Add vfs.SearchPath for searching binaries.

--
MOS_MIGRATED_REVID=95097699

1 files changed, 69 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/vfs/SearchPath.java b/src/main/java/com/google/devtools/build/lib/vfs/SearchPath.java
new file mode 100644
index 0000000000..8bb59b98ff
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/vfs/SearchPath.java
@@ -0,0 +1,69 @@
+// Copyright 2015 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.vfs;
+
+import com.google.common.base.Splitter;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.annotation.Nullable;
+
+/**
+ * Parse and search $PATH, the binary search path for executables.
+ */
+public class SearchPath {
+  private static final Splitter SEPARATOR = Splitter.on(':');
+
+  /**
+   * Parses a $PATH value into a list of paths. A Null search path is treated as an empty one.
+   */
+  public static List<Path> parse(FileSystem fs, @Nullable String searchPath) {
+    List<Path> paths = new ArrayList<>();
+    if (searchPath == null) {
+      return paths;
+    }
+    for (String p : SEPARATOR.split(searchPath)) {
+      paths.add(fs.getPath(p));
+    }
+    return paths;
+  }
+
+  /**
+   * Finds the first executable called {@code exe} in the searchPath.
+   * If {@code exe} is not a basename, it will always return null. This should be equivalent to
+   * running which(1).
+   */
+  @Nullable
+  public static Path which(List<Path> searchPath, String exe) {
+    PathFragment fragment = new PathFragment(exe);
+    if (fragment.segmentCount() != 1 || fragment.isAbsolute()) {
+      return null;
+    }
+
+    for (Path p : searchPath) {
+      Path ch = p.getChild(exe);
+
+      try {
+        if (ch.exists() && ch.isExecutable()) {
+          return ch;
+        }
+      } catch (IOException e) {
+        // Like which(1), we ignore any IO exception (disk on fire, permission denied etc.)
+      }
+    }
+    return null;
+  }
+}