From 36ad4335e001672c47df2b5f70dde0c7ed418363 Mon Sep 17 00:00:00 2001
From: Florian Meyer <fflorian.meyer@outlook.com>
Date: Sun, 9 Aug 2026 11:32:20 +0200
Subject: [PATCH] fix: distinguish native FormData in edge runtimes

---
 src/services/http/Transport.ts  | 18 ++++++++++-----
 test/unit/httpTransport.spec.ts | 40 +++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/src/services/http/Transport.ts b/src/services/http/Transport.ts
index e1509699d..58b4a5fb9 100644
--- a/src/services/http/Transport.ts
+++ b/src/services/http/Transport.ts
@@ -1,7 +1,6 @@
 import * as http from 'http'
 import * as https from 'https'
 import { URLSearchParams } from 'url'
-import FormData from 'form-data'
 
 type HeaderMap = Record<string, string>
 type RequestUrl = string | URL
@@ -11,6 +10,10 @@ interface PipeableBody {
   pipe(destination: NodeJS.WritableStream): NodeJS.WritableStream
 }
 
+interface NodeFormDataBody extends PipeableBody {
+  getHeaders(): HeaderMap
+}
+
 export interface IHttpTransportOptions {
   method?: string
   headers?: HeaderMap
@@ -28,8 +31,9 @@ export interface IBufferedResponse {
 export async function sendFetchRequest(url: RequestUrl, options: IHttpTransportOptions): Promise<Response> {
   // Native fetch supports WHATWG FormData, but this SDK's public upload contract
   // uses the npm form-data stream; without this path, multipart uploads are
-  // stringified as "[object FormData]" and break existing callers.
-  if (isFormDataBody(options.body)) {
+  // stringified as "[object FormData]" and break existing callers. Detect the
+  // stream contract because edge runtimes may shim the FormData constructor.
+  if (isNodeFormDataBody(options.body)) {
     const response = await sendNodeRequest(url, options)
     const responseBody = shouldOmitResponseBody(response.status) ? null : await response.binary()
 
@@ -71,7 +75,7 @@ function buildRequestInit(options: IHttpTransportOptions): RequestInit & { duple
 }
 
 function normalizeHeaders(headers: HeaderMap | undefined, body: unknown): HeaderMap | undefined {
-  if (isFormDataBody(body)) {
+  if (isNodeFormDataBody(body)) {
     return mergeHeaders(headers, body.getHeaders())
   }
 
@@ -100,8 +104,10 @@ function mergeHeaders(headers: HeaderMap | undefined, nextHeaders: HeaderMap): H
   return mergedHeaders
 }
 
-function isFormDataBody(body: unknown): body is FormData {
-  return body instanceof FormData
+function isNodeFormDataBody(body: unknown): body is NodeFormDataBody {
+  return (
+    isPipeableBody(body) && 'getHeaders' in body && typeof (body as { getHeaders?: unknown }).getHeaders === 'function'
+  )
 }
 
 function isPipeableBody(body: unknown): body is PipeableBody {
diff --git a/test/unit/httpTransport.spec.ts b/test/unit/httpTransport.spec.ts
index e7366d3ff..473acd3e4 100644
--- a/test/unit/httpTransport.spec.ts
+++ b/test/unit/httpTransport.spec.ts
@@ -81,6 +81,46 @@ describe('HTTP transport', () => {
     }
   })
 
+  it('supports WHATWG FormData when form-data is provided by a runtime shim', async () => {
+    let capturedRequest: ICapturedRequest | undefined
+    const server = await createServer(async (request: ICapturedRequest, response: http.ServerResponse) => {
+      capturedRequest = request
+      response.statusCode = 204
+      response.end()
+    })
+    const nativeFormData = new globalThis.FormData()
+    nativeFormData.append('field', 'value')
+    const originalHasInstance = Object.getOwnPropertyDescriptor(FormData, Symbol.hasInstance)
+    Object.defineProperty(FormData, Symbol.hasInstance, {
+      configurable: true,
+      value: (body: unknown) => body instanceof globalThis.FormData,
+    })
+
+    try {
+      const client = new Client()
+      const response = await client.apiRequest({
+        method: 'POST',
+        overlapUrl: `${server.baseUrl}/upload`,
+        body: nativeFormData,
+        defaultJson: false,
+      })
+
+      expect(response.status).toBe(204)
+      expect(capturedRequest).toBeDefined()
+      const req = capturedRequest as ICapturedRequest
+      expect(String(req.headers['content-type'])).toContain('multipart/form-data; boundary=')
+      expect(req.body.toString()).toContain('name="field"')
+      expect(req.body.toString()).toContain('value')
+    } finally {
+      if (originalHasInstance) {
+        Object.defineProperty(FormData, Symbol.hasInstance, originalHasInstance)
+      } else {
+        Reflect.deleteProperty(FormData, Symbol.hasInstance)
+      }
+      await server.close()
+    }
+  })
+
   it('returns generated ResponseContext bodies through native fetch', async () => {
     let capturedRequest: ICapturedRequest | undefined
     const server = await createServer(async (request: ICapturedRequest, response: http.ServerResponse) => {