[incremental-delivery]: Remove the content-length requirement (#728)

This removes the need for `Content-Length`, and handles the boundaries such that the next boundary is flushed as soon as possible.

References:
- graphql/graphql-over-http#152
- fmg relay-tools/fetch-multipart-graphql#22
- [meros](https://github.com/maraisr/meros)

Author: maraisr

src/__tests__/http-test.ts

@@ -1074,16 +1074,12 @@ function runTests(server: Server) {
           '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 26',
           '',
           '{"data":{},"hasNext":true}',
-          '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 78',
           '',
           '{"data":{"test":"Hello World"},"path":[],"label":"deferLabel","hasNext":false}',
-          '',
           '-----',
           '',
         ].join('\r\n'),
@@ -1204,13 +1200,10 @@ function runTests(server: Server) {
           '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 35',
           '',
           ['{', '  "data": {},', '  "hasNext": true', '}'].join('\n'),
-          '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 79',
           '',
           [
             '{',
@@ -1221,7 +1214,6 @@ function runTests(server: Server) {
             '  "hasNext": false',
             '}',
           ].join('\n'),
-          '',
           '-----',
           '',
         ].join('\r\n'),
@@ -1413,16 +1405,12 @@ function runTests(server: Server) {
           '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 94',
           '',
           '{"errors":[{"message":"Custom error format: Throws!"}],"data":{"thrower":null},"hasNext":true}',
-          '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 57',
           '',
           '{"data":{"test":"Hello World"},"path":[],"hasNext":false}',
-          '',
           '-----',
           '',
         ].join('\r\n'),
@@ -1464,16 +1452,12 @@ function runTests(server: Server) {
           '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 46',
           '',
           '{"data":{"test":"Hello World"},"hasNext":true}',
-          '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 105',
           '',
           '{"data":{"thrower":null},"path":[],"errors":[{"message":"Custom error format: Throws!"}],"hasNext":false}',
-          '',
           '-----',
           '',
         ].join('\r\n'),
@@ -2453,16 +2437,12 @@ function runTests(server: Server) {
           '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 48',
           '',
           '{"data":{"test2":"Modification"},"hasNext":true}',
-          '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 64',
           '',
           '{"errors":[{"message":"I did something wrong"}],"hasNext":false}',
-          '',
           '-----',
           '',
         ].join('\r\n'),
@@ -2527,10 +2507,9 @@ function runTests(server: Server) {
           '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 47',
           '',
           '{"data":{"test":"Hello, World"},"hasNext":true}',
-          '',
+          '---\r\n',
         ].join('\r\n'),
       );
       expect(fakeReturn.callCount).to.equal(1);
@@ -2592,10 +2571,9 @@ function runTests(server: Server) {
           '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 47',
           '',
           '{"data":{"test":"Hello, World"},"hasNext":true}',
-          '',
+          '---\r\n',
         ].join('\r\n'),
       );
     });
@@ -2748,16 +2726,12 @@ function runTests(server: Server) {
           '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 124',
           '',
           '{"data":{"hello":"Hello Rob"},"hasNext":true,"extensions":{"preservedResult":{"data":{"hello":"Hello Rob"},"hasNext":true}}}',
-          '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 148',
           '',
           '{"data":{"test":"Hello World"},"path":[],"hasNext":false,"extensions":{"preservedResult":{"data":{"test":"Hello World"},"path":[],"hasNext":false}}}',
-          '',
           '-----',
           '',
         ].join('\r\n'),
@@ -2828,16 +2802,12 @@ function runTests(server: Server) {
           '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 45',
           '',
           '{"data":{"hello":"Hello Rob"},"hasNext":true}',
-          '',
           '---',
           'Content-Type: application/json; charset=utf-8',
-          'Content-Length: 57',
           '',
           '{"data":{"test":"Hello World"},"path":[],"hasNext":false}',
-          '',
           '-----',
           '',
         ].join('\r\n'),

src/index.ts

@@ -462,6 +462,7 @@ export function graphqlHTTP(options: Options): Middleware {
 
     if (isAsyncIterable(executeResult)) {
       response.setHeader('Content-Type', 'multipart/mixed; boundary="-"');
+      response.write('\r\n---\r\n');
       sendPartialResponse(pretty, response, formattedResult);
       try {
         for await (let payload of executeResult) {
@@ -489,7 +490,6 @@ export function graphqlHTTP(options: Options): Middleware {
           hasNext: false,
         });
       }
-      response.write('\r\n-----\r\n');
       response.end();
       finishedIterable = true;
       return;
@@ -625,16 +625,14 @@ function sendPartialResponse(
 ): void {
   const json = JSON.stringify(result, null, pretty ? 2 : 0);
   const chunk = Buffer.from(json, 'utf8');
-  const data = [
-    '',
-    '---',
-    'Content-Type: application/json; charset=utf-8',
-    'Content-Length: ' + String(chunk.length),
-    '',
-    chunk,
-    '',
-  ].join('\r\n');
-  response.write(data);
+  const data = ['Content-Type: application/json; charset=utf-8', '', chunk];
+  // @ts-expect-error
+  if (result.hasNext === true) {
+    data.push('---\r\n');
+  } else {
+    data.push('-----\r\n');
+  }
+  response.write(data.join('\r\n'));
   // flush response if compression middleware is used
   if (
     typeof response.flush === 'function' &&