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zeekay
1943f1c093
Multi-tenant commerce and billing: orders, subscriptions, invoices, plans, usage metering and a credit ledger. One Go binary. MIT OR Apache-2.0. Claude-Session: https://claude.ai/code/session_01SAtaDFm8VDiWrhYHNNtxMw
37 lines
1.4 KiB
Go
37 lines
1.4 KiB
Go
package square
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import (
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"crypto/sha256"
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"encoding/hex"
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)
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// keyMax is Square's hard limit on idempotency_key. A longer key is rejected
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// outright — VALUE_TOO_LONG / INVALID_REQUEST_ERROR — before any money moves,
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// so the charge fails rather than double-charging. The limit is Square's fact
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// and is enforced here, at Square's boundary: callers compose keys for their
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// own reasons (see api/billing gatewayKey) and other processors have their own
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// limits, so no caller should have to know this number.
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const keyMax = 45
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// fitKey fits an idempotency key into Square's limit.
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//
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// A key already within the limit passes through UNCHANGED, so keys in flight
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// keep replaying the charges they already made.
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//
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// A longer key becomes the hex sha256 of the WHOLE key, cut to the limit. That
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// is deterministic — the same key always maps to the same Square key, so
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// idempotency survives the mapping and a retry still de-dups — and it is 180
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// bits wide, so two distinct keys cannot collide onto one charge.
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//
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// Cutting the key itself would be deterministic but NOT collision-free:
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// composed keys share a prefix (op:subject:...), so two different money moves
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// can cut to the same key, and Square would answer the second with the first
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// one's payment — a charge that silently never happens.
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func fitKey(key string) string {
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if len(key) <= keyMax {
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return key
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}
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sum := sha256.Sum256([]byte(key))
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return hex.EncodeToString(sum[:])[:keyMax]
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}
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