include IPv4 Option padding and type packing/unpacking

examples/de.go

@@ -1,8 +1,8 @@
 package main
 
 import (
-	`fmt`
-	`log`
+	"fmt"
+	"log"
 	"strconv"
 )
 

examples/frag.go

@@ -1,8 +1,8 @@
 package main
 
 import (
-	`fmt`
-	`log`
+	"fmt"
+	"log"
 	"strconv"
 )
 

examples/v4optspad.go

@@ -0,0 +1,73 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+)
+
+const (
+	padVal   uint8 = 0x00 // Padded with NUL/null-bytes
+	alignLen int   = 4    // 4-Byte alignment
+)
+
+var (
+	// See the examples/v4opts.go for how these bytes are constructed.
+	opts []byte = []byte{
+		// This is an example.
+		// Option 1
+		0x94,       // Type 148, RTRALT (Router Alert) (RFC 2113)
+		0x04,       // Length (4 bytes)
+		0x00, 0x00, // "Router shall examine packet"
+		// EOOL
+		0x00,
+		// Padding will go here.
+	}
+)
+
+func main() {
+
+	var optLen int
+	var padLen int
+	var pad []byte
+
+	optLen = len(opts)
+
+	fmt.Println("Before padding:")
+	// Prints:
+	/*
+		0x9404000000
+		(Length: 5)
+	*/
+	fmt.Printf("%#02x\n(Length: %d)\n\n", opts, optLen)
+
+	/*
+		The remainder of the current length divided by
+		alignLen (4) (modulo) is subtracted from the alignLen
+		to determine how much must be added to reach the next
+		"boundary". It's then modulo'd *again* to rule out
+		currently being on an alignment bounary.
+	*/
+	padLen = (alignLen - (optLen % alignLen)) % alignLen
+	// Prints:
+	/*
+		Pad length needed:      3
+	*/
+	fmt.Printf("Pad length needed:\t%d\n\n", padLen)
+	pad = bytes.Repeat([]byte{padVal}, padLen)
+
+	opts = append(opts, pad...)
+
+	// Alternatively, this can be implemented with a loop, though it's likely less efficient:
+	/*
+		for len(opts) % alignLen != 0 {}
+			opts = append(opts, padVal)
+		}
+	*/
+
+	// Prints:
+	/*
+		Padded:
+		0x9404000000000000
+	*/
+	fmt.Printf("Padded:\n%#x\n", opts)
+}

examples/v4optstype.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"strconv"
+)
+
+const (
+	ClassControl uint8 = iota
+	ClassReserved
+	ClassDebug
+	ClassReserved2
+)
+
+var (
+	classStr map[uint8]string = map[uint8]string{
+		ClassControl:   "Control",
+		ClassReserved:  "Reserved (1)",
+		ClassDebug:     "Debugging/Measurement",
+		ClassReserved2: "Reserved (2)",
+	}
+)
+
+const (
+	/// This is the same type from examples/v4optspad.go.
+	ip4OptTypBits string = "10010100" // [1001 0100], or 148 (0x94)
+)
+
+var (
+	v4TypCpyOffset uint8 = 0x80             // 128
+	v4TypCpyMask   uint8 = 0x01             // Mask to 1 bit
+	v4TypCpyPos    uint8 = 8 - v4TypCpyMask // 7 or 0x07 (8 (bits) - mask = Shifted to 7th bit)
+
+	v4TypClsOffset uint8 = 0x60 // 96
+	v4TypClsMask   uint8 = 0x05 // mask to 5 bits
+	v4TypClsPos    uint8 = 8 - v4TypClsMask
+
+	v4TypNumOffset uint8 = 0x1f // 31
+)
+
+func ToV4OptTyp(copied, class, num uint8) (typ uint8) {
+
+	typ = ((copied & v4TypCpyMask) << v4TypCpyPos) | ((class & v4TypClsMask) << v4TypClsPos) | (num & v4TypNumOffset)
+
+	return
+}
+
+func FromV4OptTyp(typ uint8) (copied, class, num uint8) {
+
+	copied = (typ & v4TypCpyOffset) >> v4TypCpyPos
+	class = (typ & v4TypClsOffset) >> v4TypClsPos
+	num = (typ & v4TypNumOffset)
+
+	return
+}
+
+func main() {
+
+	var err error
+	var u64 uint64
+	var typ uint8
+	var cpd uint8
+	var cls uint8
+	var num uint8
+
+	// Given a type of ip4OptTypBits (see const at top)...
+	if u64, err = strconv.ParseUint(ip4OptTypBits, 2, 8); err != nil {
+		log.Panicln(err)
+	}
+	typ = uint8(u64)
+	// Prints:
+	/*
+		Type is:	148 (0x0094)
+	*/
+	fmt.Printf("Type is:\t%d (%#04x)\n", typ, typ)
+
+	cpd, cls, num = FromV4OptTyp(typ)
+	// Prints:
+	/*
+		Copied:		1 (0x0001)
+		Class:		0 (0x0000)
+		Number:		20 (0x0014)
+	*/
+	fmt.Printf(
+		"Copied:\t\t%d %#04x)\n"+
+			"Class:\t\t%d (%#04x)\n"+
+			"Number:\t\t%d (%#04x)\n",
+		cpd, cpd,
+		cls, cls,
+		num, num,
+	)
+
+	typ = ToV4OptTyp(cpd, cls, num)
+	// Prints:
+	/*
+		Confirmed Type:	148 (0x94)
+	*/
+	fmt.Printf("Confirmed Type:\t%d (%#02x)\n\n", typ, typ)
+
+	fmt.Println("Class Name:")
+	// Prints:
+	/*
+		Control
+	*/
+	for c, cNm := range classStr {
+		if c == cls {
+			fmt.Println(cNm)
+		}
+	}
+}

examples/vihl.go

@@ -1,8 +1,8 @@
 package main
 
 import (
-	`fmt`
-	`log`
+	"fmt"
+	"log"
 	"strconv"
 )
 

examples/vtf.go

@@ -1,8 +1,8 @@
 package main
 
 import (
-	`fmt`
-	`log`
+	"fmt"
+	"log"
 	"strconv"
 )