fix: formdata post, wrong inference of json payload

src/fetch/index.ts

@@ -62,14 +62,6 @@ export const edenFetch = <App extends Elysia<any, any, any, any, any, any, any>>
 				endpoint = endpoint.replace(`:${key}`, value as string)
 			})
 
-		// @ts-ignore
-		const contentType = options.headers?.['Content-Type']
-
-		if (!contentType || contentType === 'application/json')
-			try {
-				body = JSON.stringify(body)
-			} catch (error) {}
-
 		const fetch = config?.fetcher || globalThis.fetch
 
         const nonNullishQuery = query
@@ -85,14 +77,19 @@ export const edenFetch = <App extends Elysia<any, any, any, any, any, any, any>>
             : ''
 
 		const requestUrl = `${server}${endpoint}${queryStr}`
-		const headers = body
-			? {
-					'content-type': 'application/json',
-					// @ts-ignore
-					...options.headers
-				}
-			: // @ts-ignore
-				options.headers
+		const headers = new Headers(options.headers || {})
+        const contentType = headers.get('content-type')
+        if (
+            !(body instanceof FormData) &&
+            !(body instanceof URLSearchParams) &&
+            (!contentType || contentType === 'application/json')
+        ) {
+            try {
+                body = JSON.stringify(body)
+                if (!contentType) headers.set('content-type', 'application/json')
+            } catch (error) {}
+        }
+
 		const init = {
 			...options,
 			// @ts-ignore

test/fetch.test.ts

@@ -1,5 +1,5 @@
 /* eslint-disable @typescript-eslint/no-unused-vars */
-import { Elysia, t } from 'elysia'
+import { Elysia, form, t } from 'elysia'
 import { edenFetch } from '../src'
 
 import { describe, expect, it, beforeAll } from 'bun:test'
@@ -13,6 +13,17 @@ const json = {
 const app = new Elysia()
     .get('/', () => 'hi')
     .post('/', () => 'post')
+    .post('/form-data', ({ body }) => {
+        return {
+            file: body.file.name,
+            size: body.file.size
+        }
+    }, {
+        body: t.Object({
+            file: t.File()
+        }),
+        parse: 'formdata'
+    })
     .get('/json', ({ body }) => json)
     .get(
         '/json-utf8',
@@ -165,6 +176,22 @@ describe('Eden Fetch', () => {
         expect(data).toEqual(false)
     })
 
+    it('parse form data', async () => {
+        const formData = new FormData();
+        formData.append('file', new File(['test'], 'test.txt', { type: 'text/plain' }))
+
+        const { data } = await fetch('/form-data', {
+            method: 'POST',
+            // @ts-ignore
+            body: formData
+        })
+
+        expect(data).toEqual({
+            file: 'test.txt',
+            size: 4
+        })
+    })
+
     // ! FIX ME
     // it('handle throw error', async () => {
     //     const { data, error } = await fetch('/throw-error', {