Erlang and OTP in Action.pdf - Synrc

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The get entry point is, perhaps, the simplest of the three. This is used for retrieving a a value
from the cache. It expects the request to come in as an GET request with the following
format.
GET /key
If we receive this request then we return the value in the cache associated with that key.
The delete entry point follows closely the format of the get request, with the exception
that it expectes it to come in as an HTTP DELETE request. We expect a url of the following
form.
DELETE /key
If we receive this request we are expected to delete the value specified by key from the
cache.
Finally we have the most complex of the entry points, the put entry point. We expect this
request to come in as an HTTP PUT request. The main difference between this entry point
and the get/put entry point is that the message has a body. That body will contain the value
we are expected to insert into the cache. We expect a url of the following form.
PUT /key
If we receive this request we are expected to insert a new value into the simple_cache.
This value will be identified by the ‘key’ in the url with a value specified by the body of the
message.
Implementing Our Protocol in the HTTP Server
We implement our protocol in the handle_message function of our HTTP server. The code
is listed in code listing 11.10.
Code listing 11.10 – handle_message/2
handle_message({http_request, 'GET', {abs_path, [$/|Key]}, _}, _Body) ->
case simple_cache:lookup(Key) of
{ok, Value} -> create_http_message(200, "text/html", Value);
{error, not_found} -> create_http_message(404)
end;
handle_message({http_request,'PUT',{abs_path, [$/|Key]},_}, Body) ->
simple_cache:insert(Key, Body),
create_http_message(200);
handle_message({http_request, 'DELETE', {abs_path, [$/|Key]}, _}, _Body) ->
simple_cache:delete(Key),
create_http_message(200).
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