: 500,
        });
      });
  },
});
 
console.log(`\nDrash running at http://${hostname}:${port}`);

bun run app.ts

Verification

With the application running on localhost:1447:

curl -X POST localhost:1447/chat -d '{"prompt":"What shipped in Drash v3?"}'
->  {"text":"...","sources":[{"title":"...","url":"https://..."}]}

curl -N -X POST localhost:1447/chat/stream -d '{"prompt":"Who won?"}'
->  data: {"text":"..."} ... event: sources ... event: done

curl -X POST localhost:1447/chat -d '{"prompt":"What is 2 + 2?"}'
->  {"text":"4","sources":[]}            # No search needed. Not an error.

curl -X POST localhost:1447/chat -d 'not json'   ->  400  Body must be JSON
curl -X POST localhost:1447/chat -d '{}'         ->  400  Body must have a `prompt` string
curl -X GET localhost:1447/chat                  ->  501  Not Implemented
curl -X POST localhost:1447/nope                 ->  404  Not Found

-N on the second one turns off curl’s buffering. Without it you still get every frame, but they arrive in a lump at the end, which makes a working stream look like a broken one.

The last two come from the chain rather than from your code, on URLs your server was happy to hand over.

The third one is worth running deliberately. It is the case that proves sources: [] is an ordinary answer, and it is the one a client written against the first example will crash on.

Pointing the Client Somewhere Else

baseURL is the only line that makes this a Perplexity application:

const client = new OpenAI({
  apiKey: process.env.PERPLEXITY_API_KEY,
  baseURL: "https://api.perplexity.ai",
});

The SDK builds its request paths relative to that, so client.chat.completions.create() posts to https://api.perplexity.ai/chat/completions. The request body, the streaming format, and the error classes are all the ones the SDK already implements, because that is the API Perplexity chose to speak.

Two things follow that are easy to get wrong.

The model names are not OpenAI’s. gpt-5 is a 400 here. Perplexity’s search models are the sonar family — sonar for ordinary questions, sonar-pro for ones worth more searching, sonar-reasoning when the answer needs working through. A wrong name comes back as OpenAI.BadRequestError, which the table below maps to a 400 for your caller. That is the correct status only if the caller chose the model; if the model name is yours, it is a 500 waiting to be mislabelled, so keep it in a constant rather than reading it off the request body.

Nothing outside Chat Completions is portable. The client will happily let you call client.responses.create() or client.embeddings.create(), and both fail at the endpoint. Treat the OpenAI SDK here as a Chat Completions client that happens to ship with extras.

Reading the Sources

This is the part no SDK types for you. The completion carries the pages the answer was built from, on a field the OpenAI schema does not declare:

function readSources(payload: unknown): Source[] {
  const raw = payload as {
    search_results?: { title?: string; url?: string }[];
    citations?: string[];
  };
 
  if (Array.isArray(raw?.search_results)) {
    return raw.search_results
      .filter((result): result is Source => typeof result.url === "string")
      .map((result) => ({ title: result.title, url: result.url }));
  }
 
  if (Array.isArray(raw?.citations)) {
    return raw.citations.map((url) => ({ url }));
  }
 
  return [];
}

The cast is doing real work. The SDK’s response type has no search_results and no citations, so completion.search_results does not compile — and if you silence that with any, you also silence the shape check. Casting to a narrow type that describes exactly what you expect, then verifying with Array.isArray before you touch it, keeps the compiler useful.

Both fields are checked because the API has used both: citations was a flat list of URLs, search_results carries a title alongside each one. Reading both means the endpoint keeps working across that change instead of quietly returning [].

And [] is a legitimate answer. A question that needs no search — arithmetic, a rewrite of text you supplied — produces a reply with no sources attached. An empty list is not a failure and should not be treated as one.

Carrying Sources Through a Stream

The non-streaming endpoint has it easy: the completion is a single object, so the text and the sources are read from the same value. A stream has to hold onto them:

let sources: Source[] = [];
 
for await (const chunk of stream) {
  const found = readSources(chunk);
 
  if (found.length > 0) {
    sources = found;
  }
 
  const text = chunk.choices[0]?.delta.content;
 
  if (text) {
    send(`data: ${JSON.stringify({ text })}\n\n`);
  }
}
 
send(`event: sources\ndata: ${JSON.stringify({ sources })}\n\n`);
send("event: done\ndata: {}\n\n");

The list rides along on chunks and grows as the model cites more, so keeping the last non-empty one and emitting it after the text is finished gives the client a single, complete list. The alternative — forwarding each chunk’s sources as they arrive — makes the client responsible for deduplicating, which is work you can just do once here.

Sending it as a named sources event rather than mixing it into the data: frames is what keeps the client simple:

data: {"text":"The release "}

data: {"text":"shipped in March."}

event: sources
data: {"sources":[{"title":"Release notes","url":"https://..."}]}

event: done
data: {}

A client appending data: frames to a text box needs no special case, and one that wants to render citations listens for one more event.

What Your Runtime Expects Back

Bun uses the same polyfill entry point as Node because it has no global URLPattern, but Bun.serve passes a Request and takes a Response — so this page is the Deno build with a different import specifier and different server glue. That is the only difference between the two.

Handling Errors From the API

Error handling covers how a throw reaches your .catch(). What is specific here is the translation step in front of it: a failure talking to Perplexity is a failure of your server, so the status you return is rarely the status you received:

These classes are chosen by HTTP status code, not by provider, which is why the same four work against an endpoint the SDK was not written for. apiErrorToHTTPError in the sample does exactly that and nothing else. Returning the unrecognized error unchanged matters: a TypeError in your own code is a bug, and turning it into a tidy 502 hides it.

send(`event: error\ndata: ${JSON.stringify({ message: "upstream failed" })}\n\n`);

Getting the API Key to the Resource

The key is read once, at startup, from process.env.PERPLEXITY_API_KEY, and one client is built that both resources close over. Bun loads a .env file from the working directory on its own, so a key kept there needs no flag.

Where to Next

• Calling OpenAI — the same two endpoints without the baseURL, and the page that explains the streaming chunks in full
• Calling Claude — a client that is not OpenAI-shaped, for comparison
• Creating Middleware — put an API key check or a request log in front of both endpoints
• Rate Limiter — the bundled middleware for capping how often a caller can reach an endpoint this expensive
• Grouping Resources — mount both under /api/v1 and share middleware between them

This example sends one prompt and gets one answer. Holding a conversation means sending the whole history on every request, since the API keeps no state between calls — the messages array grows, and where you store it is your decision, not Drash’s.

The finished app is in the repository at examples/runtimes/bun/calling-perplexity.