--- /dev/null
+// Copyright (c) 2015-2016 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 = ptrSize
+ offsetScalar = uintptr(0)
+ offsetFlag = 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 = 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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