Fix proxying of Docker exec

This notably broke tools like ddev which use 'exec' as a key part of
their setup workflow. This broke because the initial request is an
upgrade _and_ includes a body with the exec attach options. Previously
we only forwarded the body after Docker accepted the upgrade, which
deadlocked: Docker never replied, waiting for the params, and we never
sent them, waiting for the upgrade. We now send the params upstream with
the initial request.

Author: pimterry

src/interceptors/docker/docker-proxy.ts

@@ -94,7 +94,6 @@ async function createDockerProxy(proxyPort: number, httpsConfig: { certPath: str
             path: req.url,
         });
 
-
         bodyStream.pipe(dockerReq);
 
         return dockerReq;
@@ -282,6 +281,11 @@ async function createDockerProxy(proxyPort: number, httpsConfig: { certPath: str
             return;
         }
 
+        // We have to include initial data in the upstream request. This is especially important for
+        // commands like /exec/.../start, which send JSON config {detach:...} in the initial request,
+        // which the docker daemon waits before it will accept the upgrade (or 400s, if it's missing).
+        req.unshift(head);
+
         const dockerReq = sendToDocker(req);
         dockerReq.on('error', (e) => {
             console.error('Docker proxy error', e);
@@ -339,7 +343,6 @@ async function createDockerProxy(proxyPort: number, httpsConfig: { certPath: str
             // We only write upgrade head data if it's non-empty. For some bizarre reason on
             // Windows, writing empty data to a named pipe here kills the connection entirely.
             if (dockerHead.length) socket.write(dockerHead);
-            if (head.length) dockerSocket.write(head);
 
             dockerSocket.on('error', (e) => {
                 console.error('Docker proxy error', e);

test/interceptors/docker-terminal-interception.spec.ts

@@ -181,6 +181,34 @@ Successfully built <hash>
         expect(stderr).to.equal('');
     });
 
+    it("should support proxying 'docker exec'", async function () {
+        const { server, httpsConfig } = await testSetup;
+
+        const terminalEnvOverrides = getTerminalEnvVars(server.port, httpsConfig, process.env, {});
+
+        // Launch a background Node.js container that stays running for 10 seconds
+        const runResult = await spawnToResult(
+            'docker', ['run', '-d', '--rm', 'node:14', '-e', 'setTimeout(() => {}, 10000000)'],
+            {
+                env: { ...process.env, ...terminalEnvOverrides }
+            }
+        );
+
+        expect(runResult.exitCode).to.equal(0);
+        const containerId = runResult.stdout.trim();
+
+        const execResult = await spawnToResult(
+            'docker', ['exec', containerId, 'node', '-e', 'console.log("exec" + "-test-" + "output")'],
+            {
+                env: { ...process.env, ...terminalEnvOverrides },
+            }
+        );
+
+        expect(execResult.exitCode).to.equal(0);
+        expect(execResult.stderr).to.equal('');
+        expect(execResult.stdout).to.include('exec-test-output'); // Executed command is run & output returned
+    });
+
     it("should intercept 'docker-compose up'", async function () {
         this.timeout(30000);