[feature] update proof-of-work to allow setting required rounds (#4186)

# Description

This updates our proof-of-work middleware, NoLLaMas, to work on a more easily configurable algorithm (thank you f0x for bringing this to my attention!). Instead of requiring that a solution with pre-determined number of '0' chars be found, it now pre-computes a result with a pre-determined nonce value that it expects the client to iterate up-to. (though with some level of jitter applied, to prevent it being too-easily gamed). This allows the user to configure roughly how many hash-encode rounds they want their clients to have to complete.

## Checklist

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4186
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

web/source/nollamas/index.js

@@ -43,18 +43,18 @@ document.addEventListener("DOMContentLoaded", function() {
 
 	// Read the challenge and difficulty from
 	// data attributes on the nollamas section.
+	const seed = nollamas.dataset.nollamasSeed;
 	const challenge = nollamas.dataset.nollamasChallenge;
-	const difficulty = nollamas.dataset.nollamasDifficulty;
 
-	console.log("challenge:", challenge);     // eslint-disable-line no-console
-	console.log("difficulty:", difficulty); // eslint-disable-line no-console
+	console.log("seed:", seed);           // eslint-disable-line no-console
+	console.log("challenge:", challenge); // eslint-disable-line no-console
 
 	// Prepare the worker with task function.
 	const worker = new Worker("/assets/dist/nollamasworker.js");
 	const startTime = performance.now();
 	worker.postMessage({
 		challenge: challenge,
-		difficulty: difficulty,
+		seed:      seed,
 	});
 
 	// Set the main worker function.

web/source/nollamasworker/index.js

@@ -19,32 +19,22 @@
 
 import sha256 from "./sha256";
 
-let compute = async function(challengeStr, diffStr) {
+let compute = async function(seedStr, challengeStr) {
 	const textEncoder = new TextEncoder();
 
-	// Get difficulty1 as number and generate
-	// expected zero ASCII prefix to check for.
-	const diff1 = parseInt(diffStr, 10);
-	const zeros = "0".repeat(diff1);
-
-	// Calculate hex encoded prefix required to check solution, where we
-	// need diff1 no. chars in hex, and hex encoding doubles input length.
-	const prefixLen = diff1 / 2 + (diff1 % 2 != 0 ? 2 : 0);
-
 	let nonce = 0;
 	while (true) { // eslint-disable-line no-constant-condition
 
 		// Create possible solution string from challenge string + nonce.
-		const solution = textEncoder.encode(challengeStr + nonce.toString());
+		const solution = textEncoder.encode(seedStr + nonce.toString());
 
-		// Generate SHA256 hashsum of solution string, and hex encode the
-		// necessary prefix length we need to check for a valid solution.
-		const prefixArray = Array.from(sha256(solution).slice(0, prefixLen));
-		const prefixHex = prefixArray.map(b => b.toString(16).padStart(2, "0")).join("");
+		// Generate hex encoded SHA256 hashsum of solution.
+		const hashArray = Array.from(sha256(solution));
+		const hashAsHex = hashArray.map(b => b.toString(16).padStart(2, "0")).join("");
 
-		// Check if the hex encoded hash has
-		// difficulty defined zeroes prefix.
-		if (prefixHex.startsWith(zeros)) {
+		// Check whether hex encoded
+		// solution matches challenge.
+		if (hashAsHex == challengeStr) {
 			return nonce;
 		}
 
@@ -56,11 +46,8 @@ let compute = async function(challengeStr, diffStr) {
 onmessage = async function(e) {
 	console.log('worker started'); // eslint-disable-line no-console
 
-	const challenge = e.data.challenge;
-	const difficulty = e.data.difficulty;
-
-	// Compute the nonce that produces solution with args.
-	let nonce = await compute(challenge, difficulty);
+	// Compute nonce value that produces 'challenge' for seed.
+	let nonce = await compute(e.data.seed, e.data.challenge);
 
 	// Post the solution nonce back to caller.
 	postMessage({ nonce: nonce, done: true });

web/template/nollamas.tmpl

@@ -20,8 +20,8 @@
 {{- with . }}
 <main>
     <section class="nollamas"
+        data-nollamas-seed="{{ .seed }}"
         data-nollamas-challenge="{{ .challenge }}"
-        data-nollamas-difficulty="{{ .difficulty }}"
     >
         <h1>Checking you're not a creepy crawler...</h1>
         <noscript>