Hydrometeor is a long-polling webserver based on a pubsub model, written in Erlang
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There's not a lot here yet. But if you want instructions:


  1. Install the latest version of Erlang.

  2. Get the repository (look up how to use Git?)

  3. run make in this directory. Make sure everything looks ok

  4. Adjust hm_rel-1.rel to correspond with your Erlang versions. Whether you make changes or not run erl -pa ./ebin then on the Erlang command line run systools:make_script("hm_rel-1", [local]).. Then quit the Erlang shell. This updates the boot script to correspond with your versions. I'm probably going to remove this step once I understand more about Erlang releases etc.

  5. Make sure start.sh is executable: chmod +x start.sh.

  6. ./start.sh

  7. Have fun! You might need to look in the code to know what to do.


Hydrometeor doesn't have a configuration file (yet), but most configurable parameters are easily located. Here's some you might want:

  • Listening port: src/hm_sup.erl.
  • Long-polling connection timeout: src/hm_web.erl at the top.
  • URI for Hydrometeor API: src/hm_web.erl default is '/hm1backend'.
  • Maximum channel log size: src/hm_server.erl at the top.
  • Maximum channel age: src/hm_server.erl at the top.
  • Channel 'state' file: src/hm_server.erl at the top.
  • Housekeeping interval: src/hm_app.erl at the top. You can also control what housekeeping does here (write in your own Erlang if you want).


At the moment you can use the Erlang shell you are dumped in to send messages, like:

hm_server:send("testchannel", <<"Hello there!">>).

Alternatively, you can send HTTP POST data to the server:

curl -d "channel=testchannel&message=testmessage" http://localhost:9002/hm1backend/admin/send

Before sending that, in another terminal run a curl command ready to receive it:

curl "http://localhost:9002/hm1backend/subscribe?channel=testchannel"

Messages are sent in a format of id,message for the moment. The id can be used with a since parameter. So for example, send another message:

hm_server:send("testchannel", <<"Hello again!">>).

Now run the curl command:

curl "http://localhost:9002/hm1backend/subscribe?channel=testchannel&since=1"

You should receive 2,Hello again! straight away.