zzstoatzz.io
forked from
chadtmiller.com/pds.js
A zero-dependency AT Protocol Personal Data Server written in JavaScript
docs: add 'why' comments to protocol-specific logic
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
chadtmiller.com
+9
-3
src/pds.js
+9
-3
src/pds.js
···
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encodeHead(parts, 3, bytes.length)
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parts.push(...bytes)
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} else if (val instanceof CID) {
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-
// CID - encode with CBOR tag 42 + 0x00 prefix
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+
// CID links in DAG-CBOR use tag 42 + 0x00 multibase prefix
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+
// The 0x00 prefix indicates "identity" multibase (raw bytes)
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parts.push(0xd8, CBOR_TAG_CID)
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encodeHead(parts, 2, val.bytes.length + 1) // +1 for 0x00 prefix
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-
parts.push(0x00) // multibase identity prefix
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+
parts.push(0x00)
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parts.push(...val.bytes)
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} else if (val instanceof Uint8Array) {
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// Regular byte string
···
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for (const item of val) encode(item)
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} else if (typeof val === 'object') {
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// DAG-CBOR: sort keys by length first, then lexicographically
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+
// (differs from standard CBOR which sorts lexicographically only)
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const keys = Object.keys(val).filter(k => val[k] !== undefined)
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keys.sort((a, b) => {
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if (a.length !== b.length) return a.length - b.length
···
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)
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const sig = new Uint8Array(signature)
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-
// Low-S normalization: if S > N/2, replace S with N - S
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const r = sig.slice(0, 32)
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const s = sig.slice(32, 64)
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const sBigInt = bytesToBigInt(s)
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+
// Low-S normalization: Bitcoin/ATProto require S <= N/2 to prevent
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+
// signature malleability (two valid signatures for same message)
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if (sBigInt > P256_N_DIV_2) {
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const newS = P256_N - sBigInt
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const newSBytes = bigIntToBytes(newS, 32)
···
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}
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}
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+
// MST depth = leading zeros in SHA-256 hash / 2
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+
// This creates a probabilistic tree where ~50% of keys are at depth 0,
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+
// ~25% at depth 1, etc., giving O(log n) lookups
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const depth = Math.floor(zeros / 2)
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keyDepthCache.set(key, depth)
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return depth