String encoding utility methods and tests for Unicode, UTF-8, -16 and -32.

utils/string_encoding/Utf16.dart

+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#library("UTF16");
+#import("UnicodeCore.dart");
+#import("Unicode.dart");
+
+/**
+ * Produce a String from a sequence of UTF16 encoded bytes.
+ */
+String decodeFromUtf16(List<int> bytes) {
+  List<int> codeUnits = _utf16ToUtf16CodeUnits(bytes);
+  // TODO is16BitCodeUnit() is used to work around a bug with frog/dartc
+  // (http://code.google.com/p/dart/issues/detail?id=1357). Consider
+  // removing after this issue is resolved.
+  if (is16BitCodeUnit()) {
+    return new String.fromCharCodes(codeUnits);
+  } else {
+    return new String.fromCharCodes(utf16CodeUnitsToCodepoints(codeUnits));
+  }
+}
+
+/**
+ * Produce a String from a sequence of UTF16-BE encoded bytes.
+ */
+String decodeFromUtf16be(List<int> bytes) {
+  List<int> codeUnits = _utf16beToUtf16CodeUnits(bytes);
+  // TODO is16BitCodeUnit() is used to work around a bug with frog/dartc
+  // (http://code.google.com/p/dart/issues/detail?id=1357). Consider
+  // removing after this issue is resolved.
+  if (is16BitCodeUnit()) {
+    return new String.fromCharCodes(codeUnits);
+  } else {
+    return new String.fromCharCodes(utf16CodeUnitsToCodepoints(codeUnits));
+  }
+}
+
+/**
+ * Produce a String from a sequence of UTF16-LE encoded bytes.
+ */
+String decodeFromUtf16le(List<int> bytes) {
+  List<int> codeUnits = _utf16leToUtf16CodeUnits(bytes);
+  // TODO is16BitCodeUnit() is used to work around a bug with frog/dartc
+  // (http://code.google.com/p/dart/issues/detail?id=1357). Consider
+  // removing after this issue is resolved.
+  if (is16BitCodeUnit()) {
+    return new String.fromCharCodes(codeUnits);
+  } else {
+    return new String.fromCharCodes(utf16CodeUnitsToCodepoints(codeUnits));
+  }
+}
+
+/**
+ * Produce a sequence of UTF16 encoded bytes.
+ */
+List<int> encodeAsUtf16(String str) => encodeAsUtf16be(str);
+
+/**
+ * Produce a sequence of UTF16-BE encoded bytes.
+ */
+List<int> encodeAsUtf16be(String str) {
+  List<int> utf16CodeUnits = _stringToUtf16CodeUnits(str);
+  List<int> encoding = <int>[0xfe, 0xff];
+  for (int unit in utf16CodeUnits) {
+    encoding.add((unit & 0xff00) >> 8);
+    encoding.add(unit & 0xff);
+  }
+  return encoding;
+}
+
+/**
+ * Produce a sequence of UTF16-LE encoded bytes.
+ */
+List<int> encodeAsUtf16le(String str) {
+  List<int> utf16CodeUnits = _stringToUtf16CodeUnits(str);
+  List<int> encoding = <int>[0xff, 0xfe];
+  for (int unit in utf16CodeUnits) {
+    encoding.add(unit & 0xff);
+    encoding.add((unit & 0xff00) >> 8);
+  }
+  return encoding;
+}
+
+List<int> _stringToUtf16CodeUnits(String str) {
+  List<int> codepoints = <int>[];
+  // TODO is16BitCodeUnit() is used to work around a bug with frog/dartc
+  // (http://code.google.com/p/dart/issues/detail?id=1357). Consider
+  // removing after this issue is resolved.
+  if (is16BitCodeUnit()) {
+    return str.charCodes();
+  } else {
+    return codepointsToUtf16CodeUnits(str.charCodes());
+  }
+}
+
+/**
+ * Convert UTF-16BE encoded bytes to utf16 code units by grouping 1-2 bytes
+ * to produce the code unit (0-(2^16)-1).
+ */
+List<int> _utf16beToUtf16CodeUnits(List<int> utf16beEncodedBytes,
+    [int start = 0, int length = - 1]) {
+  List<int> codeUnits = <int>[];
+  int end = length >= 0 ?
+      Math.min(utf16beEncodedBytes.length, start + length) :
+      utf16beEncodedBytes.length;
+  int i = start;
+  int lastIndex = end - 1;
+  while (i < lastIndex) {
+    int hi = utf16beEncodedBytes[i++];
+    int lo = utf16beEncodedBytes[i++];
+    codeUnits.add((hi * 256) + lo);
+  }
+  return codeUnits;
+}
+
+/**
+ * Convert UTF-16LE encoded bytes to utf16 code units by grouping 1-2 bytes
+ * to produce the code unit (0-(2^16)-1).
+ */
+List<int> _utf16leToUtf16CodeUnits(List<int> utf16leEncodedBytes,
+    [int start = 0, int length = - 1]) {
+  List<int> codeUnits = <int>[];
+  int end = length >= 0 ?
+      Math.min(utf16leEncodedBytes.length, start + length) :
+      utf16leEncodedBytes.length;
+  int i = start;
+  int lastIndex = end - 1;
+  while (i < lastIndex) {
+    int lo = utf16leEncodedBytes[i++];
+    int hi = utf16leEncodedBytes[i++];
+    codeUnits.add((hi * 256) + lo);
+  }
+  return codeUnits;
+}
+
+/**
+ * Convert UTF-16 encoded bytes to utf16 code units by grouping 1-2 bytes
+ * to produce the code unit (0-(2^16)-1). Relies on BOM to determine
+ * endian-ness, and defaults to BE.
+ */
+List<int> _utf16ToUtf16CodeUnits(List<int> utf16EncodedBytes,
+     [int start = 0, int length = - 1]) {
+   int end = length >= 0 ?
+       Math.min(utf16EncodedBytes.length, start + length) :
+       utf16EncodedBytes.length;
+
+  if((start + 1 < end) && utf16EncodedBytes[start] == 0xfe &&
+      utf16EncodedBytes[start + 1] == 0xff) {
+    return _utf16beToUtf16CodeUnits(utf16EncodedBytes, start + 2,
+        end - (start + 2));
+  } else if((start + 2 <= end) && utf16EncodedBytes[start] == 0xff &&
+      utf16EncodedBytes[start + 1] == 0xfe) {
+    return _utf16leToUtf16CodeUnits(utf16EncodedBytes, start + 2,
+        end - (start + 2));
+  } else {
+    return _utf16beToUtf16CodeUnits(utf16EncodedBytes, start, end - start);
+  }
+}