fix: normalize OpenAI-compatible paths with arbitrary prefixes (#107)

Providers like BigModel (/v4/chat/completions), DeepSeek, and others
use non-standard base URLs. Normalize any path ending in a known
endpoint suffix to /v1/<endpoint> before routing.

Closes #107

Author: jpr5

src/__tests__/provider-compat.test.ts

@@ -209,6 +209,92 @@ describe("Together AI compatibility", () => {
   });
 });
 
+describe("OpenAI-compatible path prefix normalization", () => {
+  it("normalizes /v4/chat/completions to /v1/chat/completions", async () => {
+    instance = await createServer(CATCH_ALL_FIXTURES);
+
+    const { status, body } = await httpPost(`${instance.url}/v4/chat/completions`, {
+      model: "bigmodel-4",
+      stream: false,
+      messages: [{ role: "user", content: "hello" }],
+    });
+
+    expect(status).toBe(200);
+    const parsed = JSON.parse(body);
+    expect(parsed.choices).toBeDefined();
+    expect(parsed.choices[0].message.content).toBe("Hello from aimock!");
+    expect(parsed.object).toBe("chat.completion");
+  });
+
+  it("normalizes /api/coding/paas/v4/chat/completions to /v1/chat/completions", async () => {
+    instance = await createServer(CATCH_ALL_FIXTURES);
+
+    const { status, body } = await httpPost(`${instance.url}/api/coding/paas/v4/chat/completions`, {
+      model: "bigmodel-4",
+      stream: false,
+      messages: [{ role: "user", content: "hello" }],
+    });
+
+    expect(status).toBe(200);
+    const parsed = JSON.parse(body);
+    expect(parsed.choices).toBeDefined();
+    expect(parsed.choices[0].message.content).toBe("Hello from aimock!");
+    expect(parsed.object).toBe("chat.completion");
+  });
+
+  it("still handles standard /v1/chat/completions (regression)", async () => {
+    instance = await createServer(CATCH_ALL_FIXTURES);
+
+    const { status, body } = await httpPost(`${instance.url}/v1/chat/completions`, {
+      model: "gpt-4o",
+      stream: false,
+      messages: [{ role: "user", content: "hello" }],
+    });
+
+    expect(status).toBe(200);
+    const parsed = JSON.parse(body);
+    expect(parsed.choices).toBeDefined();
+    expect(parsed.choices[0].message.content).toBe("Hello from aimock!");
+    expect(parsed.object).toBe("chat.completion");
+  });
+
+  it("normalizes /custom/embeddings to /v1/embeddings", async () => {
+    instance = await createServer(CATCH_ALL_FIXTURES);
+
+    const { status, body } = await httpPost(`${instance.url}/custom/embeddings`, {
+      model: "text-embedding-3-small",
+      input: "test embedding via custom prefix",
+    });
+
+    expect(status).toBe(200);
+    const parsed = JSON.parse(body);
+    expect(parsed.object).toBe("list");
+    expect(parsed.data[0].embedding).toBeInstanceOf(Array);
+  });
+
+  it("combines /openai/ prefix strip with path normalization", async () => {
+    instance = await createServer(CATCH_ALL_FIXTURES);
+
+    // /openai/v1/chat/completions is the Groq-style path — the /openai/ strip
+    // should still work alongside the new normalization logic
+    const { status, body } = await httpPost(
+      `${instance.url}/openai/v1/chat/completions`,
+      {
+        model: "llama-3.3-70b-versatile",
+        stream: false,
+        messages: [{ role: "user", content: "hello" }],
+      },
+      { Authorization: "Bearer mock-groq-key" },
+    );
+
+    expect(status).toBe(200);
+    const parsed = JSON.parse(body);
+    expect(parsed.choices).toBeDefined();
+    expect(parsed.choices[0].message.content).toBe("Hello from aimock!");
+    expect(parsed.object).toBe("chat.completion");
+  });
+});
+
 describe("vLLM compatibility", () => {
   // vLLM uses standard /v1/chat/completions with custom model names
   it("handles vLLM-style request via /v1/chat/completions", async () => {

src/server.ts

@@ -749,6 +749,26 @@ export async function createServer(
       pathname = pathname.slice(7); // remove "/openai" prefix, keep the rest
     }
 
+    // Normalize OpenAI-compatible paths with arbitrary prefixes.
+    // Providers like BigModel (/v4/chat/completions), DeepSeek, etc.
+    // use non-standard base URLs. Normalize to /v1/<endpoint>.
+    if (!azureDeploymentId && pathname !== "/v1/chat/completions") {
+      const COMPAT_SUFFIXES = [
+        "/chat/completions",
+        "/embeddings",
+        "/responses",
+        "/audio/speech",
+        "/audio/transcriptions",
+        "/images/generations",
+      ];
+      for (const suffix of COMPAT_SUFFIXES) {
+        if (pathname.endsWith(suffix)) {
+          pathname = "/v1" + suffix;
+          break;
+        }
+      }
+    }
+
     // Health / readiness probes
     if (pathname === HEALTH_PATH && req.method === "GET") {
       setCorsHeaders(res);