1 package danger

     2 

     3 import (

     4 	"fmt"

     5 	"reflect"

     6 	"unsafe"

     7 )

     8 

     9 const maxInt = uintptr(int(^uint(0) >> 1))

    10 

    11 func SubsliceOffset(data []byte, subslice []byte) int {

    12 	datap := (*reflect.SliceHeader)(unsafe.Pointer(&data))

    13 	hlp := (*reflect.SliceHeader)(unsafe.Pointer(&subslice))

    14 

    15 	if hlp.Data < datap.Data {

    16 		panic(fmt.Errorf("subslice address (%d) is before data address (%d)", hlp.Data, datap.Data))

    17 	}

    18 	offset := hlp.Data - datap.Data

    19 

    20 	if offset > maxInt {

    21 		panic(fmt.Errorf("slice offset larger than int (%d)", offset))

    22 	}

    23 

    24 	intoffset := int(offset)

    25 

    26 	if intoffset > datap.Len {

    27 		panic(fmt.Errorf("slice offset (%d) is farther than data length (%d)", intoffset, datap.Len))

    28 	}

    29 

    30 	if intoffset+hlp.Len > datap.Len {

    31 		panic(fmt.Errorf("slice ends (%d+%d) is farther than data length (%d)", intoffset, hlp.Len, datap.Len))

    32 	}

    33 

    34 	return intoffset

    35 }

    36 

    37 func BytesRange(start []byte, end []byte) []byte {

    38 	if start == nil || end == nil {

    39 		panic("cannot call BytesRange with nil")

    40 	}

    41 	startp := (*reflect.SliceHeader)(unsafe.Pointer(&start))

    42 	endp := (*reflect.SliceHeader)(unsafe.Pointer(&end))

    43 

    44 	if startp.Data > endp.Data {

    45 		panic(fmt.Errorf("start pointer address (%d) is after end pointer address (%d)", startp.Data, endp.Data))

    46 	}

    47 

    48 	l := startp.Len

    49 	endLen := int(endp.Data-startp.Data) + endp.Len

    50 	if endLen > l {

    51 		l = endLen

    52 	}

    53 

    54 	if l > startp.Cap {

    55 		panic(fmt.Errorf("range length is larger than capacity"))

    56 	}

    57 

    58 	return start[:l]

    59 }

    60 

    61 func Stride(ptr unsafe.Pointer, size uintptr, offset int) unsafe.Pointer {

    62 	// TODO: replace with unsafe.Add when Go 1.17 is released

    63 	//   https://github.com/golang/go/issues/40481

    64 	return unsafe.Pointer(uintptr(ptr) + uintptr(int(size)*offset))

    65 }