go-zookeeper库的使用

## go-zookeeper库使用
[samuel/go-zookeeper/zk]是zookeeper的golang客户端，也是个人感觉目前最好用的ZK-golang的客户端了，本文档主要介绍该库的使用方法，并给出自己使用的一个简单事例，至于该库的内部实现，可能会在其他文档中有所阐述。


### 使用事例
    package main

    import (
        "fmt"
        "github.com/samuel/go-zookeeper/zk"
        "sync"
        "time"
    )
    
    // conenct zookeeper cluster
    func connect_zk() (*zk.Conn, error) {
        c, _, err := zk.Connect([]string{"127.0.0.1:2182"}, time.Second*1)
        // c, session, err := zk.Connect([]string{"127.0.0.1:2182"}, time.Second*1)
        if err != nil {
            return nil, err
        }
        return c,nil
    }
    
    func delete_node(c *zk.Conn, nodePath string) {
        c.Delete(nodePath, -1)
    }

    func create_node(c *zk.Conn, nodePath string) error {
        if _, err := c.Create(nodePath, []byte{1, 2, 3, 4}, 0, zk.WorldACL(zk.PermAll)); err != nil {
            fmt.Printf("Create returned error: %+v\n", err)
            return err
        }
        return nil
    }

    func get_node(c *zk.Conn, path string) {
        data, stat, err := c.Get(path)
        if err != nil {
            fmt.Printf("Get returned error: %+v\n", err)
        } else {
            fmt.Printf("Get node, data: %+v, state: %+v\n", data, stat)
        }
    }

    func watch_node(c *zk.Conn) {
        var wg sync.WaitGroup
        path := "/gozk-test-2"

        delete_node(c, path)
    
        _, _, childCh, _ := c.ChildrenW("/")
        /*
        if err != nil {
            fmt.Printf("Watch error: %v\n", err)
            return
        }
        */

        wg.Add(1)
        go Watcher(wg, childCh)

        create_node(c, path)

        /*
        if path, err = c.Create("/gozk-test-2", []byte{1, 2, 3, 4}, 0, zk.WorldACL(zk.PermAll)); err != nil {
            fmt.Printf("Creat node: %v error: %v\n", "/gozk-test-2", err)
            return
        } else if path != "/gozk-test-2" {
            fmt.Printf("Create returned different path '%s' != '%s'", path, "/gozk-test-2")
            return
        }
        */

        // add watcher for new added node
        _, _, addCh, _ := c.ChildrenW("/gozk-test-2")
        wg.Add(1)
        go Watcher(wg, addCh)

        delete_node(c, path)

        wg.Wait()
    }
    
    func main() {
        path := "/gozk-test"
        // connect zk-server
        c, err := connect_zk()
        if err != nil {
            return
        }

        // create zk-node, delete it if already exist
        delete_node(c, path)
        err = create_node(c, path)
        if err != nil {
            return
        }

        get_node(c, path)

        watch_node(c)
    }

    func Watcher(wg sync.WaitGroup, childCh <-chan zk.Event) {
        defer wg.Done()
        select {
        case ev := <-childCh:
            if ev.Err != nil {
                fmt.Printf("Child watcher error: %+v\n", ev.Err)
                return
            }
            fmt.Printf("Receive event: %+v\n", ev)
        case _ = <-time.After(time.Second * 2):
            fmt.Printf("Child Watcher timeout")
            return
        }
    }
    
### 运行结果

    Get node, data: [1 2 3 4], state: &{Czxid:115 Mzxid:115 Ctime:1406017529127 Mtime:1406017529127 Version:0 Cversion:0 Aversion:0 EphemeralOwner:0 DataLength:4 NumChildren:0 Pzxid:115}
    Receive event: {Type:EventNodeChildrenChanged State:StateSyncConnected Path:/ Err:<nil>}
    Receive event: {Type:EventNodeDeleted State:StateSyncConnected Path:/gozk-test-2 Err:<nil>}
    
[samuel/go-zookeeper/zk]:https://github.com/samuel/go-zookeeper.git