Requires DelimEmitter from my Loggie project.

count-occurrences.js

"use strict";

var DelimEmitter = require("./delimemitter").DelimEmitter;

exports.countInString = function(haystack, needle) {
  var count = 0;
  var position = 0;
  while(true) {
    position = haystack.indexOf(needle, position);
    if(position !== -1) {
      count += 1;
      position += needle.length;
    } else{
      break;
    }
  }
  return count;
};

exports.countInStream = function(stream, needle, callback) {
  // Argument validation
  if(typeof stream !== "object") {
    throw new Error("The stream must be a Read Stream.");
  }
  if(typeof needle !== "string" && !Buffer.isBuffer(needle)) {
    throw new Error("The needle must be a string or a Buffer.");
  }
  if(typeof callback !== "function") {
    throw new Error("The callback must be a function.");
  }

  // turn the needle to a Buffer if need be
  if(typeof needle === "string") {
    needle = new Buffer(needle);
  }

  var callbackFired = false;
  var count = 0;
  var lastData;

  var delimemitter = new DelimEmitter(stream, {
    delimiter: needle,
    includeDelimiter: true
  });
  
  // each data block should contain a delimiter, except perhaps the last
  delimemitter.on("data", function(data) {
    lastData = data;
    count += 1;
  });

  // if there is an error on the stream
  stream.on("error", function(error) {
    if(!callbackFired) {
      callback(error);
      callbackFired = true;
    }
  });

  // when we've hit the end of the file, return the number of occurrences
  stream.on("end", function() {
    if(!callbackFired) {
      // if the last data block doesn't actually contain a delimiter, then subtract it
      if(lastData.indexOf(needle) === -1) {
        count -= 1;
      }

      callback(null, count);
      callbackFired = true;
    }
  });
};