web commit by http://jcflack.myopenid.com/: Oh, *that's* where XML RPC is specified! :)

[ikiwiki.git] / doc / plugins / write / external.mdwn

diff --git a/doc/plugins/write/external.mdwn b/doc/plugins/write/external.mdwn
index 3612dd9c3f09517f6e97f338653b33c2508ee0db..47834567a7cfb81417702cbef0db10de48efefa3 100644 (file)
--- a/doc/plugins/write/external.mdwn
+++ b/doc/plugins/write/external.mdwn
@@ -1,13 +1,20 @@
 External plugins are standalone, executable programs, that can be written
 in any language. When ikiwiki starts up, it runs the program, and
-communicates with it using XML RPC. If you want to [[write]] an external
+communicates with it using [XML RPC][xmlrpc]. If you want to [[write]] an external
 plugin, read on..
 
+[xmlrpc]: http://www.xmlrpc.com/
+
 ikiwiki contains one sample external plugin, named `externaldemo`. This is
 written in perl, but is intended to be an example of how to write an
 external plugin in your favorite programming language. Wow us at how much
 easier you can do the same thing in your favorite language. ;-)
 
+There's now a second external plugin, the [[rst]] plugin, written in
+python. It uses a `proxy.py`, a helper library for ikiwiki python plugins.
+
+[[toc ]]
+
 ## How external plugins use XML RPC
 
 While XML RPC is typically used over http, ikiwiki doesn't do that.
@@ -43,6 +50,14 @@ to access any such global hash. To get the "url" configuration value,
 call `getvar("config", "url")`. To set it, call 
 `setvar("config", "url", "http://example.com/)`.
 
+The `%pagestate` is a special hash with a more complex format. To access
+it, external plugins can use the `getstate` and `setstate` RPCs. To access
+stored state, call `getstate("page", "id", "key")`, and to store state,
+call `setstate("page", "id", "key", "value")`.
+
+To access ikiwiki's ARGV array, call `getargv()`. To change its ARGV, call
+`setargv(array)`.
+
 ## Notes on function parameters
 
 The [[plugin_interface_documentation|write]] talks about functions that take
@@ -66,6 +81,19 @@ Other languages might not find it so easy. If not, it might be a good idea
 to convert these named parameters into something more natural for the
 language as part of their XML RPC interface.
 
+## undef
+
+XML RPC has a limitation that it does not have a way to pass
+undef/NULL/None. There is an extension to the protocol that supports this,
+but it is not yet available in the [[cpan XML::RPC]] library used by
+ikiwiki.
+
+Until the extension is available, ikiwiki allows undef to be communicated
+over XML RPC by passing a sentinal value, a hash with a single key "null"
+with a value of an empty string. External plugins that need to communicate
+null values to or from ikiwiki will have to translate between undef and
+the sentinal.
+
 ## Function injection
 
 Some parts of ikiwiki are extensible by adding functions. For example, the
@@ -85,13 +113,10 @@ to 1.
 
 Since XML RPC can't pass around references to objects, it can't be used
 with functions that take or return such references. That means you can't
-use XML RPC for `cgi` or `formbuilder` hooks (which are passed CGI and
+100% use XML RPC for `cgi` or `formbuilder` hooks (which are passed CGI and
 FormBuilder perl objects), or use it to call `template()` (which returns a
 perl HTML::Template object).
 
-Also. the `getopt` hook doesn't work, as ARGV is not available to the external
-plugin.
-
 ## Performance issues
 
 Since each external plugin is a separate process, when ikiwiki is
@@ -115,8 +140,8 @@ number of calls.
 Injecting a replacement for a commonly called ikiwiki function
 could result in a lot more RPC calls than expected and slow
 eveything down. `pagetitle`, for instance, is called about 100 times
-per page build. Memoizing injected functions whenever possible is a very
-good idea.
+per page build. Whenever possible, you should tell ikiwiki to memoize
+injected functions.
 
 In general, use common sense, and your external plugin will probably
 perform ok.