Simple Login Screen using StoryBoard

https://docs.google.com/file/d/0B4h1L6UWmdivUHJXaHVRN2tsT0k

Asynchronous download using Coroutine - Lua

require("socket")

function download()
    local host, file, port = "www.w3.org", "/TR/REC-html32.html", 80
    local connection = assert(socket.connect(host, port))
    local count = 0    -- counts number of bytes read

    connection:send("GET " .. file .. " HTTP/1.0\r\n\r\n")

    while true do
        local response, status = receive(connection)

        if(response ~= nill) then count = count + string.len(response) end
        --print(response)
        if status == "closed" then break end
    end

    connection:close()

    print(file, count)
end

--[[function receive(connection)
    connection:settimeout(0)
    return connection:receive(2^10)
end]]--

function receive(connection)
    connection:settimeout(0)   -- do not block

    local response, status = connection:receive(2^10)

    if status == "timeout" then
        coroutine.yield(connection)
    end

    return response, status
end

threads = {}    -- list of all live threads

function get ()
  -- create coroutine
  local co = coroutine.create(function ()    download()  end)
  -- insert it in the list
  table.insert(threads, co)
end

function dispatcher()
    while true do
        local count = table.getn(threads)

        if(count <= 0) then break end

        for i = 1, count do
            local status, ret = coroutine.resume(threads[i])

            if not ret then table.remove(threads, i) break end
        end
    end
end

get()
get()
get()
get()
get()

dispatcher()

Permutations using Coroutines in Lua

First let's look at the algorithm for Permutations using recursion

algorithm Permutation(array, count)
              if array index is 0, display the array

              for each item in array until count
                     swap last and first item                    
                     Permutation(array, count -1)
                     swap last and first item                    
              end
end

now the code

function permuterate (a, n)
      if n == 0 then
        --printResult(a)
        coroutine.yield(a)
      else
        for i=1,n do

        --print("iteration=", i, "n=", n, "last=", a[n], "i th=",a[i])
          -- put i-th element as the last one
          a[n], a[i] = a[i], a[n]

          -- generate all permutations of the other elements
          permuterate(a, n - 1)

          --print("i=", i, "n=", n, "last=", a[n], "i th=",a[i])
          -- restore i-th element
          a[n], a[i] = a[i], a[n]

        end
      end
end

function printResult (a)
    for i,v in ipairs(a) do
        io.write(v, " ")
    end
    io.write("\n")
end

function createPermuterate(list)
    local pick = table.getn(list)
    local co = coroutine.create(function () permuterate(list, pick) end)

    return function()
                local _, value = coroutine.resume(co)

                return value
            end
end

function createPermuterate1(list)
    local pick = table.getn(list)
    return coroutine.wrap(function () permuterate(list, pick) end)
end

for p in createPermuterate{"1","2","3";n=3} do
    printResult(p)
end

for p in createPermuterate1{1,2,3;n=3} do
    printResult(p)
end

Coroutine in Lua - Consumer driven Producer-Consumer implementation

function send(task)
    coroutine.yield(task)
end

function receive()
    return coroutine.resume(co)
end

function consumer()
    while true do
        local _, task = receive()

        if(task == nil) then break end

        print("Processed item", task)
    end
end

co = coroutine.create(function ()
    local file = io.open("io.txt", "r")

    while true do
        local task = file:read("*line")

        if(task ~= nil) then
            send(task)
            print("waiting for consumer to signal")
        else
            break
        end
    end
end)

consumer()

Closure, Coroutine, Idempotent and Reentrancy

Closure - First class function that have access to free variables in a lexical environment
Coroutine - is a subroutine that have multiple entry points for suspending and resuming at certain locations - ex, C# we can use yield.
Idempotent - is an operation that be called multiple times without changing the result beyond initial application - ex, Cancel Order/Change address are idempotent, but Placing an order is not.
Reentrant - a re-entrant block of code is one that can be entered by another actor before an earlier invocation has finished, without affecting the path that the first actor would have taken through the code. That is, it is possible to re-enter the code while it's already running and still produce correct results.
Virtual Machine - Software emulation of a computer, two types - System VM and Process VM. Process VM provides portability and flexibility, and is bound to a single process. Loads when process load, and unloads when process goes out of scope. Process will be restricted to the resources/abstraction provided by VM. CLR is an example of Process VM

C# Closure

As per wiki, Closure is a first class function with free variables that are bound in the lexical environment.

First class function is function that are treated as variable. C# we have delegates.
Free variables, are ones that are accessible to function which are not either passed as argument or defined locally.
Lexical environment means scope.

We call it closure because, first class function closes the variable it refers. In the example below, though myVar goes out of scope after first inc(), it is closed by the first class function(inc). It would print 7 & 9.

static void Main(string[] args)

{

    var inc = GetAFunc();

    Console.WriteLine(inc(5));

    Console.WriteLine(inc(6));

}

 

public static Func<int,int> GetAFunc()

{

    var myVar = 1;

    Func<int, int> inc = delegate(int var1)

                            {

                                myVar = myVar + 1;

                                return var1 + myVar;

                            };

    return inc;

}

 

 

http://www.codethinked.com/c-closures-explained

The Network Device Enrollment Service received an http message without the "Operation" tag, or with an invalid "Operation" tag.

We were facing this issue on one of our Microsoft NDES server setup, when tried to enrol/request certificate. IIS logs(C:\inetpub\logs\LogFiles\W3SVC1) shows the http response code being returned is 404.15.

HTTP Error 404.15 - Not Found
The request filtering module is configured to deny a request where the query string is too long.

So server denies our request because while enrol/requesting certificate, we need to send the CSR(certificate response)in query string, so length is big. Checking the CertSrv/mscep's Request Filtering/Max Query String(bytes) setting on that erroneous server was 2048. Increasing this size to 65536 solved the issue. Between by default when you install NDES, the limit would be 65536, but looks like not always the case to be. We can also directly edit the values in applicatioHost.config(C:\Windows\system32\inetsrv\config)