85 lines
2.1 KiB
JavaScript
85 lines
2.1 KiB
JavaScript
|
|
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);
|
|
};
|
|
};
|