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本文主要研究一下golang的zap的Core

Core

zap@v1.16.0/zapcore/core.go

type Core interface {
    LevelEnabler

    // With adds structured context to the Core.
    With([]Field) Core
    // Check determines whether the supplied Entry should be logged (using the
    // embedded LevelEnabler and possibly some extra logic). If the entry
    // should be logged, the Core adds itself to the CheckedEntry and returns
    // the result.
    //
    // Callers must use Check before calling Write.
    Check(Entry, *CheckedEntry) *CheckedEntry
    // Write serializes the Entry and any Fields supplied at the log site and
    // writes them to their destination.
    //
    // If called, Write should always log the Entry and Fields; it should not
    // replicate the logic of Check.
    Write(Entry, []Field) error
    // Sync flushes buffered logs (if any).
    Sync() error
}

Core接口内嵌了LevelEnabler，定义了With、Check、Write、Sync方法

LevelEnabler

zap@v1.16.0/zapcore/level.go

type LevelEnabler interface {
    Enabled(Level) bool
}

LevelEnabler定义了Enabled方法

nopCore

zap@v1.16.0/zapcore/core.go

type nopCore struct{}

// NewNopCore returns a no-op Core.
func NewNopCore() Core                                        { return nopCore{} }
func (nopCore) Enabled(Level) bool                            { return false }
func (n nopCore) With([]Field) Core                           { return n }
func (nopCore) Check(_ Entry, ce *CheckedEntry) *CheckedEntry { return ce }
func (nopCore) Write(Entry, []Field) error                    { return nil }
func (nopCore) Sync() error                                   { return nil }

nopCore实现了Core接口，为空操作

ioCore

zap@v1.16.0/zapcore/core.go

type ioCore struct {
    LevelEnabler
    enc Encoder
    out WriteSyncer
}

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

func (c *ioCore) Check(ent Entry, ce *CheckedEntry) *CheckedEntry {
    if c.Enabled(ent.Level) {
        return ce.AddCore(ent, c)
    }
    return ce
}

func (c *ioCore) Write(ent Entry, fields []Field) error {
    buf, err := c.enc.EncodeEntry(ent, fields)
    if err != nil {
        return err
    }
    _, err = c.out.Write(buf.Bytes())
    buf.Free()
    if err != nil {
        return err
    }
    if ent.Level > ErrorLevel {
        // Since we may be crashing the program, sync the output. Ignore Sync
        // errors, pending a clean solution to issue #370.
        c.Sync()
    }
    return nil
}

func (c *ioCore) Sync() error {
    return c.out.Sync()
}

func (c *ioCore) clone() *ioCore {
    return &ioCore{
        LevelEnabler: c.LevelEnabler,
        enc:          c.enc.Clone(),
        out:          c.out,
    }
}

ioCore内嵌了LevelEnabler，定义了Encoder、WriteSyncer(out)属性，实现了Core接口；其With方法执行的是clone以及addFields；Check方法先判断c.Enabled(ent.Level)，若为true才执行ce.AddCore(ent, c)；Write方法先通过encoder的EncodeEntry序列化entry，然后将bytes写入到WriteSyncer，若entry的level大于ErrorLevel的还会执行Sync方法；Sync方法执行out.Sync；clone方法则用原来core来重新一个新的ioCore

addFields

zap@v1.16.0/zapcore/field.go

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

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())
    }
}

addFields方法遍历fields，执行Field的AddTo方法；AddTo方法会根据f.Type来执行ObjectEncoder的对应方法

实例

func newCoreDemo() {
    temp, err := ioutil.TempFile("", "zapcore-test-iocore")
    if err != nil {
        panic(err)
    }
    fmt.Println(temp.Name())
    //defer os.Remove(temp.Name())

    cfg := zapcore.EncoderConfig{
        MessageKey:     "msg",
        LevelKey:       "level",
        NameKey:        "name",
        TimeKey:        "ts",
        CallerKey:      "caller",
        FunctionKey:    "func",
        StacktraceKey:  "stacktrace",
        LineEnding:     "\n",
        EncodeTime:     zapcore.EpochTimeEncoder,
        EncodeLevel:    zapcore.LowercaseLevelEncoder,
        EncodeDuration: zapcore.SecondsDurationEncoder,
        EncodeCaller:   zapcore.ShortCallerEncoder,
    }
    cfg.TimeKey = ""

    core := zapcore.NewCore(
        zapcore.NewJSONEncoder(cfg),
        temp,
        zapcore.InfoLevel,
    ).With([]zapcore.Field{zapcore.Field{Type: zapcore.Int64Type, Integer: int64(1), Key: "k"}})

    if ce := core.Check(zapcore.Entry{Level: zapcore.DebugLevel, Message: "debug"}, nil); ce != nil {
        ce.Write(zapcore.Field{Type: zapcore.Int64Type, Integer: int64(2), Key: "k"})
    }
    if ce := core.Check(zapcore.Entry{Level: zapcore.InfoLevel, Message: "info"}, nil); ce != nil {
        ce.Write(zapcore.Field{Type: zapcore.Int64Type, Integer: int64(3), Key: "k"})
    }
    if ce := core.Check(zapcore.Entry{Level: zapcore.WarnLevel, Message: "warn"}, nil); ce != nil {
        ce.Write(zapcore.Field{Type: zapcore.Int64Type, Integer: int64(4), Key: "k"})
    }

}

这里NewJSONEncoder使用指定的zapcore.EncoderConfig，zapcore.NewCore的out设置为temp文件，level级别为InfoLevel，因而只会输出level及以上的entry

输出

{"level":"info","msg":"info","k":1,"k":3}
{"level":"warn","msg":"warn","k":1,"k":4}

其中k为1的是withField全局指定的，然后k为2因为是debug级别所以没有输出出来

小结

Core接口内嵌了LevelEnabler，定义了With、Check、Write、Sync方法；它有nopCore及ioCore两种实现，ioCore内嵌了LevelEnabler，定义了Encoder、WriteSyncer(out)属性，其中encoder用来序列化entry为bytes，而WriteSyncer则用于写入bytes。

doc

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