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Adam.S
Adam.S

Posted on • Edited on • Originally published at bas-man.dev

Swift: Deconstruct SPF an Outline and Background

#swift #beginners #spf #package

What is SPF

If you have not followed my rust series on deconstructing SPF you can check it out here.

Here is some back ground on SPF.

What is a qualifier

A qualifier changes the way that a mechanism is interpreted, they are

  • + Pass
  • - Fail
  • ~ SoftFail
  • ? Neutral
    • Neutral is the default if no qualifier is matched.

What is a mechanism

An SPF mechanism can be one of several types

  • Include
  • A
  • Mx
  • Ip4
  • Ip6
  • All
  • Ptr
  • Exists
  • Redirect (Technially this is a Modifier, but I will be using it as a Mechanism)

I will be attempting to just learn some of the basics of the Swift language. So I will be looking at things like:

  • enum
  • struct
  • Optional variables
  • Perhaps more if I find that I need them.

Swift: The building blocks

Qualifiers

So I need to have a way to handle qualifiers

enum Qualifier: String { case Pass = "+" case Fail = "-" case SoftFail = "~" case Neutral = "?" case None = "" }
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This enumeration will manage my qualifiers. I have added a None for the moment since in many cases, there is no qualifier provided, and I think I might want to be able to reproduce the mechanism in the future.

Mechanism

To handle these I will create a second enumeration

enum MechanismKind { case Redirect, Include, A, MX, Ip4, Ip6, All; }
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Although Redirect is a modifier, I am listing it here as a mechanism. I am also omitting ptr and exists. These may or may not be handled.

A mechanism is made up of a qualifier and some mechanism value. It also needs to have a kind. So a struct will probably work here.

struct Mechanism { var kind: MechanismKind; var qualifier: Qualifier; var mechanism: String; }
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Examples

Let's say we have an SPF record of the following type:

"v=spf1 a ip4:x.x.x.x ~all"
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We want to have a struct that will represent A and another that represents Ip4

These are conceptual examples only.

A 
struct { kind => MechanismKind.A qualifier => Qualifers.None mechanism => "" }
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Ip4 
struct { kind => MechanismKind.Ip4 qualifier => None mechanism => "x.x.x.x" }
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Seeing this I can see that there will be some good cases to make some variables Optional

SPF

This struct will probably look something like what follows.

struct SPF { var redirect: Mechanism?; var is_redirect: Bool = false; var include: Mechanism?; var a: Mechanism?; var mx: Mechanism?; var all: Mechanism?; }
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This is merely a rough outline. Most will need to be a list of records.
You might notice the use if the ? at the end of Mechanism. This denotes that the variable is optional and hence can have a nil value. That meaning it can be absent.

I refer you to the Swift Documentation

In the next article we will start to develop some code focused on the struct for a Mechanism

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