fix: batch channel not close when client close

[cyruslo]

Fix #100

[xuthus5]

the client will block because the channel is not closed, a simple demo to verify the idea, End of data will never have a chance to print.

package main

import (
	"fmt"
	"time"
)

func reader(ch <-chan int) {
	for record := range ch {
		fmt.Println(record)
	}
	fmt.Println("End of data")
}

func main() {
	var ch = make(chan int)
	go reader(ch)
	for i := 0; i < 10; i++ {
		ch <- i
	}
	time.Sleep(time.Second * 10)
}

[hezhangjian]

Currently, we don't have any restrictions, so we can still call WritePointWithRp after closing it. It may contains some leak.

[xuthus5]

Currently, we don't have any restrictions, so we can still call after closing it. It may contains some leak.WritePointWithRp

Close() semantics have no effect.

[xuthus5]

Close method:

func (c *client) Close() error {
	c.batchContextCancel()
	c.dataChanMap.Range(func(key, value interface{}) bool {
		close(value.(chan *sendBatchWithCB))
		c.dataChanMap.Delete(key)
		return true
	})
	return nil
}

WritePointWithRp method on new line 58, add a context cancel judgment to prevent the program from writing data to a closed channel:

if c.batchContext.Err() != nil {
    return errors.New("batch write failed, error: " + c.batchContext.Err().Error())
}