X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/6eb3cf7e76c53b05154bb2104e395922bd0eed4e..d3ca495e61e0e9d66095b1aba2fd1995e564e841:/doc/plugins/write/external.mdwn?ds=sidebyside

diff --git a/doc/plugins/write/external.mdwn b/doc/plugins/write/external.mdwn
index 4492cd0da..272f74a7c 100644
--- a/doc/plugins/write/external.mdwn
+++ b/doc/plugins/write/external.mdwn
@@ -1,8 +1,10 @@
 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
@@ -11,7 +13,7 @@ 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 ]]
+[[!toc ]]
 
 ## How external plugins use XML RPC
 
@@ -27,7 +29,7 @@ stdin, using XML RPC. Dispatch the command, and return its result to
 stdout, also using XML RPC. After reading a command, and before returning
 the result, the plugin can output XML RPC requests of its own, calling
 functions in ikiwiki. Note: *Never* make an XML RPC request at any other
-time. Ikiwiki won't be listening for it, and you will deadlock.
+time. IkiWiki won't be listening for it, and you will deadlock.
 
 When ikiwiki starts up an external plugin, the first RPC it will make
 is to call the plugin's `import()` function. That function typically makes
@@ -42,7 +44,7 @@ supported in ikiwiki version 2.6.
 
 ## Accessing data structures
 
-Ikiwiki has a few global data structures such as `%config`, which holds
+IkiWiki has a few global data structures such as `%config`, which holds
 its configuration. External plugins can use the `getvar` and `setvar` RPCs
 to access any such global hash. To get the "url" configuration value,
 call `getvar("config", "url")`. To set it, call 
@@ -79,6 +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
@@ -119,12 +134,12 @@ large quantity of data conversion going on. In contrast, `preprocess` hooks
 are called generally rarely, and pass around minimal data.
 
 External plugins should avoid making RPC calls unnecessarily (ie, in a loop).
-Memoizing the results of appropriate RPC calls is one good way to minimise the
+Memoizing the results of appropriate RPC calls is one good way to minimize the
 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
+everything down. `pagetitle`, for instance, is called about 100 times
 per page build. Whenever possible, you should tell ikiwiki to memoize
 injected functions.