聊聊golang的zap的Field

序

本文主要研究一下golang的zap的Field

Field

zap@v1.16.0/zapcore/field.go

type Field struct {
    Key       string
    Type      FieldType
    Integer   int64
    String    string
    Interface interface{}
}

Field定义了Key、FieldType、Integer、String、Interface属性

AddTo

zap@v1.16.0/zapcore/field.go

func (f Field) AddTo(enc ObjectEncoder) {
    var err error

    switch f.Type {
    case ArrayMarshalerType:
        err = enc.AddArray(f.Key, f.Interface.(ArrayMarshaler))
    case ObjectMarshalerType:
        err = enc.AddObject(f.Key, f.Interface.(ObjectMarshaler))
    case BinaryType:
        enc.AddBinary(f.Key, f.Interface.([]byte))
    case BoolType:
        enc.AddBool(f.Key, f.Integer == 1)
    case ByteStringType:
        enc.AddByteString(f.Key, f.Interface.([]byte))
    case Complex128Type:
        enc.AddComplex128(f.Key, f.Interface.(complex128))
    case Complex64Type:
        enc.AddComplex64(f.Key, f.Interface.(complex64))
    case DurationType:
        enc.AddDuration(f.Key, time.Duration(f.Integer))
    case Float64Type:
        enc.AddFloat64(f.Key, math.Float64frombits(uint64(f.Integer)))
    case Float32Type:
        enc.AddFloat32(f.Key, math.Float32frombits(uint32(f.Integer)))
    case Int64Type:
        enc.AddInt64(f.Key, f.Integer)
    case Int32Type:
        enc.AddInt32(f.Key, int32(f.Integer))
    case Int16Type:
        enc.AddInt16(f.Key, int16(f.Integer))
    case Int8Type:
        enc.AddInt8(f.Key, int8(f.Integer))
    case StringType:
        enc.AddString(f.Key, f.String)
    case TimeType:
        if f.Interface != nil {
            enc.AddTime(f.Key, time.Unix(0, f.Integer).In(f.Interface.(*time.Location)))
        } else {
            // Fall back to UTC if location is nil.
            enc.AddTime(f.Key, time.Unix(0, f.Integer))
        }
    case TimeFullType:
        enc.AddTime(f.Key, f.Interface.(time.Time))
    case Uint64Type:
        enc.AddUint64(f.Key, uint64(f.Integer))
    case Uint32Type:
        enc.AddUint32(f.Key, uint32(f.Integer))
    case Uint16Type:
        enc.AddUint16(f.Key, uint16(f.Integer))
    case Uint8Type:
        enc.AddUint8(f.Key, uint8(f.Integer))
    case UintptrType:
        enc.AddUintptr(f.Key, uintptr(f.Integer))
    case ReflectType:
        err = enc.AddReflected(f.Key, f.Interface)
    case NamespaceType:
        enc.OpenNamespace(f.Key)
    case StringerType:
        err = encodeStringer(f.Key, f.Interface, enc)
    case ErrorType:
        encodeError(f.Key, f.Interface.(error), enc)
    case SkipType:
        break
    default:
        panic(fmt.Sprintf("unknown field type: %v", f))
    }

    if err != nil {
        enc.AddString(fmt.Sprintf("%sError", f.Key), err.Error())
    }
}

AddTo方法根据Field的类型来执行encoder的对应方法将Field的key和value添加到encoder中

Equals

zap@v1.16.0/zapcore/field.go

func (f Field) Equals(other Field) bool {
    if f.Type != other.Type {
        return false
    }
    if f.Key != other.Key {
        return false
    }

    switch f.Type {
    case BinaryType, ByteStringType:
        return bytes.Equal(f.Interface.([]byte), other.Interface.([]byte))
    case ArrayMarshalerType, ObjectMarshalerType, ErrorType, ReflectType:
        return reflect.DeepEqual(f.Interface, other.Interface)
    default:
        return f == other
    }
}

Equals方法用于判断两个Field是否相等，对于BinaryType或ByteStringType使用bytes.Equal判断，对于ArrayMarshalerType、ObjectMarshalerType、ErrorType、ReflectType使用reflect.DeepEqual判断，其他的默认用==判断

addFields

zap@v1.16.0/zapcore/field.go

func addFields(enc ObjectEncoder, fields []Field) {
    for i := range fields {
        fields[i].AddTo(enc)
    }
}

addFields方法用于将fields批量添加到encoder中

With

zap@v1.16.0/zapcore/core.go

func (c *ioCore) With(fields []Field) Core {
    clone := c.clone()
    addFields(clone.enc, fields)
    return clone
}

zapcore的With方法用于将fields添加到core中，core的Field属于全局通用的Field

logger

zap@v1.16.0/logger.go

func (log *Logger) With(fields ...Field) *Logger {
    if len(fields) == 0 {
        return log
    }
    l := log.clone()
    l.core = l.core.With(fields)
    return l
}

func (log *Logger) Info(msg string, fields ...Field) {
    if ce := log.check(InfoLevel, msg); ce != nil {
        ce.Write(fields...)
    }
}

logger的With方法最后是执行core的With，添加的是全局的；而Info之类方法提供的Field参数属于动态的，每条log自己的动态Field，它最后调用的是encoder的EncodeEntry(Entry, []Field)方法

Write

zap@v1.16.0/zapcore/json_encoder.go

func (enc *jsonEncoder) EncodeEntry(ent Entry, fields []Field) (*buffer.Buffer, error) {
    final := enc.clone()
    final.buf.AppendByte('{')

    if final.LevelKey != "" {
        final.addKey(final.LevelKey)
        cur := final.buf.Len()
        final.EncodeLevel(ent.Level, final)
        if cur == final.buf.Len() {
            // User-supplied EncodeLevel was a no-op. Fall back to strings to keep
            // output JSON valid.
            final.AppendString(ent.Level.String())
        }
    }
    if final.TimeKey != "" {
        final.AddTime(final.TimeKey, ent.Time)
    }
    if ent.LoggerName != "" && final.NameKey != "" {
        final.addKey(final.NameKey)
        cur := final.buf.Len()
        nameEncoder := final.EncodeName

        // if no name encoder provided, fall back to FullNameEncoder for backwards
        // compatibility
        if nameEncoder == nil {
            nameEncoder = FullNameEncoder
        }

        nameEncoder(ent.LoggerName, final)
        if cur == final.buf.Len() {
            // User-supplied EncodeName was a no-op. Fall back to strings to
            // keep output JSON valid.
            final.AppendString(ent.LoggerName)
        }
    }
    if ent.Caller.Defined {
        if final.CallerKey != "" {
            final.addKey(final.CallerKey)
            cur := final.buf.Len()
            final.EncodeCaller(ent.Caller, final)
            if cur == final.buf.Len() {
                // User-supplied EncodeCaller was a no-op. Fall back to strings to
                // keep output JSON valid.
                final.AppendString(ent.Caller.String())
            }
        }
        if final.FunctionKey != "" {
            final.addKey(final.FunctionKey)
            final.AppendString(ent.Caller.Function)
        }
    }
    if final.MessageKey != "" {
        final.addKey(enc.MessageKey)
        final.AppendString(ent.Message)
    }
    if enc.buf.Len() > 0 {
        final.addElementSeparator()
        final.buf.Write(enc.buf.Bytes())
    }
    addFields(final, fields)
    final.closeOpenNamespaces()
    if ent.Stack != "" && final.StacktraceKey != "" {
        final.AddString(final.StacktraceKey, ent.Stack)
    }
    final.buf.AppendByte('}')
    if final.LineEnding != "" {
        final.buf.AppendString(final.LineEnding)
    } else {
        final.buf.AppendString(DefaultLineEnding)
    }

    ret := final.buf
    putJSONEncoder(final)
    return ret, nil
}

jsonEncoder的Write方法执行的是Field的addFields(final, fields)，将Field的key、value添加到encoder中

实例

func fieldDemo() {
    logger, err := zap.NewProduction()
    defer logger.Sync()
    if err != nil {
        panic(err)
    }
    logger = logger.With(zap.String("appId", "demoApp"))
    logger.Info("failed to fetch URL",
        // Structured context as strongly typed Field values.
        zap.String("url", "https://example.com"),
        zap.Int("attempt", 3),
        zap.Duration("backoff", time.Second),
    )
}

输出

{"level":"info","ts":1608304623.277035,"caller":"zap/zap_demo.go:28","msg":"failed to fetch URL","appId":"demoApp","url":"https://example.com","attempt":3,"backoff":1}

小结

Field的AddTo方法根据Field的类型来执行encoder的对应方法将Field的key和value添加到encoder中；logger的With方法最后是执行core的With，添加的是全局的；而Info之类方法提供的Field参数属于动态的，每条log自己的动态Field，它最后调用的是encoder的EncodeEntry(Entry, []Field)方法

doc

• zap

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