go-spew/spew/format.go

/*
 * Copyright (c) 2013 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.
 */

package spew

import (
	"bytes"
	"fmt"
	"reflect"
	"strconv"
	"strings"
)

// supportedFlags is a list of all the character flags supported by fmt package.
const supportedFlags = "0-+# "

// formatState implements the fmt.Formatter interface and contains information
// about the state of a formatting operation.  The NewFormatter function can
// be used to get a new Formatter which can be used directly as arguments
// in standard fmt package printing calls.
type formatState struct {
	value    interface{}
	buffer   bytes.Buffer
	depth    int
	pointers map[uintptr]int // Holds map of points and depth they were seen at
	fs       fmt.State
}

// buildDefaultFormat recreates the original format string without precision
// and width information to pass in to fmt.Sprintf in the case of an
// unrecognized type.  Unless new types are added to the language, this
// function won't ever be called.
func (f *formatState) buildDefaultFormat() (format string) {
	buf := bytes.NewBuffer(percentBytes)

	for _, flag := range supportedFlags {
		if f.fs.Flag(int(flag)) {
			buf.WriteRune(flag)
		}
	}

	buf.WriteRune('v')

	format = buf.String()
	return format
}

// constructOrigFormat recreates the original format string including precision
// and width information to pass along to the standard fmt package.  This allows
// automatic deferral of all format strings this package doesn't support.
func (f *formatState) constructOrigFormat(verb rune) (format string) {
	buf := bytes.NewBuffer(percentBytes)

	for _, flag := range supportedFlags {
		if f.fs.Flag(int(flag)) {
			buf.WriteRune(flag)
		}
	}

	if width, ok := f.fs.Width(); ok {
		buf.WriteString(strconv.Itoa(width))
	}

	if precision, ok := f.fs.Precision(); ok {
		buf.Write(precisionBytes)
		buf.WriteString(strconv.Itoa(precision))
	}

	buf.WriteRune(verb)

	format = buf.String()
	return format
}

// formatPtr handles formatting of pointers by indirecting them as necessary.
func (f *formatState) formatPtr(v reflect.Value) {
	// Display nil if top level poiner is nil.
	if v.IsNil() {
		f.buffer.Write(nilAngleBytes)
		return
	}

	// Remove pointers at or below the current depth from map used to detect
	// circular refs.
	for k, depth := range f.pointers {
		if depth >= f.depth {
			delete(f.pointers, k)
		}
	}

	plusSyntax := f.fs.Flag('+')

	// Keep list of all dereferenced pointers to possibly show later.
	pointerChain := make([]uintptr, 0)

	// Figure out how many levels of indirection there are by derferencing
	// pointers and unpacking interfaces down the chain while detecting circular
	// references.
	nilFound := false
	cycleFound := false
	indirects := 0
	ve := v
	for ve.Kind() == reflect.Ptr {
		indirects++
		if ve.IsNil() {
			nilFound = true
			break
		}
		addr := ve.Pointer()
		pointerChain = append(pointerChain, addr)
		if pd, ok := f.pointers[addr]; ok && pd < f.depth {
			cycleFound = true
			break
		}
		f.pointers[addr] = f.depth

		ve = ve.Elem()
		if ve.Kind() == reflect.Interface {
			if ve.IsNil() {
				nilFound = true
				break
			}
			ve = ve.Elem()
		}
	}

	// Display indirection level.
	f.buffer.Write(openAngleBytes)
	f.buffer.WriteString(strings.Repeat("*", indirects))
	f.buffer.Write(closeAngleBytes)

	// Display pointer information depending on flags.
	if plusSyntax && (len(pointerChain) > 0) {
		f.buffer.Write(openParenBytes)
		for i, addr := range pointerChain {
			if i > 0 {
				f.buffer.Write(pointerChainBytes)
			}
			printHexPtr(&f.buffer, addr)
		}
		f.buffer.Write(closeParenBytes)
	}

	// Display dereferenced value.
	switch {
	case nilFound == true:
		f.buffer.Write(nilAngleBytes)

	case cycleFound == true:
		f.buffer.Write(circularShortBytes)

	default:
		f.format(ve)
	}
}

// format is the main workhorse for providing the Formatter interface.  It
// uses the passed reflect value to figure out what kind of object we are
// dealing with and formats it appropriately.  It is a recursive function,
// however circular data structures are detected and handled properly.
func (f *formatState) format(v reflect.Value) {
	// Call error/Stringer interfaces if they exist and the handle methods
	// flag is enabled.
	kind := v.Kind()
	if !Config.DisableMethods {
		if (kind != reflect.Invalid) && (kind != reflect.Interface) {
			if handled := handleMethods(&f.buffer, v); handled {
				return
			}
		}
	}

	switch kind {
	case reflect.Invalid:
		f.buffer.Write(invalidAngleBytes)

	case reflect.Bool:
		printBool(&f.buffer, v.Bool())

	case reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Int:
		printInt(&f.buffer, v.Int())

	case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uint:
		printUint(&f.buffer, v.Uint())

	case reflect.Float32:
		printFloat(&f.buffer, v.Float(), 32)

	case reflect.Float64:
		printFloat(&f.buffer, v.Float(), 64)

	case reflect.Complex64:
		printComplex(&f.buffer, v.Complex(), 32)

	case reflect.Complex128:
		printComplex(&f.buffer, v.Complex(), 64)

	case reflect.Array, reflect.Slice:
		f.buffer.WriteRune('[')
		f.depth++
		if (Config.MaxDepth != 0) && (f.depth > Config.MaxDepth) {
			f.buffer.Write(maxShortBytes)
		} else {
			numEntries := v.Len()
			for i := 0; i < numEntries; i++ {
				if i > 0 {
					f.buffer.WriteRune(' ')
				}
				f.format(unpackValue(v.Index(i)))
			}
		}
		f.depth--
		f.buffer.WriteRune(']')

	case reflect.String:
		f.buffer.WriteString(v.String())

	case reflect.Interface:
		// Do nothing.  We should never get here due to unpackValue calls

	case reflect.Map:
		f.buffer.Write(openMapBytes)
		f.depth++
		if (Config.MaxDepth != 0) && (f.depth > Config.MaxDepth) {
			f.buffer.Write(maxShortBytes)
		} else {
			keys := v.MapKeys()
			for i, key := range keys {
				if i > 0 {
					f.buffer.WriteRune(' ')
				}
				f.format(unpackValue(key))
				f.buffer.WriteRune(':')
				f.format(unpackValue(v.MapIndex(key)))
			}
		}
		f.depth--
		f.buffer.Write(closeMapBytes)

	case reflect.Ptr:
		f.formatPtr(v)

	case reflect.Struct:
		numFields := v.NumField()
		f.buffer.WriteRune('{')
		f.depth++
		if (Config.MaxDepth != 0) && (f.depth > Config.MaxDepth) {
			f.buffer.Write(maxShortBytes)
		} else {
			vt := v.Type()
			for i := 0; i < numFields; i++ {
				if i > 0 {
					f.buffer.WriteRune(' ')
				}
				vtf := vt.Field(i)
				if f.fs.Flag('+') {
					f.buffer.WriteString(vtf.Name)
					f.buffer.WriteRune(':')
				}
				f.format(unpackValue(v.Field(i)))
			}
		}
		f.depth--
		f.buffer.WriteRune('}')

	case reflect.Uintptr:
		printHexPtr(&f.buffer, uintptr(v.Uint()))

	case reflect.UnsafePointer, reflect.Chan, reflect.Func:
		printHexPtr(&f.buffer, v.Pointer())

	// There were not any other types at the time this code was written, but
	// fall back to letting the default fmt package handle it if any get added.
	default:
		format := f.buildDefaultFormat()
		if v.CanInterface() {
			f.buffer.WriteString(fmt.Sprintf(format, v.Interface()))
		} else {
			f.buffer.WriteString(fmt.Sprintf(format, v.String()))
		}
	}
}

// Format satisfies the fmt.Formatter interface. See NewFormatter for usage
// details.
func (f *formatState) Format(fs fmt.State, verb rune) {
	f.fs = fs

	// Use standard formatting for verbs that are not v or #v.
	if (verb != 'v') || (verb == 'v' && fs.Flag('#')) {
		format := f.constructOrigFormat(verb)
		fmt.Fprintf(fs, format, f.value)
		return
	}

	if f.value == nil {
		fmt.Fprint(fs, string(nilAngleBytes))
		return
	}

	f.format(reflect.ValueOf(f.value))
	f.buffer.WriteTo(fs)
}

/*
NewFormatter returns a custom formatter that satisfies the fmt.Formatter
interface.  As a result, it integrates cleanly with standard fmt package
printing functions.  The formatter is useful for inline printing of smaller data
types similar to the standard %v format specifier.

The custom formatter only responds to the %v and %+v verb combinations.  Any
other variations such as %x, %q, and %#v will be sent to the the standard fmt
package for formatting.  In addition, the custom formatter ignores the width and
precision arguments (however they will still work on the format specifiers not
handled by the custom formatter).

Typically this function shouldn't be called directly.  It is much easier to make
use of the custom formatter is to call one of the convenience functions such as
Printf, Println, or Printf.
*/
func NewFormatter(v interface{}) (f fmt.Formatter) {
	fs := &formatState{value: v}
	fs.pointers = make(map[uintptr]int)
	return fs
}