golang实现mysql udf

UDF(user-defined function)

当mysql提供的内置函数(count,min,max等)没法知足需求时，udf用于扩展自定义函数，知足特定查询需求。
在这里，假定一种db应用场景，有一个 t_quest_db的table，有2个字段 roleid(INT), data(blob)。data为本身编码的二进制数据字段，当想要经过select查询出肉眼可见的内容时，就须要用到UDF了。

主要代码实现

示例代码用到cgo，附上完整示例代码：https://files.cnblogs.com/files/fitness/udftest.zip

// 本文件实现t_quest_db的data字段的序列化和反序列化

package udfdll

import (
    "bytes"
    "encoding/gob"
)

type PlayerDoingQuestDbData struct {
    TaskId           int
    TaskDbId         int64
    AcceptTime       int32
    ProgressMap      map[int]string
    IsProgressFinish bool
}

type PlayerDoneQuestDbData struct {
    TaskId            int
    LastDoneTimestamp int32 // 上次完成任务的时间戳
    PeriodDoneTimes   int   // 任务周期内完成的次数(天/周)
}

// 这个结构存db, 对应t_quest_db的data字段
type PlayerAllQuestDbData struct {
    DoneTaskMap  map[int]*PlayerDoneQuestDbData
    DoingTaskMap map[int64]*PlayerDoingQuestDbData
}

// 把this编码为二进制，存入data字段
func (this *PlayerAllQuestDbData) ToDbBlob() ([]byte, error) {
    buf := bytes.NewBuffer([]byte{})
    enc := gob.NewEncoder(buf)
    if err := enc.Encode(this); err != nil {
        return nil, err
    }

    return buf.Bytes(), nil
}

// 解析data字段
func (this *PlayerAllQuestDbData) FromDbBlob(data []byte) error {
    if len(data) > 0 {
        dec := gob.NewDecoder(bytes.NewBuffer(data))
        if err := dec.Decode(this); err != nil {
            return err
        }
    }

    if this.DoneTaskMap == nil {
        this.DoneTaskMap = make(map[int]*PlayerDoneQuestDbData)
    }

    if this.DoingTaskMap == nil {
        this.DoingTaskMap = make(map[int64]*PlayerDoingQuestDbData)
    }

    return nil
}

// 本文件实现UDF扩展

package main

/*
#cgo CFLAGS: -Iinclude
#include <mysql.h>
#include <string.h>
#include <stdlib.h>
*/
import "C"
import (
    "bytes"
    _ "encoding/gob"
    "encoding/json"
    "fmt"
    "strings"
    "unsafe"
)

func main() {}

func getUintPointerValue(pointer *uint32, offset int) *C.uint {
    return (*C.uint)(unsafe.Pointer(uintptr(unsafe.Pointer(pointer)) + uintptr(offset)*uintptr(unsafe.Sizeof(C.uint(0)))))
}

func getCharPointerValue(pointer **C.char, offset int) **C.char {
    var c C.char
    return (**C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(pointer)) + uintptr(offset)*uintptr(unsafe.Sizeof(&c))))
}

func getUlongPointerValue(pointer *C.ulong, offset int) *C.ulong {
    return (*C.ulong)(unsafe.Pointer(uintptr(unsafe.Pointer(pointer)) + uintptr(offset)*uintptr(unsafe.Sizeof(C.ulong(0)))))
}

func getBytePointerValue(pointer *C.char, offset int) *C.char {
    return (*C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(pointer)) + uintptr(offset)*uintptr(unsafe.Sizeof(C.char(0)))))
}

//export questblob_init
func questblob_init(init *C.UDF_INIT, args *C.UDF_ARGS, msg *C.char) C.my_bool {
    init.maybe_null = 1
    if args.arg_count < 2 {
        s := C.CString("UnExpected err: args count len < 1")
        C.strcpy(msg, s)
        C.free(unsafe.Pointer(s))
        return 1
    }
    *getUintPointerValue(args.arg_type, 0) = C.STRING_RESULT
    *getUintPointerValue(args.arg_type, 1) = C.STRING_RESULT
    return 0
}

//export questblob_deinit
func questblob_deinit(init *C.UDF_INIT) {
    C.free(unsafe.Pointer(init.ptr))
}

//export questblob
func questblob(init *C.UDF_INIT, args *C.UDF_ARGS, result *C.char, length *C.ulong, is_null *C.char, error *C.char) *C.char {
    *is_null = 1
    chars := getCharPointerValue(args.args, 0)
    arglen := getUlongPointerValue(args.lengths, 0)
    names := getCharPointerValue(args.args, 1)
    namelen := getUlongPointerValue(args.lengths, 1)
    rb := C.GoBytes(unsafe.Pointer(*chars), C.int(*arglen))
    name := C.GoStringN(*names, C.int(*namelen))
    nameInfos := strings.Split(name, ".")

    _ = nameInfos[0] // 数据库表名
    _ = nameInfos[1] // 数据库字段名，实际状况中可根据这两个string，决定构造那个对象
    errStringPrefix := fmt.Sprintf("[Error]table:'%s' column:'%s' ", nameInfos[0], nameInfos[1])

    data := &PlayerAllQuestDbData{}
    err := data.FromDbBlob(bytes.NewBuffer(rb).Bytes())
    if err != nil {
        *is_null = 0
        errString := errStringPrefix + err.Error()
        *length = C.ulong(len([]byte(errString)))
        errS := C.CString(errString)
        init.ptr = errS
        return errS
    }

    rb, err = json.Marshal(data)
    if err != nil {
        *is_null = 0
        errString := errStringPrefix + " Marshal error: " + err.Error()
        *length = C.ulong(len([]byte(errString)))
        errS := C.CString(errString)
        init.ptr = errS
        return errS
    }

    *is_null = 0
    *length = C.ulong(len(rb))
    s := C.CString(string(rb))
    init.ptr = s
    return s
}

生成dll

windows运行build.bat,生成libquestblob.dll, 拷贝到mysql的plugin目录下。

使用

CREATE FUNCTION questblob RETURNS STRING SONAME 'libquestblob.dll'; #此语句执行一次便可
SELECT roleid, cast(questblob(t_quest_db.data, 't_quest_db.data') AS CHAR) FROM t_quest_db;