Tales of a developer

I'm still working on my  expiring records  module in Erlang (see  here  and  here  for my previous posts on this). Previously, I had started using Mnesia, but only a RAM based table. I've now switched it over to a replicated disc based table. That was easy enough, but it took a while to figure out how to do, nonetheless. I had assumed that simply adding ... { disc_copies , [ node ()]} ... to the arguments to  mnesia:create_table  would be enough. This resulted in an error: { app_test , init_per_testcase , {{ badmatch , { aborted , { bad_type , expiring_records , disc_copies , nonode@nohost }}}, ... After some head-scratching and lots of Googling I realized that I was missing a call to  mnesia:create_schema  to allow it to create disc based tables. My tests for this module are done with  common_test  so I set up a per suite initializat...

Continuing with my  expiring records  module (see  my previous blog ), I've now switched it over to using  Mnesia , rather than a dictionary object stored in the state of my  gen_server  instance. It is still not a truly global, cross-node key/value store for expiring records, but it is getting there. I wanted to focus first on getting my tests to pass again with a RAM based table on one node. I just need to tweak the values passed in when creating the Mnesia table, I think, to make this work with a disc based table, replicated across nodes. Currently the table is created like this: prepare_table () -> case catch mnesia : table_info ( expiring_records , attributes ) of { 'EXIT' , _ } -> % % Table does not exist - create it erlang : display ( " Creating table " ), mnesia : create_table ( expiring_records , [ { attributes , record_info ( fields , record )}, ...

I'm continuing my experiments with Erlang - this time trying out  gen_server  with a simple key/value store with a twist - the values have an expiration date. As a first iteration I'm simply using a dictionary to store the values, and only expiring records when they are looked up. My plan is to extend this later on so that this can be a global key/value store across multiple Erlang nodes but for now I'm focusing on two things - get something going using  gen_server , and try out the  common_test  testing framework. The code is here:  https://github.com/snorristurluson/erl-expiring-records Let's first take a look at a couple of the test functions, to show the usage of this: get_non_expired_record ( Config ) -> Pid = ? config ( pid , Config ), Record = { " bingo " , " bongo " , erlang : system_time ( second ) + 3600 }, ok = gen_server : call ( Pid , { add , Record }), { ok , " bongo " } = gen_server : call...

In a  previous blog  I described a simple echo bot, that echoes back anything you say to it. This time I will talk about a bot that generates traffic for the chat server, that can be used for load-testing both the chat server as well as any chat clients connected to it. I've dubbed it  JumperBot  - it jumps between chat rooms, saying a few random phrases in each room, then jumping to the next one. This bot builds on the same framework as the  EchoBot  - refer to the previous blog if you are interested in the details. The source lives on GitHub:  https://github.com/snorristurluson/xmpp-chatbot Configure the server In an  earlier blog  I described the setup of Prosody as the chat server to run against. Before we can connect bots to the server we have to make sure they can log in, either by creating accounts for them: prosodyctl register jumperbot_0 localhost jumperbot prosodyctl register jumperbot_1 localhost jumperbot ... or by ...

I've been digging deeper into my experiments with Erlang and have improved the JSON parser I discussed in a  previous blog . The code lives at  https://github.com/snorristurluson/erl-simple-json  in case you want to take a look. The project is now set up to take advantage of  rebar3 , the Erlang build system, and tests are run automatically on  Travis CI . Thanks,  Lou Xun ! The parser now does proper tokenizing, rather than the simple string split operations I did in my first pass. The parser itself is surprisingly simple when it's working with tokens - here it is in its entirety: parse_json ( Input ) -> { Value , <<>>} = parse_json_value ( Input ), Value . parse_json_value ( Input ) -> { Token , Rest } = tokens : tokenize ( Input ), case Token of open_brace -> populate_object ( dict : new (), Rest ); open_square_bracket -> populate_list ([], Rest ); { ...