dhcpv6: intro Getters for Options

Allow the Options type to have getters for each specific options, in
order to avoid users having to cast options to their specific type.

This commit introduces a getter for exactly one option: the
ClientArchType.

i.e. users can replace

archTypes := msg.GetOneOption(OptionClientArchType).(*OptClientArchType)

with

archTypes := msg.Options.ArchTypes()

Because a few message types and options embed options (normal message,
relay message, IANA/IATA option) and each have a restricted set of
options that can be used inside them, we'll introduce at least 3 or more
Options subtypes:

- MessageOptions
- RelayOptions
- IdentityOptions

Perhaps others will join at a later time, such as VendorOptions or
AddressOptions for the IAAddress options field.

Signed-off-by: Chris Koch <chrisko@google.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/iana/archtype.go b/iana/archtype.go
index 255687c..865659b 100644
--- a/iana/archtype.go
+++ b/iana/archtype.go
@@ -49,6 +49,16 @@ func (a Arch) String() string {
 // Archs represents multiple Arch values.
 type Archs []Arch
 
+// Contains returns whether b is one of the Archs in a.
+func (a Archs) Contains(b Arch) bool {
+	for _, t := range a {
+		if t == b {
+			return true
+		}
+	}
+	return false
+}
+
 // ToBytes returns the serialized option defined by RFC 4578 (DHCPv4) and RFC
 // 5970 (DHCPv6) as the Client System Architecture Option.
 func (a Archs) ToBytes() []byte {