github
@@ -52,7 +52,7 @@ import {
   initConfig,
   runDatabaseInitCluster,
 } from "./init";
-import { KnownLanguage } from "./languages";
+import { JavaEnvVars, KnownLanguage } from "./languages";
 import { getActionsLogger, Logger } from "./logging";
 import {
   downloadOverlayBaseDatabaseFromCache,
@@ -756,13 +756,13 @@ async function run(startedAt: Date) {
 
     // Enable Java network debugging if the FF is enabled.
     if (await features.getValue(Feature.JavaNetworkDebugging)) {
-      // Get the existing value of `JAVA_OPTS`, if any.
+      // Get the existing value of `JAVA_TOOL_OPTIONS`, if any.
       const existingJavaToolOptions =
-        getOptionalEnvVar("JAVA_TOOL_OPTIONS") || "";
+        getOptionalEnvVar(JavaEnvVars.JAVA_TOOL_OPTIONS) || "";
 
       // Add the network debugging options.
       core.exportVariable(
-        "JAVA_TOOL_OPTIONS",
+        JavaEnvVars.JAVA_TOOL_OPTIONS,
         `${existingJavaToolOptions} -Djavax.net.debug=all`,
       );
     }

@@ -19,3 +19,11 @@ export enum KnownLanguage {
   rust = "rust",
   swift = "swift",
 }
+
+/** Java-specific environment variable names that we may care about. */
+export enum JavaEnvVars {
+  JAVA_HOME = "JAVA_HOME",
+  JAVA_TOOL_OPTIONS = "JAVA_TOOL_OPTIONS",
+  JDK_JAVA_OPTIONS = "JDK_JAVA_OPTIONS",
+  _JAVA_OPTIONS = "_JAVA_OPTIONS",
+}
@@ -22,6 +22,7 @@ import {
   ProxyConfig,
 } from "./start-proxy";
 import { generateCertificateAuthority } from "./start-proxy/ca";
+import { checkProxyEnvironment } from "./start-proxy/environment";
 import { checkConnections } from "./start-proxy/reachability";
 import { ActionName, sendUnhandledErrorStatusReport } from "./status-report";
 import * as util from "./util";
@@ -76,6 +77,19 @@ async function run(startedAt: Date) {
         .join("\n")}`,
     );
 
+    // Check the environment for any configurations which may affect the proxy.
+    // This is a best effort process to give us insights into potential factors
+    // which may affect the operation of our proxy.
+    if (core.isDebug() || util.isInTestMode()) {
+      try {
+        await checkProxyEnvironment(logger, language);
+      } catch (err) {
+        logger.debug(
+          `Unable to inspect runner environment: ${util.getErrorMessage(err)}`,
+        );
+      }
+    }
+
     const ca = generateCertificateAuthority(
       await features.getValue(Feature.ImprovedProxyCertificates),
     );

@@ -0,0 +1,213 @@
+import * as fs from "fs";
+import * as os from "os";
+import path from "path";
+
+import * as toolrunner from "@actions/exec/lib/toolrunner";
+import * as io from "@actions/io";
+import test, { ExecutionContext } from "ava";
+import sinon from "sinon";
+
+import { JavaEnvVars, KnownLanguage } from "../languages";
+import {
+  checkExpectedLogMessages,
+  getRecordingLogger,
+  LoggedMessage,
+  setupTests,
+} from "../testing-utils";
+import { withTmpDir } from "../util";
+
+import {
+  checkJavaEnvVars,
+  checkJdkSettings,
+  checkProxyEnvironment,
+  checkProxyEnvVars,
+  discoverActionsJdks,
+  JAVA_PROXY_ENV_VARS,
+  ProxyEnvVars,
+} from "./environment";
+
+setupTests(test);
+
+function stubToolrunner() {
+  sinon.stub(io, "which").throws(new Error("Java not installed"));
+  sinon.stub(toolrunner, "ToolRunner").returns({
+    exec: async () => {
+      return 0;
+    },
+  });
+}
+
+function assertEnvVarLogMessages(
+  t: ExecutionContext<any>,
+  envVars: string[],
+  messages: LoggedMessage[],
+  expectSet: boolean | string,
+) {
+  const template = (envVar: string) => {
+    if (typeof expectSet === "string") {
+      return `Environment variable '${envVar}' is set to '${expectSet}'`;
+    }
+    return expectSet
+      ? `Environment variable '${envVar}' is set to '${envVar}'`
+      : `Environment variable '${envVar}' is not set`;
+  };
+
+  const expected: string[] = [];
+
+  for (const envVar of envVars) {
+    expected.push(template(envVar));
+  }
+
+  checkExpectedLogMessages(t, messages, expected);
+}
+
+test("checkJavaEnvironment - none set", (t) => {
+  const messages: LoggedMessage[] = [];
+  const logger = getRecordingLogger(messages);
+
+  checkJavaEnvVars(logger);
+  assertEnvVarLogMessages(t, JAVA_PROXY_ENV_VARS, messages, false);
+});
+
+test("checkJavaEnvironment - logs values when variables are set", (t) => {
+  const messages: LoggedMessage[] = [];
+  const logger = getRecordingLogger(messages);
+
+  for (const envVar of Object.values(JavaEnvVars)) {
+    process.env[envVar] = envVar;
+  }
+
+  checkJavaEnvVars(logger);
+  assertEnvVarLogMessages(t, JAVA_PROXY_ENV_VARS, messages, true);
+});
+
+test("discoverActionsJdks - discovers JDK paths", (t) => {
+  // Clear GHA variables that may interfere with this test in CI.
+  for (const envVar of Object.keys(process.env)) {
+    if (envVar.startsWith("JAVA_HOME_")) {
+      delete process.env[envVar];
+    }
+  }
+
+  const jdk8 = "/usr/lib/jvm/temurin-8-jdk-amd64";
+  const jdk17 = "/usr/lib/jvm/temurin-17-jdk-amd64";
+  const jdk21 = "/usr/lib/jvm/temurin-21-jdk-amd64";
+
+  process.env[JavaEnvVars.JAVA_HOME] = jdk17;
+  process.env["JAVA_HOME_8_X64"] = jdk8;
+  process.env["JAVA_HOME_17_X64"] = jdk17;
+  process.env["JAVA_HOME_21_X64"] = jdk21;
+
+  const results = discoverActionsJdks();
+  t.is(results.size, 3);
+  t.true(results.has(jdk8));
+  t.true(results.has(jdk17));
+  t.true(results.has(jdk21));
+});
+
+test("checkJdkSettings - does not throw for an empty directory", async (t) => {
+  const messages: LoggedMessage[] = [];
+  const logger = getRecordingLogger(messages);
+
+  await withTmpDir(async (tmpDir) => {
+    t.notThrows(() => checkJdkSettings(logger, tmpDir));
+  });
+});
+
+test("checkJdkSettings - finds files and logs relevant properties", async (t) => {
+  const messages: LoggedMessage[] = [];
+  const logger = getRecordingLogger(messages);
+
+  await withTmpDir(async (tmpDir) => {
+    const dir = path.join(tmpDir, "conf");
+    fs.mkdirSync(dir);
+
+    const file = path.join(dir, "net.properties");
+    fs.writeFileSync(
+      file,
+      [
+        "irrelevant.property=foo",
+        "http.proxyHost=proxy.example.com",
+        "http.unrelated=bar",
+      ].join(os.EOL),
+      {},
+    );
+    checkJdkSettings(logger, tmpDir);
+
+    checkExpectedLogMessages(t, messages, [
+      `Found '${file}'.`,
+      `Found 'http.proxyHost=proxy.example.com' in '${file}'`,
+    ]);
+  });
+});
+
+test("checkProxyEnvVars - none set", (t) => {
+  const messages: LoggedMessage[] = [];
+  const logger = getRecordingLogger(messages);
+
+  checkProxyEnvVars(logger);
+  assertEnvVarLogMessages(t, Object.values(ProxyEnvVars), messages, false);
+});
+
+test("checkProxyEnvVars - logs values when variables are set", (t) => {
+  const messages: LoggedMessage[] = [];
+  const logger = getRecordingLogger(messages);
+
+  for (const envVar of Object.values(ProxyEnvVars)) {
+    process.env[envVar] = envVar;
+  }
+
+  checkProxyEnvVars(logger);
+  assertEnvVarLogMessages(t, Object.values(ProxyEnvVars), messages, true);
+});
+
+test("checkProxyEnvVars - credentials are removed from URLs", (t) => {
+  const messages: LoggedMessage[] = [];
+  const logger = getRecordingLogger(messages);
+
+  for (const envVar of Object.values(ProxyEnvVars)) {
+    process.env[envVar] = "https://secret:password@proxy.local";
+  }
+
+  checkProxyEnvVars(logger);
+  assertEnvVarLogMessages(
+    t,
+    Object.values(ProxyEnvVars),
+    messages,
+    "https://proxy.local/",
+  );
+});
+
+test("checkProxyEnvironment - includes base checks for all known languages", async (t) => {
+  stubToolrunner();
+
+  for (const language of Object.values(KnownLanguage)) {
+    const messages: LoggedMessage[] = [];
+    const logger = getRecordingLogger(messages);
+
+    await checkProxyEnvironment(logger, language);
+    assertEnvVarLogMessages(t, Object.keys(ProxyEnvVars), messages, false);
+  }
+});
+
+test("checkProxyEnvironment - includes Java checks for Java", async (t) => {
+  const messages: LoggedMessage[] = [];
+  const logger = getRecordingLogger(messages);
+
+  stubToolrunner();
+
+  await checkProxyEnvironment(logger, KnownLanguage.java);
+  assertEnvVarLogMessages(t, Object.keys(ProxyEnvVars), messages, false);
+  assertEnvVarLogMessages(t, JAVA_PROXY_ENV_VARS, messages, false);
+});
+
+test("checkProxyEnvironment - includes language-specific checks if the language is undefined", async (t) => {
+  const messages: LoggedMessage[] = [];
+  const logger = getRecordingLogger(messages);
+
+  stubToolrunner();
+
+  await checkProxyEnvironment(logger, undefined);
+  assertEnvVarLogMessages(t, Object.keys(ProxyEnvVars), messages, false);
+  assertEnvVarLogMessages(t, JAVA_PROXY_ENV_VARS, messages, false);
+});