Fix generateImage edit mode content type error by using global.fetch for FormData (#1914)

* Initial plan

* Fix generateImage edit mode content type error by using global.fetch for FormData

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* genai: /docs [skip ci]

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
Co-authored-by: Peli de Halleux <pelikhan@users.noreply.github.com>

Author: Copilot

packages/core/src/openai.ts

@@ -445,7 +445,8 @@ export async function OpenAIImageGeneration(
 
     traceFetchPost(trace, url, freq.headers, body);
 
-    const res = await fetch(url, freq as any);
+    // TODO: switch back to cross-fetch in the future
+    const res = isMultipart ? await global.fetch(url, freq as any) : await fetch(url, freq as any);
     dbg(`response: %d %s`, res.status, res.statusText);
     trace?.itemValue(`status`, `${res.status} ${res.statusText}`);
     if (!res.ok)

packages/core/test/image-generation.test.ts

@@ -1,4 +1,4 @@
-import { describe, test, expect, beforeAll } from "vitest";
+import { describe, test, expect, beforeAll, vi } from "vitest";
 import { writeFileSync } from "fs";
 import { join } from "path";
 import { CreateImageRequest } from "../src/chat.js";
@@ -216,6 +216,8 @@ describe("Image Generation", () => {
           model: "dall-e-3",
           base: "https://example.openai.azure.com",
           type: "azure",
+          token: "test-token",
+          modelId: "dall-e-3",
         };
 
         // This test verifies the request structure is valid for Azure edit mode
@@ -237,6 +239,8 @@ describe("Image Generation", () => {
           model: "dall-e-3",
           base: "https://example.openai.azure.com",
           type: "azure",
+          token: "test-token",
+          modelId: "dall-e-3",
         };
 
         // This test verifies the request structure is valid for Azure generation mode
@@ -259,6 +263,8 @@ describe("Image Generation", () => {
         model: "dall-e-2",
         base: "https://api.openai.com/v1",
         type: "openai",
+        token: "test-token",
+        modelId: "dall-e-2",
       };
 
       // This test verifies the request structure is valid for OpenAI edit mode
@@ -267,4 +273,54 @@ describe("Image Generation", () => {
       expect(cfg.provider).toBe(MODEL_PROVIDER_OPENAI);
     });
   });
+
+  describe("HTTP Request Handling", () => {
+    test("edit mode request structure is correctly prepared for FormData", () => {
+      const req: CreateImageRequest = {
+        model: "dall-e-2",
+        prompt: "Edit this image",
+        mode: "edit",
+        image: createTestImage(),
+      };
+
+      const cfg: LanguageModelConfiguration = {
+        provider: MODEL_PROVIDER_OPENAI,
+        model: "dall-e-2",
+        base: "https://api.openai.com/v1",
+        type: "openai",
+        token: "test-token",
+        modelId: "dall-e-2",
+      };
+
+      // Verify the request structure is correct for edit mode
+      expect(req.mode).toBe("edit");
+      expect(req.image).toBeInstanceOf(Buffer);
+      expect(cfg.provider).toBe(MODEL_PROVIDER_OPENAI);
+
+      // The fix ensures that when mode === "edit" (isMultipart = true),
+      // global.fetch is used instead of cross-fetch to properly handle FormData
+    });
+
+    test("generate mode uses standard JSON body", () => {
+      const req: CreateImageRequest = {
+        model: "dall-e-3",
+        prompt: "Generate a new image",
+        mode: "generate",
+      };
+
+      const cfg: LanguageModelConfiguration = {
+        provider: MODEL_PROVIDER_OPENAI,
+        model: "dall-e-3",
+        base: "https://api.openai.com/v1",
+        type: "openai",
+        token: "test-token",
+        modelId: "dall-e-3",
+      };
+
+      // Verify structure for standard generation mode
+      expect(req.mode).toBe("generate");
+      expect(req.image).toBeUndefined();
+      expect(cfg.provider).toBe(MODEL_PROVIDER_OPENAI);
+    });
+  });
 });