influxdb input: Use non-panicking type assertion

closes #1268

CHANGELOG.md

@@ -27,6 +27,7 @@ time before a new metric is included by the plugin.
 - [#1252](https://github.com/influxdata/telegraf/pull/1252): Fix systemd service. Thanks @zbindenren!
 - [#1221](https://github.com/influxdata/telegraf/pull/1221): Fix influxdb n_shards counter.
 - [#1258](https://github.com/influxdata/telegraf/pull/1258): Fix potential kernel plugin integer parse error.
+- [#1268](https://github.com/influxdata/telegraf/pull/1268): Fix potential influxdb input type assertion panic.
 
 ## v0.13.1 [2016-05-24]
 

plugins/inputs/influxdb/influxdb.go

@@ -157,7 +157,8 @@ func (i *InfluxDB) gatherURL(
 			return err
 		}
 
-		if key.(string) == "memstats" {
+		if keyStr, ok := key.(string); ok {
+			if keyStr == "memstats" {
 				var m memstats
 				if err := dec.Decode(&m); err != nil {
 					continue
@@ -195,6 +196,7 @@ func (i *InfluxDB) gatherURL(
 						"url": url,
 					})
 			}
+		}
 
 		// Attempt to parse a whole object into a point.
 		// It might be a non-object, like a string or array.