libcurl integration

This page is a place to discuss the integration of libcurl into Kamailio.

There are currently five modules that use the curl library:

• utils
• xcap_client
• auth_identity
• curl
• async_http (currently on a pull-request)

libcurl and some libraries that it uses (openSSL) can conflict if initialised multiple times. If users wish to use more than one feature that depends on libcurl, the conflict must be resolved. This is likely to be achieved by having a single module that wrappers libcurl and is responsible for global initialisation etc. The different ways it can be called can be exported by APIs to other modules.

• Synchronous queries
• Asynchronous queries that suspend the transaction and resume on completion
• Asynchronous queries that call an event_route on completion
• Ability to configure 'named connections' with preset curl options (keys/certs, verify flags etc)
• query functions exported via a C API to other modules

Any more? See also TODO.txt in the curl module

• Ability to pass a list of HTTP header to add
• Ability to retrieve response headers (e.g. header callback function) - required for xcap_client module

The curl module currently offers a synchronous query function which can use named connections set up in modparams. Client certificates and parameters can be configured globally or per connection and there is an exported API. This uses the curl 'easy' interface without worker processes.

The async_http module offers an asynchronous query function which can optionally suspend the transaction. This uses the curl 'multi' interface and creates worker processes.

The final solution will be a combination of these, however consensus should be reached on the architecture. Should these be combined into a single module, or should one depend on the other? It should of course be easy to understand by the end user.

Items to discuss:

• Name of modules(s)
• Definition of API functions and parameters
• Use of worker pools

Names

• The curl module has been renamed to “Http_client”
• Need new name for the new module

Please add your own comments below (hpw)

• (gv) I think it was mentioned at the meeting in Brussels: it would be nice to have a separate configuration file with the “connections”, which can be reloaded at run time (like http://kamailio.org/docs/modules/stable/modules/tls.html#tls.r.tls.reload).
• (oej) The “curl” prefix needs to go away from the functions, parameters and api in the http_client module. New names discussed on sr-dev