include IPv4 Option padding and type packing/unpacking

README.adoc

@@ -270,7 +270,7 @@ A flag's presence can be checked via a bit-wise `AND` against _flag_ being equal
 [%collapsible]
 .Example in Go
 =====
-.`hasflag.go`
+.`examples/hasflag.go`
 [source,go]
 ----
 include::examples/hasflag.go[]
@@ -390,7 +390,7 @@ IP:P:: <<spec_bcast_protonum, IP/Transport Protocol Number>> _(1 Byte)_
 IP:C:: Header Checksum (RFC https://datatracker.ietf.org/doc/html/rfc1071[1071^], https://datatracker.ietf.org/doc/html/rfc1071[1141^], https://datatracker.ietf.org/doc/html/rfc1624[1624^]) _(2 Bytes)_
 IP:S:: Source IPv4 Address _(32 Bits/4 Bytes)_
 IP:D:: Destination IPv4 Address _(32 Bits/4 Bytes)_
-IP:O:: Options (Optional) (See the https://www.iana.org/assignments/ip-parameters/ip-parameters.xhtml[IANA Registered IP Parameters^] for details) _(Variable Length)_
+IP:O:: Options + Null Padding (Optional) _(Variable Length, see <<xtra_pad_v4opts,Addendum>>)_
 
 [id="spec_bcast_v6"]
 ==== IPv6
@@ -541,6 +541,7 @@ To *retrieve* the Version and IHL, the value is bit-shifted to the *right* by 4
 [%collapsible]
 .Example in Go
 ====
+.`examples/vihl.go`
 [source,go]
 ----
 include::examples/vihl.go[]
@@ -571,6 +572,7 @@ Notable ECN mentions are:
 [%collapsible]
 .Example in Go
 ====
+.`examples/de.go`
 [source,go]
 ----
 include::examples/de.go[]
@@ -586,12 +588,31 @@ The Fragmentation Flags and Offset are defined in https://datatracker.ietf.org/d
 [%collapsible]
 .Example in Go
 ====
+.`examples/frag.go`
 [source,go]
 ----
 include::examples/frag.go[]
 ----
 ====
 
+[id="xtra_bitpacked_ip4opt_t"]
+==== IPv4 Option Type
+The *Type* field of an <<xtra_pad_v4opts,IPv4 option>> is a single byte that consists of:
+
+* A "Copy" flag _(1 Bit)_
+* A "Class" flag _(2 Bits)_
+* An Option "Number" _(5 Bits)_
+
+[%collapsible]
+.Example in Go
+====
+.`examples/v4optstype.go`
+[source,go]
+----
+include::examples/v4optstype.go[]
+----
+====
+
 [id="xtra_bitpacked_vtf"]
 ==== IP Version, Traffic Class, Flow Label (IPv6)
 IPv6 thankfully only has one bitpacking in the header. Unfortunately, it's a triple-whammy.
@@ -607,8 +628,58 @@ The IP Version takes up 4 bits (just as in IPv4, except it will always be `6` th
 [%collapsible]
 .Example in Go
 ====
+.`examples/vtf.go`
 [source,go]
 ----
 include::examples/vtf.go[]
 ----
 ====
+
+
+[id="xtra_pad"]
+=== Padded Fields
+
+[id="xtra_pad_v4opts"]
+==== IPv4 Options
+The IPv4 options, if specified, *must* align to a 32-bit/4-byte multiple size.
+(In other words, its total length of bytes *must* be cleanly divisible by 4;
+or said another way its total length of bits must be cleanly divisible by 32).
+
+It uses null-byte (`0x00`) padding to achieve this.
+
+[%collapsible]
+.Example in Go
+====
+.`examples/v4optspad.go`
+[source,go]
+----
+include::examples/v4optspad.go[]
+----
+====
+
+For more extensive details, see https://datatracker.ietf.org/doc/html/rfc791#section-3.1[RFC 791 § 3.1^]
+and the https://www.iana.org/assignments/ip-parameters/ip-parameters.xhtml[IANA Registered IP Paramaeters^]
+(the *Value* column is what should be used as the *Type*, see <<xtra_bitpacked_ip4opt_t>>.
+
+Each option (with two exceptions) is a TLV (<<xtra_pad_v4opts_t,type>> / <<xtra_pad_v4opts_l,length>> / <<xtra_pad_v4opts_v,value>>) structured field.
+
+The two exceptions for the above are `EOOL` (`0x00`) and `NOP` (`0x01`), both of which occupy only a single byte -- they are *unvalued*, so they have no length or value field.
+
+[id="xtra_pad_v4opts_t"]
+===== Type
+See <<xtra_bitpacked_ip4opt_t>> for details.
+
+[id="xtra_pad_v4opts_l"]
+===== Length
+The *Length* is the length of this _entire_ option as an 8-bit unsigned integer.
+
+In other words it includes the length of the <<xtra_pad_v4opts_t>> field, the <<xtra_pad_v4opts_l>> field (this field), 
+*and* the <<xtra_pad_v4opts_v>> field together.
+
+This is not present for `EOOL` (`0x00`) and `NOP` (`0x01`) (or any other "non-valued" options).
+
+[id="xtra_pad_v4opts_v"]
+===== Value
+Value is the option's value. Its <<xtra_pad_v4opts_l>> is variable depending on the <<xtra_pad_v4opts_t>>.
+
+This is not present for `EOOL` (`0x00`) and `NOP` (`0x01`) (or any other "non-valued" options).