Add read_buffer_size option to statsd input (influxdata#4598)

Author: danielnelson

plugins/inputs/statsd/README.md

@@ -58,6 +58,10 @@
   ## calculation of percentiles. Raising this limit increases the accuracy
   ## of percentiles but also increases the memory usage and cpu time.
   percentile_limit = 1000
+
+  ## Maximum socket buffer size in bytes, once the buffer fills up, metrics
+  ## will start dropping.  Defaults to the OS default.
+  # read_buffer_size = 65535
 ```
 
 ### Description

plugins/inputs/statsd/statsd.go

@@ -76,6 +76,8 @@ type Statsd struct {
 	// see https://github.com/influxdata/telegraf/pull/992
 	UDPPacketSize int `toml:"udp_packet_size"`
 
+	ReadBufferSize int `toml:"read_buffer_size"`
+
 	sync.Mutex
 	// Lock for preventing a data race during resource cleanup
 	cleanup sync.Mutex
@@ -411,6 +413,10 @@ func (s *Statsd) udpListen() error {
 	}
 	log.Println("I! Statsd UDP listener listening on: ", s.UDPlistener.LocalAddr().String())
 
+	if s.ReadBufferSize > 0 {
+		s.UDPlistener.SetReadBuffer(s.ReadBufferSize)
+	}
+
 	buf := make([]byte, UDP_MAX_PACKET_SIZE)
 	for {
 		select {