SAIF.Framework.DNS business rules¶

This page captures business rules enforced by this library.

BR-001: Lookup arguments must not be null¶

Field	Value
Statement	The `domain` and `dnsServer` arguments must not be null for any public lookup call.
Trigger	Call to `Resolver.MXLookup(domain, dnsServer)` or `Resolver.Lookup(request, dnsServer)`.
Enforcement	Explicit null checks at the start of each method, throwing `ArgumentNullException`.
Outcome	Prevents null-reference failures downstream in socket/message construction code.
Confidence	Verified
Source	SAIF.Framework.DNS\Resolver.cs

Field	Value
Statement	A domain name supplied to the public `Question` constructor must be between 1 and 255 characters.
Trigger	`Question(string domain, DnsType dnsType, DnsClass dnsClass)` constructor invoked.
Enforcement	Length check in the constructor throwing `ArgumentException` when violated; a per-label 63-character regex check exists in source but is commented out and not enforced.
Outcome	Rejects domain strings that violate the RFC1035 overall length limit before a `Question` object is created.
Confidence	Verified
Source	SAIF.Framework.DNS\Question.cs

Field	Value
Statement	The `DnsType` supplied to the public `Question` constructor must be a defined enum value other than `None`.
Trigger	`Question` public constructor invoked with a `DnsType` argument.
Enforcement	`Enum.IsDefined` check in the constructor throwing `ArgumentOutOfRangeException` when violated.
Outcome	Rejects invalid or undefined query types before a `Question` object is created.
Confidence	Verified
Source	SAIF.Framework.DNS\Question.cs

Field	Value
Statement	The `DnsClass` supplied to the public `Question` constructor must be a defined enum value other than `None`.
Trigger	`Question` public constructor invoked with a `DnsClass` argument.
Enforcement	`Enum.IsDefined` check in the constructor throwing `ArgumentOutOfRangeException` when violated.
Outcome	Rejects invalid or undefined query classes before a `Question` object is created.
Confidence	Verified
Source	SAIF.Framework.DNS\Question.cs

Field	Value
Statement	A DNS UDP request is retried up to 2 additional times before the operation is considered failed.
Trigger	No matching-id response is received within the 1-second receive timeout on a given attempt.
Enforcement	`Resolver.UdpTransfer` retry loop, bounded by the constant `_udpRetryAttempts` (2).
Outcome	After exhausting all attempts, `NoResponseException` is thrown to the caller.
Confidence	Verified
Source	SAIF.Framework.DNS\Resolver.cs

Field	Value
Statement	A returned UDP datagram is only accepted as a valid reply if its 2-byte transaction id matches the request's stamped id.
Trigger	Every UDP receive performed inside `Resolver.UdpTransfer`.
Enforcement	Byte-level comparison of `responseMessage[0..1]` against `requestMessage[0..1]`.
Outcome	Mismatched or unrelated packets are ignored, which implicitly drives the retry loop (see BR-005).
Confidence	Verified
Source	SAIF.Framework.DNS\Resolver.cs

Field	Value
Statement	A malformed embedded `Question` encountered while parsing the questions section of a reply aborts construction of the entire `Response`.
Trigger	`Response` constructor parsing the questions section of a raw reply.
Enforcement	`try`/`catch` around `new Question(pointer)`; any caught exception is rethrown as `InvalidResponseException`.
Outcome	The caller receives a clear, typed exception instead of a partially-parsed or corrupt `Response` object.
Confidence	Verified
Source	SAIF.Framework.DNS\Response.cs

Field	Value
Statement	MX records are ordered by ascending preference (a lower numeric value indicates higher priority), tie-broken by descending domain-name comparison.
Trigger	`Resolver.MXLookup` return path, or any `Array.Sort` performed over an `MXRecord[]`.
Enforcement	`MXRecord.CompareTo` (`IComparable` implementation).
Outcome	Callers iterating the returned array process the most-preferred mail exchanger first.
Confidence	Verified
Source	SAIF.Framework.DNS\MXRecord.cs

Rule enforcement in this library is entirely input-validation and transport-retry logic; no persistence, workflow, or authorization rules apply, consistent with this library performing no database or security interactions.
The per-label 63-character domain validation described in Question.cs exists only as a commented-out Regex.IsMatch call and is not currently enforced; whether this was an intentional relaxation or an oversight is unknown.**

Note: Statements marked with ** could not be confirmed; treat as unknown until verified.