1 files changed, 66 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/FileContentsProxy.java b/src/main/java/com/google/devtools/build/lib/skyframe/FileContentsProxy.java
new file mode 100644
index 0000000000..344c364e08
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+++ b/src/main/java/com/google/devtools/build/lib/skyframe/FileContentsProxy.java
@@ -0,0 +1,66 @@
+// Copyright 2014 Google Inc. 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.skyframe;
+
+import java.io.Serializable;
+import java.util.Objects;
+
+/**
+ * In case we can't get a fast digest from the filesystem, we store this metadata as a proxy to
+ * the file contents. Currently it is a pair of the mtime and "value id" (which is right now just
+ * the ivalue number). We may wish to augment this object with the following data:
+ * a. the device number
+ * b. the ctime, which cannot be tampered with in userspace
+ *
+ * <p>For an example of why mtime alone is insufficient, note that 'mv' preserves timestamps. So if
+ * files 'a' and 'b' initially have the same timestamp, then we would think 'b' is unchanged after
+ * the user executes `mv a b` between two builds.
+ */
+public final class FileContentsProxy implements Serializable {
+  private final long mtime;
+  private final long valueId;
+
+  private FileContentsProxy(long mtime, long valueId) {
+    this.mtime = mtime;
+    this.valueId = valueId;
+  }
+
+  public static FileContentsProxy create(long mtime, long valueId) {
+    return new FileContentsProxy(mtime, valueId);
+  }
+
+  @Override
+  public boolean equals(Object other) {
+    if (other == this) {
+      return true;
+    }
+
+    if (!(other instanceof FileContentsProxy)) {
+      return false;
+    }
+
+    FileContentsProxy that = (FileContentsProxy) other;
+    return mtime == that.mtime && valueId == that.valueId;
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(mtime, valueId);
+  }
+
+  @Override
+  public String toString() {
+    return "mtime: " + mtime + " valueId: " + valueId;
+  }
+}