commit

node_modules/streamsearch/lib/sbmh.js

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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;