Give the ICMP Code its own type

This is  a preparatory commit for a larger commit working on
ICMP generation in error cases.
This is removal of technical debt and cleanup in the gvisor code
as part of gvisor issue 2211.

Updates #2211.

PiperOrigin-RevId: 326615389

1 files changed, 31 insertions, 12 deletions

diff --git a/pkg/tcpip/header/icmpv6.go b/pkg/tcpip/header/icmpv6.go
index a13b4b809..20b01d8f4 100644
--- a/pkg/tcpip/header/icmpv6.go
+++ b/pkg/tcpip/header/icmpv6.go
@@ -92,7 +92,6 @@ const (
 // ICMPv6Type is the ICMP type field described in RFC 4443 and friends.
 type ICMPv6Type byte
 
-// Typical values of ICMPv6Type defined in RFC 4443.
 const (
 	ICMPv6DstUnreachable ICMPv6Type = 1
 	ICMPv6PacketTooBig   ICMPv6Type = 2
@@ -110,18 +109,38 @@ const (
 	ICMPv6RedirectMsg     ICMPv6Type = 137
 )
 
-// Values for ICMP destination unreachable code as defined in RFC 4443 section
-// 3.1.
+// ICMPv6Code is the ICMP code field described in RFC 4443.
+type ICMPv6Code byte
+
+// ICMP codes used with Destination Unreachable (Type 1). As per RFC 4443
+// section 3.1.
+const (
+	ICMPv6NetworkUnreachable ICMPv6Code = 0
+	ICMPv6Prohibited         ICMPv6Code = 1
+	ICMPv6BeyondScope        ICMPv6Code = 2
+	ICMPv6AddressUnreachable ICMPv6Code = 3
+	ICMPv6PortUnreachable    ICMPv6Code = 4
+	ICMPv6Policy             ICMPv6Code = 5
+	ICMPv6RejectRoute        ICMPv6Code = 6
+)
+
+// ICMP codes used with Time Exceeded (Type 3). As per RFC 4443 section 3.3.
 const (
-	ICMPv6NetworkUnreachable = 0
-	ICMPv6Prohibited         = 1
-	ICMPv6BeyondScope        = 2
-	ICMPv6AddressUnreachable = 3
-	ICMPv6PortUnreachable    = 4
-	ICMPv6Policy             = 5
-	ICMPv6RejectRoute        = 6
+	ICMPv6HopLimitExceeded  ICMPv6Code = 0
+	ICMPv6ReassemblyTimeout ICMPv6Code = 1
 )
 
+// ICMP codes used with Parameter Problem (Type 4). As per RFC 4443 section 3.4.
+const (
+	ICMPv6ErroneousHeader ICMPv6Code = 0
+	ICMPv6UnknownHeader   ICMPv6Code = 1
+	ICMPv6UnknownOption   ICMPv6Code = 2
+)
+
+// ICMPv6UnusedCode is the code value used with ICMPv6 messages which don't use
+// the code field. (Types not mentioned above.)
+const ICMPv6UnusedCode ICMPv6Code = 0
+
 // Type is the ICMP type field.
 func (b ICMPv6) Type() ICMPv6Type { return ICMPv6Type(b[0]) }
 
@@ -129,10 +148,10 @@ func (b ICMPv6) Type() ICMPv6Type { return ICMPv6Type(b[0]) }
 func (b ICMPv6) SetType(t ICMPv6Type) { b[0] = byte(t) }
 
 // Code is the ICMP code field. Its meaning depends on the value of Type.
-func (b ICMPv6) Code() byte { return b[1] }
+func (b ICMPv6) Code() ICMPv6Code { return ICMPv6Code(b[1]) }
 
 // SetCode sets the ICMP code field.
-func (b ICMPv6) SetCode(c byte) { b[1] = c }
+func (b ICMPv6) SetCode(c ICMPv6Code) { b[1] = byte(c) }
 
 // Checksum is the ICMP checksum field.
 func (b ICMPv6) Checksum() uint16 {