[core-http] validate proxySettings when creating proxy agent (#7149)

* [core-http] validate proxySettings when creating proxy agent

Throw separate errors for invalid host and invalid port

Resolves #4544.

sdk/core/core-http/lib/proxyAgent.ts

@@ -15,9 +15,20 @@ export function createProxyAgent(
   proxySettings: ProxySettings,
   headers?: HttpHeaders
 ): ProxyAgent {
+  const host = URLBuilder.parse(proxySettings.host).getHost() as string;
+  if (!host) {
+    throw new Error(
+      "Expecting a non-empty host in proxy settings."
+    );
+  }
+  if (!isValidPort(proxySettings.port)) {
+    throw new Error(
+      "Expecting a valid port number in the range of [0, 65535] in proxy settings."
+    );
+  }
   const tunnelOptions: tunnel.HttpsOverHttpsOptions = {
     proxy: {
-      host: URLBuilder.parse(proxySettings.host).getHost() as string,
+      host: host,
       port: proxySettings.port,
       headers: (headers && headers.rawHeaders()) || {}
     }
@@ -58,3 +69,9 @@ export function createTunnel(
     return tunnel.httpOverHttp(tunnelOptions);
   }
 }
+
+function isValidPort(port: number) {
+  // any port in 0-65535 range is valid (RFC 793) even though almost all implementations
+  // will reserve 0 for a specific purpose, and a range of numbers for ephemeral ports
+  return 0 <= port && port <= 65535;
+}

sdk/core/core-http/test/proxyAgent.node.ts

@@ -63,6 +63,47 @@ describe("proxyAgent", () => {
       agent.proxyOptions.headers!.should.contain({ "user-agent": "Node.js" });
       done();
     });
+
+    [
+      { host: "host", port: 0 },
+      { host: "host", port: 65535 }
+    ].forEach((testCase) => {
+      it(`should not throw error when being given a valid proxy settings of { host: '${testCase.host}', port: ${testCase.port} }.`, function(done) {
+        const proxySettings = {
+          host: testCase.host,
+          port: testCase.port
+        };
+
+        const fn = function() {
+          createProxyAgent("http://example.com", proxySettings);
+        };
+        fn.should.not.throw();
+        done();
+      });
+    });
+
+    [
+      { host: "", port: 8080, expectInvalidHostError: true },
+      { host: "host", port: -1, expectInvalidHostError: false },
+      { host: "host", port: 65536, expectInvalidHostError: false }
+    ].forEach((testCase) => {
+      it(`should throw error when being given an invalid proxy settings of { host: '${testCase.host}', port: ${testCase.port} }.`, function(done) {
+        const proxySettings = {
+          host: testCase.host,
+          port: testCase.port
+        };
+
+        const fn = function() {
+          createProxyAgent("http://example.com", proxySettings);
+        };
+        fn.should.throw(
+          testCase.expectInvalidHostError?
+            "Expecting a non-empty host in proxy settings." :
+            "Expecting a valid port number in the range of [0, 65535] in proxy settings."
+        );
+        done();
+      });
+    });
   });
 
   describe("createTunnel", () => {