feat(fetch, node)!: drop the content-type of an empty body

packages/core/README.md

@@ -228,7 +228,9 @@ The `standard-server` header closes this gap. It carries the sender's `StandardB
 
 Adapters set the header automatically for the ambiguous body types: a `Blob` or `File` body is sent with `standard-server: file`, and a `ReadableStream` body with `standard-server: octet-stream`, alongside the usual content headers. A header you set yourself always wins, and assigning an empty array removes it entirely.
 
-Other body types get their usual `content-type` (`application/json`, `application/x-www-form-urlencoded`, `text/event-stream`, or none when empty) unless you set one. If yours would be read as another body type, such as JSON sent as `application/problem+json`, adapters add the matching `standard-server` header; otherwise they clear it. `FormData` always gets its generated multipart `content-type`, which carries the boundary.
+Other body types get their usual `content-type` (`application/json`, `application/x-www-form-urlencoded`, or `text/event-stream`) unless you set one. If yours would be read as another body type, such as JSON sent as `application/problem+json`, adapters add the matching `standard-server` header; otherwise they clear it. `FormData` always gets its generated multipart `content-type`, which carries the boundary.
+
+An empty body is always sent without `content-type`. To send an empty response with your own headers, such as for `HEAD`, use an already-closed `ReadableStream`.
 
 The header is optional: when it is absent or invalid, the receiver falls back to content-header inference, so plain HTTP clients work as-is. Just set the header yourself whenever the content type alone could be misread:
 

packages/fetch/src/body.test.ts

@@ -316,7 +316,12 @@ describe('toFetchBody', () => {
   }
 
   it('undefined', () => {
-    const [body, headers] = toFetchBody(undefined, baseHeaders, {})
+    // a given content-type and hint are dropped
+    const [body, headers] = toFetchBody(
+      undefined,
+      { ...baseHeaders, 'content-type': 'text/html', 'standard-server': 'file' },
+      {},
+    )
 
     expect(body).toBe(undefined)
     expect(headers).toEqual({
@@ -554,7 +559,6 @@ describe('toFetchBody', () => {
     ['url-search-params as text', new URLSearchParams('a=b'), 'text/plain', 'url-search-params'],
     ['event stream as event-stream', (async function* () {})(), 'text/event-stream', undefined],
     ['event stream as text', (async function* () {})(), 'text/plain', 'event-stream'],
-    ['undefined as html', undefined, 'text/html', 'none'],
   ])('keeps a given content-type and replaces a user hint: %s', (_, body, contentType, hint) => {
     const headers = { 'content-type': contentType, 'standard-server': 'file' }
 

packages/fetch/src/body.ts

@@ -146,7 +146,7 @@ export function toFetchBody(
   headers['content-length'] = undefined
 
   if (body === undefined) {
-    headers['standard-server'] = getRequiredStandardBodyHint('none', headers)
+    headers['content-type'] = undefined
     return [undefined, headers]
   }
 

packages/node/src/body.test.ts

@@ -591,7 +591,12 @@ describe('toNodeHttpBody', () => {
   }
 
   it('undefined', async () => {
-    const [body, headers] = toNodeHttpBody(undefined, baseHeaders, {})
+    // a given content-type and hint are dropped
+    const [body, headers] = toNodeHttpBody(
+      undefined,
+      { ...baseHeaders, 'content-type': 'text/html', 'standard-server': 'file' },
+      {},
+    )
 
     expect(body).toBe(undefined)
     expect(headers).toEqual({
@@ -948,7 +953,6 @@ describe('toNodeHttpBody', () => {
     ['url-search-params as text', new URLSearchParams('a=b'), 'text/plain', 'url-search-params'],
     ['event stream as event-stream', (async function* () {})(), 'text/event-stream', undefined],
     ['event stream as text', (async function* () {})(), 'text/plain', 'event-stream'],
-    ['undefined as html', undefined, 'text/html', 'none'],
   ])('keeps a given content-type and replaces a user hint: %s', (_, body, contentType, hint) => {
     const headers = { 'content-type': contentType, 'standard-server': 'file' }
 

packages/node/src/body.ts

@@ -147,7 +147,7 @@ export function toNodeHttpBody(
   headers['content-length'] = undefined
 
   if (body === undefined) {
-    headers['standard-server'] = getRequiredStandardBodyHint('none', headers)
+    headers['content-type'] = undefined
     return [undefined, headers]
   }
 

tests/data-transfer.test.ts

@@ -198,11 +198,6 @@ describe.each([
         await expect(reader.read()).resolves.toEqual({ done: true })
       },
     },
-    {
-      name: 'undefined as text/html',
-      createBody: () => undefined,
-      contentType: 'text/html',
-    },
     {
       name: 'json-object as application/problem+json',
       createBody: () => ({ a: 1, b: [2, 3, { c: 4 }] }),