pve-common/README.dev

====================================
Setup PVE v2 Development Environment
====================================

1.  Install Debian 'squeeze'
2.  Install prerequisites for development environment:

apt-get -y install build-essential subversion debhelper autotools-dev \
doxygen check pkg-config libnss3-dev groff quilt dpatch libxml2-dev \
libncurses5-dev libslang2-dev libldap2-dev xsltproc python-pexpect \
python-pycurl libdbus-1-dev openipmi sg3-utils libnet-snmp-perl \
libnet-telnet-perl snmp python-openssl libxml2-utils automake autoconf \
libsqlite3-dev sqlite3 libfuse-dev libglib2.0-dev librrd-dev \
librrds-perl rrdcached lintian libdevel-cycle-perl libjson-perl \
liblinux-inotify2-perl libio-stringy-perl unzip fuse-utils \
libcrypt-openssl-random-perl libcrypt-openssl-rsa-perl \
libauthen-pam-perl libterm-readline-gnu-perl libssl-dev open-iscsi \
libapache2-mod-perl2 libfilesys-df-perl libfile-readbackwards-perl \
libpci-dev texi2html libgnutls-dev libsdl1.2-dev bridge-utils \
libvncserver0 rpm2cpio  apache2-mpm-prefork libintl-perl \
libapache2-request-perl libnet-dns-perl vlan libio-socket-ssl-perl \
libfile-sync-perl ifenslave-2.6 libnet-ldap-perl console-data

3.  Download and install the following svn modules in order from top to bottom:

svn://devel.proxmox.com/var/svn/pve/

libqb/trunk
corosync/trunk
openais/trunk
pve-common/trunk
pve-cluster/trunk
redhat-cluster/trunk
pve-access-control/trunk
pve-storage/pve2
pve-qemu-kvm/pve2
qemu-server/pve2
vncterm/pve2
pve-manager/pve2
pve-kernel-2.6.32-rh/pve2

Most source can be installed with 'make dinstall' command.

4.  Reboot the system.
5.  Learn to use the quilt patch scripts.
6.  Happy coding.

There is an experimental package containing the API documentation
as ExtJS application:

pve2-api-doc/trunk


REST vs. SOAP
=============

We decided to change our SOAP API (1.X) and use a REST like API. The
concept is described in [1] (Resource Oriented Architecture
(ROA)). The main advantage is that we are able to remove a lot of code
(the whole SOAP stack) to reduce software complexity.

We also moved away from server side content generation. Instead we use
the ExtJS Rich Internet Application Framework
(http://www.sencha.com). 

That framework, like any other AJAX toolkit, can talk directly to the
REST API using JSON. So we were able to remove the server side
template toolkit completely.

JSON and JSON Schema
====================

We use JSON as data format, because it is simple and parse-able by any
web browser.

Additionally, we use JSON Schema [2] to formally describe our API. So
we can automatically generate the whole API Documentation, and we can
verify all parameters and return values.

An great side effect was that we are able to use JSON Schema to
produce command line argument parsers automatically. In fact, the REST
API and the command line tools use the same code.

Object linkage is done using the JSON Hyper Schema (links property).

A small utility called 'pvesh' exposes the whole REST API on the command
line.

So here is a summary of the advantage:

   - easy, human readable data format (native web browser format)
   - automatic parameter verification (we can also verify return values)
   - automatic generation of API documentation
   - easy way to create command line tools (using same API).

API Implementation (PVE::RESTHandler)
=====================================

All classes exposing methods on the API use PVE::RESTHandler as base class.

  use base qw(PVE::RESTHandler);

To expose methods, one needs to call register_method():

  __PACKAGE__->register_method ($schema);

Where $schema is a PVE method schema as described in
PVE::JSONSchema. It includes a description of parameters and return
values, and a reference to the actual code

__PACKAGE__->register_method ({
    name => 'echo', 
    path => 'echo', 
    method => 'GET',
    description => "simple return value of parameter 'text'",
    parameters => {
	additionalProperties => 0,
	properties => {
	    text => {
	    	 type => 'string',
	    }	  
	},
    },
    returns => {
	type => 'string',
    },
    code => sub {
	my ($conn, $resp, $param) = @_;

	return $param->{text};
    }
});

The 'name' property is only used if you want to call the method
directly from Perl. You can do that using:

  print __PACKAGE__->echo({ text => "a test" });

We use Perl's AUTOLOAD feature to implement this. Note: You need to
pass parameters a HASH reference.

There is a special helper method called cli_handler(). This is used by
the CLIHandler Class for command line tools, where you want to pass
arguments as array of strings. This uses Getopt::Long to parse parameters.

There is a second way to map names to methods - using the 'path'
property.  And you can register subclasses. That way you can set up a
filesystem like hierarchy to access methods. 

Here is an example:
----------------------------
package C1;

__PACKAGE__->register_method ({
    subclass => "C2",  
    path => 'sub2',
});


__PACKAGE__->register_method ({
    name => 'list1',    
    path => 'index',
    method => 'GET',
    ...
});

package C2;

__PACKAGE__->register_method ({
    name => 'list2',    
    path => 'index',
    method => 'GET',
    ...
});
-------------------------------

The utily method find_handler (in PVE::RESTHandler) can be use to do
'path' related method lookups.

C1->find_handler('GET', "/index")      => C1::list1
C1->find_handler('GET', "/sub2/index") => C2::list2

The HTTP server use the URL (a path) to find the corresponding method. 


References
==========
[1] RESTful Web Services
Web services for the real world

By
    Leonard Richardson, Sam Ruby
Publisher:
    O'Reilly Media
Released:
    May 2007 

[2] JSON Schema links: http://json-schema.org/