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'use strict';
/*
Based heavily on the Streaming Boyer-Moore-Horspool C++ implementation
by Hongli Lai at: https://github.com/FooBarWidget/boyer-moore-horspool
*/
function memcmp(buf1, pos1, buf2, pos2, num) {
for (let i = 0; i < num; ++i) {
if (buf1[pos1 + i] !== buf2[pos2 + i])
return false;
}
return true;
}
class SBMH {
constructor(needle, cb) {
if (typeof cb !== 'function')
throw new Error('Missing match callback');
if (typeof needle === 'string')
needle = Buffer.from(needle);
else if (!Buffer.isBuffer(needle))
throw new Error(`Expected Buffer for needle, got ${typeof needle}`);
const needleLen = needle.length;
this.maxMatches = Infinity;
this.matches = 0;
this._cb = cb;
this._lookbehindSize = 0;
this._needle = needle;
this._bufPos = 0;
this._lookbehind = Buffer.allocUnsafe(needleLen);
// Initialize occurrence table.
this._occ = [
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen, needleLen, needleLen,
needleLen, needleLen, needleLen, needleLen
];
// Populate occurrence table with analysis of the needle, ignoring the last
// letter.
if (needleLen > 1) {
for (let i = 0; i < needleLen - 1; ++i)
this._occ[needle[i]] = needleLen - 1 - i;
}
}
reset() {
this.matches = 0;
this._lookbehindSize = 0;
this._bufPos = 0;
}
push(chunk, pos) {
let result;
if (!Buffer.isBuffer(chunk))
chunk = Buffer.from(chunk, 'latin1');
const chunkLen = chunk.length;
this._bufPos = pos || 0;
while (result !== chunkLen && this.matches < this.maxMatches)
result = feed(this, chunk);
return result;
}
destroy() {
const lbSize = this._lookbehindSize;
if (lbSize)
this._cb(false, this._lookbehind, 0, lbSize, false);
this.reset();
}
}
function feed(self, data) {
const len = data.length;
const needle = self._needle;
const needleLen = needle.length;
// Positive: points to a position in `data`
// pos == 3 points to data[3]
// Negative: points to a position in the lookbehind buffer
// pos == -2 points to lookbehind[lookbehindSize - 2]
let pos = -self._lookbehindSize;
const lastNeedleCharPos = needleLen - 1;
const lastNeedleChar = needle[lastNeedleCharPos];
const end = len - needleLen;
const occ = self._occ;
const lookbehind = self._lookbehind;
if (pos < 0) {
// Lookbehind buffer is not empty. Perform Boyer-Moore-Horspool
// search with character lookup code that considers both the
// lookbehind buffer and the current round's haystack data.
//
// Loop until
// there is a match.
// or until
// we've moved past the position that requires the
// lookbehind buffer. In this case we switch to the
// optimized loop.
// or until
// the character to look at lies outside the haystack.
while (pos < 0 && pos <= end) {
const nextPos = pos + lastNeedleCharPos;
const ch = (nextPos < 0
? lookbehind[self._lookbehindSize + nextPos]
: data[nextPos]);
if (ch === lastNeedleChar
&& matchNeedle(self, data, pos, lastNeedleCharPos)) {
self._lookbehindSize = 0;
++self.matches;
if (pos > -self._lookbehindSize)
self._cb(true, lookbehind, 0, self._lookbehindSize + pos, false);
else
self._cb(true, undefined, 0, 0, true);
return (self._bufPos = pos + needleLen);
}
pos += occ[ch];
}
// No match.
// There's too few data for Boyer-Moore-Horspool to run,
// so let's use a different algorithm to skip as much as
// we can.
// Forward pos until
// the trailing part of lookbehind + data
// looks like the beginning of the needle
// or until
// pos == 0
while (pos < 0 && !matchNeedle(self, data, pos, len - pos))
++pos;
if (pos < 0) {
// Cut off part of the lookbehind buffer that has
// been processed and append the entire haystack
// into it.
const bytesToCutOff = self._lookbehindSize + pos;
if (bytesToCutOff > 0) {
// The cut off data is guaranteed not to contain the needle.
self._cb(false, lookbehind, 0, bytesToCutOff, false);
}
self._lookbehindSize -= bytesToCutOff;
lookbehind.copy(lookbehind, 0, bytesToCutOff, self._lookbehindSize);
lookbehind.set(data, self._lookbehindSize);
self._lookbehindSize += len;
self._bufPos = len;
return len;
}
// Discard lookbehind buffer.
self._cb(false, lookbehind, 0, self._lookbehindSize, false);
self._lookbehindSize = 0;
}
pos += self._bufPos;
const firstNeedleChar = needle[0];
// Lookbehind buffer is now empty. Perform Boyer-Moore-Horspool
// search with optimized character lookup code that only considers
// the current round's haystack data.
while (pos <= end) {
const ch = data[pos + lastNeedleCharPos];
if (ch === lastNeedleChar
&& data[pos] === firstNeedleChar
&& memcmp(needle, 0, data, pos, lastNeedleCharPos)) {
++self.matches;
if (pos > 0)
self._cb(true, data, self._bufPos, pos, true);
else
self._cb(true, undefined, 0, 0, true);
return (self._bufPos = pos + needleLen);
}
pos += occ[ch];
}
// There was no match. If there's trailing haystack data that we cannot
// match yet using the Boyer-Moore-Horspool algorithm (because the trailing
// data is less than the needle size) then match using a modified
// algorithm that starts matching from the beginning instead of the end.
// Whatever trailing data is left after running this algorithm is added to
// the lookbehind buffer.
while (pos < len) {
if (data[pos] !== firstNeedleChar
|| !memcmp(data, pos, needle, 0, len - pos)) {
++pos;
continue;
}
data.copy(lookbehind, 0, pos, len);
self._lookbehindSize = len - pos;
break;
}
// Everything until `pos` is guaranteed not to contain needle data.
if (pos > 0)
self._cb(false, data, self._bufPos, pos < len ? pos : len, true);
self._bufPos = len;
return len;
}
function matchNeedle(self, data, pos, len) {
const lb = self._lookbehind;
const lbSize = self._lookbehindSize;
const needle = self._needle;
for (let i = 0; i < len; ++i, ++pos) {
const ch = (pos < 0 ? lb[lbSize + pos] : data[pos]);
if (ch !== needle[i])
return false;
}
return true;
}
module.exports = SBMH;
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