Moved utf8 border detect to utils, fixed bugs & added tests

lib/inflate.js

@@ -211,20 +211,7 @@ Inflate.prototype.push = function(data, mode) {
 
         if (this.options.to === 'string') {
 
-          // realign size to utf8 char border & move tail to start of buffer
-          next_out_utf8_index = strm.next_out_index - 6;
-          if (next_out_utf8_index < 0) { next_out_utf8_index = 0; }
-
-          tail = strings.utf8tail(strm.next_out[next_out_utf8_index]);
-          while (next_out_utf8_index + tail <= strm.next_out_index) {
-            next_out_utf8_index += tail;
-            tail = strings.utf8tail(strm.next_out[next_out_utf8_index]);
-          }
-
-          // shit happened - broken tail. then take it all.
-          if (next_out_utf8_index === 0) {
-            next_out_utf8_index = strm.next_out_index;
-          }
+          next_out_utf8_index = strings.utf8border(strm.next_out, strm.next_out_index);
 
           tail = strm.next_out_index - next_out_utf8_index;
           utf8str = strings.buf2string(strm.next_out, next_out_utf8_index);

lib/utils/strings.js

@@ -172,7 +172,29 @@ exports.buf2string = function (buf, max) {
 };
 
 
-// calculate tail size of utf8 char by current byte value
-exports.utf8tail = function(code) {
-  return _utf8len[code];
+// Calculate max possible position in utf8 buffer,
+// that will not break sequence. If that's not possible
+// - (very small limits) return max size as is.
+//
+// buf[] - utf8 bytes array
+// max   - length limit (mandatory);
+exports.utf8border = function(buf, max) {
+  var pos;
+
+  max = max || buf.length;
+  if (max > buf.length) { max = buf.length; }
+
+  // go back from last position, until start of sequence found
+  pos = max-1;
+  while (pos >= 0 && (buf[pos] & 0xC0) === 0x80) { pos--; }
+
+  // Fuckup - very small and broken sequence,
+  // return max, because we should return something anyway.
+  if (pos < 0) { return max; }
+
+  // If we came to start of buffer - that means vuffer is too small,
+  // return max too.
+  if (pos === 0) { return max; }
+
+  return (pos + _utf8len[buf[pos]] > max) ? pos : max;
 };

test/strings.js

@@ -40,11 +40,40 @@ function a2utf16(arr) {
 
 describe('Encode/Decode', function () {
 
-  var utf16sample = a2utf16([0x1f3b5, 'abcd', 0x266a, 0x35, 0xe800, 0x10ffff, 0x0fffff]);
+  // Create sample, that contains all types of utf8 (1-4byte) after conversion
+  var utf16sample = a2utf16([0x1f3b5, 'a', 0x266a, 0x35, 0xe800, 0x10ffff, 0x0fffff]);
+  // use node Buffer internal conversion as "done right"
   var utf8sample = new Uint8Array(new Buffer(utf16sample));
 
-  console.log(utf16sample, utf16sample.length);
-  console.log(new Buffer(utf16sample));
+  it('utf-8 border detect', function () {
+    var ub = strings.utf8border;
+    assert.equal(ub(utf8sample, 1), 1);
+    assert.equal(ub(utf8sample, 2), 2);
+    assert.equal(ub(utf8sample, 3), 3);
+    assert.equal(ub(utf8sample, 4), 4);
+
+    assert.equal(ub(utf8sample, 5), 5);
+
+    assert.equal(ub(utf8sample, 6), 5);
+    assert.equal(ub(utf8sample, 7), 5);
+    assert.equal(ub(utf8sample, 8), 8);
+
+    assert.equal(ub(utf8sample, 9), 9);
+
+    assert.equal(ub(utf8sample, 10), 9);
+    assert.equal(ub(utf8sample, 11), 9);
+    assert.equal(ub(utf8sample, 12), 12);
+
+    assert.equal(ub(utf8sample, 13), 12);
+    assert.equal(ub(utf8sample, 14), 12);
+    assert.equal(ub(utf8sample, 15), 12);
+    assert.equal(ub(utf8sample, 16), 16);
+
+    assert.equal(ub(utf8sample, 17), 16);
+    assert.equal(ub(utf8sample, 18), 16);
+    assert.equal(ub(utf8sample, 19), 16);
+    assert.equal(ub(utf8sample, 20), 20);
+  });
 
   it('Encode string to utf8 buf', function () {
     assert.ok(cmp(