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Diffstat (limited to 'spew/common.go')
| -rw-r--r-- | spew/common.go | 241 |
1 files changed, 241 insertions, 0 deletions
diff --git a/spew/common.go b/spew/common.go new file mode 100644 index 0000000..69b95e4 --- /dev/null +++ b/spew/common.go @@ -0,0 +1,241 @@ +/* + * Copyright (c) 2013 Dave Collins <[email protected]> + * + * 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. + */ + +package spew + +import ( + "fmt" + "io" + "reflect" + "strconv" + "unsafe" +) + +// reflectValue mirrors the struct layout of the reflect package Value type. +var reflectValue struct { + typ unsafe.Pointer + val unsafe.Pointer + flag uintptr +} + +// flagIndir indicates whether the value field of a reflect.Value is the actual +// data or a pointer to the data. +const flagIndir = 1 << 1 + +// 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)) + unsafe.Offsetof(reflectValue.val)) + rvf := *(*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(&v)) + unsafe.Offsetof(reflectValue.flag))) + if rvf&flagIndir != 0 { + vt = reflect.PtrTo(v.Type()) + indirects++ + } + + 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 ( + panicBytes = []byte("(PANIC=") + plusBytes = []byte("+") + iBytes = []byte("i") + trueBytes = []byte("true") + falseBytes = []byte("false") + interfaceBytes = []byte("(interface {}) ") + commaNewlineBytes = []byte(",\n") + newlineBytes = []byte("\n") + openBraceBytes = []byte("{") + openBraceNewlineBytes = []byte("{\n") + closeBraceBytes = []byte("}") + closeBraceNewlinBytes = []byte("}\n") + asteriskBytes = []byte("*") + colonSpaceBytes = []byte(": ") + openParenBytes = []byte("(") + closeParenBytes = []byte(")") + spaceBytes = []byte(" ") + pointerChainBytes = []byte("->") + nilAngleBytes = []byte("<nil>") + maxNewlineBytes = []byte("<max depth reached>\n") + maxShortBytes = []byte("<max>") + circularBytes = []byte("<already shown>") + circularShortBytes = []byte("<shown>") + invalidAngleBytes = []byte("<invalid>") + percentBytes = []byte("%") + precisionBytes = []byte(".") + openAngleBytes = []byte("<") + closeAngleBytes = []byte(">") + openMapBytes = []byte("map[") + closeMapBytes = []byte("]") +) + +// hexDigits is used to map a decimal value to a hex digit. +var hexDigits = "0123456789abcdef" + +// unpackValue returns values inside of non-nil inteferfaces when possible. +// This is useful for data types like structs, arrays, slices, and maps which +// can contain varying types packed inside an interface. +func unpackValue(v reflect.Value) reflect.Value { + if v.Kind() == reflect.Interface && !v.IsNil() { + v = v.Elem() + } + return v +} + +// catchPanic handles any panics that might occur during the handleMethods +// calls. +func catchPanic(w io.Writer, v reflect.Value) { + if err := recover(); err != nil { + w.Write(panicBytes) + fmt.Fprintf(w, "%v", err) + w.Write(closeParenBytes) + } +} + +// handleMethods attempts to call the Error and String methods on the underlying +// type the passed reflect.Value represents and outputes the result to Writer w. +// +// It handles panics in any called methods by catching and displaying the error +// as the formatted value. +func handleMethods(w io.Writer, v reflect.Value) (handled bool) { + // We need an interface to check if the type implements the error or + // Stringer interface. However, the reflect package won't give us an + // an interface on certain things like unexported struct fields in order + // to enforce visibility rules. We use unsafe to bypass these restrictions + // since this package does not mutate the values. + if !v.CanInterface() { + v = unsafeReflectValue(v) + } + + // Choose whether or not to do error and Stringer interface lookups against + // the base type or a pointer to the base type depending on settings. + // Technically calling one of these methods with a pointer receiver can + // mutate the value, however, types which choose to satisify an error or + // Stringer interface with a pointer receiver should not be mutating their + // state inside these interface methods. + var viface interface{} + if !Config.DisablePointerMethods { + if !v.CanAddr() { + v = unsafeReflectValue(v) + } + viface = v.Addr().Interface() + } else { + viface = v.Interface() + } + + // Is it an error or Stringer? + switch iface := viface.(type) { + case error: + defer catchPanic(w, v) + w.Write([]byte(iface.Error())) + return true + + case fmt.Stringer: + defer catchPanic(w, v) + w.Write([]byte(iface.String())) + return true + } + return false +} + +// printBool outputs a boolean value as true or false to Writer w. +func printBool(w io.Writer, val bool) { + if val { + w.Write(trueBytes) + } else { + w.Write(falseBytes) + } +} + +// printInt outputs a signed integer value to Writer w. +func printInt(w io.Writer, val int64) { + w.Write([]byte(strconv.FormatInt(val, 10))) +} + +// printUint outputs an unsigned integer value to Writer w. +func printUint(w io.Writer, val uint64) { + w.Write([]byte(strconv.FormatUint(val, 10))) +} + +// printFloat outputs a floating point value using the specified precision, +// which is expected to be 32 or 64bit, to Writer w. +func printFloat(w io.Writer, val float64, precision int) { + w.Write([]byte(strconv.FormatFloat(val, 'g', -1, precision))) +} + +// printComplex outputs a complex value using the specified float precision +// for the real and imaginary parts to Writer w. +func printComplex(w io.Writer, c complex128, floatPrecision int) { + r := real(c) + w.Write(openParenBytes) + w.Write([]byte(strconv.FormatFloat(r, 'g', -1, floatPrecision))) + i := imag(c) + if i >= 0 { + w.Write(plusBytes) + } + w.Write([]byte(strconv.FormatFloat(i, 'g', -1, floatPrecision))) + w.Write(iBytes) + w.Write(closeParenBytes) +} + +// printHexPtr outputs a uintptr formatted as hexidecimal with a leading '0x' +// prefix to Writer w. +func printHexPtr(w io.Writer, p uintptr) { + // Null pointer. + num := uint64(p) + if num == 0 { + w.Write(nilAngleBytes) + return + } + + // Max uint64 is 16 bytes in hex + 2 bytes for '0x' prefix + buf := make([]byte, 18) + + // It's simpler to construct the hex string right to left. + base := uint64(16) + i := len(buf) - 1 + for num >= base { + buf[i] = hexDigits[num%base] + num /= base + i-- + } + buf[i] = hexDigits[num] + + // Add '0x' prefix. + i-- + buf[i] = 'x' + i-- + buf[i] = '0' + + // Strip unused leading bytes. + buf = buf[i:] + w.Write(buf) +} |