string_decoder: Improve test coverage

The test cases are still essentially the same, but now all possible ways
of writing a buffer into the decoder are tested, which has exposed a few
failing scenarios that had not been discovered so far!

test/simple/test-string-decoder.js

@@ -22,109 +22,14 @@
 var common = require('../common');
 var assert = require('assert');
 var StringDecoder = require('string_decoder').StringDecoder;
-var decoder = new StringDecoder('utf8');
-
-
-
-var buffer = new Buffer('$');
-assert.deepEqual('$', decoder.write(buffer));
-
-buffer = new Buffer('¢');
-assert.deepEqual('', decoder.write(buffer.slice(0, 1)));
-assert.deepEqual('¢', decoder.write(buffer.slice(1, 2)));
-
-buffer = new Buffer('€');
-assert.deepEqual('', decoder.write(buffer.slice(0, 1)));
-assert.deepEqual('', decoder.write(buffer.slice(1, 2)));
-assert.deepEqual('€', decoder.write(buffer.slice(2, 3)));
-
-buffer = new Buffer([0xF0, 0xA4, 0xAD, 0xA2]);
-var s = '';
-s += decoder.write(buffer.slice(0, 1));
-s += decoder.write(buffer.slice(1, 2));
-s += decoder.write(buffer.slice(2, 3));
-s += decoder.write(buffer.slice(3, 4));
-assert.ok(s.length > 0);
-
-// CESU-8
-buffer = new Buffer('EDA0BDEDB18D', 'hex'); // THUMBS UP SIGN (in CESU-8)
-var s = '';
-s += decoder.write(buffer.slice(0, 1));
-s += decoder.write(buffer.slice(1, 2));
-s += decoder.write(buffer.slice(2, 3)); // complete lead surrogate
-assert.equal(s, '');
-s += decoder.write(buffer.slice(3, 4));
-s += decoder.write(buffer.slice(4, 5));
-s += decoder.write(buffer.slice(5, 6)); // complete trail surrogate
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
-
-var s = '';
-s += decoder.write(buffer.slice(0, 2));
-s += decoder.write(buffer.slice(2, 4)); // complete lead surrogate
-assert.equal(s, '');
-s += decoder.write(buffer.slice(4, 6)); // complete trail surrogate
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
-
-var s = '';
-s += decoder.write(buffer.slice(0, 3)); // complete lead surrogate
-assert.equal(s, '');
-s += decoder.write(buffer.slice(3, 6)); // complete trail surrogate
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
-
-var s = '';
-s += decoder.write(buffer.slice(0, 4)); // complete lead surrogate
-assert.equal(s, '');
-s += decoder.write(buffer.slice(4, 5));
-s += decoder.write(buffer.slice(5, 6)); // complete trail surrogate
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
-
-var s = '';
-s += decoder.write(buffer.slice(0, 5)); // complete lead surrogate
-assert.equal(s, '');
-s += decoder.write(buffer.slice(5, 6)); // complete trail surrogate
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
-
-var s = '';
-s += decoder.write(buffer.slice(0, 6));
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
-
-
-// UCS-2
-decoder = new StringDecoder('ucs2');
-buffer = new Buffer('ab', 'ucs2');
-assert.equal(decoder.write(buffer), 'ab'); // 2 complete chars
-buffer = new Buffer('abc', 'ucs2');
-assert.equal(decoder.write(buffer.slice(0, 3)), 'a'); // 'a' and first of 'b'
-assert.equal(decoder.write(buffer.slice(3, 6)), 'bc'); // second of 'b' and 'c'
-
-
-// UTF-16LE
-buffer = new Buffer('3DD84DDC', 'hex'); // THUMBS UP SIGN (in CESU-8)
-var s = '';
-s += decoder.write(buffer.slice(0, 1));
-s += decoder.write(buffer.slice(1, 2)); // complete lead surrogate
-assert.equal(s, '');
-s += decoder.write(buffer.slice(2, 3));
-s += decoder.write(buffer.slice(3, 4)); // complete trail surrogate
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
-
-var s = '';
-s += decoder.write(buffer.slice(0, 2)); // complete lead surrogate
-assert.equal(s, '');
-s += decoder.write(buffer.slice(2, 4)); // complete trail surrogate
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
-
-var s = '';
-s += decoder.write(buffer.slice(0, 3)); // complete lead surrogate
-assert.equal(s, '');
-s += decoder.write(buffer.slice(3, 4)); // complete trail surrogate
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
-
-var s = '';
-s += decoder.write(buffer.slice(0, 4));
-assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
 
+process.stdout.write('scanning ');
 
+// UTF-8
+test('utf-8', new Buffer('$', 'utf-8'), '$');
+test('utf-8', new Buffer('¢', 'utf-8'), '¢');
+test('utf-8', new Buffer('€', 'utf-8'), '€');
+test('utf-8', new Buffer('𤭢', 'utf-8'), '𤭢');
 // A mixed ascii and non-ascii string
 // Test stolen from deps/v8/test/cctest/test-strings.cc
 // U+02E4 -> CB A4
@@ -132,32 +37,86 @@ assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
 // U+12E4 -> E1 8B A4
 // U+0030 -> 30
 // U+3045 -> E3 81 85
-var expected = '\u02e4\u0064\u12e4\u0030\u3045';
-var buffer = new Buffer([0xCB, 0xA4, 0x64, 0xE1, 0x8B, 0xA4,
-                         0x30, 0xE3, 0x81, 0x85]);
-var charLengths = [0, 0, 1, 2, 2, 2, 3, 4, 4, 4, 5, 5];
+test(
+  'utf-8',
+  new Buffer([0xCB, 0xA4, 0x64, 0xE1, 0x8B, 0xA4, 0x30, 0xE3, 0x81, 0x85]),
+  '\u02e4\u0064\u12e4\u0030\u3045'
+);
 
-// Split the buffer into 3 segments
-//  |----|------|-------|
-//  0    i      j       buffer.length
-// Scan through every possible 3 segment combination
-// and make sure that the string is always parsed.
-common.print('scanning ');
-for (var j = 2; j < buffer.length; j++) {
-  for (var i = 1; i < j; i++) {
-    var decoder = new StringDecoder('utf8');
+// CESU-8
+test('utf-8', new Buffer('EDA0BDEDB18D', 'hex'), '\ud83d\udc4d'); // thumbs up
 
-    var sum = decoder.write(buffer.slice(0, i));
+// UCS-2
+test('ucs2', new Buffer('ababc', 'ucs2'), 'ababc');
 
-    // just check that we've received the right amount
-    // after the first write
-    assert.equal(charLengths[i], sum.length);
+// UTF-16LE
+test('ucs2', new Buffer('3DD84DDC', 'hex'),  '\ud83d\udc4d'); // thumbs up
+
+console.log(' crayon!');
 
-    sum += decoder.write(buffer.slice(i, j));
-    sum += decoder.write(buffer.slice(j, buffer.length));
-    assert.equal(expected, sum);
-    common.print('.');
+// test verifies that StringDecoder will correctly decode the given input
+// buffer with the given encoding to the expected output. It will attempt all
+// possible ways to write() the input buffer, see writeSequences(). The
+// singleSequence allows for easy debugging of a specific sequence which is
+// useful in case of test failures.
+function test(encoding, input, expected, singleSequence) {
+  var sequences;
+  if (!singleSequence) {
+    sequences = writeSequences(input.length);
+  } else {
+    sequences = [singleSequence];
   }
+  sequences.forEach(function(sequence) {
+    var decoder = new StringDecoder(encoding);
+    var output = '';
+    sequence.forEach(function(write) {
+      output += decoder.write(input.slice(write[0], write[1]));
+    });
+    process.stdout.write('.');
+    if (output !== expected) {
+      var message =
+        'Expected "'+unicodeEscape(expected)+'", '+
+        'but got "'+unicodeEscape(output)+'"\n'+
+        'Write sequence: '+JSON.stringify(sequence)+'\n'+
+        'Decoder charBuffer: 0x'+decoder.charBuffer.toString('hex')+'\n'+
+        'Full Decoder State: '+JSON.stringify(decoder, null, 2);
+      assert.fail(output, expected, message);
+    }
+  });
+}
+
+// unicodeEscape prints the str contents as unicode escape codes.
+function unicodeEscape(str) {
+  var r = '';
+  for (var i = 0; i < str.length; i++) {
+    r += '\\u'+str.charCodeAt(i).toString(16);
+  }
+  return r;
+}
+
+// writeSequences returns an array of arrays that describes all possible ways a
+// buffer of the given length could be split up and passed to sequential write
+// calls.
+//
+// e.G. writeSequences(3) will return: [
+//   [ [ 0, 3 ] ],
+//   [ [ 0, 2 ], [ 2, 3 ] ],
+//   [ [ 0, 1 ], [ 1, 3 ] ],
+//   [ [ 0, 1 ], [ 1, 2 ], [ 2, 3 ] ]
+// ]
+function writeSequences(length, start, sequence) {
+  if (start === undefined) {
+    start = 0;
+    sequence = []
+  } else if (start === length) {
+    return [sequence];
+  }
+  var sequences = [];
+  for (var end = length; end > start; end--) {
+    var subSequence = sequence.concat([[start, end]]);
+    var subSequences = writeSequences(length, end, subSequence, sequences);
+    sequences = sequences.concat(subSequences);
+  }
+  return sequences;
 }
-console.log(' crayon!');