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|
package structr
import (
"reflect"
"strings"
"github.com/zeebo/xxh3"
)
// Hasher provides hash checksumming for a configured
// index, based on an arbitrary combination of generic
// paramter struct type's fields. This provides hashing
// both by input of the fields separately, or passing
// an instance of the generic paramter struct type.
//
// Supported field types by the hasher include:
// - ~int
// - ~int8
// - ~int16
// - ~int32
// - ~int64
// - ~float32
// - ~float64
// - ~string
// - slices / ptrs of the above
type Hasher[StructType any] struct {
// fields contains our representation
// of struct fields contained in the
// creation of sums by this hasher.
fields []structfield
// zero specifies whether zero
// value fields are permitted.
zero bool
}
// NewHasher returns a new initialized Hasher for the receiving generic
// parameter type, comprising of the given field strings, and whether to
// allow zero values to be incldued within generated hash checksum values.
func NewHasher[T any](fields []string, allowZero bool) Hasher[T] {
var h Hasher[T]
// Preallocate expected struct field slice.
h.fields = make([]structfield, len(fields))
// Get the reflected struct ptr type.
t := reflect.TypeOf((*T)(nil)).Elem()
for i, fieldName := range fields {
// Split name to account for nesting.
names := strings.Split(fieldName, ".")
// Look for a usable struct field from type.
sfield, ok := findField(t, names, allowZero)
if !ok {
panicf("failed finding field: %s", fieldName)
}
// Set parsed struct field.
h.fields[i] = sfield
}
// Set config flags.
h.zero = allowZero
return h
}
// FromParts generates hash checksum (used as index key) from individual key parts.
func (h *Hasher[T]) FromParts(parts ...any) (sum uint64, ok bool) {
hh := getHasher()
sum, ok = h.fromParts(hh, parts...)
putHasher(hh)
return
}
func (h *Hasher[T]) fromParts(hh *xxh3.Hasher, parts ...any) (sum uint64, ok bool) {
if len(parts) != len(h.fields) {
// User must provide correct number of parts for key.
panicf("incorrect number key parts: want=%d received=%d",
len(parts),
len(h.fields),
)
}
if h.zero {
// Zero values are permitted,
// mangle all values and ignore
// zero value return booleans.
for i, part := range parts {
// Write mangled part to hasher.
_ = h.fields[i].hasher(hh, part)
}
} else {
// Zero values are NOT permitted.
for i, part := range parts {
// Write mangled field to hasher.
z := h.fields[i].hasher(hh, part)
if z {
// The value was zero for
// this type, return early.
return 0, false
}
}
}
return hh.Sum64(), true
}
// FromValue generates hash checksum (used as index key) from a value, via reflection.
func (h *Hasher[T]) FromValue(value T) (sum uint64, ok bool) {
rvalue := reflect.ValueOf(value)
hh := getHasher()
sum, ok = h.fromRValue(hh, rvalue)
putHasher(hh)
return
}
func (h *Hasher[T]) fromRValue(hh *xxh3.Hasher, rvalue reflect.Value) (uint64, bool) {
// Follow any ptrs leading to value.
for rvalue.Kind() == reflect.Pointer {
rvalue = rvalue.Elem()
}
if h.zero {
// Zero values are permitted,
// mangle all values and ignore
// zero value return booleans.
for i := range h.fields {
// Get the reflect value's field at idx.
fv := rvalue.FieldByIndex(h.fields[i].index)
fi := fv.Interface()
// Write mangled field to hasher.
_ = h.fields[i].hasher(hh, fi)
}
} else {
// Zero values are NOT permitted.
for i := range h.fields {
// Get the reflect value's field at idx.
fv := rvalue.FieldByIndex(h.fields[i].index)
fi := fv.Interface()
// Write mangled field to hasher.
z := h.fields[i].hasher(hh, fi)
if z {
// The value was zero for
// this type, return early.
return 0, false
}
}
}
return hh.Sum64(), true
}
type structfield struct {
// index is the reflected index
// of this field (this takes into
// account struct nesting).
index []int
// hasher is the relevant function
// for hashing value of structfield
// into the supplied hashbuf, where
// return value indicates if zero.
hasher func(*xxh3.Hasher, any) bool
}
|
