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

utils/string_encoding/unicode_core.dart

+// Copyright (c) 2012, 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("unicode_core");
+
+/*
+ * Test for presence of bug related to the use of UTF-16 code units for
+ * Dart compiled to JS.
+ */
+bool _test16BitCodeUnit = null;
+// 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.
+bool is16BitCodeUnit() {
+  if (_test16BitCodeUnit == null) {
+    _test16BitCodeUnit = (new String.fromCharCodes([0x1D11E])) ==
+        (new String.fromCharCodes([0xD11E]));
+  }
+  return _test16BitCodeUnit;
+}
+
+/**
+ * Invalid codepoints or encodings may be substituted with the value U+fffd.
+ */
+final int UNICODE_REPLACEMENT_CHARACTER_CODEPOINT = 0xfffd;
+final int UNICODE_BOM = 0xfeff;
+final int UNICODE_UTF_BOM_LO = 0xff;
+final int UNICODE_UTF_BOM_HI = 0xfe;
+
+final int UNICODE_BYTE_ZERO_MASK = 0xff;
+final int UNICODE_BYTE_ONE_MASK = 0xff00;
+final int UNICODE_VALID_RANGE_MAX = 0x10ffff;
+final int UNICODE_PLANE_ONE_MAX = 0xffff;
+final int UNICODE_UTF16_RESERVED_LO = 0xd800;
+final int UNICODE_UTF16_RESERVED_HI = 0xdfff;
+final int UNICODE_UTF16_OFFSET = 0x10000;
+final int UNICODE_UTF16_SURROGATE_UNIT_0_BASE = 0xd800;
+final int UNICODE_UTF16_SURROGATE_UNIT_1_BASE = 0xdc00;
+final int UNICODE_UTF16_HI_MASK = 0xffc00;
+final int UNICODE_UTF16_LO_MASK = 0x3ff;
+
+/**
+ * Encode code points as UTF16 code units.
+ */
+List<int> codepointsToUtf16CodeUnits(
+    List<int> codepoints, [int offset = 0, int length,
+    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
+  if (!(offset >= 0)) {
+    throw new IllegalArgumentException("offset");
+  }
+
+  if (!(length == null || length >= 0)) {
+    throw new IllegalArgumentException("length");
+  }
+
+  int end = length != null ?
+      Math.min(codepoints.length, offset + length) :
+      codepoints.length;
+
+  int encodedLength = 0;
+  for (int i = offset; i < end; i++) {
+    int value = codepoints[i];
+    if ((value >= 0 && value < UNICODE_UTF16_RESERVED_LO) || 
+        (value > UNICODE_UTF16_RESERVED_HI && value <= UNICODE_PLANE_ONE_MAX)) {
+      encodedLength++;
+    } else if (value > UNICODE_PLANE_ONE_MAX && 
+        value <= UNICODE_VALID_RANGE_MAX) {
+      encodedLength += 2;
+    } else {
+      encodedLength++;
+    }
+  }
+  
+  void addReplacementCodepoint(List<int> codepointBuffer, int offset,
+      int replacementCodepoint) {
+    if(replacementCodepoint != null) {
+      codepointBuffer[offset] = replacementCodepoint;
+    } else {
+      throw new IllegalArgumentException("Invalid encoding");
+    }
+  }
+  List<int> codeUnitsBuffer = new List<int>(encodedLength);
+  int j = 0;
+  for (int i = offset; i < end; i++) {
+    int value = codepoints[i];
+    if ((value >= 0 && value < UNICODE_UTF16_RESERVED_LO) || 
+        (value > UNICODE_UTF16_RESERVED_HI && value <= UNICODE_PLANE_ONE_MAX)) {
+      codeUnitsBuffer[j++] = value;
+    } else if (value > UNICODE_PLANE_ONE_MAX && 
+        value <= UNICODE_VALID_RANGE_MAX) {
+      int base = value - UNICODE_UTF16_OFFSET;
+      codeUnitsBuffer[j++] = UNICODE_UTF16_SURROGATE_UNIT_0_BASE +
+          ((base & UNICODE_UTF16_HI_MASK) >> 10);
+      codeUnitsBuffer[j++] = UNICODE_UTF16_SURROGATE_UNIT_1_BASE +
+          (base & UNICODE_UTF16_LO_MASK);
+    } else {
+      addReplacementCodepoint(codeUnitsBuffer, j++, replacementCodepoint);
+    }
+  }
+  return codeUnitsBuffer;
+}
+
+/**
+ * Decodes the utf16 codeunits to codepoints.
+ */
+List<int> utf16CodeUnitsToCodepoints(
+    List<int> utf16CodeUnits, [int offset = 0, int length,
+    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
+  if (!(offset >= 0)) {
+    throw new IllegalArgumentException("offset");
+  }
+
+  if (!(length == null || length >= 0)) {
+    throw new IllegalArgumentException("length");
+  }
+
+  int end = length != null ?
+      Math.min(utf16CodeUnits.length, offset + length) :
+      utf16CodeUnits.length;
+
+  void addReplacementCodepoint(void f(int v), int replacementCodepoint) {
+    if(replacementCodepoint != null) {
+      f(replacementCodepoint);
+    } else {
+      throw new IllegalArgumentException("Invalid encoding");
+    }
+  }
+
+  void apply(void f(int v)) {
+    int i = offset;
+    // skip the first entry if it is a BOM.
+    if (end > 0 && utf16CodeUnits[0] == UNICODE_BOM) {
+      i++;
+    }
+    while (i < end) {
+      int value = utf16CodeUnits[i++];
+      if (value < 0) {
+        addReplacementCodepoint(f, replacementCodepoint);
+        continue;
+      }
+      if (value < UNICODE_UTF16_RESERVED_LO || 
+          (value > UNICODE_UTF16_RESERVED_HI &&
+          value <= UNICODE_PLANE_ONE_MAX)) {
+        // transfer directly
+        f(value);
+      } else if (value < UNICODE_UTF16_SURROGATE_UNIT_1_BASE && i < end) {
+        // merge surrogate pair
+        int nextValue = utf16CodeUnits[i++];
+        if (nextValue >= UNICODE_UTF16_SURROGATE_UNIT_1_BASE && 
+            nextValue <= UNICODE_UTF16_RESERVED_HI) {
+          value = (value - UNICODE_UTF16_SURROGATE_UNIT_0_BASE) << 10;
+          value += UNICODE_UTF16_OFFSET +
+              (nextValue - UNICODE_UTF16_SURROGATE_UNIT_1_BASE);
+          f(value);
+        } else {
+          if (nextValue >= UNICODE_UTF16_SURROGATE_UNIT_0_BASE &&
+             nextValue < UNICODE_UTF16_SURROGATE_UNIT_1_BASE) {
+            i--;
+          }
+          addReplacementCodepoint(f, replacementCodepoint);
+          continue;
+        }
+      } else {
+        addReplacementCodepoint(f, replacementCodepoint);
+        continue;
+      }
+    }
+  }
+  int codepointBufferLength = 0;
+  apply(void _(int value) {
+      codepointBufferLength++;
+  });
+
+  List<int> codepointBuffer = new List<int>(codepointBufferLength);
+  int i = 0;
+  apply(void _(int value) {
+      codepointBuffer[i++] = value;
+  });
+  return codepointBuffer;
+}