comment-inline.js

        function HTMLEscape(s)
        {
            return s.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
        }
        
        function CommentPreview()
        {
            $("#commentPreviewLabelArea").html("<b>Loading comment preview....</b><p>");
            $.post("/commentsubmit.py", $("#commentForm").serialize() + "&preview=true",
                function(data) {
                    $("#commentLoadingArea").html("");
                    $("#commentPreviewLabelArea").html("<b>Comment preview:</b><p>");
                    $("#commentPreviewArea").html(data);
                    
                    var target = $("#commentPreviewLabelArea");
                    var top = target.offset().top;
                    $("html,body").animate({scrollTop : top}, 100);
                });
            
            return false;
        }
        
        $(document).ajaxError(function(event, request, settings) {
            if(settings.url.indexOf("/commentsubmit.py?") === 0)
            {
                $("#commentLoadingArea").html("");
                $("#commentPreviewLabelArea").html("<b>Error getting comment preview:</b><p>")
                $("#commentPreviewArea").html(
                    "Server returned " + request.status + " " + HTMLEscape(request.statusText) + "<p>" +
                    HTMLEscape(request.responseText));
            }
        });
        
        var gHashcashStarted = false;
        function StartHashcashIfNecessary()
        {
            if(gHashcashStarted)
                return;
            gHashcashStarted = true;
            
            $("#commentLoadingArea").text("Fetching salt...");
            $.getJSON("/commentsubmit.py?action=getsalt", function(result) {
                var salt = result["salt"];
                var zeroes = result["zeroes"];
                var workCount = result["work_count"];
                
                $("#commentLoadingArea").text("Computing hashcash....");
                HashcashBG(salt, zeroes, workCount,
                    function(progress) {
                        $("#commentLoadingArea").text("Computing hashcash (" + progress + " complete out of " + workCount + ").");
                    },
                    function(buf) {
                        var hash = Sha1.hash(salt + buf, 0);
                        $("#saltinput").val(salt);
                        $("#hashcash").val(buf);
                        $("#commentLoadingArea").text("");
                        $("#submit").removeAttr("disabled");
                    });

            }).error(function(request, status, error) {
                $("#commentLoadingArea").text("Error loading hashcash salt: " + error);
                
                gHashcashStarted = false;
                setTimeout("StartHashcashIfNecessary()", 2000);
            });
        }

commentsubmit.py

#!/usr/bin/python

import cgi
import datetime
import hashlib
import json
import md5
import os
import sys
import sqlite3
import time

import Comments
import CommentsDB


blacklist = ['112.111.174.222', '58.22.64.84']

HASHCASH_ZEROES = 13
HASHCASH_WORK_COUNT = 128
HASHCASH_SQLITE_PATH = 'hashcash-salts.sqlite3'
SALT_TIMEOUT = 7 * 24 * 60 * 60 # time out after a week, whatever


def getField(form, field):
    if form.has_key(field):
        return form[field].value
    else:
        return None

def main():
    form = cgi.FieldStorage()
    action = getField(form, "action")
    if action == "delete":
        deleteComment(form)
    elif action == "getsalt":
        getSalt(form)
    else:
        addComment(form)

def deleteComment(form):
    print "Content-Type: text/html; charset=utf-8\n\n"
    
    md5 = getField(form, "md5")
    
    db = CommentsDB.connect()
    cursor = db.cursor()
    
    query = "delete from comments where md5=?"
    cursor.execute(query, (md5,))
    
    db.commit()
    db.close()
    
    print '<meta http-equiv="refresh" content="0;/recentcomments.html">'
    print "The comment %s has been deleted" % md5

def DBConnect():
    with sqlite3.connect(HASHCASH_SQLITE_PATH) as connection:
        cursor = connection.cursor()
        cursor.execute("SELECT name FROM sqlite_master WHERE type='table' AND name='salts';")
        if not cursor.fetchone():
            cursor.execute("CREATE TABLE salts(salt TEXT UNIQUE, zeroes INT, work_count INT, created TIMESTAMP DEFAULT CURRENT_TIMESTAMP)")
        
        return connection

def DBPrune():
    with DBConnect() as connection:
        cursor = connection.cursor()
        cursor.execute("DELETE FROM salts WHERE strftime('%s', 'now') - strftime('%s', created) > ?", (SALT_TIMEOUT, ))

def getSalt(form):
    DBPrune()
    
    print 'Content-Type: application/json'
    print ''
    
    salt = os.urandom(20).encode('hex')
    zeroes = HASHCASH_ZEROES
    workCount = HASHCASH_WORK_COUNT
    
    with DBConnect() as connection:
        connection.execute("INSERT INTO salts(salt, zeroes, work_count) VALUES(?, ?, ?);", (salt, zeroes, workCount))
    
    d = {
        'salt' : salt,
        'zeroes' : zeroes,
        'work_count' : workCount
    }
    print json.dumps(d)

def CountLeadingZeroes(s):
    if len(s) == 0:
        return 0
    
    c = ord(s[0])
    if c == 0:
        return 8 + CountLeadingZeroes(s[1:])
    
    zeroes = 0;
    while (c & 0x80) == 0:
        c <<= 1
        zeroes += 1
    return zeroes

def HashcashGood(salt, hashcashes):
    with DBConnect() as connection:
        cursor = connection.cursor()
        cursor.execute('SELECT zeroes, work_count FROM salts WHERE salt=?', (salt,))
        row = cursor.fetchone()
        cursor.execute('DELETE FROM salts WHERE salt=?', (salt,))
        connection.commit()
        
        if not row:
            return False
        else:
            zeroesTarget = row[0]
            workCount = row[1]
    
    hashcashList = set(hashcashes.split(','))
    if len(hashcashList) < workCount:
        return False
    
    for hashcash in hashcashList:
        toHash = salt + hashcash
        hash = hashlib.sha1(toHash).digest()
        zeroes = CountLeadingZeroes(hash)
        if zeroes < zeroesTarget:
            return False
    return True

def addComment(form):
    print "Content-Type: text/html; charset=utf-8\n\n"
    
    errors = []
    
    page = getField(form, "page")
    name = getField(form, "name")
    url  = getField(form, "url")
    comment = getField(form, "comment")
    preview = getField(form, "preview")
    
    salt = getField(form, "salt")
    hashcash = getField(form, "hashcash")
    
    if not page:
        errors.append("Empty page given for comment.")
    if not name:
        errors.append("Please fill in the name field.")
        name = ""
    if not comment:
        errors.append("Please fill in the comments field.")
        comment = ""
    
    if not url:
        url = ""
    
    comment = comment.decode('utf-8')
    name = name.decode('utf-8')
    page = page.decode('utf-8')
    
    if page and len(page) > 250:
        errors.append("Page name too long.")
    if name and len(name) > 250:
        errors.append("Name too long, please use 250 characters or less.")
    if url and len(url) > 250:
        errors.append("URL too long, please use 250 characters or less.")
    if comment and len(comment) > 65000:
        errors.append("Comment too long, please use 65000 characters or less.")
    
    if url and url.find("http://") != 0 and url.find("mailto:") != 0 and url.find("https://") != 0:
        errors.append("Invalid web site %s, use something that starts with http://, https://, or mailto:." % url)
    
    # Make sure to check the hashcash at the very end. HashcashGood burns the hashcash when it checks it,
    # so if it runs when there are errors, a failed comment will burn the hashcash, and then subsequent
    # submissions from browsers that don't trigger a hashcash recomputation (i.e. Safari) will continue
    # to fail when they should work.
    if not preview and not errors and not HashcashGood(salt, hashcash):
        errors.append("Bad hashcash value.")
    
    if errors:
        print "<ul><li>"
        print "<li>".join(errors)
        print "</ul>"
        return
    
    date = datetime.datetime.utcnow()
    hash = md5.new(comment.encode('utf-8')).hexdigest()
    ip = os.environ["REMOTE_ADDR"]
    
    if preview:
        print Comments.commentsHTMLForComment(page, time.mktime(date.utctimetuple()), name, url, comment, hash, ip, False, False).encode('utf-8')
        return
    
    if ip not in blacklist:
        db = CommentsDB.connect()
        cursor = db.cursor()
        
        query = "select md5 from comments where name=? and md5=?"
        cursor.execute(query, (name, hash))
        result = cursor.fetchall()
        if not result:
            tzoff = time.mktime(time.gmtime(0))
            query = "insert into comments (page, date, name, url, comment, md5, ip) values (?, ?, ?, ?, ?, ?, ?)"
            tuple = (page, time.mktime(date.utctimetuple()) - tzoff, name, url, comment, hash, ip)
            cursor.execute(query, tuple)
        db.commit()
        db.close()
    
    redirURL = "/" + page + "#comment-" + hash
    print "<meta http-equiv=\"Refresh\" content=\"0;URL=%s\">" % redirURL
    print "Your comment has been accepted."

sys.stderr = sys.stdout
main()

hashcash.js

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
/*  SHA-1 implementation in JavaScript | (c) Chris Veness 2002-2010 | www.movable-type.co.uk      */
/*   - see http://csrc.nist.gov/groups/ST/toolkit/secure_hashing.html                             */
/*         http://csrc.nist.gov/groups/ST/toolkit/examples.html                                   */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

var Sha1 = {};  // Sha1 namespace

/**
 * Generates SHA-1 hash of string
 *
 * @param {String} msg                String to be hashed
 * @param {Boolean} [utf8encode=true] Encode msg as UTF-8 before generating hash
 * @returns {String}                  Hash of msg as hex character string
 */
Sha1.hash = function(msg, utf8encode) {
  utf8encode =  (typeof utf8encode == 'undefined') ? true : utf8encode;
  
  // convert string to UTF-8, as SHA only deals with byte-streams
  if (utf8encode) msg = Utf8.encode(msg);
  
  // constants [§4.2.1]
  var K = [0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xca62c1d6];
  
  // PREPROCESSING 
  
  msg += String.fromCharCode(0x80);  // add trailing '1' bit (+ 0's padding) to string [§5.1.1]
  
  // convert string msg into 512-bit/16-integer blocks arrays of ints [§5.2.1]
  var l = msg.length/4 + 2;  // length (in 32-bit integers) of msg + ‘1’ + appended length
  var N = Math.ceil(l/16);   // number of 16-integer-blocks required to hold 'l' ints
  var M = new Array(N);
  
  for (var i=0; i<N; i++) {
    M[i] = new Array(16);
    for (var j=0; j<16; j++) {  // encode 4 chars per integer, big-endian encoding
      M[i][j] = (msg.charCodeAt(i*64+j*4)<<24) | (msg.charCodeAt(i*64+j*4+1)<<16) | 
        (msg.charCodeAt(i*64+j*4+2)<<8) | (msg.charCodeAt(i*64+j*4+3));
    } // note running off the end of msg is ok 'cos bitwise ops on NaN return 0
  }
  // add length (in bits) into final pair of 32-bit integers (big-endian) [§5.1.1]
  // note: most significant word would be (len-1)*8 >>> 32, but since JS converts
  // bitwise-op args to 32 bits, we need to simulate this by arithmetic operators
  M[N-1][14] = ((msg.length-1)*8) / Math.pow(2, 32); M[N-1][14] = Math.floor(M[N-1][14])
  M[N-1][15] = ((msg.length-1)*8) & 0xffffffff;
  
  // set initial hash value [§5.3.1]
  var H0 = 0x67452301;
  var H1 = 0xefcdab89;
  var H2 = 0x98badcfe;
  var H3 = 0x10325476;
  var H4 = 0xc3d2e1f0;
  
  // HASH COMPUTATION [§6.1.2]
  
  var W = new Array(80); var a, b, c, d, e;
  for (var i=0; i<N; i++) {
  
    // 1 - prepare message schedule 'W'
    for (var t=0;  t<16; t++) W[t] = M[i][t];
    for (var t=16; t<80; t++) W[t] = Sha1.ROTL(W[t-3] ^ W[t-8] ^ W[t-14] ^ W[t-16], 1);
    
    // 2 - initialise five working variables a, b, c, d, e with previous hash value
    a = H0; b = H1; c = H2; d = H3; e = H4;
    
    // 3 - main loop
    for (var t=0; t<80; t++) {
      var s = Math.floor(t/20); // seq for blocks of 'f' functions and 'K' constants
      var T = (Sha1.ROTL(a,5) + Sha1.f(s,b,c,d) + e + K[s] + W[t]) & 0xffffffff;
      e = d;
      d = c;
      c = Sha1.ROTL(b, 30);
      b = a;
      a = T;
    }
    
    // 4 - compute the new intermediate hash value
    H0 = (H0+a) & 0xffffffff;  // note 'addition modulo 2^32'
    H1 = (H1+b) & 0xffffffff; 
    H2 = (H2+c) & 0xffffffff; 
    H3 = (H3+d) & 0xffffffff; 
    H4 = (H4+e) & 0xffffffff;
  }

  return Sha1.toHexStr(H0) + Sha1.toHexStr(H1) + 
    Sha1.toHexStr(H2) + Sha1.toHexStr(H3) + Sha1.toHexStr(H4);
}

//
// function 'f' [§4.1.1]
//
Sha1.f = function(s, x, y, z)  {
  switch (s) {
  case 0: return (x & y) ^ (~x & z);           // Ch()
  case 1: return x ^ y ^ z;                    // Parity()
  case 2: return (x & y) ^ (x & z) ^ (y & z);  // Maj()
  case 3: return x ^ y ^ z;                    // Parity()
  }
}

//
// rotate left (circular left shift) value x by n positions [§3.2.5]
//
Sha1.ROTL = function(x, n) {
  return (x<<n) | (x>>>(32-n));
}

//
// hexadecimal representation of a number 
//   (note toString(16) is implementation-dependant, and  
//   in IE returns signed numbers when used on full words)
//
Sha1.toHexStr = function(n) {
  var s="", v;
  for (var i=7; i>=0; i--) { v = (n>>>(i*4)) & 0xf; s += v.toString(16); }
  return s;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
/*  Utf8 class: encode / decode between multi-byte Unicode characters and UTF-8 multiple          */
/*              single-byte character encoding (c) Chris Veness 2002-2010                         */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

var Utf8 = {};  // Utf8 namespace

/**
 * Encode multi-byte Unicode string into utf-8 multiple single-byte characters 
 * (BMP / basic multilingual plane only)
 *
 * Chars in range U+0080 - U+07FF are encoded in 2 chars, U+0800 - U+FFFF in 3 chars
 *
 * @param {String} strUni Unicode string to be encoded as UTF-8
 * @returns {String} encoded string
 */
Utf8.encode = function(strUni) {
  // use regular expressions & String.replace callback function for better efficiency 
  // than procedural approaches
  var strUtf = strUni.replace(
      /[\u0080-\u07ff]/g,  // U+0080 - U+07FF => 2 bytes 110yyyyy, 10zzzzzz
      function(c) { 
        var cc = c.charCodeAt(0);
        return String.fromCharCode(0xc0 | cc>>6, 0x80 | cc&0x3f); }
    );
  strUtf = strUtf.replace(
      /[\u0800-\uffff]/g,  // U+0800 - U+FFFF => 3 bytes 1110xxxx, 10yyyyyy, 10zzzzzz
      function(c) { 
        var cc = c.charCodeAt(0); 
        return String.fromCharCode(0xe0 | cc>>12, 0x80 | cc>>6&0x3F, 0x80 | cc&0x3f); }
    );
  return strUtf;
}

/**
 * Decode utf-8 encoded string back into multi-byte Unicode characters
 *
 * @param {String} strUtf UTF-8 string to be decoded back to Unicode
 * @returns {String} decoded string
 */
Utf8.decode = function(strUtf) {
  // note: decode 3-byte chars first as decoded 2-byte strings could appear to be 3-byte char!
  var strUni = strUtf.replace(
      /[\u00e0-\u00ef][\u0080-\u00bf][\u0080-\u00bf]/g,  // 3-byte chars
      function(c) {  // (note parentheses for precence)
        var cc = ((c.charCodeAt(0)&0x0f)<<12) | ((c.charCodeAt(1)&0x3f)<<6) | ( c.charCodeAt(2)&0x3f); 
        return String.fromCharCode(cc); }
    );
  strUni = strUni.replace(
      /[\u00c0-\u00df][\u0080-\u00bf]/g,                 // 2-byte chars
      function(c) {  // (note parentheses for precence)
        var cc = (c.charCodeAt(0)&0x1f)<<6 | c.charCodeAt(1)&0x3f;
        return String.fromCharCode(cc); }
    );
  return strUni;
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

var leadingZeroesTable = {
    "0" : 4,
    "1" : 3,
    "2" : 2,
    "3" : 2,
    "4" : 1,
    "5" : 1,
    "6" : 1,
    "7" : 1,
    "8" : 0,
    "9" : 0,
    "a" : 0,
    "b" : 0,
    "c" : 0,
    "d" : 0,
    "e" : 0,
    "f" : 0
};

var incrementTable = {
    "0" : "1",
    "1" : "2",
    "2" : "3",
    "3" : "4",
    "4" : "5",
    "5" : "6",
    "6" : "7",
    "7" : "8",
    "8" : "9",
    "9" : "a",
    "a" : "b",
    "b" : "c",
    "c" : "d",
    "d" : "e",
    "e" : "f"
}

function CountLeadingZeroes(s)
{
    var zeroes = 0;
    var i = 0;
    
    while(i < s.length)
    {
        var c = s.charAt(i);
        zeroes += leadingZeroesTable[c];
        if(c != "0")
            break;
        
        i++;
    }
    
    return zeroes;
}

function Increment(s)
{
    if(s.length == 0)
        return "0";
    
    var c = s.charAt(0);
    var rest = s.slice(1);
    
    if(c == "f")
        return "0" + Increment(rest);
    else
        return incrementTable[c] + rest;
}

function Hashcash(salt, zeroes) {
    var buf = "";
    return function(iterations) {
        var hash;
        
        while(iterations > 0)
        {
            buf = Increment(buf);
            hash = Sha1.hash(salt + buf, 0);
            var lz = CountLeadingZeroes(hash);
            if(lz >= zeroes)
                return buf
            
            iterations--;
        }
        
        return false;
    };
}

function HashcashBG(salt, zeroes, workCount, progresscb, donecb) {
    var iterations = 100;
    var delay = 1;
    var processor = Hashcash(salt, zeroes);
    var results = []
    
    var f = function() {
        var buf = processor(iterations);
        if(buf)
        {
            results.push(buf);
            if(results.length >= workCount)
            {
                donecb(results.join(","));
            }
            else
            {
                progresscb(results.length);
                setTimeout(f, delay);
            }
        }
        else
        {
            setTimeout(f, delay);
        }
    };
    f();
}