msgp的用法和一些局限性

msgp是golang用来做序列化的一个工具

获取方式：
go get github.com/tinylib/msgp

以官网例子来看

wujingcideMacBook-Pro:msgp wujingci$ cat my_types.go
package main

type Person struct {
    Name       string `msg:"name"`
    Address    string `msg:"address"`
    Age        int    `msg:"age"`
    Hidden     string `msg:"-"` // this field is ignored
    unexported bool             // this field is also ignored
}
wujingcideMacBook-Pro:msgp wujingci$ msgp -file=my_types.go
======== MessagePack Code Generator =======
>>> Input: "my_types.go"
my_types.go: Person: Hidden: ignored.
>>> Wrote and formatted "my_types_gen_test.go"
>>> Wrote and formatted "my_types_gen.go"
wujingcideMacBook-Pro:msgp wujingci$ ls
my_types.go     my_types_gen.go     my_types_gen_test.go

my_types_gen.go就是生成出来的代码
包含EncodeMsg, DecodeMsg, MarshalMsg, UnmarshalMsg

我们常常会用marshal出来的结果去存redis，这时候我们就发现生成代码里

func (z Person) MarshalMsg(b []byte) (o []byte, err error) {
    o = msgp.Require(b, z.Msgsize())
    // map header, size 3
    // string "name"
    o = append(o, 0x83, 0xa4, 0x6e, 0x61, 0x6d, 0x65)
    o = msgp.AppendString(o, z.Name)
    // string "address"
    o = append(o, 0xa7, 0x61, 0x64, 0x64, 0x72, 0x65, 0x73, 0x73)
    o = msgp.AppendString(o, z.Address)
    // string "age"
    o = append(o, 0xa3, 0x61, 0x67, 0x65)
    o = msgp.AppendInt(o, z.Age)
    return
}

所有的key都会被塞入，而我们实际上为了节约空间，有些默认值或者空值是不需要插入的，这样就造成了大量的空间浪费。