From 5d5e40f90947e3ccdd5112fa9c7485f923abfb25 Mon Sep 17 00:00:00 2001
From: Florian Forster <octo@leeloo.lan.home.verplant.org>
Date: Fri, 13 Nov 2009 15:56:04 +0100
Subject: [PATCH] erlang plugin: Sample implementation of register_read.

It doesn't do anything useful yet but demonstrates how Funs (even
anonymous functions) can be called.
---
 bindings/erlang/collectd.erl |  5 ++++-
 src/erlang.c                 | 51 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/bindings/erlang/collectd.erl b/bindings/erlang/collectd.erl
index f4b31c6a..cee7c1b5 100644
--- a/bindings/erlang/collectd.erl
+++ b/bindings/erlang/collectd.erl
@@ -1,11 +1,14 @@
 -module(collectd).
--export([dispatch_values/1]).
+-export([dispatch_values/1, register_read/1]).
 
 -include("collectd.hrl").
 
 dispatch_values (VL) when is_record (VL, value_list) ->
 	call_cnode (dispatch_values, VL).
 
+register_read (Callback) ->
+	call_cnode (register_read, Callback).
+
 call_cnode(Func, Args) ->
 	{any, 'collectd@leeloo.lan.home.verplant.org'} ! {Func, Args},
 	receive
diff --git a/src/erlang.c b/src/erlang.c
index c2d243fa..3da9e0f4 100644
--- a/src/erlang.c
+++ b/src/erlang.c
@@ -504,6 +504,55 @@ static int handle_dispatch_values (ce_connection_info_t *cinfo, /* {{{ */
 	return (0);
 } /* }}} int handle_dispatch_values */
 
+/* Returns non-zero only if the request could not be handled gracefully. */
+static int handle_register_read (ce_connection_info_t *cinfo, /* {{{ */
+		const ErlMessage *req)
+{
+	ETERM *eterm_cb;
+	ETERM *rpc_args;
+	ETERM *rpc_reply;
+
+	if ((cinfo == NULL) || (req == NULL))
+		return (EINVAL);
+
+	eterm_cb = erl_element (2, req->msg);
+
+	if (ERL_TYPE (eterm_cb) != ERL_FUNCTION)
+	{
+		erl_free_term (eterm_cb);
+		send_error (cinfo->fd, req->from,
+				"Argument to `register_read' must be a callback function.");
+		return (0);
+	}
+
+	send_atom (cinfo->fd, req->from, "success");
+
+	/* FIXME: The following demonstrates how to call this function. This should
+	 * be moved somewhere else, of course. */
+
+	/* --- 8< --- */
+	rpc_args = erl_format ("[~w,[]]", eterm_cb);
+	if (rpc_args == NULL)
+	{
+		erl_free_term (eterm_cb);
+		send_error (cinfo->fd, req->from,
+				"erl_format failed. Sorry.");
+		return (0);
+	}
+
+	rpc_reply = erl_rpc (cinfo->fd,
+			/* module = */ "erlang", /* function = */ "apply",
+			/* arguments = */ rpc_args);
+
+	erl_free_compound (rpc_args);
+	/* Right now, the return value is not used. */
+	erl_free_compound (rpc_reply);
+	/* --- >8 --- */
+
+	erl_free_term (eterm_cb); /* XXX: This must stay here. */
+	return (0);
+} /* }}} int handle_dispatch_values */
+
 static void *handle_client_thread (void *arg) /* {{{ */
 {
 	ce_connection_info_t *cinfo;
@@ -562,6 +611,8 @@ static void *handle_client_thread (void *arg) /* {{{ */
 			reply = NULL;
 			if (strcmp ("dispatch_values", ERL_ATOM_PTR (func)) == 0)
 				status = handle_dispatch_values (cinfo, &emsg);
+			else if (strcmp ("register_read", ERL_ATOM_PTR (func)) == 0)
+				status = handle_register_read (cinfo, &emsg);
 			else
 			{
 				ERROR ("erlang plugin: Received request for invalid function `%s'.",
-- 
2.11.0