Sunday, January 18, 2015

Bedrock + Barewords = Bug

This morning, after being sufficiently caffeinated with a full pot of coffee, I was able to isolate a Bedrock bug that has been bugging me.  Bedrock was failing to throw an exception on what I would consider a syntax error (missing right end tag >).  


  <null:foo $baz.some_method()
  <var $foo>

Bedrock however, happily parsed the expressions and went along it's merry way...argghhh!

Is it a bug in Bedrock?  Probably, but IMHO it's really a problem with Bedrock's loosely defined grammar.

Saturday, January 10, 2015

Love me some more Chromebook!

New beta channel release appears to have fixed memory management issues.

For the first time since I've owned my Chromebook I experienced a lot of "He's Dead Jim" out of memory issues.  So far the new update of January 8th seems to have corrected the problem.

New 15.6" Acer Chromebook

Looks like Acer is going to enter the 15" market.  They were giving sneak peeks at the CES in Las Vegas of a new Acert 15.6" Chromebook.

According to the representive they'll have several models including an i3 4GB model.  Lower end models (2GB, lower resolution) will start at $249.  Since it comes in at almost 5lbs I don't think it will replace my current C720 as my go to road device, but the increased screen size will make this a nice addition to the den.

The experiments with crouton and running Ubuntu on my 2GB model were very successful, so I suspect there will soon be an emerging Linux laptop pattern fueled by these Chromebooks.  I'd go with the 4GB model for those contemplating running unity.

Love me some Chromebook!  Can't wait to get my hands on one.  Rumors suggest March...

Wednesday, December 31, 2014

RESTful APIs with Bedrock (part V)

This is the 5th in a series of blogs on using Bedrock to create a RESTful API.  So far we've checked off several requirements for building a RESTful API.  We've been able to demonstrate the basics of creating a RESTful API using Apache and Bedrock.  We've satisfied requirements #1 through #4 and #6.
  1. Parse a URI
  2. Determine the operation to be performed
  3. Determine the result format requested by the client
  4. Retrieve, validate, and de-serialize client data
  5. Retrieve data from the back end
  6. Serialize data to send back to client
  7. Set HTTP response headers
  8. Handle errors
We'll round out the discussion by showing how Bedrock can satisfy the 3 remaining requirements.

Tuesday, December 30, 2014

RESTful APIs with Bedrock (part IV)

To recap our 8 requirements of a web development framework for creating our RESTful API:
  1. Parse a URI
  2. Determine the operation to be performed
  3. Determine the result format requested by the client
  4. Retrieve, validate, and de-serialize client data
  5. Retrieve data from the back end
  6. Serialize data to send back to client
  7. Set HTTP response headers
  8. Handle errors

In yesterday's blog we talked about using Apache directives to help us create meaningful URIs and using Bedrock to interpret the extra path information and HTTP method in order to satisfy requirements 1 & 2.

Today we'll examine #3 and #4 and touch on #6.

Monday, December 29, 2014

Perl Regular Expression Capture Groups

After cursing Bedrock for not giving me access to capture groups in regular expressions, I finally bit the bullet and figured out how to implement this in a somewhat sane manner.

RESTful APIs with Bedrock (Part III)

The other day I blogged about using Bedrock to create a RESTful API.  Today I'm going to talk about setting up Apache in order to support a RESTful interface based on URIs.  Last time we pulled these requirements for a REST API framework from Michael McClennen's talk:

  1. Parse a URI
  2. Determine the operation to be performed
  3. Determine the result format requested by the client
  4. Retrieve, validate, and deserialize client data
  5. Retrieve data from the back end
  6. Serialize data to send back to client
  7. Set HTTP response headers
  8. Handle errors

Let's configure Apache to help us with #1, and #2 as we implement a hypothetical RESTful interface for a contact database.

First, we'll create an Apache RewriteRule that maps our desired API's base URI to a Bedrock page.  We add the directives below to our Virtual host configuration file.

RewriteEngine On
RewriteRule  ^contacts(/.*)?$ rest-api/contacts-api.jroc/$1

Using this rule URIs that begin with contacts will now be rewritten to point to a URI that implements our REST interface in Bedrock.  The Bedrock file contacts-api.jroc is a Bedrock script (page) that returns a document of type application/json.  By convention (and as implemented by the Bedrock handler), any Bedrock script with an extension of .jroc will be considered to return a JSON document.

That's just another way of saying that Bedrock will set the mime-type header to application/json for you automatically.  Of course you could have named the file contacts-api.roc and then set the Content-Type header yourself.

<null $header.set('Content-Type', 'application/json')>

Files in the rest-api directory are configured using Apache directives so they will be processed by the either the Bedrock mod_perl Apache handler or the Bedrock handler implemented as a CGI.

<Directory /var/www/vhosts/myhost/htdocs/rest-api>
# Bedrock - mod-perl for .roc (if mod_perl)
  <IfModule mod_perl.c>
    AddHandler    perl-script .roc .jroc .html
    PerlHandler   Apache::Bedrock
  </IfModule>

  Action bedrock-cgi /cgi-bin/bedrock.cgi virtual

  <IfModule !mod_perl.c>
    AddHandler    bedrock-cgi .roc .jroc
  </IfModule>
...
</Directory>

We can now use the PATH_INFO environment variable to interpret our URI since all the stuff after  contacts/ in our URI will be considered extra path information and presented to us in that environment variable...well sort of.   As it turns out, when Bedrock is configured using the CGI version, PATH_INFO will contain the filename (contacts-api.jroc) as well as the extra path info.  For this reason, Bedrock provides an environment variable named BEDROCK_PATH_INFO only available when the Bedrock handler is configured as a CGI script that contains only the extra path information.

PATH_INFO => (/env.roc/foo)
BEDROCK_PATH_INFO => (/foo)

Our REST API script can now grab the extra path information necessary for us to interpret the URI.

<null:path_info --default=$env.PATH_INFO $env.BEDROCK_PATH_INFO>

Under mod_perl we'll use the PATH_INFO variable, but as a CGI handler we'll use the value Bedrock provides as BEDROCK_PATH_INFO.  Since the BEDROCK_PATH_INFO variable is only set when the Bedrock handler is a CGI, our $path_info will be set  using the default value under mod_perl.

The URI gives us the context, but what about the method?  Using Bedrock's $env object that exposes  environment variables to your Bedrock pages, we can examine the HTTP method sent by the client.  By testing  $env.REQUEST_METHOD we can determine the HTTP method.  The value will probably be either GET, PUT, POST, or DELETE, as set by the client and defined by your API.  It would then be easy enough to test that value along with the URI to determine the operation to be performed.  That is to say, the operation to be performed will be a function of the HTTP method and the URI.

<if $env.REQUEST_METHOD --eq 'GET'>

# /contacts/friends
   <if $path_info --eq '/friends'>
   ...
   <elseif $path_info --eq '/business'>
   ...
   <else>
     <raise '400'>
   </if>

<elseif $env.REQUEST_METHOD --eq 'PUT'>
...
</if>

This now satisfies our first two requirements we discussed last time, namely:
  • Parse a URI
  • Determine the operation to be performed
Next time: Determining the result format and de-serializing our input data.

Wednesday, December 24, 2014

RESTful APIs with Bedrock (Part II)

Reading the Perl blogs I saw a link to a Michael McClennen RESTful talk.  It was an interesting introduction to those with no background on REST and offered some insights and interpretations based on his experience.  The talk does a good job balancing an informational talk on RESTful interfaces in Perl with a gentle sales pitch for his new CPAN module (Web::DataServices).

First off, anyone that publishes on CPAN has my great respect.   Clearly this author knows his stuff, shares it and that's a very good thing.   I'm not sure I will become a user of this module, primarily because of the dependencies (Moo, etc), but more to the point I'm not (yet) convinced one needs a complete RESTful framework that sits on top of a web development framework.

Having said that, I reserve the right to change my mind and I imagine the author spent a lot of time thinking of that as well and ultimately concluded this his effort was worthy of the problem.   Congrats to Michael on publishing his module and adding another building block or at least reference for Perl developers.  I admire that effort and wish I had the time and energy to do the same.

So, do we really need a RESTful API framework?


I'm not sure.  Why don't I think we need a RESTful framework?  Well, I would hope that that the web framework itself that was chosen is robust enough to implement the RESTful architecture and your API without a lot of overhead or hair pulling.  After all, the RESTful architecture is supposed to reflect the stateless and simple nature of the web.  Sort of, I guess.  Paraphrasing a slide from Michael's presentation, there's not too much one needs from a framework to produce a RESTful API.  Here's what we'd like from our framework in order to implement our API.