Propagate the error message when a credential helper fails.

src/main/java/com/google/devtools/build/lib/authandtls/credentialhelper/CredentialHelper.java

@@ -77,15 +77,15 @@ public GetCredentialsResponse getCredentials(CredentialHelperEnvironment environ
 
       process.waitFor();
       if (process.timedout()) {
-        throw new IOException(
+        throw new CredentialHelperException(
             String.format(
                 Locale.US,
                 "Failed to get credentials for '%s' from helper '%s': process timed out",
                 uri,
                 path));
       }
       if (process.exitValue() != 0) {
-        throw new IOException(
+        throw new CredentialHelperException(
             String.format(
                 Locale.US,
                 "Failed to get credentials for '%s' from helper '%s': process exited with code %d."
@@ -99,7 +99,7 @@ public GetCredentialsResponse getCredentials(CredentialHelperEnvironment environ
       try {
         GetCredentialsResponse response = GSON.fromJson(stdout, GetCredentialsResponse.class);
         if (response == null) {
-          throw new IOException(
+          throw new CredentialHelperException(
               String.format(
                   Locale.US,
                   "Failed to get credentials for '%s' from helper '%s': process exited without"
@@ -110,7 +110,7 @@ public GetCredentialsResponse getCredentials(CredentialHelperEnvironment environ
         }
         return response;
       } catch (JsonSyntaxException e) {
-        throw new IOException(
+        throw new CredentialHelperException(
             String.format(
                 Locale.US,
                 "Failed to get credentials for '%s' from helper '%s': error parsing output. stderr:"

src/main/java/com/google/devtools/build/lib/authandtls/credentialhelper/CredentialHelperException.java

@@ -0,0 +1,26 @@
+// Copyright 2022 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.build.lib.authandtls.credentialhelper;
+
+/** An {@link Exception} thrown while invoking a credential helper. */
+public class CredentialHelperException extends RuntimeException {
+  public CredentialHelperException(String message) {
+    super(message);
+  }
+
+  public CredentialHelperException(String message, Throwable cause) {
+    super(message, cause);
+  }
+}

src/main/java/com/google/devtools/build/lib/remote/util/BUILD

@@ -19,6 +19,7 @@ java_library(
         "//src/main/java/com/google/devtools/build/lib/actions:execution_requirements",
         "//src/main/java/com/google/devtools/build/lib/analysis:blaze_version_info",
         "//src/main/java/com/google/devtools/build/lib/authandtls",
+        "//src/main/java/com/google/devtools/build/lib/authandtls/credentialhelper",
         "//src/main/java/com/google/devtools/build/lib/cmdline",
         "//src/main/java/com/google/devtools/build/lib/remote:ExecutionStatusException",
         "//src/main/java/com/google/devtools/build/lib/remote/common",

src/main/java/com/google/devtools/build/lib/remote/util/Utils.java

@@ -39,6 +39,7 @@
 import com.google.devtools.build.lib.actions.SpawnResult;
 import com.google.devtools.build.lib.actions.Spawns;
 import com.google.devtools.build.lib.authandtls.CallCredentialsProvider;
+import com.google.devtools.build.lib.authandtls.credentialhelper.CredentialHelperException;
 import com.google.devtools.build.lib.remote.ExecutionStatusException;
 import com.google.devtools.build.lib.remote.common.BulkTransferException;
 import com.google.devtools.build.lib.remote.common.CacheNotFoundException;
@@ -387,6 +388,7 @@ private static String executionStatusExceptionErrorMessage(ExecutionStatusExcept
   public static String grpcAwareErrorMessage(IOException e) {
     io.grpc.Status errStatus = io.grpc.Status.fromThrowable(e);
     if (e.getCause() instanceof ExecutionStatusException) {
+      // Display error message returned by the remote service.
       try {
         return "Remote Execution Failure:\n"
             + executionStatusExceptionErrorMessage((ExecutionStatusException) e.getCause());
@@ -398,9 +400,20 @@ public static String grpcAwareErrorMessage(IOException e) {
       }
     }
     if (!errStatus.getCode().equals(io.grpc.Status.UNKNOWN.getCode())) {
-      // If the error originated in the gRPC library then display it as "STATUS: error message"
-      // to the user
-      return String.format("%s: %s", errStatus.getCode().name(), errStatus.getDescription());
+      // Display error message returned by the gRPC library, prefixed by the status code.
+      StringBuilder sb = new StringBuilder();
+      sb.append(errStatus.getCode().name());
+      sb.append(": ");
+      sb.append(errStatus.getDescription());
+      // If the error originated from a credential helper, print additional debugging information.
+      for (Throwable t = errStatus.getCause(); t != null; t = t.getCause()) {
+        if (t instanceof CredentialHelperException) {
+          sb.append(": ");
+          sb.append(t.getMessage());
+          break;
+        }
+      }
+      return sb.toString();
     }
     return e.getMessage();
   }