PHP - OpenID library integration

An excellent introduction to the openID library as a consumer from the PHP here.

Erlang based WebSocket client in place

An erlang based WebSocket client in place here , for clients that deal with web socket protocol as yet. 

Storing Data in a Hash - Erlang

Came across this nice example in the Erlang mailing list for storing data in an hashmap.

-module(db_server).

-export([start/0, init/1, write/2, read/1, delete/1]).

start() ->
register(server, spawn(db_server, init, [dict:new()])).

init(Records) ->
receive
{add, Pid, Key, Value} ->
RecordsNew = dict:store(Key, Value, Records),
Pid ! {ok, Key, Value},
init(RecordsNew);
{show, Pid, Key} ->
case dict:find(Key, Records) of
{ok, Value} -> Pid ! {ok, Value};
error ->  Pid ! {error, no_such_value}
end,
init(Records);
{delete, Pid, Key} ->
RecordsNew = dict:erase(Key, Records),
Pid ! {ok, ok},
init(RecordsNew)           
end.

write(Key, Value) ->
server ! {add, self(), Key, Value},
receive Res ->
Res
end.

read(Key) ->
server ! {show, self(), Key},
receive Res ->
Res
end.

delete(Key) ->
server ! {delete, self(), Key},
receive Res ->
Res
end.

Deleting tags from remote in git

Happened to go through a build process , and while flipping around with versions - it created some tags on the remote repository that I wanted to get rid of entirely.

For example - lets assume the tag name is artifactA-0.1.0 .

$ git tag -d artifactA-0.1.0 

This deletes the tag locally ( in your local clone )
To push the change to remote and to delete the tag remotely as well - we can give -

$ git push origin :artifactA-0.1.0

where , I assume origin is the name of the remote branch from which I cloned initially.

This should delete the tag remotely as well.

GPG agent

When preparing some artifacts to be published to a maven repository - needed some help with gpg publishing.

More often that not - when the gpg key verification was happening - it was reporting about a missing file -    ~/.gnupg/S.gpg-agent .

'touch'ing would not help because that is not a file , but a socket for the agent to listen on.

$ gpg-agent --use-standard-socket --daemon 2>/dev/null

This makes the agent listen on the socket.

Google Collections SVN repository

Google Collections 1.0 was released recently towards the end of December 2009. While very useful from an API and performance perspective, the API had quite an amount of surprises / deprecations / removals in its later stages ( 0.7 / 0.8 etc.) .

With 1.0 the API seems to have been stabilized and as an added benefit for those integrating with mvn - it is also available here as the mvn repository - http://google-maven-repository.googlecode.com/svn/repository/com/google/collections/google-collections/1.0/ .

com.google.collections / google-collections / 1.0 should do the trick in ivy.xml / pom.xml as appropriate.

libevent 2.0 released

As per this update on the google developer blog , libevent 2.0 seems to be released.

For those of you new to the library - libevent provides a platform agnostic event handling library so that the user does deal with the quirks of the operating systems like Linux and Solaris and chooses the best event handling adapter present in the kernel ( Eg: In Linux, from 2.6 - epoll performs much better than poll / select . The former in O(1) in handling of connections whereas the latter group is O(n) in event handling proportional to the number of active connections at that time instant ).

More details are available in the book available here.

Specifically about the update - it seems like the developers on Windows would benefit a lot from the API changes made. I will probably write a more detailed review of the same after playing around with the software / API on various platforms and distributions.

Resetting / Overwriting /etc/resolv.conf in EC2 instance

Creates a new EC2 instance ( CentOS ) and by default it comes with a dns resolver to the outside world.

For our purposes - we had set up an internal dns server running (bind - process 'named' on a particular host).

When we were launching our pool of servers - we wanted to make sure that the new instances fall under the same domain that we specify it to be.

We also wanted to set the nameserver of the newly created instances pointing to the internal DNS server we have to resolve the ambiguity we have.

Before making the change - the file /etc/resolv.conf was looking as follows.

# cat /etc/resolv.conf
; generated by /sbin/dhclient-script
search some.internal.aws.domain
nameserver 172.x.y.z 

where 172.x.y.z was something set by Amazon EC2 by default.

Edit /etc/dhclient.conf ( Create one , if it does not exist )

supersede  domain-name "ec2.mycompany.com" ;
prepend domain-name-servers 10.p.q.r ;my internal company dns

I also found it useful to create an Elastic IP and associate the dns server instance with the elastic ip,
and then have the prepend domain-name-servers refer to the elastic ip , instead of the internal ip.
So - even if the internal dns server fails = we can reconstruct it from another AMI and associate with the elastic ip without affecting the rest of the system.

To see the changes to /etc/dhclient , do the following

$ dhclient -r ; dhclient 

This command forcibly renews the dhcp lease that will force the new credentials from /etc/dhclient.conf to be read.

After doing this , verify /etc/resolv.conf

search ec2.mycompany.com
nameserver 10.p.q.r    ; our DNS server
nameserver 172.x.y.z  ; the one set by amzn

So that completes the process and we are good about it.

Zookeeper build

Was trying to build Zookeeper from trunk ( 3.3.0 ) .

Came across this error  -

create-cppunit-configure:
     [exec] configure.ac:33: warning: macro `AM_PATH_CPPUNIT' not found in library
     [exec] libtoolize: putting auxiliary files in `.'.
     [exec] libtoolize: copying file `./config.guess'
     [exec] libtoolize: copying file `./config.sub'
     [exec] libtoolize: copying file `./install-sh'
     [exec] libtoolize: copying file `./ltmain.sh'
     [exec] libtoolize: Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.ac and
     [exec] libtoolize: rerunning libtoolize, to keep the correct libtool macros in-tree.
     [exec] libtoolize: Consider adding `-I m4' to ACLOCAL_AMFLAGS in Makefile.am.
     [exec] configure.ac:33: warning: macro `AM_PATH_CPPUNIT' not found in library
     [exec] configure.ac:33: error: possibly undefined macro: AM_PATH_CPPUNIT
     [exec]       If this token and others are legitimate, please use m4_pattern_allow.
     [exec]       See the Autoconf documentation.
     [exec] autoreconf: /usr/bin/autoconf failed with exit status: 1

Installed -

$  sudo apt-get install libcppunit-dev

Ended up with ..

     [exec] .../zookeeper/src/c/configure: line 5015: syntax error near unexpected token `1.10.2'
     [exec] .../zookeeper/src/c/configure: line 5015: `   AM_PATH_CPPUNIT(1.10.2)'

Hmm.. bad times.

Installing Thrift Continued

Continuing my previous post of installing Thrift - needed to install the following obvious ones as well.

 sudo apt-get install flex bison 

And then , run ./configure once again to make sure all the libraries are linked together.

 ./configure

This should regenerate the makefiles once again, after installing flex and bison.

Installing Thrift

Checked out thrift from the trunk on my ubuntu box ( 9.10 ) .

The first step on the installation was running the program

$ ./bootstrap.sh

It failed with some errors , some fairly obvious (missing autoconf ) - some not so obvious.
The first step is to get autoconf installed.

$ sudo apt-get install autoconf

Then ran into this error.

$ ./bootstrap.sh
configure.ac:44: error: possibly undefined macro: AC_PROG_LIBTOOL
      If this token and others are legitimate, please use m4_pattern_allow.
      See the Autoconf documentation.
configure.ac:26: installing `./install-sh'
configure.ac:26: installing `./missing'
compiler/cpp/Makefile.am: installing `./depcomp'
configure.ac: installing `./ylwrap'
lib/cpp/Makefile.am:24: Libtool library used but `LIBTOOL' is undefined
lib/cpp/Makefile.am:24:   The usual way to define `LIBTOOL' is to add `AC_PROG_LIBTOOL'
lib/cpp/Makefile.am:24:   to `configure.ac' and run `aclocal' and `autoconf' again.
lib/cpp/Makefile.am:24:   If `AC_PROG_LIBTOOL' is in `configure.ac', make sure
lib/cpp/Makefile.am:24:   its definition is in aclocal's search path.
test/Makefile.am:30: Libtool library used but `LIBTOOL' is undefined
test/Makefile.am:30:   The usual way to define `LIBTOOL' is to add `AC_PROG_LIBTOOL'
test/Makefile.am:30:   to `configure.ac' and run `aclocal' and `autoconf' again.
test/Makefile.am:30:   If `AC_PROG_LIBTOOL' is in `configure.ac', make sure
test/Makefile.am:30:   its definition is in aclocal's search path.

The fix was to install libtool.
$ sudo apt-get install libtool


And then comes the boost libraries -

$ sudo apt-get install libboost1.40-dev libboost1.40-doc

(Your boost library version might be different from mine but you get the idea !!).