Restructure the Kernel string table.

pkg/kernel/lib/binary/ast_from_binary.dart

 // Copyright (c) 2016, 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 kernel.ast_from_binary;
 
 import 'dart:convert';
 import 'dart:typed_data';
 
 import '../ast.dart';
 import '../transformations/flags.dart';
@@ skipping 12 matching lines @@
 
 class BinaryBuilder {
   final List<VariableDeclaration> variableStack = <VariableDeclaration>[];
   final List<LabeledStatement> labelStack = <LabeledStatement>[];
   int labelStackBase = 0;
   final List<SwitchCase> switchCaseStack = <SwitchCase>[];
   final List<TypeParameter> typeParameterStack = <TypeParameter>[];
   final String filename;
   final List<int> _bytes;
   int _byteIndex = 0;
-  List<String> _stringTable;
-  List<String> _sourceUriTable;
+  final List<String> _stringTable = <String>[];
+  final List<String> _sourceUriTable = <String>[];
   List<CanonicalName> _linkTable;
   int _transformerFlags = 0;
   Library _currentLibrary;
 
   // If something goes wrong, this list should indicate what library,
   // class, and member was being built.
   List<String> debugPath = <String>[];
 
   bool _isReadingLibraryImplementation = false;
 
@@ skipping 30 matching lines @@
         readByte();
   }
 
   List<int> readUtf8Bytes() {
     List<int> bytes = new Uint8List(readUInt());
     bytes.setRange(0, bytes.length, _bytes, _byteIndex);
     _byteIndex += bytes.length;
     return bytes;
   }
 
-  String readStringEntry() {
-    int numBytes = readUInt();
+  String readStringEntry(int numBytes) {
     // Utf8Decoder will skip leading BOM characters, but we must preserve them.
     // Collect leading BOMs before passing the bytes onto Utf8Decoder.
     int numByteOrderMarks = 0;
     while (_byteIndex + 2 < _bytes.length &&
         _bytes[_byteIndex] == 0xef &&
         _bytes[_byteIndex + 1] == 0xbb &&
         _bytes[_byteIndex + 2] == 0xbf) {
       ++numByteOrderMarks;
       _byteIndex += 3;
       numBytes -= 3;
     }
     String string =
         const Utf8Decoder().convert(_bytes, _byteIndex, _byteIndex + numBytes);
     _byteIndex += numBytes;
     if (numByteOrderMarks > 0) {
       return '\ufeff' * numByteOrderMarks + string;
     }
     return string;
   }
 
-  void readStringTable() {
+  void readStringTable(List<String> table) {
+    // Read the table of end offsets.
     int length = readUInt();
-    _stringTable = new List<String>(length);
+    List<int> endOffsets = new List<int>(length);
     for (int i = 0; i < length; ++i) {
-      _stringTable[i] = readStringEntry();
+      endOffsets[i] = readUInt();
+    }
+    // Read the UTF-8 encoded strings.
+    table.length = length;
+    int startOffset = 0;
+    for (int i = 0; i < length; ++i) {
+      table[i] = readStringEntry(endOffsets[i] - startOffset);
+      startOffset = endOffsets[i];
     }
   }
 
   String readUriReference() {
     return _sourceUriTable[readUInt()];
   }
 
   void readSourceUriTable() {

[jensj, 2017/04/04 09:42:16]

This method isn't called anymore is it? It doesn't seem to match the description
of the binary either so that's probably a good thing.

[Kevin Millikin (Google), 2017/04/04 11:02:58]

You are right.  I've removed it.

     int length = readUInt();
     _sourceUriTable = new List<String>(length);
     for (int i = 0; i < length; ++i) {
-      _sourceUriTable[i] = readStringEntry();
+      int numBytes = readUInt();
+      _sourceUriTable[i] = readStringEntry(numBytes);
     }
   }
 
   String readStringReference() {
     return _stringTable[readUInt()];
   }
 
   String readStringOrNullIfEmpty() {
     var string = readStringReference();
     return string.isEmpty ? null : string;
@@ skipping 109 matching lines @@
       throw 'Unrecognized bytes following program data';
     }
   }
 
   void _readOneProgram(Program program) {
     int magic = readMagicWord();
     if (magic != Tag.ProgramFile) {
       throw fail('This is not a binary dart file. '
           'Magic number was: ${magic.toRadixString(16)}');
     }
-    readStringTable();
+    readStringTable(_stringTable);
     Map<String, Source> uriToSource = readUriToSource();
     program.uriToSource.addAll(uriToSource);
     readLinkTable(program.root);
     int numberOfLibraries = readUInt();
     List<Library> libraries = new List<Library>(numberOfLibraries);
     for (int i = 0; i < numberOfLibraries; ++i) {
       libraries[i] = readLibrary(program);
     }
     var mainMethod = readMemberReference(allowNull: true);
     program.mainMethodName ??= mainMethod;
   }
 
   Map<String, Source> readUriToSource() {
-    readSourceUriTable();
+    readStringTable(_sourceUriTable);
     int length = _sourceUriTable.length;
     Map<String, Source> uriToSource = <String, Source>{};
     for (int i = 0; i < length; ++i) {
       String uri = _sourceUriTable[i];
       List<int> sourceCode = readUtf8Bytes();
       int lineCount = readUInt();
       List<int> lineStarts = new List<int>(lineCount);
       int previousLineStart = 0;
       for (int j = 0; j < lineCount; ++j) {
         int lineStart = readUInt() + previousLineStart;
@@ skipping 847 matching lines @@
       ..fileOffset = offset
       ..fileEqualsOffset = fileEqualsOffset;
   }
 
   int readOffset() {
     // Offset is saved as unsigned,
     // but actually ranges from -1 and up (thus the -1)
     return readUInt() - 1;
   }
 }