add dhcpv4.GetOption and dhcpv4.GetSingleOption methods (#63)

GetOption and GetOneOption are convenience methods for getting a DHCPv4
option from its Option Code.

GetOption returns a list of options that match since the DHCP RFC allows
for an option to be present multiple times with its values appended
together.  (Note: I am not sure I've ever seen this done and it's not clear if
how option parsing would work for more complex values.  Is appending
done at the byte level? )

GetOneOption will return the first found option that matches a code.

2 files changed, 47 insertions, 0 deletions

diff --git a/dhcpv4/dhcpv4.go b/dhcpv4/dhcpv4.go
index 3deda86..226c077 100644
--- a/dhcpv4/dhcpv4.go
+++ b/dhcpv4/dhcpv4.go
@@ -511,6 +511,31 @@ func (d *DHCPv4) Options() []Option {
 	return d.options
 }
 
+// GetOption will attempt to get all options that match a DHCPv4 option
+// from its OptionCode.  If the option was not found it will return an
+// empty list.
+func (d *DHCPv4) GetOption(code OptionCode) []Option {
+	opts := []Option{}
+	for _, opt := range d.Options() {
+		if opt.Code() == code {
+			opts = append(opts, opt)
+		}
+	}
+	return opts
+}
+
+// GetOneOption will attempt to get an  option that match a Option code.
+// If there are multiple options with the same OptionCode it will only return
+// the first one found.  If no matching option is found nil will be returned.
+func (d *DHCPv4) GetOneOption(code OptionCode) Option {
+	for _, opt := range d.Options() {
+		if opt.Code() == code {
+			return opt
+		}
+	}
+	return nil
+}
+
 // StrippedOptions works like Options, but it does not return anything after the
 // End option.
 func (d *DHCPv4) StrippedOptions() []Option {
diff --git a/dhcpv4/dhcpv4_test.go b/dhcpv4/dhcpv4_test.go
index 065b6e0..4e4f7b5 100644
--- a/dhcpv4/dhcpv4_test.go
+++ b/dhcpv4/dhcpv4_test.go
@@ -300,6 +300,28 @@ func TestNewToBytes(t *testing.T) {
 	require.Equal(t, expected, got)
 }
 
+func TestGetOption(t *testing.T) {
+	d, err := New()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	hostnameOpt := &OptionGeneric{OptionCode: OptionHostName, Data: []byte("darkstar")}
+	bootFileOpt1 := &OptionGeneric{OptionCode: OptionBootfileName, Data: []byte("boot.img")}
+	bootFileOpt2 := &OptionGeneric{OptionCode: OptionBootfileName, Data: []byte("boot2.img")}
+	d.AddOption(hostnameOpt)
+	d.AddOption(bootFileOpt1)
+	d.AddOption(bootFileOpt2)
+
+	require.Equal(t, d.GetOption(OptionHostName), []Option{hostnameOpt})
+	require.Equal(t, d.GetOption(OptionBootfileName), []Option{bootFileOpt1, bootFileOpt2})
+	require.Equal(t, d.GetOption(OptionRouter), []Option{})
+
+	require.Equal(t, d.GetOneOption(OptionHostName), hostnameOpt)
+	require.Equal(t, d.GetOneOption(OptionBootfileName), bootFileOpt1)
+	require.Equal(t, d.GetOneOption(OptionRouter), nil)
+}
+
 // TODO
 //      test broadcast/unicast flags
 //      test Options setter/getter