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// Copyright (c) 2015 Dave Collins <dave@davec.name>
//
// Permission to use, copy, modify, and distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
// NOTE: Due to the following build constraints, this file will only be compiled
// when the code is not running on Google App Engine, compiled by GopherJS, and
// "-tags safe" is not added to the go build command line. The "disableunsafe"
// tag is deprecated and thus should not be used.
// +build !js,!appengine,!safe,!disableunsafe
package spew
import (
"reflect"
"unsafe"
)
const (
// UnsafeDisabled is a build-time constant which specifies whether or
// not access to the unsafe package is available.
UnsafeDisabled = false
// ptrSize is the size of a pointer on the current arch.
ptrSize = unsafe.Sizeof((*byte)(nil))
)
var (
// offsetPtr, offsetScalar, and offsetFlag are the offsets for the
// internal reflect.Value fields. These values are valid before golang
// commit ecccf07e7f9d which changed the format. The are also valid
// after commit 82f48826c6c7 which changed the format again to mirror
// the original format. Code in the init function updates these offsets
// as necessary.
offsetPtr = uintptr(ptrSize)
offsetScalar = uintptr(0)
offsetFlag = uintptr(ptrSize * 2)
// flagKindWidth and flagKindShift indicate various bits that the
// reflect package uses internally to track kind information.
//
// flagRO indicates whether or not the value field of a reflect.Value is
// read-only.
//
// flagIndir indicates whether the value field of a reflect.Value is
// the actual data or a pointer to the data.
//
// These values are valid before golang commit 90a7c3c86944 which
// changed their positions. Code in the init function updates these
// flags as necessary.
flagKindWidth = uintptr(5)
flagKindShift = uintptr(flagKindWidth - 1)
flagRO = uintptr(1 << 0)
flagIndir = uintptr(1 << 1)
)
func init() {
// Older versions of reflect.Value stored small integers directly in the
// ptr field (which is named val in the older versions). Versions
// between commits ecccf07e7f9d and 82f48826c6c7 added a new field named
// scalar for this purpose which unfortunately came before the flag
// field, so the offset of the flag field is different for those
// versions.
//
// This code constructs a new reflect.Value from a known small integer
// and checks if the size of the reflect.Value struct indicates it has
// the scalar field. When it does, the offsets are updated accordingly.
vv := reflect.ValueOf(0xf00)
if unsafe.Sizeof(vv) == (ptrSize * 4) {
offsetScalar = ptrSize * 2
offsetFlag = ptrSize * 3
}
// Commit 90a7c3c86944 changed the flag positions such that the low
// order bits are the kind. This code extracts the kind from the flags
// field and ensures it's the correct type. When it's not, the flag
// order has been changed to the newer format, so the flags are updated
// accordingly.
upf := unsafe.Pointer(uintptr(unsafe.Pointer(&vv)) + offsetFlag)
upfv := *(*uintptr)(upf)
flagKindMask := uintptr((1<<flagKindWidth - 1) << flagKindShift)
if (upfv&flagKindMask)>>flagKindShift != uintptr(reflect.Int) {
flagKindShift = 0
flagRO = 1 << 5
flagIndir = 1 << 6
// Commit adf9b30e5594 modified the flags to separate the
// flagRO flag into two bits which specifies whether or not the
// field is embedded. This causes flagIndir to move over a bit
// and means that flagRO is the combination of either of the
// original flagRO bit and the new bit.
//
// This code detects the change by extracting what used to be
// the indirect bit to ensure it's set. When it's not, the flag
// order has been changed to the newer format, so the flags are
// updated accordingly.
if upfv&flagIndir == 0 {
flagRO = 3 << 5
flagIndir = 1 << 7
}
}
}
// unsafeReflectValue converts the passed reflect.Value into a one that bypasses
// the typical safety restrictions preventing access to unaddressable and
// unexported data. It works by digging the raw pointer to the underlying
// value out of the protected value and generating a new unprotected (unsafe)
// reflect.Value to it.
//
// This allows us to check for implementations of the Stringer and error
// interfaces to be used for pretty printing ordinarily unaddressable and
// inaccessible values such as unexported struct fields.
func unsafeReflectValue(v reflect.Value) (rv reflect.Value) {
indirects := 1
vt := v.Type()
upv := unsafe.Pointer(uintptr(unsafe.Pointer(&v)) + offsetPtr)
rvf := *(*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(&v)) + offsetFlag))
if rvf&flagIndir != 0 {
vt = reflect.PtrTo(v.Type())
indirects++
} else if offsetScalar != 0 {
// The value is in the scalar field when it's not one of the
// reference types.
switch vt.Kind() {
case reflect.Uintptr:
case reflect.Chan:
case reflect.Func:
case reflect.Map:
case reflect.Ptr:
case reflect.UnsafePointer:
default:
upv = unsafe.Pointer(uintptr(unsafe.Pointer(&v)) +
offsetScalar)
}
}
pv := reflect.NewAt(vt, upv)
rv = pv
for i := 0; i < indirects; i++ {
rv = rv.Elem()
}
return rv
}
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