types/ipproto: import and test string parsing for ipproto

IPProto has been being converted to and from string formats in multiple
locations with variations in behavior. TextMarshaller and JSONMarshaller
implementations are now added, along with defined accepted and preferred
formats to centralize the logic into a single cross compatible
implementation.

Updates tailscale/corp#15043
Fixes tailscale/corp#15141

Signed-off-by: James Tucker <james@tailscale.com>

types/ipproto/ipproto.go

@@ -4,7 +4,13 @@
 // Package ipproto contains IP Protocol constants.
 package ipproto
 
-import "fmt"
+import (
+	"fmt"
+	"strconv"
+
+	"tailscale.com/util/nocasemaps"
+	"tailscale.com/util/vizerror"
+)
 
 // Version describes the IP address version.
 type Version uint8
@@ -69,6 +75,7 @@ const (
 	Fragment Proto = 0xFF
 )
 
+// Deprecated: use MarshalText instead.
 func (p Proto) String() string {
 	switch p {
 	case Unknown:
@@ -97,3 +104,96 @@ func (p Proto) String() string {
 		return fmt.Sprintf("IPProto-%d", int(p))
 	}
 }
+
+// Prefer names from
+// https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml
+// unless otherwise noted.
+var (
+	// preferredNames is the set of protocol names that re produced by
+	// MarshalText, and are the preferred representation.
+	preferredNames = map[Proto]string{
+		51:     "ah",
+		DCCP:   "dccp",
+		8:      "egp",
+		50:     "esp",
+		47:     "gre",
+		ICMPv4: "icmp",
+		IGMP:   "igmp",
+		9:      "igp",
+		4:      "ipv4",
+		ICMPv6: "ipv6-icmp",
+		SCTP:   "sctp",
+		TCP:    "tcp",
+		UDP:    "udp",
+	}
+
+	// acceptedNames is the set of protocol names that are accepted by
+	// UnmarshalText.
+	acceptedNames = map[string]Proto{
+		"ah":        51,
+		"dccp":      DCCP,
+		"egp":       8,
+		"esp":       50,
+		"gre":       47,
+		"icmp":      ICMPv4,
+		"icmpv4":    ICMPv4,
+		"icmpv6":    ICMPv6,
+		"igmp":      IGMP,
+		"igp":       9,
+		"ip-in-ip":  4, // IANA says "ipv4"; Wikipedia/popular use says "ip-in-ip"
+		"ipv4":      4,
+		"ipv6-icmp": ICMPv6,
+		"sctp":      SCTP,
+		"tcp":       TCP,
+		"tsmp":      TSMP,
+		"udp":       UDP,
+	}
+)
+
+// UnmarshalText implements encoding.TextUnmarshaler. If the input is empty, p
+// is set to 0. If an error occurs, p is unchanged.
+func (p *Proto) UnmarshalText(b []byte) error {
+	if len(b) == 0 {
+		*p = 0
+		return nil
+	}
+
+	if u, err := strconv.ParseUint(string(b), 10, 8); err == nil {
+		*p = Proto(u)
+		return nil
+	}
+
+	if newP, ok := nocasemaps.GetOk(acceptedNames, string(b)); ok {
+		*p = newP
+		return nil
+	}
+
+	return vizerror.Errorf("proto name %q not known; use protocol number 0-255", b)
+}
+
+// MarshalText implements encoding.TextMarshaler.
+func (p Proto) MarshalText() ([]byte, error) {
+	if s, ok := preferredNames[p]; ok {
+		return []byte(s), nil
+	}
+	return []byte(strconv.Itoa(int(p))), nil
+}
+
+// MarshalJSON implements json.Marshaler.
+func (p Proto) MarshalJSON() ([]byte, error) {
+	return []byte(strconv.Itoa(int(p))), nil
+}
+
+// UnmarshalJSON implements json.Unmarshaler. If the input is empty, p is set to
+// 0. If an error occurs, p is unchanged. The input must be a JSON number or an
+// accepted string name.
+func (p *Proto) UnmarshalJSON(b []byte) error {
+	if len(b) == 0 {
+		*p = 0
+		return nil
+	}
+	if b[0] == '"' {
+		b = b[1 : len(b)-1]
+	}
+	return p.UnmarshalText(b)
+}