Issue 16314. Skip leading UTF-8 BOM.

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/source/FileBasedSource.java

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/source/FileBasedSource.java
diff --git a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/source/FileBasedSource.java b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/source/FileBasedSource.java
index 1e1af482743980b8b80ec2ebe3ca738839260b62..92d271ccc39ef7f5a5951c2a6fbf05a4b8a8e36f 100644
--- a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/source/FileBasedSource.java
+++ b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/source/FileBasedSource.java
@@ -223,6 +223,7 @@ public class FileBasedSource implements Source {
       }
       if (byteBuffer != null) {
         byteBuffer.rewind();
+        skipOptionalBOM(byteBuffer);
         return new TimestampedData<CharSequence>(modificationTime, UTF_8_CHARSET.decode(byteBuffer));
       }
     } catch (IOException exception) {
@@ -235,7 +236,7 @@ public class FileBasedSource implements Source {
     InputStreamReader reader = null;
     String contents;
     try {
-      reader = new InputStreamReader(new FileInputStream(file), "UTF-8");
+      reader = new InputStreamReader(getFileInputStreamWithoutBOM(), "UTF-8");
       contents = FileUtilities.getContents(reader);
     } finally {
       if (reader != null) {
@@ -286,6 +287,7 @@ public class FileBasedSource implements Source {
       }
       if (byteBuffer != null) {
         byteBuffer.rewind();
+        skipOptionalBOM(byteBuffer);
         receiver.accept(UTF_8_CHARSET.decode(byteBuffer), modificationTime);
         return;
       }
@@ -299,7 +301,7 @@ public class FileBasedSource implements Source {
     InputStreamReader reader = null;
     String contents;
     try {
-      reader = new InputStreamReader(new FileInputStream(file), "UTF-8");
+      reader = new InputStreamReader(getFileInputStreamWithoutBOM(), "UTF-8");
       contents = FileUtilities.getContents(reader);
     } finally {
       if (reader != null) {
@@ -314,6 +316,21 @@ public class FileBasedSource implements Source {
   }
 
   /**
+   * Returns a {@link FileInputStream} for the {@link #file} with skipped optional leading UTF-8
+   * BOM.
+   */
+  private FileInputStream getFileInputStreamWithoutBOM() throws Exception {
+    FileInputStream in = new FileInputStream(file);
+    // check if there is an UTF-8 BOM
+    if (in.read() == (byte) 0xEF && in.read() == (byte) 0xBB && in.read() == (byte) 0xBF) {
+      return in;
+    }
+    // re-open scream

[Brian Wilkerson, 2014/05/07 20:26:57]

"scream" --> "stream"

+    in.close();
+    return new FileInputStream(file);
+  }
+
+  /**
    * Record the time the IO took if it was slow
    */
   private void reportIfSlowIO(long nanos) {
@@ -328,4 +345,14 @@ public class FileBasedSource implements Source {
       }
     }
   }
+
+  /**
+   * Skips an optional UTF-8 BOM.
+   */
+  private void skipOptionalBOM(ByteBuffer byteBuffer) {
+    if (byteBuffer.remaining() >= 3 && byteBuffer.get(0) == (byte) 0xEF
+        && byteBuffer.get(1) == (byte) 0xBB && byteBuffer.get(2) == (byte) 0xBF) {
+      byteBuffer.position(3);
+    }
+  }
 }