types/netlogtype: add constants for maximum serialized sizes of ConnectionCounts (#6163)

There is a finite limit to the maximum message size that logtail can upload.
We need to make sure network logging messages remain under this size.
These constants allow us to compute the maximum number of ConnectionCounts
we can buffer before we must flush.

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

types/netlogtype/netlogtype.go

@@ -18,17 +18,45 @@ import (
 
 // Message is the log message that captures network traffic.
 type Message struct {
-	NodeID tailcfg.StableNodeID `json:"nodeId"` // e.g., "n123456CNTRL"
+	NodeID tailcfg.StableNodeID `json:"nodeId" cbor:"0,keyasint"` // e.g., "n123456CNTRL"
 
-	Start time.Time `json:"start"` // inclusive
+	Start time.Time `json:"start" cbor:"12,keyasint"` // inclusive
-	End   time.Time `json:"end"`   // inclusive
+	End   time.Time `json:"end"   cbor:"13,keyasint"` // inclusive
 
-	VirtualTraffic  []ConnectionCounts `json:"virtualTraffic,omitempty"`
+	VirtualTraffic  []ConnectionCounts `json:"virtualTraffic,omitempty"  cbor:"14,keyasint,omitempty"`
-	SubnetTraffic   []ConnectionCounts `json:"subnetTraffic,omitempty"`
+	SubnetTraffic   []ConnectionCounts `json:"subnetTraffic,omitempty"   cbor:"15,keyasint,omitempty"`
-	ExitTraffic     []ConnectionCounts `json:"exitTraffic,omitempty"`
+	ExitTraffic     []ConnectionCounts `json:"exitTraffic,omitempty"     cbor:"16,keyasint,omitempty"`
-	PhysicalTraffic []ConnectionCounts `json:"physicalTraffic,omitempty"`
+	PhysicalTraffic []ConnectionCounts `json:"physicalTraffic,omitempty" cbor:"17,keyasint,omitempty"`
 }
 
+const (
+	maxJSONConnCounts = `{` + maxJSONConn + `,` + maxJSONCounts + `}`
+	maxJSONConn       = `"proto":` + maxJSONProto + `,"src":` + maxJSONAddrPort + `,"dst":` + maxJSONAddrPort
+	maxJSONProto      = `255`
+	maxJSONAddrPort   = `"[ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff]:65535"`
+	maxJSONCounts     = `"txPkts":` + maxJSONCount + `,"txBytes":` + maxJSONCount + `,"rxPkts":` + maxJSONCount + `,"rxBytes":` + maxJSONCount
+	maxJSONCount      = `18446744073709551615`
+
+	// MaxConnectionCountsJSONSize is the maximum size of a ConnectionCounts
+	// when it is serialized as JSON, assuming no superfluous whitespace.
+	// It does not include the trailing comma that often appears when
+	// this object is nested within an array.
+	// It assumes that netip.Addr never has IPv6 zones.
+	MaxConnectionCountsJSONSize = len(maxJSONConnCounts)
+
+	maxCBORConnCounts = "\xbf" + maxCBORConn + maxCBORCounts + "\xff"
+	maxCBORConn       = "\x00" + maxCBORProto + "\x01" + maxCBORAddrPort + "\x02" + maxCBORAddrPort
+	maxCBORProto      = "\x18\xff"
+	maxCBORAddrPort   = "\x52\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
+	maxCBORCounts     = "\x0c" + maxCBORCount + "\x0d" + maxCBORCount + "\x0e" + maxCBORCount + "\x0f" + maxCBORCount
+	maxCBORCount      = "\x1b\xff\xff\xff\xff\xff\xff\xff\xff"
+
+	// MaxConnectionCountsCBORSize is the maximum size of a ConnectionCounts
+	// when it is serialized as CBOR.
+	// It assumes that netip.Addr never has IPv6 zones.
+	MaxConnectionCountsCBORSize = len(maxCBORConnCounts)
+)
+
 // ConnectionCounts is a flattened struct of both a connection and counts.
 type ConnectionCounts struct {
 	Connection
@@ -37,19 +65,19 @@ type ConnectionCounts struct {
 
 // Connection is a 5-tuple of proto, source and destination IP and port.
 type Connection struct {
-	Proto ipproto.Proto  `json:"proto,omitzero,omitempty"`
+	Proto ipproto.Proto  `json:"proto,omitzero,omitempty" cbor:"0,keyasint,omitempty"`
-	Src   netip.AddrPort `json:"src,omitzero"`
+	Src   netip.AddrPort `json:"src,omitzero,omitempty"   cbor:"1,keyasint,omitempty"`
-	Dst   netip.AddrPort `json:"dst,omitzero"`
+	Dst   netip.AddrPort `json:"dst,omitzero,omitempty"   cbor:"2,keyasint,omitempty"`
 }
 
 func (c Connection) IsZero() bool { return c == Connection{} }
 
 // Counts are statistics about a particular connection.
 type Counts struct {
-	TxPackets uint64 `json:"txPkts,omitzero,omitempty"`
+	TxPackets uint64 `json:"txPkts,omitzero,omitempty"  cbor:"12,keyasint,omitempty"`
-	TxBytes   uint64 `json:"txBytes,omitzero,omitempty"`
+	TxBytes   uint64 `json:"txBytes,omitzero,omitempty" cbor:"13,keyasint,omitempty"`
-	RxPackets uint64 `json:"rxPkts,omitzero,omitempty"`
+	RxPackets uint64 `json:"rxPkts,omitzero,omitempty"  cbor:"14,keyasint,omitempty"`
-	RxBytes   uint64 `json:"rxBytes,omitzero,omitempty"`
+	RxBytes   uint64 `json:"rxBytes,omitzero,omitempty" cbor:"15,keyasint,omitempty"`
 }
 
 func (c Counts) IsZero() bool { return c == Counts{} }

types/netlogtype/netlogtype_test.go

@@ -0,0 +1,40 @@
+// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package netlogtype
+
+import (
+	"encoding/json"
+	"math"
+	"net/netip"
+	"testing"
+
+	"github.com/fxamacker/cbor/v2"
+	"github.com/google/go-cmp/cmp"
+	"tailscale.com/util/must"
+)
+
+func TestMaxSize(t *testing.T) {
+	maxAddr := netip.AddrFrom16([16]byte{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255})
+	maxAddrPort := netip.AddrPortFrom(maxAddr, math.MaxUint16)
+	cc := ConnectionCounts{
+		// NOTE: These composite literals are deliberately unkeyed so that
+		// added fields result in a build failure here.
+		// Newly added fields should result in an update to both
+		// MaxConnectionCountsJSONSize and MaxConnectionCountsCBORSize.
+		Connection{math.MaxUint8, maxAddrPort, maxAddrPort},
+		Counts{math.MaxUint64, math.MaxUint64, math.MaxUint64, math.MaxUint64},
+	}
+
+	outJSON := must.Get(json.Marshal(cc))
+	if string(outJSON) != maxJSONConnCounts {
+		t.Errorf("JSON mismatch (-got +want):\n%s", cmp.Diff(string(outJSON), maxJSONConnCounts))
+	}
+
+	outCBOR := must.Get(cbor.Marshal(cc))
+	maxCBORConnCountsAlt := "\xa7" + maxCBORConnCounts[1:len(maxCBORConnCounts)-1] // may use a definite encoding of map
+	if string(outCBOR) != maxCBORConnCounts && string(outCBOR) != maxCBORConnCountsAlt {
+		t.Errorf("CBOR mismatch (-got +want):\n%s", cmp.Diff(string(outCBOR), maxCBORConnCounts))
+	}
+}