| |
| var Match = require ('../match'); |
| |
| /** |
| * Charset recognizer for UTF-8 |
| */ |
| module.exports = function() { |
| this.name = function() { |
| return 'UTF-8'; |
| }; |
| this.match = function(det) { |
| |
| var hasBOM = false, |
| numValid = 0, |
| numInvalid = 0, |
| input = det.fRawInput, |
| trailBytes = 0, |
| confidence; |
| |
| if (det.fRawLength >= 3 && |
| (input[0] & 0xff) == 0xef && (input[1] & 0xff) == 0xbb && (input[2] & 0xff) == 0xbf) { |
| hasBOM = true; |
| } |
| |
| // Scan for multi-byte sequences |
| for (var i = 0; i < det.fRawLength; i++) { |
| var b = input[i]; |
| if ((b & 0x80) == 0) |
| continue; // ASCII |
| |
| // Hi bit on char found. Figure out how long the sequence should be |
| if ((b & 0x0e0) == 0x0c0) { |
| trailBytes = 1; |
| } else if ((b & 0x0f0) == 0x0e0) { |
| trailBytes = 2; |
| } else if ((b & 0x0f8) == 0xf0) { |
| trailBytes = 3; |
| } else { |
| numInvalid++; |
| if (numInvalid > 5) |
| break; |
| trailBytes = 0; |
| } |
| |
| // Verify that we've got the right number of trail bytes in the sequence |
| for (;;) { |
| i++; |
| if (i >= det.fRawLength) |
| break; |
| |
| if ((input[i] & 0xc0) != 0x080) { |
| numInvalid++; |
| break; |
| } |
| if (--trailBytes == 0) { |
| numValid++; |
| break; |
| } |
| } |
| } |
| |
| // Cook up some sort of confidence score, based on presense of a BOM |
| // and the existence of valid and/or invalid multi-byte sequences. |
| confidence = 0; |
| if (hasBOM && numInvalid == 0) |
| confidence = 100; |
| else if (hasBOM && numValid > numInvalid * 10) |
| confidence = 80; |
| else if (numValid > 3 && numInvalid == 0) |
| confidence = 100; |
| else if (numValid > 0 && numInvalid == 0) |
| confidence = 80; |
| else if (numValid == 0 && numInvalid == 0) |
| // Plain ASCII. |
| confidence = 10; |
| else if (numValid > numInvalid * 10) |
| // Probably corruput utf-8 data. Valid sequences aren't likely by chance. |
| confidence = 25; |
| else |
| return null |
| |
| return new Match(det, this, confidence); |
| }; |
| }; |