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formatter.go
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formatter.go
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// Copyright 2022 The Swarm Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Note: the following code is derived (borrows) from: github.com/go-logr/logr
package log
import (
"bytes"
"encoding"
"fmt"
"path/filepath"
"reflect"
"runtime"
"strconv"
"strings"
)
// MessageCategory indicates which category or categories
// of messages should include the caller in the log lines.
type MessageCategory int
const (
CategoryNone MessageCategory = iota
CategoryAll
CategoryError
CategoryWarning
CategoryInfo
CategoryDebug
)
// Marshaler is an optional interface that logged values may choose to
// implement. Loggers with structured output, such as JSON, should
// log the object return by the MarshalLog method instead of the
// original value.
type Marshaler interface {
// MarshalLog can be used to:
// - ensure that structs are not logged as strings when the original
// value has a String method: return a different type without a
// String method
// - select which fields of a complex type should get logged:
// return a simpler struct with fewer fields
// - log unexported fields: return a different struct
// with exported fields
//
// It may return any value of any type.
MarshalLog() interface{}
}
// PseudoStruct is a list of key-value pairs that gets logged as a struct.
// E.g.: PseudoStruct{"f1", 1, "f2", true, "f3", []int{}}.
type PseudoStruct []interface{}
// fmtOptions carries parameters which influence the way logs are generated/formatted.
type fmtOptions struct {
caller MessageCategory
logCallerFunc bool
logTimestamp bool
timestampLayout string
maxLogDepth int
jsonOutput bool
callerDepth int
}
const (
null = "null" // null is a placeholder for nil values.
noValue = "<no-value>" // noValue is a placeholder for missing values.
// maxLogDepthExceeded is printed as the last value in
// the recursive chain when the depth limit is exceeded.
maxLogDepthExceeded = `"<max-log-depth-exceeded>"`
)
// caller represents the original call site for a log line. The File and
// Line fields will always be provided, while the Func field is optional.
type caller struct {
// File is the basename of the file for this call site.
File string `json:"file"`
// Line is the line number in the file for this call site.
Line int `json:"line"`
// Func is the function name for this call site, or empty if
// fmtOptions.logCallerFunc is not enabled.
Func string `json:"function,omitempty"`
}
// newFormatter constructs a formatter which
// behavior is influenced by the given options.
func newFormatter(opts fmtOptions) *formatter {
return &formatter{opts: opts}
}
// formatter is responsible for formatting the output of the log messages.
type formatter struct {
opts fmtOptions
}
// render produces a log line where the base is
// never escaped; the opposite is true for args.
func (f *formatter) render(base, args []interface{}) []byte {
buf := bytes.NewBuffer(make([]byte, 0, 1024))
if f.opts.jsonOutput {
buf.WriteByte('{')
}
f.flatten(buf, base, false, false)
f.flatten(buf, args, len(base) > 0, true)
if f.opts.jsonOutput {
buf.WriteByte('}')
}
buf.WriteByte('\n')
return buf.Bytes()
}
// flatten renders a list of key-value pairs into a buffer. If continuing is
// true, it assumes that the buffer has previous values and will emit a
// separator (which depends on the output format) before the first pair is
// written. If escapeKeys is true, the keys are assumed to have
// non-JSON-compatible characters in them and must be evaluated for escapes.
func (f *formatter) flatten(buf *bytes.Buffer, kvList []interface{}, continuing bool, escapeKeys bool) {
// This logic overlaps with sanitize() but saves one type-cast per key,
// which can be measurable.
if len(kvList)%2 != 0 {
kvList = append(kvList, noValue)
}
for i := 0; i < len(kvList); i += 2 {
k, ok := kvList[i].(string)
if !ok {
k = f.nonStringKey(kvList[i])
kvList[i] = k
}
v := kvList[i+1]
if i > 0 || continuing {
if f.opts.jsonOutput {
buf.WriteByte(',')
} else {
// In theory the format could be something we don't understand.
// In practice, we control it, so it won't be.
buf.WriteByte(' ')
}
}
if escapeKeys {
buf.WriteString(prettyString(k))
} else {
// The following is faster.
buf.WriteByte('"')
buf.WriteString(k)
buf.WriteByte('"')
}
if f.opts.jsonOutput {
buf.WriteByte(':')
} else {
buf.WriteByte('=')
}
buf.WriteString(f.prettyWithFlags(v, 0, 0))
}
}
// prettyWithFlags prettifies the given value.
// TODO: This is not fast. Most of the overhead goes here.
func (f *formatter) prettyWithFlags(value interface{}, flags uint32, depth int) string {
const flagRawStruct = 0x1 // Do not print braces on structs.
if depth > f.opts.maxLogDepth {
return maxLogDepthExceeded
}
// Handle types that take full control of logging.
if v, ok := value.(Marshaler); ok {
// Replace the value with what the type wants to get logged.
// That then gets handled below via reflection.
value = invokeMarshaler(v)
}
// Handle types that want to format themselves.
switch v := value.(type) {
case fmt.Stringer:
value = invokeStringer(v)
case error:
value = invokeError(v)
}
// Handling the most common types without reflect is a small perf win.
switch v := value.(type) {
case bool:
return strconv.FormatBool(v)
case string:
return prettyString(v)
case int:
return strconv.FormatInt(int64(v), 10)
case int8:
return strconv.FormatInt(int64(v), 10)
case int16:
return strconv.FormatInt(int64(v), 10)
case int32:
return strconv.FormatInt(int64(v), 10)
case int64:
return strconv.FormatInt(v, 10)
case uint:
return strconv.FormatUint(uint64(v), 10)
case uint8:
return strconv.FormatUint(uint64(v), 10)
case uint16:
return strconv.FormatUint(uint64(v), 10)
case uint32:
return strconv.FormatUint(uint64(v), 10)
case uint64:
return strconv.FormatUint(v, 10)
case uintptr:
return strconv.FormatUint(uint64(v), 10)
case float32:
return strconv.FormatFloat(float64(v), 'f', -1, 32)
case float64:
return strconv.FormatFloat(v, 'f', -1, 64)
case complex64:
return `"` + strconv.FormatComplex(complex128(v), 'f', -1, 64) + `"`
case complex128:
return `"` + strconv.FormatComplex(v, 'f', -1, 128) + `"`
case PseudoStruct:
buf := bytes.NewBuffer(make([]byte, 0, 1024))
v = f.sanitize(v)
if flags&flagRawStruct == 0 {
buf.WriteByte('{')
}
for i := 0; i < len(v); i += 2 {
if i > 0 {
buf.WriteByte(',')
}
k, _ := v[i].(string) // sanitize() above means no need to check success arbitrary keys might need escaping.
buf.WriteString(prettyString(k))
buf.WriteByte(':')
buf.WriteString(f.prettyWithFlags(v[i+1], 0, depth+1))
}
if flags&flagRawStruct == 0 {
buf.WriteByte('}')
}
return buf.String()
}
buf := bytes.NewBuffer(make([]byte, 0, 256))
t := reflect.TypeOf(value)
if t == nil {
return null
}
v := reflect.ValueOf(value)
switch t.Kind() {
case reflect.Bool:
return strconv.FormatBool(v.Bool())
case reflect.String:
return prettyString(v.String())
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return strconv.FormatInt(v.Int(), 10)
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return strconv.FormatUint(v.Uint(), 10)
case reflect.Float32:
return strconv.FormatFloat(v.Float(), 'f', -1, 32)
case reflect.Float64:
return strconv.FormatFloat(v.Float(), 'f', -1, 64)
case reflect.Complex64:
return `"` + strconv.FormatComplex(v.Complex(), 'f', -1, 64) + `"`
case reflect.Complex128:
return `"` + strconv.FormatComplex(v.Complex(), 'f', -1, 128) + `"`
case reflect.Struct:
if flags&flagRawStruct == 0 {
buf.WriteByte('{')
}
for i := 0; i < t.NumField(); i++ {
fld := t.Field(i)
if fld.PkgPath != "" {
// Reflect says this field is only defined for non-exported fields.
continue
}
if !v.Field(i).CanInterface() {
// Reflect isn't clear exactly what this means, but we can't use it.
continue
}
name := ""
omitempty := false
if tag, found := fld.Tag.Lookup("json"); found {
if tag == "-" {
continue
}
if comma := strings.Index(tag, ","); comma != -1 {
if n := tag[:comma]; n != "" {
name = n
}
rest := tag[comma:]
if strings.Contains(rest, ",omitempty,") || strings.HasSuffix(rest, ",omitempty") {
omitempty = true
}
} else {
name = tag
}
}
if omitempty && isEmpty(v.Field(i)) {
continue
}
if i > 0 {
buf.WriteByte(',')
}
if fld.Anonymous && fld.Type.Kind() == reflect.Struct && name == "" {
buf.WriteString(f.prettyWithFlags(v.Field(i).Interface(), flags|flagRawStruct, depth+1))
continue
}
if name == "" {
name = fld.Name
}
// Field names can't contain characters which need escaping.
buf.WriteByte('"')
buf.WriteString(name)
buf.WriteByte('"')
buf.WriteByte(':')
buf.WriteString(f.prettyWithFlags(v.Field(i).Interface(), 0, depth+1))
}
if flags&flagRawStruct == 0 {
buf.WriteByte('}')
}
return buf.String()
case reflect.Slice, reflect.Array:
buf.WriteByte('[')
for i := 0; i < v.Len(); i++ {
if i > 0 {
buf.WriteByte(',')
}
e := v.Index(i)
buf.WriteString(f.prettyWithFlags(e.Interface(), 0, depth+1))
}
buf.WriteByte(']')
return buf.String()
case reflect.Map:
buf.WriteByte('{')
// This does not sort the map keys, for best perf.
it := v.MapRange()
i := 0
for it.Next() {
if i > 0 {
buf.WriteByte(',')
}
// If a map key supports TextMarshaler, use it.
var keystr string
if m, ok := it.Key().Interface().(encoding.TextMarshaler); ok {
txt, err := m.MarshalText()
if err != nil {
keystr = fmt.Sprintf("<error-MarshalText: %s>", err.Error())
} else {
keystr = string(txt)
}
keystr = prettyString(keystr)
} else {
// prettyWithFlags will produce already-escaped values.
keystr = f.prettyWithFlags(it.Key().Interface(), 0, depth+1)
if t.Key().Kind() != reflect.String {
// JSON only does string keys. Unlike Go's standard JSON, we'll convert just about anything to a string.
keystr = prettyString(keystr)
}
}
buf.WriteString(keystr)
buf.WriteByte(':')
buf.WriteString(f.prettyWithFlags(it.Value().Interface(), 0, depth+1))
i++
}
buf.WriteByte('}')
return buf.String()
case reflect.Ptr, reflect.Interface:
if v.IsNil() {
return null
}
return f.prettyWithFlags(v.Elem().Interface(), 0, depth)
}
return fmt.Sprintf(`"<unhandled-%s>"`, t.Kind().String())
}
// caller captures basic information about the caller (filename, line, function).
func (f *formatter) caller() caller {
pc, file, line, ok := runtime.Caller(f.opts.callerDepth + 3)
if !ok {
return caller{"<unknown>", 0, ""}
}
caller := caller{File: filepath.Base(file), Line: line}
if f.opts.logCallerFunc {
if fp := runtime.FuncForPC(pc); fp != nil {
caller.Func = fp.Name()
}
}
return caller
}
// nonStringKey converts non-string value v to string.
func (f *formatter) nonStringKey(v interface{}) string {
return fmt.Sprintf("<non-string-key: %s>", f.snippet(v))
}
// snippet produces a short snippet string of an arbitrary value.
func (f *formatter) snippet(v interface{}) string {
const snipLen = 16
snip := f.prettyWithFlags(v, 0, 0)
if len(snip) > snipLen {
snip = snip[:snipLen]
}
return snip
}
// sanitize ensures that a list of key-value pairs has a value for every key
// (adding a value if needed) and that each key is a string (substituting a key
// if needed).
func (f *formatter) sanitize(kvList []interface{}) []interface{} {
if len(kvList)%2 != 0 {
kvList = append(kvList, noValue)
}
for i := 0; i < len(kvList); i += 2 {
_, ok := kvList[i].(string)
if !ok {
kvList[i] = f.nonStringKey(kvList[i])
}
}
return kvList
}
// isEmpty is similar to the IsZero() reflect.Value method, except that
// in the case of Array and Struct it does not go into depth.
func isEmpty(v reflect.Value) bool {
switch v.Kind() {
case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
return v.Len() == 0
case reflect.Bool:
return !v.Bool()
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return v.Int() == 0
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return v.Uint() == 0
case reflect.Float32, reflect.Float64:
return v.Float() == 0
case reflect.Complex64, reflect.Complex128:
return v.Complex() == 0
case reflect.Interface, reflect.Ptr:
return v.IsNil()
}
return false
}
// prettyString prettify the given string.
// TODO: try to avoid allocations.
func prettyString(s string) string {
// Avoid escaping (which does allocations) if we can.
if needsEscape(s) {
return strconv.Quote(s)
}
b := bytes.NewBuffer(make([]byte, 0, 1024))
b.WriteByte('"')
b.WriteString(s)
b.WriteByte('"')
return b.String()
}
// needsEscape determines whether the input string needs
// to be escaped or not, without doing any allocations.
func needsEscape(s string) bool {
for _, r := range s {
if !strconv.IsPrint(r) || r == '\\' || r == '"' {
return true
}
}
return false
}
// invokeMarshaler returns panic-safe output from the Marshaler.MarshalLog() method.
func invokeMarshaler(m Marshaler) (ret interface{}) {
defer func() {
if r := recover(); r != nil {
ret = fmt.Sprintf("<panic: %s>", r)
}
}()
return m.MarshalLog()
}
// invokeStringer returns panic-safe output from the fmt.Stringer.String() method.
func invokeStringer(s fmt.Stringer) (ret string) {
defer func() {
if r := recover(); r != nil {
ret = fmt.Sprintf("<panic: %s>", r)
}
}()
return s.String()
}
// invokeError returns panic-safe output from the error. Error() method.
func invokeError(e error) (ret string) {
defer func() {
if r := recover(); r != nil {
ret = fmt.Sprintf("<panic: %s>", r)
}
}()
return e.Error()
}