Extend client telemetry with per-host stats and limits (#174)

Extends CLI telemetry objects to include packet capture statistics by host.
Also adds fields to track whether the CLI hit an upper limit imposed on the
number of hosts, ports, or interfaces it collects.

client_telemetry/pcap_stats.go

@@ -1,10 +1,12 @@
 package client_telemetry
 
-// We produce a set of packet counters indexed by interface and
+// We produce a set of packet counters indexed by interface, host and
 // port number (*either* source or destination.)
 type PacketCounts struct {
 	// Flow
 	Interface string `json:"interface"`
+	SrcHost   string `json:"src_host"`
+	DstHost   string `json:"dst_host"`
 	SrcPort   int    `json:"src_port"`
 	DstPort   int    `json:"dst_port"`
 
@@ -41,13 +43,25 @@ func (c *PacketCounts) Copy() *PacketCounts {
 // Reflects the version of the JSON encoding.  Increase the minor version
 // number for backwards-compatible changes and the major number for non-
 // backwards compatible changes.
-const Version = "v0.2"
+const Version = "v0.3"
 
 type PacketCountSummary struct {
 	Version        string                   `json:"version"`
 	Total          PacketCounts             `json:"total"`
 	TopByPort      map[int]*PacketCounts    `json:"top_by_port"`
 	TopByInterface map[string]*PacketCounts `json:"top_by_interface"`
+	TopByHost      map[string]*PacketCounts `json:"top_by_host"`
+
+	// Maximum number of elements allowed in the TopByX maps.
+	ByPortOverflowLimit      int `json:"by_port_overflow_limit"`
+	ByInterfaceOverflowLimit int `json:"by_interface_overflow_limit"`
+	ByHostOverflowLimit      int `json:"by_host_overflow_limit"`
+
+	// Counts for elements in excess of the overflow limits.  Nil means
+	// there was no overflow.
+	ByPortOverflow      *PacketCounts `json:"by_port_overflow,omitempty"`
+	ByInterfaceOverflow *PacketCounts `json:"by_interface_overflow,omitempty"`
+	ByHostOverflow      *PacketCounts `json:"by_host_overflow,omitempty"`
 }
 
 func NewPacketCountSummary() *PacketCountSummary {