add proxy support through global-agent, add proxy tests, update README

src/proxy.js

@@ -0,0 +1,24 @@
+const {bootstrap} = require('global-agent');
+const core = require("@actions/core");
+const MAJOR_NODEJS_VERSION = parseInt(process.version.slice(1).split('.')[0], 10);
+
+/**
+ * Will enable global-agent proxy if the necessary
+ * [global-agent environment variables](https://github.com/gajus/global-agent?tab=readme-ov-file#environment-variables)
+ * has been set.
+ * Important note: `global-agent` only works with Node.js v10 and above.
+ * Node.js versions below v10 are not supported
+ *
+ * The bootstrap routine guards against multiple initializations of global-agent
+ */
+function enableProxy() {
+  if (MAJOR_NODEJS_VERSION >= 10) {
+    bootstrap();
+  } else {
+    core.debug('proxy configuration does not work with Node.js below v10')
+  }
+}
+
+module.exports = {
+  enableProxy
+}

src/proxy.test.js

@@ -0,0 +1,72 @@
+const {enableProxy } = require('./proxy')
+const got = require('got');
+
+describe('global-agent proxy support works as expected', () => {
+
+  it('should fail with a request specific RequestError if got tries to request any-host without proxy', async () => {
+    const expectedRequestErrorMessage = `getaddrinfo ENOTFOUND any-host`;
+    try {
+      await got.get('http://any-host')
+      throw new Error('Test fail if the got request succeeds against expectation');
+    } catch(e) {
+      expect(e).toBeDefined();
+      expect(e.message).toEqual(expectedRequestErrorMessage);
+      expect(e.code).toEqual('ENOTFOUND');
+    }
+  });
+
+  it('should fail with a proxy specific RequestError if got tries to request through the defined proxy', async () => {
+    const PROXY_HOST = "my-test-proxy-server";
+    process.env.GLOBAL_AGENT_HTTP_PROXY = `http://${PROXY_HOST}:8000`;
+    enableProxy();
+    const expectedRequestErrorMessage = `getaddrinfo ENOTFOUND ${PROXY_HOST}`;
+    try {
+      await got.get('http://any-host')
+      throw new Error('Test fail if the got request succeeds against expectation');
+    } catch(e) {
+      expect(e).toBeDefined();
+      expect(e.message).toEqual(expectedRequestErrorMessage);
+      expect(e.code).toEqual('ENOTFOUND');
+    }
+  });
+
+  it('should fail with a request specific RequestError if HTTP_PROXY URL is undefined', async () => {
+    // set proxy url to undefined at runtime
+    global.GLOBAL_AGENT.HTTP_PROXY = undefined;
+    const expectedRequestErrorMessage = `getaddrinfo ENOTFOUND any-host`;
+    try {
+      await got.get('http://any-host')
+      throw new Error('Test fail if the got request succeeds against expectation');
+    } catch(e) {
+      expect(e).toBeDefined();
+      expect(e.message).toEqual(expectedRequestErrorMessage);
+      expect(e.code).toEqual('ENOTFOUND');
+    }
+  });
+
+  it('should fail with a request specific RequestError if HTTP_PROXY URL is empty', async () => {
+    // set proxy url to empty string at runtime
+    global.GLOBAL_AGENT.HTTP_PROXY = '';
+    const expectedRequestErrorMessage = `getaddrinfo ENOTFOUND any-host`;
+    try {
+      await got.get('http://any-host')
+      throw new Error('Test fail if the got request succeeds against expectation');
+    } catch(e) {
+      expect(e).toBeDefined();
+      expect(e.message).toEqual(expectedRequestErrorMessage);
+      expect(e.code).toEqual('ENOTFOUND');
+    }
+  });
+
+  it('should fail with UNEXPECTED_STATE_ERROR if HTTP_PROXY URL protocol does not start with "http:"', async () => {
+    // set proxy url to string with blanks at runtime
+    global.GLOBAL_AGENT.HTTP_PROXY = 'file://';
+    try {
+      await got.get('http://any-host')
+      throw new Error('Test fail if the got request succeeds against expectation');
+    } catch(e) {
+      expect(e).toBeDefined();
+      expect(e.code).toEqual('UNEXPECTED_STATE_ERROR');
+    }
+  });
+})