Fix: Duplicate Content-Type header when Content-Type header is capitalized.

src/RESTDataSource.ts

@@ -483,6 +483,10 @@ export abstract class RESTDataSource {
  // If Content-Type header has not been previously set, set to application/json
  if (!augmentedRequest.headers) {
  augmentedRequest.headers = { 'content-type': 'application/json' };
+ // replace capitalized content-type header with lower case, ensures no dupliate content-types
+ } else if (augmentedRequest.headers['Content-Type']) {
+ augmentedRequest.headers['content-type'] = augmentedRequest.headers['Content-Type'];
+ delete augmentedRequest.headers['Content-Type'];
  } else if (!augmentedRequest.headers['content-type']) {
  augmentedRequest.headers['content-type'] = 'application/json';
  }

src/__tests__/RESTDataSource.test.ts

@@ -260,6 +260,37 @@ describe('RESTDataSource', () => {
  await dataSource.getFoo('1');
  });
 
+ it('contains only one Content-Type header when Content-Type already exists is application/json', async () => {
+ const requestOptions = {
+ headers: {
+ 'Content-Type': 'application/json',
+ },
+ body: JSON.parse(JSON.stringify({ foo: 'bar' })),
+ };
+ const dataSource = new (class extends RESTDataSource {
+ override baseURL = 'https://api.example.com';
+
+ postFoo() {
+ return this.post('foo', requestOptions);
+ }
+ })();
+
+ const spyOnHttpFetch = jest.spyOn(dataSource['httpCache'], 'fetch');
+
+ nock(apiUrl)
+ .post('/foo')
+ .reply(200, { foo: 'bar' }, { 'Content-Type': 'application/json' });
+
+ const data = await dataSource.postFoo();
+ expect(spyOnHttpFetch.mock.calls[0][1]).toEqual({
+ headers: {"content-type": "application/json"},
+ body: "{\"foo\":\"bar\"}",
+ method: "POST",
+ params: new URLSearchParams()
+ })
+ expect(data).toEqual({ foo: 'bar' });
+ });
+
  it('serializes a request body that is an object as JSON', async () => {
  const expectedFoo = { foo: 'bar' };
  const dataSource = new (class extends RESTDataSource {