Proper EDNS handling and cleaner NOERROR response in DNSSERVER

[Kolkman]

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Description of Change

Bugs

The code solves two bugs:

• BUG 1: When trouble shooting a dnsserver with the 'dig' (one of the main DNS troubleshooting tools) the server doesn't answer because it doesn't handle EDNS (OPT records in the additional section).

  That has been fixed, the additional section in the query can safely be ignored. (mostly change around line 123)

• BUG 2: The code also returns an A record when the QUERY Type not 'A' (or 'ANY').

  This has been fixed too. For an A and ANY query type the server returns an A record. (mostly change around line 114)

Feature

The code continues to return a 'SERVFAIL' when no match with QNAME occurs. However, with the fix of bug 2 we created a proper 'No Data' response, (RFC2308 2.2) for queries that have a match for the name, but not for the type. The function DNSServer::replyWithNoAnsw implements that functionality.

The server now behaves somewhat more conform the DNS protocl specifications.

(most of the code changes)

Tests scenarios

I tested this code on an ESP32 and WireShark as protocol analyzer - there is no reason to suspect that it does not work on other platforms (to which I have no access).

Related links

• RFC2308 Section 2.2.

[CLAassistant]

All committers have signed the CLA.

[github-actions[bot]]

	Warnings
:warning:	Some issues found for the commit messages in this PR: the commit message "Proper EDNS handling and cleaner NOERROR response": summary looks empty type/action looks empty the commit message "Removing commented out code fragments": summary looks empty type/action looks empty the commit message "Spelling Corrected and minor clarification in comments": summary looks empty type/action looks empty the commit message "fix(pr): Fix typo": summary looks too short Please fix these commit messages - here are some basic tips: follow Conventional Commits style correct format of commit message should be: <type/action>(<scope/component>): <summary>, for example fix(esp32): Fixed startup timeout issue allowed types are: change,ci,docs,feat,fix,refactor,remove,revert,test sufficiently descriptive message summary should be between 10 to 72 characters and start with upper case letter avoid Jira references in commit messages (unavailable/irrelevant for our customers) TIP: Install pre-commit hooks and run this check when committing (uses the Conventional Precommit Linter).
:warning:	The source branch "DNSServer-EDNS" incorrect format: contains uppercase letters. This can cause troubles on case-insensitive file systems (macOS). Please rename your branch.

👋 Hello Kolkman, we appreciate your contribution to this project!

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[me-no-dev]

@Kolkman small typo reported by the CI: https://github.com/espressif/arduino-esp32/actions/runs/15443489960/job/43466846177?pr=11411#step:9:29

[github-actions[bot]]

Test Results

 76 files   76 suites   12m 46s ⏱️  38 tests  38 ✅ 0 💤 0 ❌ 241 runs  241 ✅ 0 💤 0 ❌

Results for commit a28c02b8.

:recycle: This comment has been updated with latest results.

[me-no-dev]

@Kolkman small typo to fix: https://github.com/espressif/arduino-esp32/actions/runs/15553815702/job/43789936502?pr=11411#step:9:44

[github-actions[bot]]

Memory usage test (comparing PR against master branch)

The table below shows the summary of memory usage change (decrease - increase) in bytes and percentage for each target.

Memory	FLASH [bytes]		FLASH [%]		RAM [bytes]		RAM [%]
Target	DEC	INC	DEC	INC	DEC	INC	DEC	INC
ESP32P4	0	:warning: +734	0.00	:warning: +0.10	0	0	0.00	0.00
ESP32S3	0	:warning: +812	0.00	:warning: +0.09	0	0	0.00	0.00
ESP32S2	0	:warning: +816	0.00	:warning: +0.09	0	0	0.00	0.00
ESP32C3	0	:warning: +736	0.00	:warning: +0.08	0	0	0.00	0.00
ESP32C6	0	:warning: +740	0.00	:warning: +0.08	0	0	0.00	0.00
ESP32	0	:warning: +848	0.00	:warning: +0.09	0	0	0.00	0.00

Click to expand the detailed deltas report [usage change in BYTES]

Target	ESP32P4		ESP32S3		ESP32S2		ESP32C3		ESP32C6		ESP32
Example	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM
libraries/DNSServer/examples/CaptivePortal	:warning: +734	0	:warning: +812	0	:warning: +816	0	:warning: +736	0	:warning: +740	0	:warning: +848	0