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zeekayandHanzo Dev
99724b95b2
cloud linked a Rust staticlib (native/flags) over cgo to decide flags. That made every consumer of the flags path a cgo build, needed a prebuilt libhanzo_flags.a on the link line, and put a second language in the release pipeline for one pure function. This is that function in Go, with no dependencies at all — the rollout hash, the full property-operator set, semver ranges, the date operators, and the serde-compatible value rendering the operators compare through. The rollout hash decides which identities fall inside a percentage, so drift would split cohorts differently here than in the rest of the fleet. The port is therefore pinned to the Rust implementation's own answers: testdata/cases.json is a 621-case table covering every operator, eight rollout percentages against forty identities each, multivariate bucketing, group aggregation and the numeric/escaping edges; testdata/oracle.json is what the Rust evaluator returned for all of them; parity_test.go asserts this package still agrees. Four deliberate mutations confirm the table has teeth: shifting the hash by one bit (27 cases), changing the variant salt (27), dropping case folding from exact matching (2), and dropping the '+' from positive float exponents (4). Two divergences the port found and had to reproduce rather than fix: an integer JSON literal and a float one render differently forever (1e3 is 1000.0, never 1000), and distinct_id must be present but may be empty. Co-authored-by: Hanzo Dev <[email protected]>
25 lines
952 B
Go
25 lines
952 B
Go
package flags
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// The rollout hash. This is the single most parity-critical function in the
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// package: it decides which identities fall inside a percentage rollout, so any
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// drift here silently splits a cohort differently than the rest of the fleet
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// (and than Hanzo Insights, which is PostHog-compatible).
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//
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// sha1("{prefix}{identifier}{salt}"), first 8 bytes big-endian, shifted right 4
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// bits (= the first 15 hex characters), scaled into [0, 1).
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import (
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"crypto/sha1"
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"encoding/binary"
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)
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// longScale is 15 hex digits of headroom — the divisor PostHog picked.
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const longScale = float64(0xfffffffffffffff)
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// hashOf takes prefix "{flag_key}." (the trailing dot is part of the wire
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// contract) and salt "" for rollout gating or "variant" for variant selection.
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func hashOf(prefix, identifier, salt string) float64 {
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sum := sha1.Sum([]byte(prefix + identifier + salt))
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return float64(binary.BigEndian.Uint64(sum[:8])>>4) / longScale
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}
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