Author: wpenginebot

I just installed Hardy Heron on a webserver and found ssh over the LAN paused for a long time after connecting and before asking for the password (or connecting with ssh key).

The problem is some kind of reverse DNS lookup that doesn’t work on the LAN. After some digging and going down some blind alleys with Kerberos I found the answer buried in this thread.

On the machine being connected to (remote side/server side)

/etc/ssh/sshd_config

UseDNS no

Nothing annoys me more than having to manually add tests to a central location in order to get them to run. Here’s some code that automatically and recursively (down the directory tree) finds files ending in Test.php and loads the tests within. Now all you need to do is create the tests.

< ?php

require_once 'PHPUnit/Framework.php';
require_once 'PHPUnit/TextUI/TestRunner.php';

define(Test, '/path/to/test/dir');

class AllTests {
    public static function main() {
        PHPUnit_TextUI_TestRunner::run(self::suite());
    }

    public static function suite() {
        $suite = new PHPUnit_Framework_TestSuite('My Test Suite');
        foreach (self::find_all_tests(TEST) as $path) {
            require_once($path);
            $class = preg_replace('%.*/(.*)\.php%', '$1', $path);
            $suite->addTestSuite($class);
        }
        return $suite;
    }

    private static function find_all_tests($start_dir) {
        $res = array();
        foreach (glob("$start_dir/*Test.php") as $path) {
            $res[] = $path;
        }
        foreach (glob($start_dir . '/*', GLOB_ONLYDIR) as $subdir) {
            $res = array_merge($res, self::find_all_tests($subdir));
        }
        return $res;
    }
}

?>

To use PEAR and MAMP together run the following command:

/Applications/MAMP/bin/php5/bin/pear config-show

Look up the value of “PEAR directory” in the output and add this directory to include_path in /Applications/MAMP/conf/php5/php.ini

Change the php5 in the paths to php4 if you are using that version for some godforsaken reason.

So basically, there are 4 dimensions:

• Static (expressions have types) vs. dynamic (values have types)
• Strong (values cannot be coerced to other types without a cast) vs. weak (the runtime performs a variety of coercions for convenience)
• Latent (no type declarations) vs. manifest (type declarations)
• Nominal (subtyping relations are declared explicitly) vs. structural (subtyping relations are inferred from the operations available on types)

And you can place most languages on one of these 4 axes, though several support multiple forms of typing:

• Ocaml: static, strong, latent, structural typing
• Haskell: static, strong, latent, structural typing, with nominal typing available via newtype and manifest typing through optional type declarations.
• Erlang: dynamic, strong, latent, structural typing
• Scheme: dynamic, strong, latent, structural typing, with nominal typing available in many object systems.
• Common Lisp: dynamic, strong, latent or manifest typing. Same note about structural vs. nominal typing as Scheme, but nominal subtyping is used more often in practice.
• Python & Ruby: dynamic, strong, latent, structural typing. Nominal subtyping is available via isinstance or Ruby equivalent, but good practice frowns upon it.
• PHP: dynamic, weak, latent, nominal or structural typing. Culture is much friendlier to nominal subtyping than Python or Ruby, but it’s not required.
• Java & C : mostly static, strong, manifest, nominal typing. The casts give you a form of weak-typing when necessary, and C templates are structurally typed.
• C: static, generally weak, manifest, nominal typing.
• Assembly: dynamic, weak, latent, structural typing.

Reddit comment by Nostrademons

The table with the foreign key in it belongs_to the table that that foreign key references.

The table with the referenced primary key in it has_one or has_many of the table with the foreign key in it.

I will not forget this again!

If you need to use an explicit primary key and not an AUTO_INCREMENT with ActiveRecord I wrote this snippet that has proved very handy:

module ExplicitPrimaryKey
  attr_accessor :pk
  def before_create; self.id = pk; end
end

Then when you call the create method supply :pk => value along with the other values.

ActiveRecord is an ORM solution that grew out of Ruby on Rails. It is entirely separate and can be used outside of Rails.

If you find that ActiveRecord has saved some data starting with three hyphens in your database there IS an explanation. This is a YAML representation of an array.

ActiveRecord is an ORM solution that grew out of Ruby on Rails. It is entirely separate and can be used outside of Rails.

Just spent slightly too long working this out so I thought I’d post this for those with similar requirements.

You need to follow the steps from http://tmtm.org/en/mysql/ruby/. Use ruby extconf.rb --with-mysql-config as the first command.

We have made the OpenSocial API announced by Google on Thursday live on Ning.

It’s an experimental addition, not least because the OpenSocial API is bound to undergo some rapid evolution in the coming weeks. But it does mean that you can install gadgets and write your own gadgets right now.

Further information in Marc’s blog posts.

Motivation

There are two or three CGI libraries for Haskell. But if you ask the cognoscenti (to be found on the #haskell IRC channel) for Haskell web programming recommendations they will almost invariably point you at HAppS.

HAppS may have many virtues but it’s documentation and associated tutorial do not number among them.

Copying the first Rails screencast, Creating a Blog in Fifteen Minutes, I figured that a good example web application is a blogging system. Leaving aside that blogging is now pass�, here is my HAppS tutorial.

Please note that I am a fairly inexperienced Haskell programmer and almost all the advice I give will be wrong. Some of what I say will necessarily be vague because I don’t understand it completely myself. But the advantage to my tutorial is that it will at least be comprehensible! I hope that some Haskell gurus will read this and find my mistakes and update me in the comments. Thanks!

Installation

For installation of HAppS, please see my earlier post.

Hello, World

First, let’s get HAppS working and see something in our browser. Save the following listing to Hello.hs:

import HAppS
import HAppS.Protocols.SimpleHTTP2
 
main = stdHTTP [debugFilter, noState, h () GET $ ok $ val "Hello, World"]

If you compile that with:

ghc --make Hello.hs -o hello

And then run the resulting “hello” binary (./hello under Unix, hello under Windows). If you visit http://localhost:8000/ in your browser you should see “Hello, World” displayed.

So what have we actually done there? Well, I don’t really know. But certainly we’ve passed a list of directives to the stdHTTP function. One of which (the bit starting “h”) says: “if you get a GET request of any sort, respond with a page containing the text ‘Hello, World'”. Let’s just leave it at that for now.

Blog System

Weren’t we meant to building a blogging system? Yes! OK, let’s start with the URL scheme. We want the following paths in our system:

GET  /new 		=> Show the "create new post" form
POST /new	 	=> Create a new post using the submitted values
GET /post/$id 	=> Display the post with id $id
GET /			=> Dispaly the last 5 posts

The way to describe this scheme to HAppS is through the first and second arguments to the h request-handling function. The first argument is the path as a list (each element in the list representing a directory) and the second argument is the type of request (GET, POST and so on). So for displaying the “create new post form” we use h ["new"] GET.

Our GET /post/$id path is slightly tricky in that we don’t want to write out a very long list of post ids. We want to do some pattern matching. You can do this in HAppS with the re function. This tells HAppS to interpret the paths in the list as regular expressions. So for GET /post/$id we can use h ["post", "(0-9 )"] GET.

Putting that all together gives us:

import HAppS
import HAppS.Protocols.SimpleHTTP2
 
main = stdHTTP $ debugFilter : noState : 
           [h ["new"]                           GET  $ ok $ val "Show create post form"
           ,h ["new"]                           POST $ ok $ val "Save post and forward to display post"
           ,h (re ["post", "([0-9] )"])  GET  $ ok $ \\(id:_) () -> respond ("Display post "    id)
           ,h [""]                              GET  $ ok $ val "Display five most recent posts"
           ]

HTML in Haskell

Those calls to val are just placeholders. What we really want to return is some HTML.

The most common way to get HTML in Haskell seems to be to use one of the HTML combinator libraries such as Text.XHTL.Strict. This is only tangentially related to HAppS so I’ll just point you at this simple example and these fairly comprehensible notes and move on.

Now we have:

import HAppS
import HAppS.Protocols.SimpleHTTP2
import Text.XHtml.Strict

main :: IO ()
main = stdHTTP $ debugFilter : noState : 
           [h ["new"]                           GET  $ ok $ val showCreatePostPage
           ,h ["new"]                           POST $ ok $ val "Save post and forward to display post"
           ,h (re ["post", "([0-9] )"])  GET  $ ok $ \\(id:_) () -> respond ("Display post "    id)
           ,h [""]                              GET  $ ok $ val "Display five most recent posts"
           ]

-- Handlers

showCreatePostPage :: String
showCreatePostPage = showHtml getCreatePostPage

-- HTML Functions

getCreatePostPage :: Html
getCreatePostPage = mkHeader "New Post"
        body < < [
        (h1 << "New Post") 
            getCreatePostForm
        ]

getCreatePostForm :: Html
getCreatePostForm = (form ! [action "/new", method "post"] << (fieldset << [
        label ! [thefor "title"] << "Post Title", br,
        input ! [name "title", identifier "title", thetype "text"], br, br,
        label ! [thefor "body"] << "Post Body", br,
        textarea ! [name "body", identifier "body", rows "10", cols "40"] << "", br, br,
        submit "create" "Create Post"
    ]))

mkHeader :: String -> Html
mkHeader title = (header < < (thetitle << (title    " - HBlog")))

State

Of course I've chickened out above. Yes, I've provided some HTML that never changes. But what about the pages that depend on state? What about the display of the posts themselves? It's time to get rid of that odd-looking noState directive and start storing some blog posts. This is where it gets a little bit hairy.

While you could use a relational database with HAppS, it actually has it's own in-built haskell type-based storage system. It has lots of whizzy features that I'm not concerned about here to do with atomicicity and all that kind of shenanigans. But let's stay focused - we need a way of storing some blog posts. That means we need to define a type that derives Show and Read.

data Posts = Posts [Post] deriving (Read, Show) 
data Post = Post { pTitle :: String, pBody :: String } deriving (Read, Show)

What’s more we have to give it some instances so that HAppS can start it up, and know how to store it.

instance Serialize Posts where 
    typeString _ = "Posts"
    encodeStringM = defaultEncodeStringM
    decodeStringM = defaultDecodeStringM

instance StartState Posts where
    startStateM = return $ Posts []

OK, so now we know where we are going to store our posts. But how do we construct them in the first place? Well, Post is a record type, I will assume you know how to use record types. But what about extracting the values from the post body to slot into the record?

Strings we can get with:

v < - lookMb return req "fieldName"

where req is the Request, the second parameter passed to the function after ok in our request handlers. This code must appear in a do block.

Ints we can get with:

v < - lookMb readM req "fieldName"

Quite what the meaning of this distinction is, I don't know. So please leave a comment if you understand this better than me.

The state of the application itself (in our case a Posts, or list of Post) you can retrieve with get and update with put as long as you are within the appropriate Monad. This probably makes more sense in the context of a full example:

module Main where

import Control.Monad.State (get, put)
import Debug.Trace
import HAppS
import HAppS.Protocols.SimpleHTTP2
import Text.XHtml.Strict

main :: IO ()
main = stdHTTP $ debugFilter : 
           [h ["new"]                           GET  $ ok $ val showCreatePostPage
           ,h ["new"]                           POST $ ok createPost
           ,h (re ["post", "([0-9] )"])         GET  $ ok showPost
           ,h [""]                              GET  $ ok showPosts
           ]

-- State

data Posts = Posts [Post] deriving (Read, Show) 
data Post = Post { pTitle :: String, pBody :: String } deriving (Read, Show)

instance Serialize Posts where 
    typeString _ = "Posts"
    encodeStringM = defaultEncodeStringM
    decodeStringM = defaultDecodeStringM

instance StartState Posts where
    startStateM = return $ Posts []

-- Handlers

showCreatePostPage = showHtml getCreatePostPage

showPost (rawId:_) () = do
    (Posts posts) < - get
    let postId = read rawId :: Int
        post = posts !! postId 
    respond $ showHtml $ getPostsHtml [post]

showPosts () () = do
    (Posts posts) <- get
    respond $ showHtml $ getPostsHtml $ take 5 $ reverse posts 

createPost () req = do
    title <- lookMb return req "title"
    body  <- lookMb return req "body"
    let p = Post { pTitle = title, pBody = body }
    (Posts ps) <- get
    put (Posts (ps    [p]))
    respond $ "Post created"

-- HTML Functions

getCreatePostPage :: Html
getCreatePostPage = mkHeader "New Post"
        body << [
        (h1 << "New Post") 
            getCreatePostForm
        ]

getCreatePostForm :: Html
getCreatePostForm = (form ! [action "/new", method "post"] << (fieldset << [
        label ! [thefor "title"] << "Post Title", br,
        textfield "title", br, br,
        label ! [thefor "body"] << "Post Body", br,
        textarea ! [name "body", identifier "body", rows "10", cols "40"] << "", br, br,
        submit "create" "Create Post"
    ]))

getPostsHtml :: [Post] -> Html
getPostsHtml posts = foldl (   ) noHtml (map getPostHtml posts)

getPostHtml :: Post -> Html
getPostHtml post = 
    thediv 
        < < h2 << (pTitle post)
            p << (pBody post)

mkHeader :: String -> Html
mkHeader title = (header < < (thetitle << (title    " - HBlog")))

Once your HAppS application has state then wherever you run it it will create directories to store state information. If you change your state type, you must delete these directories (you will lose existing state of your app) to prevent errors like: *** Exception: user error (decodeStringM: parsing length field failed @ "").

Conclusion

So there you have a working blog publishing system in HAppS. It's more a proof of concept than a useable application. But hopefully it shows you how to create a simple application in HAppS without boiling your brain too much. There are zillions of improvements that could be made: add comments; make Posts a sequence and not a list; add error handling for empty fields; redirect to post display after creation; handle error when post id is greater than the number of posts; don't number posts starting from 0; allow deletion of posts; and many many others.

I must credit Eric Mertens for his sterling work on HPaste whose source code I read to make sense of much of what HAppS was doing.

Please do correct all my terrible misunderstandings and mistakes in the comments!