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97 lines
2.7 KiB
Go
97 lines
2.7 KiB
Go
// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package cmpver implements a variant of debian version number
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// comparison.
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//
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// A version is a string consisting of alternating non-numeric and
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// numeric fields. When comparing two versions, each one is broken
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// down into its respective fields, and the fields are compared
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// pairwise. The comparison is lexicographic for non-numeric fields,
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// numeric for numeric fields. The first non-equal field pair
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// determines the ordering of the two versions.
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//
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// This comparison scheme is a simplified version of Debian's version
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// number comparisons. Debian differs in a few details of
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// lexicographical field comparison, where certain characters have
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// special meaning and ordering. We don't need that, because Tailscale
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// version numbers don't need it.
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package cmpver
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import (
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"fmt"
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"strconv"
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"strings"
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"unicode"
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)
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// Compare returns an integer comparing two strings as version
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// numbers. The result will be 0 if v1==v2, -1 if v1 < v2, and +1 if
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// v1 > v2.
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func Compare(v1, v2 string) int {
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notNumber := func(r rune) bool { return !unicode.IsNumber(r) }
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var (
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f1, f2 string
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n1, n2 uint64
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err error
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)
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for v1 != "" || v2 != "" {
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// Compare the non-numeric character run lexicographically.
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f1, v1 = splitPrefixFunc(v1, notNumber)
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f2, v2 = splitPrefixFunc(v2, notNumber)
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if res := strings.Compare(f1, f2); res != 0 {
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return res
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}
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// Compare the numeric character run numerically.
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f1, v1 = splitPrefixFunc(v1, unicode.IsNumber)
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f2, v2 = splitPrefixFunc(v2, unicode.IsNumber)
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// ParseUint refuses to parse empty strings, which would only
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// happen if we reached end-of-string. We follow the Debian
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// convention that empty strings mean zero, because
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// empirically that produces reasonable-feeling comparison
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// behavior.
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n1 = 0
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if f1 != "" {
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n1, err = strconv.ParseUint(f1, 10, 64)
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if err != nil {
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panic(fmt.Sprintf("all-number string %q didn't parse as string: %s", f1, err))
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}
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}
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n2 = 0
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if f2 != "" {
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n2, err = strconv.ParseUint(f2, 10, 64)
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if err != nil {
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panic(fmt.Sprintf("all-number string %q didn't parse as string: %s", f2, err))
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}
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}
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switch {
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case n1 == n2:
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case n1 < n2:
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return -1
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case n1 > n2:
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return 1
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}
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}
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// Only way to reach here is if v1 and v2 run out of fields
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// simultaneously - i.e. exactly equal versions.
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return 0
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}
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// splitPrefixFunc splits s at the first rune where f(rune) is false.
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func splitPrefixFunc(s string, f func(rune) bool) (string, string) {
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for i, r := range s {
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if !f(r) {
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return s[:i], s[i:]
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}
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}
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return s, s[:0]
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}
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