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package structr
import (
"fmt"
"reflect"
"unicode"
"unicode/utf8"
"unsafe"
"codeberg.org/gruf/go-mangler"
"github.com/modern-go/reflect2"
)
// struct_field contains pre-prepared type
// information about a struct's field member,
// including memory offset and hash function.
type struct_field struct {
// type2 contains the reflect2
// type information for this field,
// used in repacking it as eface.
type2 reflect2.Type
// offsets defines whereabouts in
// memory this field is located.
offsets []next_offset
// struct field type mangling
// (i.e. fast serializing) fn.
mangle mangler.Mangler
// zero value data, used when
// nil encountered during ptr
// offset following.
zero unsafe.Pointer
// mangled zero value string,
// if set this indicates zero
// values of field not allowed
zerostr string
}
// next_offset defines a next offset location
// in a struct_field, first by the number of
// derefences required, then by offset from
// that final memory location.
type next_offset struct {
derefs uint
offset uintptr
}
// find_field will search for a struct field with given set of names,
// where names is a len > 0 slice of names account for struct nesting.
func find_field(t reflect.Type, names []string) (sfield struct_field) {
var (
// is_exported returns whether name is exported
// from a package; can be func or struct field.
is_exported = func(name string) bool {
r, _ := utf8.DecodeRuneInString(name)
return unicode.IsUpper(r)
}
// pop_name pops the next name from
// the provided slice of field names.
pop_name = func() string {
name := names[0]
names = names[1:]
if !is_exported(name) {
panicf("field is not exported: %s", name)
}
return name
}
// field is the iteratively searched
// struct field value in below loop.
field reflect.StructField
)
for len(names) > 0 {
// Pop next name.
name := pop_name()
var off next_offset
// Dereference any ptrs to struct.
for t.Kind() == reflect.Pointer {
t = t.Elem()
off.derefs++
}
// Check for valid struct type.
if t.Kind() != reflect.Struct {
panicf("field %s is not struct (or ptr-to): %s", t, name)
}
var ok bool
// Look for next field by name.
field, ok = t.FieldByName(name)
if !ok {
panicf("unknown field: %s", name)
}
// Set next offset value.
off.offset = field.Offset
sfield.offsets = append(sfield.offsets, off)
// Set the next type.
t = field.Type
}
// Get field type as reflect2.
sfield.type2 = reflect2.Type2(t)
// Find mangler for field type.
sfield.mangle = mangler.Get(t)
// Set possible zero value and its string.
sfield.zero = sfield.type2.UnsafeNew()
i := sfield.type2.UnsafeIndirect(sfield.zero)
sfield.zerostr = string(sfield.mangle(nil, i))
return
}
// extract_fields extracts given structfields from the provided value type,
// this is done using predetermined struct field memory offset locations.
func extract_fields(ptr unsafe.Pointer, fields []struct_field) []any {
// Prepare slice of field ifaces.
ifaces := make([]any, len(fields))
for i, field := range fields {
// loop scope.
fptr := ptr
for _, offset := range field.offsets {
// Dereference any ptrs to offset.
fptr = deref(fptr, offset.derefs)
if fptr == nil {
// Use zero value.
fptr = field.zero
break
}
// Jump forward by offset to next ptr.
fptr = unsafe.Pointer(uintptr(fptr) +
offset.offset)
}
// Repack value data ptr as empty interface.
ifaces[i] = field.type2.UnsafeIndirect(fptr)
}
return ifaces
}
// deref will dereference ptr 'n' times (or until nil).
func deref(p unsafe.Pointer, n uint) unsafe.Pointer {
for ; n > 0; n-- {
if p == nil {
return nil
}
p = *(*unsafe.Pointer)(p)
}
return p
}
// panicf provides a panic with string formatting.
func panicf(format string, args ...any) {
panic(fmt.Sprintf(format, args...))
}
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