mod_server_storage

Model functions

model/server_storage/post/key store a key, with the value of in the payload of the message.

model/server_storage/get/key - fetch a key.

model/server_storage/get - fetch all keys.

model/server_storage/delete/key - delete a key.

model/server_storage/delete - delete all values from the server storage.

Example in JavaScript from the client:

cotonic.broker.publish("bridge/origin/model/server_storage/post/foo", { "hello": "world" });

cotonic.broker.call("bridge/origin/model/server_storage/get/foo")
       .then( (msg) => console.log(msg) );

{
    dup: false
    packet_id: null
    payload: {result: {hello: "world"}, status: "ok"}
    properties: {content_type: "application/json"}
    qos: 0
    retain: false
    topic: "reply/page-3-0.4080048813145437"
    type: "publish"
}

Example in a template:

The hello key of foo is now: {{ m.server_storage.foo.hello|escape }}

Note that we must escape the value, as it originates from the client and contains arbitrary values, including HTML.

Example in Erlang:

m_server_storage:store(<<"foo">>, #{ <<"hello">> => <<"world">> }, Context),

case m_server_storage:lookup(<<"foo">>, Context) of
    {ok, Value} ->  % Found the value
    {error, no_session} -> % No session
    {error, not_found} -> % There is a session but unknown key
end.

m_server_storage:delete(<<"foo">>, Context).

Storage of secret server data

Sometimes the server code wants to attach data to the specific client that is not accessible to the client itself. An example is a secret during an OAuth handshake.

For this there is a special, unlimited, storage API, which is only accessible using the Erlang API:

m_server_storage:secure_store(<<"foo">>, #{ <<"my">> => <<"secret">> }, Context),

case m_server_storage:secure_lookup(<<"foo">>, Context) of
    {ok, Value} ->  % Found the value
    {error, no_session} -> % No session
    {error, not_found} -> % There is a session but unknown key
end.

m_server_storage:secure_delete(<<"foo">>, Context).

The keys in the secure storage are separate from the keys in the normal storage. There can be a key with the same name and different values in both storages.

Storage process

If a value is stored in the server side storage then a process is started. This process holds all stored values, and times out after 900 seconds.

Any HTTP request with the proper sid will extend the lifetime of the storage process.

The storage process holds at most 100 KB of data, above that it will respond with a full error status.

Configuration keys

There are two configuration keys, both need a number:

• mod_server_storage.storage_expire The timeout in seconds of the storage process defaults to 900 seconds.
• mod_server_storage.storage_maxsize The maximum stored size in bytes, both the keys and the values are counted. Default is 100 KB.

Note that the storage is in-memory, so it is best to set the storage maxsize and expire as low as possible.