github.com/goplusjs/reflectx@v0.5.4/name_go117.go

// +build go1.17

package reflectx

import "unsafe"

// name is an encoded type name with optional extra data.
//
// The first byte is a bit field containing:
//
//	1<<0 the name is exported
//	1<<1 tag data follows the name
//	1<<2 pkgPath nameOff follows the name and tag
//
// Following that, there is a varint-encoded length of the name,
// followed by the name itself.
//
// If tag data is present, it also has a varint-encoded length
// followed by the tag itself.
//
// If the import path follows, then 4 bytes at the end of
// the data form a nameOff. The import path is only set for concrete
// methods that are defined in a different package than their type.
//
// If a name starts with "*", then the exported bit represents
// whether the pointed to type is exported.
//
// Note: this encoding must match here and in:
//   cmd/compile/internal/reflectdata/reflect.go
//   runtime/type.go
//   internal/reflectlite/type.go
//   cmd/link/internal/ld/decodesym.go

type name struct {
	bytes *byte
}

func (n name) data(off int, whySafe string) *byte {
	return (*byte)(add(unsafe.Pointer(n.bytes), uintptr(off), whySafe))
}

func (n name) isExported() bool {
	return (*n.bytes)&(1<<0) != 0
}

func (n name) hasTag() bool {
	return (*n.bytes)&(1<<1) != 0
}

// readVarint parses a varint as encoded by encoding/binary.
// It returns the number of encoded bytes and the encoded value.
func (n name) readVarint(off int) (int, int) {
	v := 0
	for i := 0; ; i++ {
		x := *n.data(off+i, "read varint")
		v += int(x&0x7f) << (7 * i)
		if x&0x80 == 0 {
			return i + 1, v
		}
	}
}

// writeVarint writes n to buf in varint form. Returns the
// number of bytes written. n must be nonnegative.
// Writes at most 10 bytes.
func writeVarint(buf []byte, n int) int {
	for i := 0; ; i++ {
		b := byte(n & 0x7f)
		n >>= 7
		if n == 0 {
			buf[i] = b
			return i + 1
		}
		buf[i] = b | 0x80
	}
}

func (n name) name() (s string) {
	if n.bytes == nil {
		return
	}
	i, l := n.readVarint(1)
	hdr := (*stringHeader)(unsafe.Pointer(&s))
	hdr.Data = unsafe.Pointer(n.data(1+i, "non-empty string"))
	hdr.Len = l
	return
}

func (n name) tag() (s string) {
	if !n.hasTag() {
		return ""
	}
	i, l := n.readVarint(1)
	i2, l2 := n.readVarint(1 + i + l)
	hdr := (*stringHeader)(unsafe.Pointer(&s))
	hdr.Data = unsafe.Pointer(n.data(1+i+l+i2, "non-empty string"))
	hdr.Len = l2
	return
}

func (n name) pkgPath() string {
	if n.bytes == nil || *n.data(0, "name flag field")&(1<<2) == 0 {
		return ""
	}
	i, l := n.readVarint(1)
	off := 1 + i + l
	if n.hasTag() {
		i2, l2 := n.readVarint(off)
		off += i2 + l2
	}
	var nameOff int32
	// Note that this field may not be aligned in memory,
	// so we cannot use a direct int32 assignment here.
	copy((*[4]byte)(unsafe.Pointer(&nameOff))[:], (*[4]byte)(unsafe.Pointer(n.data(off, "name offset field")))[:])
	pkgPathName := name{(*byte)(resolveTypeOff(unsafe.Pointer(n.bytes), nameOff))}
	return pkgPathName.name()
}

func (n name) setPkgPath(pkgpath nameOff) bool {
	if n.bytes == nil || *n.data(0, "name flag field")&(1<<2) == 0 {
		return false
	}
	i, l := n.readVarint(1)
	off := 1 + i + l
	if n.hasTag() {
		i2, l2 := n.readVarint(off)
		off += i2 + l2
	}
	copy((*[4]byte)(unsafe.Pointer(n.data(off, "name offset field")))[:], (*[4]byte)(unsafe.Pointer(&pkgpath))[:])
	return true
}

func newNameEx(n, tag string, exported bool, pkgpath bool) name {
	if len(n) >= 1<<29 {
		panic("reflect.nameFrom: name too long: " + n[:1024] + "...")
	}
	if len(tag) >= 1<<29 {
		panic("reflect.nameFrom: tag too long: " + tag[:1024] + "...")
	}
	var nameLen [10]byte
	var tagLen [10]byte
	nameLenLen := writeVarint(nameLen[:], len(n))
	tagLenLen := writeVarint(tagLen[:], len(tag))

	var bits byte
	l := 1 + nameLenLen + len(n)
	if exported {
		bits |= 1 << 0
	}
	if len(tag) > 0 {
		l += tagLenLen + len(tag)
		bits |= 1 << 1
	}
	if !exported && pkgpath {
		bits |= 1 << 2
		l += 4
	}

	b := make([]byte, l)
	b[0] = bits
	copy(b[1:], nameLen[:nameLenLen])
	copy(b[1+nameLenLen:], n)
	if len(tag) > 0 {
		tb := b[1+nameLenLen+len(n):]
		copy(tb, tagLen[:tagLenLen])
		copy(tb[tagLenLen:], tag)
	}

	return name{bytes: &b[0]}
}