疑问

按nodejs官方的文档说明，使用Buffer操作字节流通常会比转化成String要高效。
实际情况全都是这样的吗？
本文通过一个简单的解析HTTP Request Header实例来解开此疑问。

HTTP Request Header Demo

POST /foo HTTP/1.1\r\n
Host: foo.example.com\r\n
Content-Length: 5\r\n
Connection:keep-alive\r\n
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n
Cookie:connect.sid=OY2nKGqI3obs5lYee0JKTjhf.FDtbY1Jz5Ngw5So9Jv3MUetI5ITvrIfwgCkRw%2FcXUCk\r\n
User-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_2) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.41 Safari/535.7
\r\n\r\n
q=bar

需求

获取Header中Host的值

Buffer版本

var SPACE = 0x20, // ' '
    COLON = 0x3a, // 58, :
    NEWLINE = 0x0a, // \n
    ENTER = 0x0d; // \r

exports.parse = function parse(data) {
    var line_start = 0, len = data.length;
    for(var i = 0 ; i < len; i++) {
        // Host: xxx.abc.com
        if(data[i] === COLON) {
            var key = data.toString('ascii', line_start, i).toLowerCase();
            i++; // skip ':'
            if(key === 'host') {
                var value_start = i;
                while(i < len) {
                    if(data[i] === ENTER) {
                        return data.toString('ascii', value_start, i).trim().toLowerCase();
                    }
                    i++;
                }
            }
        } else if(data[i] ===  ENTER && data[i+1] === NEWLINE) {
            i += 2;
            line_start = i;
            if(data[i] ===  ENTER && data[i+1] === NEWLINE) {
                // \r\n\r\n
                return 'Host header not found';
            }
        }
    }
    return null;
};

String版本

exports.parse = function parse(data) {
    var lines = data.toString('ascii').split("\n");
    var cut, name, host;
    for (var i = 0, len = lines.length; i < len; i++) {
        cut = lines[i].split(':');
        name = cut[0];
        if (name === 'Host') {
            if (cut[1] === undefined) {
                return 'Host header not found';
            }
            host = cut[1].trim().toLowerCase();
            return host;
        }
    }
    return null;
};

测试脚本

var buffer_parse = require('./string-buffer-benchmark-parse-header-buffer').parse
  , string_parse = require('./string-buffer-benchmark-parse-header-string').parse;

var data = new Buffer('POST /foo HTTP/1.1\r\nHost: foo.example.com\r\nContent-Length: 5\r\nConnection:keep-alive\r\nAccept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\nCookie:connect.sid=OY2nKGqI3obs5lYee0JKTjhf.FDtbY1Jz5Ngw5So9Jv3MUetI5ITvrIfwgCkRw%2FcXUCk\r\nUser-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_2) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.41 Safari/535.7\r\n\r\nq=bar');

//console.log(buffer_parse(data));
//console.log(string_parse(data), data.length);

var n = 1000000;
var start = new Date();
for(var i = 0; i < n; i++) {
    buffer_parse(data);
}
console.log('buffer_parse take: ' + (new Date() - start) + ' ms');

start = new Date();
for(var i = 0; i < n; i++) {
    string_parse(data);
}
console.log('string_parse take: ' + (new Date() - start) + ' ms');

测试结果

$ node string-buffer-benchmark.js
buffer_parse take: 1888 ms
string_parse take: 4948 ms

结论

Buffer比String快多了。