add support for custom commands in redis plugin

Now that the redis plugin has moved to hiredis, it could
be worthwhile to add support for custom commands.

This diff implements a mechanism for executing commands which
allows for setting the type and type-instance. It doesn not
support hash or array returns, but if this is deemed necessary
could be added later on.

The canonical use case for this is for people using redis
has a queue (for instance, using solutions such as rq,
sidekiq and similar solutions) who want a simple way to
ensure the work queue size is not growing. To address this
you would use:

```
<Plugin redis>
  <Node local>
    <Command "queue_length">
      Exec "LLEN myqueue"
      Instance "myqueue"
    </Command>
  </Node>
</Plugin>
```

This would then produce a redis-local/queue_length-myqueue value.

If the idea has traction I'll add the doc bits.

diff --git a/src/redis.c b/src/redis.c
index f5bb304..02f3edd 100644 (file)
--- a/src/redis.c
+++ b/src/redis.c
@@ -40,6 +40,7 @@
 #define MAX_REDIS_NODE_NAME 64
 #define MAX_REDIS_PASSWD_LENGTH 512
 #define MAX_REDIS_VAL_SIZE 256
+#define MAX_REDIS_COMMAND 2048
 
 /* Redis plugin configuration example:
  *
@@ -53,6 +54,16 @@
  * </Plugin>
  */
 
+struct redis_command_s;
+typedef struct redis_command_s redis_command_t;
+struct redis_command_s
+{
+    char command[MAX_REDIS_COMMAND];
+    char type[DATA_MAX_NAME_LEN];
+    char instance[DATA_MAX_NAME_LEN];
+    redis_command_t *next;
+};
+
 struct redis_node_s;
 typedef struct redis_node_s redis_node_t;
 struct redis_node_s
@@ -62,6 +73,7 @@ struct redis_node_s
   char passwd[MAX_REDIS_PASSWD_LENGTH];
   int port;
   struct timeval timeout;
+  redis_command_t *commands;
 
   redis_node_t *next;
 };
@@ -110,10 +122,46 @@ static int redis_node_add (const redis_node_t *rn) /* {{{ */
   return (0);
 } /* }}} */
 
+static redis_command_t *redis_config_command (oconfig_item_t *ci) /* {{{ */
+{
+    redis_command_t *rc;
+    int status;
+    int i;
+
+    rc = calloc(1, sizeof(*rc));
+    if (rc == NULL) {
+        ERROR("redis plugin: calloca failed adding redis_command.");
+        return NULL;
+    }
+    status = cf_util_get_string_buffer(ci, rc->type, sizeof(rc->type));
+    if (status != 0)
+        goto err;
+
+    for (i = 0; i < ci->children_num; i++) {
+        oconfig_item_t *option = ci->children + i;
+
+        if (strcasecmp("Exec", option->key) == 0) {
+            status = cf_util_get_string_buffer(option, rc->command, sizeof(rc->command));
+        } else if (strcasecmp("Instance", option->key) == 0) {
+            status = cf_util_get_string_buffer(option, rc->instance, sizeof(rc->instance));
+        }
+        if (status != 0)
+            goto err;
+    }
+    if (strlen(rc->command) == 0) {
+        WARNING("redis plugin: invalid command definition for: %s", rc->type);
+        goto err;
+    }
+    return rc;
+ err:
+    free(rc);
+    return NULL;
+} /* }}} */
 
 static int redis_config_node (oconfig_item_t *ci) /* {{{ */
 {
   redis_node_t rn;
+  redis_command_t *rc;
   int i;
   int status;
   int timeout;
@@ -122,6 +170,7 @@ static int redis_config_node (oconfig_item_t *ci) /* {{{ */
   sstrncpy (rn.host, REDIS_DEF_HOST, sizeof (rn.host));
   rn.port = REDIS_DEF_PORT;
   rn.timeout.tv_usec = REDIS_DEF_TIMEOUT;
+  rn.commands = NULL;
 
   status = cf_util_get_string_buffer (ci, rn.name, sizeof (rn.name));
   if (status != 0)
@@ -142,6 +191,16 @@ static int redis_config_node (oconfig_item_t *ci) /* {{{ */
         status = 0;
       }
     }
+    else if (strcasecmp ("Command", option->key) == 0)
+    {
+      rc = redis_config_command(option);
+      if (rc == NULL) {
+          status =1;
+      } else {
+          rc->next = rn.commands;
+          rn.commands = rc;
+      }
+    }
     else if (strcasecmp ("Timeout", option->key) == 0)
     {
       status = cf_util_get_int (option, &timeout);
@@ -256,9 +315,67 @@ int redis_handle_info (char *node, char const *info_line, char const *type, char
 
 } /* }}} int redis_handle_info */
 
+int redis_handle_command (redisContext *rh, redis_node_t *rn, redis_command_t *rc) /* {{{ */
+{
+    redisReply *rr;
+    const data_set_t *ds;
+    value_t val;
+
+    ds = plugin_get_ds (rc->type);
+    if (!ds) {
+        ERROR ("redis plugin: DataSet `%s' not defined.", rc->type);
+        return (-1);
+    }
+
+    if (ds->ds_num != 1) {
+        ERROR ("redis plugin: DS `%s' has too many types.", rc->type);
+        return (-1);
+    }
+
+    if ((rr = redisCommand(rh, rc->command)) == NULL) {
+        WARNING("redis plugin: unable to carry out command `%s'.", rc->command);
+        return (-1);
+    }
+
+    switch (rr->type) {
+    case REDIS_REPLY_INTEGER:
+        switch (ds->ds[0].type) {
+        case DS_TYPE_COUNTER:
+            val.counter = (counter_t)rr->integer;
+            break;
+        case DS_TYPE_GAUGE:
+            val.gauge = (gauge_t)rr->integer;
+            break;
+        case DS_TYPE_DERIVE:
+            val.gauge = (derive_t)rr->integer;
+            break;
+        case DS_TYPE_ABSOLUTE:
+            val.gauge = (absolute_t)rr->integer;
+            break;
+        }
+        break;
+    case REDIS_REPLY_STRING:
+        if (parse_value (rr->str, &val, ds->ds[0].type) == -1) {
+            WARNING("redis plugin: Unable to parse field `%s'.", rc->type);
+            freeReplyObject (rr);
+            return (-1);
+        }
+        break;
+    default:
+        WARNING("redis plugin: Cannot coerce redis type.");
+        freeReplyObject(rr);
+        return (-1);
+    }
+
+    redis_submit(rn->name, rc->type, (strlen(rc->instance) >0)?rc->instance:NULL, val);
+    freeReplyObject (rr);
+    return 0;
+} /* }}} int redis_handle_info */
+
 static int redis_read (void) /* {{{ */
 {
   redis_node_t *rn;
+  redis_command_t *rc;
 
   for (rn = nodes_head; rn != NULL; rn = rn->next)
   {
@@ -312,6 +429,10 @@ static int redis_read (void) /* {{{ */
     redis_handle_info (rn->name, rr->str, "current_connections", "slaves", "connected_slaves", DS_TYPE_GAUGE);
 
     freeReplyObject (rr);
+
+    for (rc = rn->commands; rc != NULL; rc = rc->next)
+        redis_handle_command(rh, rn, rc);
+
     redisFree (rh);
   }