simple-proxy/src/proxy/gcp.ts

import { Request, RequestHandler, Response, Router } from "express";
import { createProxyMiddleware } from "http-proxy-middleware";
import { v4 } from "uuid";
import { config } from "../config";
import { logger } from "../logger";
import { createQueueMiddleware } from "./queue";
import { ipLimiter } from "./rate-limit";
import { handleProxyError } from "./middleware/common";
import {
  createPreprocessorMiddleware,
  signGcpRequest,
  finalizeSignedRequest,
  createOnProxyReqHandler,
} from "./middleware/request";
import {
  ProxyResHandlerWithBody,
  createOnProxyResHandler,
} from "./middleware/response";
import { transformAnthropicChatResponseToOpenAI } from "./anthropic";
import { sendErrorToClient } from "./middleware/response/error-generator";

const GCP_CLAUDE_SONNET_45 = "claude-sonnet-4-5@20250929";
const GCP_CLAUDE_HAIKU_45 = "claude-haiku-4-5@20251001";
const GCP_CLAUDE_OPUS_41 = "claude-opus-4-1@20250805";
const GCP_CLAUDE_SONNET_4 = "claude-sonnet-4@20250514";
const GCP_CLAUDE_OPUS_4 = "claude-opus-4@20250514";
const GCP_CLAUDE_35_HAIKU = "claude-3-5-haiku@20241022";

let modelsCache: any = null;
let modelsCacheTime = 0;

const getModelsResponse = () => {
  if (new Date().getTime() - modelsCacheTime < 1000 * 60) {
    return modelsCache;
  }

  if (!config.gcpCredentials) return { object: "list", data: [] };

  // https://docs.anthropic.com/en/docs/about-claude/models
  const variants = [
    GCP_CLAUDE_HAIKU_45,
    GCP_CLAUDE_SONNET_45,
    GCP_CLAUDE_OPUS_41,
    GCP_CLAUDE_35_HAIKU,
    GCP_CLAUDE_SONNET_4,
    GCP_CLAUDE_OPUS_4,
  ];

  const models = variants.map((id) => ({
    id,
    object: "model",
    created: new Date().getTime(),
    owned_by: "anthropic",
    permission: [],
    root: "claude",
    parent: null,
  }));

  modelsCache = { object: "list", data: models };
  modelsCacheTime = new Date().getTime();

  return modelsCache;
};

const handleModelRequest: RequestHandler = (_req, res) => {
  res.status(200).json(getModelsResponse());
};

/** Only used for non-streaming requests. */
const gcpResponseHandler: ProxyResHandlerWithBody = async (
  _proxyRes,
  req,
  res,
  body
) => {
  if (typeof body !== "object") {
    throw new Error("Expected body to be an object");
  }

  let newBody = body;
  switch (`${req.inboundApi}<-${req.outboundApi}`) {
    case "openai<-anthropic-chat":
      req.log.info("Transforming Anthropic Chat back to OpenAI format");
      newBody = transformAnthropicChatResponseToOpenAI(body);
      break;
  }

  res.status(200).json({ ...newBody, proxy: body.proxy });
};

const gcpProxy = createQueueMiddleware({
  beforeProxy: signGcpRequest,
  proxyMiddleware: createProxyMiddleware({
    target: "bad-target-will-be-rewritten",
    router: ({ signedRequest }) => {
      if (!signedRequest) throw new Error("Must sign request before proxying");
      return `${signedRequest.protocol}//${signedRequest.hostname}`;
    },
    changeOrigin: true,
    selfHandleResponse: true,
    logger,
    on: {
      proxyReq: createOnProxyReqHandler({ pipeline: [finalizeSignedRequest] }),
      proxyRes: createOnProxyResHandler([gcpResponseHandler]),
      error: handleProxyError,
    },
  }),
});

const oaiToChatPreprocessor = createPreprocessorMiddleware(
  { inApi: "openai", outApi: "anthropic-chat", service: "gcp" },
  { afterTransform: [maybeReassignModel] }
);

/**
 * Routes an OpenAI prompt to either the legacy Claude text completion endpoint
 * or the new Claude chat completion endpoint, based on the requested model.
 */
const preprocessOpenAICompatRequest: RequestHandler = (req, res, next) => {
  oaiToChatPreprocessor(req, res, next);
};

const gcpRouter = Router();
gcpRouter.get("/v1/models", handleModelRequest);
// Native Anthropic chat completion endpoint.
gcpRouter.post(
  "/v1/messages",
  ipLimiter,
  createPreprocessorMiddleware(
    { inApi: "anthropic-chat", outApi: "anthropic-chat", service: "gcp" },
    { afterTransform: [maybeReassignModel] }
  ),
  gcpProxy
);

// OpenAI-to-GCP Anthropic compatibility endpoint.
gcpRouter.post(
  "/v1/chat/completions",
  ipLimiter,
  preprocessOpenAICompatRequest,
  gcpProxy
);

/**
 * Tries to deal with:
 * - frontends sending GCP model names even when they want to use the OpenAI-
 *   compatible endpoint
 * - frontends sending Anthropic model names that GCP doesn't recognize
 * - frontends sending OpenAI model names because they expect the proxy to
 *   translate them
 * 
 * If client sends GCP model ID it will be used verbatim. Otherwise, various
 * strategies are used to try to map a non-GCP model name to GCP model ID.
 */
function maybeReassignModel(req: Request) {
  const model = req.body.model;
  const lower = String(model).toLowerCase();

  // If it looks like an GCP model, use it as-is
  // if (model.includes("anthropic.claude")) {
  if (model.startsWith("claude-") && model.includes("@")) {
    return;
  }

  if (lower.includes("opus-4.5") || lower.includes("opus-4-5")) {
    req.body.model = GCP_CLAUDE_OPUS_41;
    return;
  }
  if (lower.includes("opus-4.1") || lower.includes("opus-4-1")) {
    req.body.model = GCP_CLAUDE_OPUS_41;
    return;
  }
  if (lower.includes("opus-4")) {
    req.body.model = GCP_CLAUDE_OPUS_4;
    return;
  }
  if (lower.includes("haiku-4.5") || lower.includes("haiku-4-5")) {
    req.body.model = GCP_CLAUDE_HAIKU_45;
    return;
  }
  if (lower.includes("sonnet-4.5") || lower.includes("sonnet-4-5")) {
    req.body.model = GCP_CLAUDE_SONNET_45;
    return;
  }
  if (lower.includes("sonnet-4")) {
    req.body.model = GCP_CLAUDE_SONNET_4;
    return;
  }
  if (lower.includes("3-5") && lower.includes("haiku")) {
    req.body.model = GCP_CLAUDE_35_HAIKU;
    return;
  }
  if (lower.includes("opus")) {
    req.body.model = GCP_CLAUDE_OPUS_41;
    return;
  }
  if (lower.includes("haiku")) {
    req.body.model = GCP_CLAUDE_HAIKU_45;
    return;
  }
  if (lower.includes("sonnet")) {
    req.body.model = GCP_CLAUDE_SONNET_45;
    return;
  }

  if (
    lower.startsWith("gpt-") ||
    lower.startsWith("o1") ||
    lower.startsWith("o3") ||
    lower.startsWith("o4") ||
    lower === "computer-use-preview"
  ) {
    req.body.model = GCP_CLAUDE_SONNET_45;
    return;
  }

  // Anthropic model names can look like:
  // - claude-v1
  // - claude-2.1
  // - claude-3-5-sonnet-20240620-v1:0
  const pattern =
    /^(claude-)?(instant-)?(v)?(\d+)([.-](\d{1}))?(-\d+k)?(-sonnet-|-opus-|-haiku-)?(\d*)/i;
  const match = model.match(pattern);

  // If there's no match, fallback to Claude3 Sonnet as it is most likely to be
  // available on GCP.
  if (!match) {
    req.body.model = GCP_CLAUDE_SONNET_4;
    return;
  }

  const [_, _cl, instant, _v, major, _sep, minor, _ctx, name, _rev] = match;
  
  const ver = minor ? `${major}.${minor}` : major;
  switch (ver) {
    case "3":
    case "3.0":
      if (name.includes("opus")) {
        req.body.model = GCP_CLAUDE_OPUS_41;
      } else if (name.includes("haiku")) {
        req.body.model = GCP_CLAUDE_HAIKU_45;
      } else {
        req.body.model = GCP_CLAUDE_SONNET_45;
      }
      return;
    case "3.5":
      req.body.model = name.includes("haiku")
        ? GCP_CLAUDE_35_HAIKU
        : GCP_CLAUDE_SONNET_45;
      return;
  }

  // Fallback to Claude Sonnet 4
  req.body.model = GCP_CLAUDE_SONNET_45;
  return;
}

export const gcp = gcpRouter;