From 31bfe87edc080028293be773fd4967d0f103fc65 Mon Sep 17 00:00:00 2001 From: Dmitri Shuralyov Date: Sat, 6 Jun 2015 18:55:53 -0700 Subject: [PATCH] Add limited support for Google App Engine. This allows the package to build and operate in a limited fashion on Google App Engine, where "unsafe" package is not available. Closes #35. --- spew/bypass.go | 131 +++++++++++++++++++++++++++++++++++++++++++++ spew/bypass_gae.go | 26 +++++++++ spew/common.go | 108 ------------------------------------- 3 files changed, 157 insertions(+), 108 deletions(-) create mode 100644 spew/bypass.go create mode 100644 spew/bypass_gae.go diff --git a/spew/bypass.go b/spew/bypass.go new file mode 100644 index 0000000..26054bb --- /dev/null +++ b/spew/bypass.go @@ -0,0 +1,131 @@ +/* + * Copyright (c) 2013 Dave Collins + * + * 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. + */ + +// +build !appengine + +package spew + +import ( + "reflect" + "unsafe" +) + +const ( + // 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<>flagKindShift != uintptr(reflect.Int) { + flagKindShift = 0 + flagRO = 1 << 5 + flagIndir = 1 << 6 + } +} + +// 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 +} diff --git a/spew/bypass_gae.go b/spew/bypass_gae.go new file mode 100644 index 0000000..bdb347f --- /dev/null +++ b/spew/bypass_gae.go @@ -0,0 +1,26 @@ +/* + * Copyright (c) 2013 Dave Collins + * + * 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. + */ + +// +build appengine + +package spew + +import "reflect" + +func UnsafeReflectValue(v reflect.Value) reflect.Value { + // This is just a stub, since "unsafe" is unavailable. + return v +} diff --git a/spew/common.go b/spew/common.go index 8252cd3..28aee87 100644 --- a/spew/common.go +++ b/spew/common.go @@ -23,116 +23,8 @@ import ( "reflect" "sort" "strconv" - "unsafe" ) -const ( - // 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<>flagKindShift != uintptr(reflect.Int) { - flagKindShift = 0 - flagRO = 1 << 5 - flagIndir = 1 << 6 - } -} - -// 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 -} - // Some constants in the form of bytes to avoid string overhead. This mirrors // the technique used in the fmt package. var (