Create app.js

app.js

@@ -0,0 +1,191 @@
+const express = require("express");
+const app = express();
+const port = 3000;
+
+app.use(express.json());
+
+app.get("//models", async (req, res) => {
+  try {
+    res.status(200).json({ object: "list", data: createFakeModelsList() });
+  } catch {}
+});
+
+app.post("//chat/completions", async (clientRequest, clientResponse) => {
+  try {
+    const {
+      frequency_penalty,
+      presence_penalty,
+      max_tokens,
+      stop,
+      temperature,
+      top_p,
+    } = clientRequest.body;
+
+    const apiRequestBody = {
+      model: "gpt-4",
+      prompt: convertChatMLPrompt(clientRequest.body.messages),
+      frequency_penalty,
+      presence_penalty,
+      max_tokens,
+      stop,
+      temperature,
+      top_p,
+    };
+
+    const apiResponse = await fetch(process.env.API_URL, {
+      method: "POST",
+      headers: {
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify(apiRequestBody),
+    });
+
+    if (clientRequest.body.stream) {
+      handleResponseAsStream(clientResponse, apiResponse);
+    } else {
+      handleResponseAsNonStreamable(clientResponse, apiResponse);
+    }
+  } catch {}
+});
+
+app.listen(port, () => {
+  console.log(`Example app listening on port ${port}`);
+});
+
+async function handleResponseAsNonStreamable(clientResponse, apiResponse) {
+  const apiText = await apiResponse.text();
+  const clientMessage = createClientMessage(apiText);
+  clientResponse.send(JSON.stringify(clientMessage));
+}
+
+async function handleResponseAsStream(clientResponse, apiResponse) {
+  const reader = apiResponse.body.getReader();
+  const nextDecoder = new TextDecoder();
+
+  clientResponse.write("data: " + JSON.stringify(createBeginChunk()) + "\n\n");
+
+  new ReadableStream({
+    start(controller) {
+      return pump();
+      function pump() {
+        return reader.read().then(({ done, value }) => {
+          const textData = nextDecoder.decode(value);
+
+          clientResponse.write(
+            "data: " + JSON.stringify(createMessageChunk(textData)) + "\n\n"
+          );
+
+          // When no more data needs to be consumed, close the stream
+          if (done) {
+            clientResponse.write(
+              "data: " + JSON.stringify(createEndChunk()) + "\n\n"
+            );
+            clientResponse.end();
+            controller.close();
+            return;
+          }
+          // Enqueue the next data chunk into our target stream
+          controller.enqueue(value);
+          return pump();
+        });
+      }
+    },
+  });
+}
+
+function getCurrentDate() {
+  return Math.floor(new Date().getTime());
+}
+
+function convertChatMLPrompt(messages) {
+  const messageStrings = [];
+  messages.forEach((m) => {
+    if (m.role === "system" && m.name === undefined) {
+      messageStrings.push("System: " + m.content);
+    } else if (m.role === "system" && m.name !== undefined) {
+      messageStrings.push(m.name + ": " + m.content);
+    } else {
+      messageStrings.push(m.role + ": " + m.content);
+    }
+  });
+  return messageStrings.join("\n") + "\nassistant:";
+}
+
+const createClientMessage = (text) => ({
+  id: "chatcmpl-123",
+  object: "chat.completion",
+  created: getCurrentDate(),
+  model: "gpt-4",
+  choices: [
+    {
+      index: 0,
+      message: { role: "assistant", content: text },
+      logprobs: null,
+      finish_reason: "stop",
+    },
+  ],
+});
+
+const createBeginChunk = () => ({
+  id: "chatcmpl-123",
+  object: "chat.completion.chunk",
+  created: getCurrentDate(),
+  model: "gpt-4",
+  system_fingerprint: "",
+  choices: [
+    {
+      index: 0,
+      delta: { role: "assistant", content: "" },
+      logprobs: null,
+      finish_reason: null,
+    },
+  ],
+});
+
+const createMessageChunk = (text) => ({
+  id: "chatcmpl-123",
+  object: "chat.completion.chunk",
+  created: getCurrentDate(),
+  model: "gpt-4",
+  system_fingerprint: "",
+  choices: [
+    {
+      index: 0,
+      delta: { content: text },
+      logprobs: null,
+      finish_reason: null,
+    },
+  ],
+});
+
+const createEndChunk = () => ({
+  id: "chatcmpl-123",
+  object: "chat.completion.chunk",
+  created: getCurrentDate(),
+  model: "gpt-4",
+  system_fingerprint: "",
+  choices: [{ index: 0, delta: {}, logprobs: null, finish_reason: "stop" }],
+});
+
+function createFakeModelsList() {
+  return [
+    {
+      id: "gpt-4",
+      object: "model",
+      created: getCurrentDate(),
+      owned_by: "openai",
+      permission: [
+        {
+          id: "modelperm-gpt-4",
+          object: "model_permission",
+          created: getCurrentDate(),
+          organization: "*",
+          group: null,
+          is_blocking: false,
+        },
+      ],
+      root: "gpt-4",
+      parent: null,
+    },
+  ];
+}