Tighten up more of the client API details

We now preserve headers _exactly_, so far as possible, to precisely
control traffic - including raw header order & casing.

This also adds a type field to the REST response message, which should
make it easier to support multiple types later, and so to potentially
stream ND-JSON for incremental responses.

Author: pimterry

src/api/rest-api.ts

@@ -97,7 +97,8 @@ export function exposeRestAPI(
         });
 
         res.send({
-            result: {
+            type: 'response', // Later we may send ND-JSON with chunked data & other types
+            response: {
                 ...result,
                 rawBody: result.rawBody?.toString('base64') ?? ''
             }

src/client/client.ts

@@ -8,6 +8,15 @@ export type RawHeaders = Array<[key: string, value: string]>;
 export interface RequestDefinition {
     method: string;
     url: string;
+
+    /**
+     * The raw headers to send. These will be sent exactly as provided - no headers
+     * will be added automatically.
+     *
+     * Note that this means omitting the 'Host' header may cause problems, as will
+     * omitting both 'Content-Length' and 'Transfer-Encoding' on requests with
+     * bodies.
+     */
     headers: RawHeaders;
     rawBody?: Uint8Array;
 }
@@ -30,12 +39,21 @@ export async function sendRequest(
 
     const request = (url.protocol === 'https' ? https : http).request(requestDefn.url, {
         method: requestDefn.method,
-
-        // Node supports sending raw headers via [key, value, key, value] array, but we need an
-        // 'any' as the types don't believe it:
-        headers: flattenPairedRawHeaders(requestDefn.headers) as any
     });
 
+    // Node supports sending raw headers via [key, value, key, value] array, but if we do
+    // so with 'headers' above then we can't removeHeader first (to disable the defaults).
+    // Instead we remove headers and then manunally trigger the 'raw' write behaviour.
+
+    request.removeHeader('connection');
+    request.removeHeader('transfer-encoding');
+    request.removeHeader('content-length');
+
+    (request as any)._storeHeader(
+        request.method + ' ' + request.path + ' HTTP/1.1\r\n',
+        flattenPairedRawHeaders(requestDefn.headers)
+    );
+
     if (requestDefn.rawBody?.byteLength) {
         request.end(requestDefn.rawBody);
     } else {

test/client/send-request.spec.ts

@@ -5,7 +5,7 @@ import { sendRequest } from '../../src/client/client';
 
 describe("The HTTP client API", () => {
 
-    const mockServer = mockttp.getLocal({ debug: true });
+    const mockServer = mockttp.getLocal();
 
     beforeEach(() => mockServer.start());
     afterEach(() => mockServer.stop());
@@ -14,9 +14,11 @@ describe("The HTTP client API", () => {
         await mockServer.forAnyRequest().thenCallback(async (request) => {
             expect(request.url).to.equal(`http://localhost:${mockServer.port}/path?qwe=asd`);
             expect(request.method).to.equal('POST');
-            expect(
-                request.rawHeaders.find(([key]) => key === 'CUSTOM-header')
-            ).to.deep.equal(['CUSTOM-header', 'CUSTOM-value']);
+            expect(request.rawHeaders).to.deep.equal([
+                ['host', `localhost:${mockServer.port}`],
+                ['content-length', '12'],
+                ['CUSTOM-header', 'CUSTOM-value']
+            ]);
             expect(await request.body.getText()).to.equal('Request body')
 
             return {