1 files changed, 118 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/worker/ErrorMessage.java b/src/main/java/com/google/devtools/build/lib/worker/ErrorMessage.java
new file mode 100644
index 0000000000..343ad1d239
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/worker/ErrorMessage.java
@@ -0,0 +1,118 @@
+// Copyright 2017 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.worker;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.base.Preconditions;
+import com.google.common.base.Throwables;
+import com.google.devtools.build.lib.vfs.FileSystemUtils;
+import com.google.devtools.build.lib.vfs.Path;
+import java.io.IOException;
+
+/** A well-formatted error message that is easy to read and easy to create. */
+@AutoValue
+abstract class ErrorMessage {
+  abstract String message();
+
+  @Override
+  public String toString() {
+    return message();
+  }
+
+  public static Builder builder() {
+    return new Builder();
+  }
+
+  public static final class Builder {
+    private String message = "Unknown error";
+    private Path logFile;
+    private String logText = "";
+    private int logSizeLimit = Integer.MAX_VALUE;
+
+    private Builder() {}
+
+    /** Sets the main text of this error message. */
+    public Builder message(String message) {
+      Preconditions.checkNotNull(message);
+      this.message = message.isEmpty() ? "Unknown error" : message;
+      return this;
+    }
+
+    /** Sets the log file that should be printed as part of the error message. */
+    public Builder logFile(Path logFile) {
+      Preconditions.checkNotNull(logFile);
+      try {
+        this.logFile = logFile;
+        return logText(FileSystemUtils.readContent(logFile, UTF_8));
+      } catch (IOException e) {
+        logSizeLimit(Integer.MAX_VALUE);
+        return logText(
+            "ERROR: IOException while trying to read log file:\n"
+                + Throwables.getStackTraceAsString(e));
+      }
+    }
+
+    /**
+     * Sets additional text, which is to be presented as a log file in the error message.
+     *
+     * <p>If the log originally comes from a file, it is recommended to use {@link #logFile}
+     * instead, because then the path to the log file can be printed together with the message.
+     */
+    public Builder logText(String logText) {
+      Preconditions.checkNotNull(logText);
+      // Set the log text to "(empty)" when the passed in string is empty, otherwise error messages
+      // like "Something failed. Check below log for details:" would be pretty confusing for users.
+      this.logText = logText.isEmpty() ? "(empty)" : logText.trim();
+      return this;
+    }
+
+    /**
+     * If the log file or text of this error message is longer than the character limit set via this
+     * method, it will be truncated so that only the last X characters of the log are printed.
+     */
+    public Builder logSizeLimit(int logSizeLimit) {
+      Preconditions.checkArgument(logSizeLimit > 0, "logSizeLimit must be positive");
+      this.logSizeLimit = logSizeLimit;
+      return this;
+    }
+
+    /** Builds and returns the formatted error message. */
+    public ErrorMessage build() {
+      StringBuilder sb = new StringBuilder(message);
+      if (!logText.isEmpty()) {
+        sb.append("\n---8<---8<--- (start of log");
+        if (logFile != null) {
+          sb.append(", file at ");
+          sb.append(logFile.getPathString());
+        }
+        sb.append(") ---8<---8<---\n");
+        // If the length of the log is longer than the limit, print only the last part.
+        if (logText.length() > logSizeLimit) {
+          sb.append("[... truncated ...]\n");
+          sb.append(logText, logText.length() - logSizeLimit, logText.length());
+          sb.append("\n---8<---8<--- (end of log snippet, ");
+          sb.append(logText.length() - logSizeLimit);
+          sb.append(" chars omitted) ---8<---8<---");
+        } else {
+          sb.append(logText);
+          sb.append("\n---8<---8<--- (end of log) ---8<---8<---");
+        }
+      }
+      return new AutoValue_ErrorMessage(sb.toString());
+    }
+  }
+}