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71029cea2d
This updates all source files to use a new standard header for copyright and license declaration. Notably, copyright no longer includes a date, and we now use the standard SPDX-License-Identifier header. This commit was done almost entirely mechanically with perl, and then some minimal manual fixes. Updates #6865 Signed-off-by: Will Norris <will@tailscale.com>
112 lines
2.9 KiB
Go
112 lines
2.9 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package deephash
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import (
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"net/netip"
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"reflect"
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"time"
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)
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var (
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timeTimeType = reflect.TypeOf((*time.Time)(nil)).Elem()
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netipAddrType = reflect.TypeOf((*netip.Addr)(nil)).Elem()
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)
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// typeIsSpecialized reports whether this type has specialized hashing.
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// These are never memory hashable and never considered recursive.
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func typeIsSpecialized(t reflect.Type) bool {
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switch t {
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case timeTimeType, netipAddrType:
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return true
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default:
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return false
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}
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}
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// typeIsMemHashable reports whether t can be hashed by directly hashing its
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// contiguous bytes in memory (e.g. structs with gaps are not mem-hashable).
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func typeIsMemHashable(t reflect.Type) bool {
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if typeIsSpecialized(t) {
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return false
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}
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if t.Size() == 0 {
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return true
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}
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switch t.Kind() {
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case reflect.Bool,
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reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
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reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr,
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reflect.Float32, reflect.Float64,
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reflect.Complex64, reflect.Complex128:
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return true
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case reflect.Array:
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return typeIsMemHashable(t.Elem())
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case reflect.Struct:
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var sumFieldSize uintptr
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for i, numField := 0, t.NumField(); i < numField; i++ {
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sf := t.Field(i)
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if !typeIsMemHashable(sf.Type) {
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return false
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}
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sumFieldSize += sf.Type.Size()
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}
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return sumFieldSize == t.Size() // ensure no gaps
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}
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return false
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}
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// typeIsRecursive reports whether t has a path back to itself.
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// For interfaces, it currently always reports true.
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func typeIsRecursive(t reflect.Type) bool {
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inStack := map[reflect.Type]bool{}
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var visitType func(t reflect.Type) (isRecursiveSoFar bool)
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visitType = func(t reflect.Type) (isRecursiveSoFar bool) {
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// Check whether we have seen this type before.
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if inStack[t] {
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return true
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}
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inStack[t] = true
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defer func() {
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delete(inStack, t)
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}()
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// Types with specialized hashing are never considered recursive.
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if typeIsSpecialized(t) {
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return false
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}
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// Any type that is memory hashable must not be recursive since
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// cycles can only occur if pointers are involved.
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if typeIsMemHashable(t) {
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return false
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}
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// Recursively check types that may contain pointers.
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switch t.Kind() {
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default:
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panic("unhandled kind " + t.Kind().String())
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case reflect.String, reflect.UnsafePointer, reflect.Func:
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return false
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case reflect.Interface:
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// Assume the worst for now. TODO(bradfitz): in some cases
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// we should be able to prove that it's not recursive. Not worth
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// it for now.
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return true
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case reflect.Array, reflect.Chan, reflect.Pointer, reflect.Slice:
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return visitType(t.Elem())
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case reflect.Map:
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return visitType(t.Key()) || visitType(t.Elem())
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case reflect.Struct:
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for i, numField := 0, t.NumField(); i < numField; i++ {
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if visitType(t.Field(i).Type) {
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return true
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}
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}
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return false
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}
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}
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return visitType(t)
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}
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