Question

《Network Programming With Go》不是很深入。

1. Architecture

Eight fallacies of distributed computing

• The network is reliable.
• Latency is zero.
• Bandwidth is infinite.
• The network is secure.
• Topology doesn't change.
• There is one administrator.
• Transport cost is zero.
• The network is homogeneous.

3. Socket level Programming

IP address type

type IP []byte
type IPMask []byte
type IPAddr {IP IP}

socket

// resolve IP
package main

import (
    "fmt"
    "net"
    "os"
)

func main() {
    name := "www.baidu.com"
    addr, err := net.ResolveIPAddr("ip", name)
    if err != nil {
        fmt.Println("Resolution error", err.Error())
        os.Exit(1)
    }
    fmt.Println("addr ip is ", addr.String())
}

// host lookup
package main

import (
    "fmt"
    "net"
)

func main() {
    addrs, err := net.LookupHost("www.baidu.com")
    if err != nil {
        fmt.Println(err)
    }
    for _, s := range addrs {
        fmt.Println(s)
    }
}

TCPAddr 包含 IP 和 Port：

type TCPAddr struct{
    IP IP
    Port int
}

使用 ResolveTCPAddr 创建一个 TCPAddr

func ResolveTCPAddr(net, addr string) (*TCPAddr, os.Error)

TCP Sockets:

func (c *TCPConn) Write(b []byte) (n int, err os.Error)
func (c *TCPConn) Read(b []byte) (n int, err os.Error)

客户端用 DialTCP 建立一个连接:

func DialTCP(net string, laddr, raddr *TCPAddr) (c *TCPConn, err os.Error)

尝试使用 tcp 发送一个 http 请求示例：

package main

import (
    "fmt"
    "io/ioutil"
    "log"
    "net"
)

func checkError(err error) {
    if err != nil {
        log.Fatal(err)
    }
}

func main() {
    // 使用 tcp 发送 http 请求示例 (只是为了测试几个函数，用 dial 最方便)

    // get addr
    addr, err := net.ResolveIPAddr("ip", "www.baidu.com")
    fmt.Println(addr)
    checkError(err)

    // create tcpAddr
    tcpAddr, err := net.ResolveTCPAddr("tcp4", fmt.Sprintf("%s:%d", addr, 80))
    checkError(err)
    // dialtcp
    conn, err := net.DialTCP("tcp", nil, tcpAddr)
    checkError(err)

    _, err = conn.Write([]byte("HEAD / HTTP/1.0\r\n\r\n"))
    checkError(err)

    res, err := ioutil.ReadAll(conn) // 读取直到 error 或者 EOF
    checkError(err)
    fmt.Println(string(res))
}

编写一个时间回显tcp服务器，tcp server 主要涉及两个函数：

func ListenTCP(net string, laddr *TCPAddr) (l *TCPListener, err os.Error)
func (l *TCPListener) Accept() (c Conn, err os.Error)

// DaytimeServer
// telnet localhost 1200
package main

import (
    "fmt"
    "net"
    "os"
    "time"
)

func main() {
    service := ":1200"
    tcpAddr, err := net.ResolveTCPAddr("tcp4", service)
    checkError(err)

    listener, err := net.ListenTCP("tcp", tcpAddr)
    checkError(err)

    for {
        conn, err := listener.Accept()
        if err != nil {
            continue
        }
        daytime := time.Now().String()
        conn.Write([]byte(daytime))
        conn.Close()
    }
}

func checkErr(err error) {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
        os.Exit(1)
    }
}

编写一个简单的tcp回显服务器：

// SimpleEchoServer
package main

import (
    "fmt"
    "net"
    "os"
)

func main() {
    service := ":1201"
    tcpAddr, err := net.ResolveTCPAddr("tcp4", service)
    checkError(err)

    listener, err := net.ListenTCP("tcp", tcpAddr)
    checkError(err)

    for {
        conn, err := listener.Accept()
        if err != nil {
            continue
        }
        handleClient(conn)
        conn.Close() // close  the client
    }
}
func handleClient(conn net.Conn) {
    var buf [512]byte
    for {
        n, err := conn.Read(buf[0:])
        if err != nil {
            return
        }
        fmt.Println(string(buf[0:]))
        _, err2 := conn.Write(buf[0:n])
        if err2 != nil {
            return
        }
    }
}

func checkError(err error) {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
        os.Exit(1)
    }
}

可以很容易修改成并发的，使用 goroutine

// SimpleEchoServer
package main

import (
    "fmt"
    "net"
    "os"
)

func main() {
    service := ":1201"
    tcpAddr, err := net.ResolveTCPAddr("tcp4", service)
    checkError(err)

    listener, err := net.ListenTCP("tcp", tcpAddr)
    checkError(err)

    for {
        conn, err := listener.Accept()
        if err != nil {
            continue
        }
        go handleClient(conn) // NOTE: use goroutine
    }
}

func handleClient(conn net.Conn) {
    defer conn.Close() // NOTE: close connection on exit
    var buf [512]byte
    for {
        n, err := conn.Read(buf[0:])
        if err != nil {
            return
        }
        fmt.Println(string(buf[0:]))
        _, err2 := conn.Write(buf[0:n])
        if err2 != nil {
            return
        }
    }
}

func checkError(err error) {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
        os.Exit(1)
    }
}

Controlling TCP connections

// Timeout
func (c *TCPConn) SetTimeout(nsec int64) os.Error

// Staying alive, a client wish to stay connected to a server even if it has nothing to send
func (c *TCPConn) SetKeepAlive(keepalive bool) os.Error

UDP Datagrams

func ResolveUDPAddr(net, addr string) (*UDPAddr, os.Error)
func DialUDP(net string, laddr, raddr *UDPAddr) (c *UDPConn, err os.Error)
func ListenUDP(net string, laddr *UDPAddr) (c *UDPConn, err os.Error)
func (c *UDPConn) ReadFromUDP(b []byte) (n int, addr *UDPAddr, err os.Error
func (c *UDPConn) WriteToUDP(b []byte, addr *UDPAddr) (n int, err os.Error)

UDP client server demo:

// UDPDaytimeClient
package main

import (
    "fmt"
    "net"
    "os"
)

func main() {
    service := "localhost:1200"
    udpAddr, err := net.ResolveUDPAddr("udp4", service)

    conn, err := net.DialUDP("udp", nil, udpAddr)
    checkError(err)

    _, err = conn.Write([]byte("anything"))
    checkError(err)
    var buf [512]byte
    n, err := conn.Read(buf[0:])
    checkError(err)

    fmt.Println(string(buf[0:n]))
}
func checkError(err error) {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
        os.Exit(1)
    }
}

// udpserver.go
package main

import (
    "fmt"
    "net"
    "os"
    "time"
)

func main() {
    service := ":1200"
    updAddr, err := net.ResolveUDPAddr("udp4", service)
    checkError(err)
    conn, err := net.ListenUDP("udp", updAddr)
    checkError(err)
    for {
        handleClient(conn)
    }
}

func handleClient(conn *net.UDPConn) {
    var buf [512]byte
    _, addr, err := conn.ReadFromUDP(buf[0:])
    if err != nil {
        return
    }
    daytime := time.Now().String()
    conn.WriteToUDP([]byte(daytime), addr)
}

func checkError(err error) {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
        os.Exit(1)
    }
}

The types Conn, PacketConn and Listener

func Dial(net, laddr, raddr string) (c Conn, err os.Error)

改写之前 tcp 发送 http 请求的例子

package main

import (
    "fmt"
    "io/ioutil"
    "log"
    "net"
)

func checkError(err error) {
    if err != nil {
        log.Fatal(err)
    }
}

func main() {
    conn, err := net.Dial("tcp", "www.baidu.com:80")
    checkError(err)
    _, err = conn.Write([]byte("HEAD / HTTP/1.0\r\n\r\n"))
    checkError(err)

    res, err := ioutil.ReadAll(conn) // 读取直到 error 或者 EOF
    checkError(err)
    fmt.Println(string(res))
}

同样的 listen 也可以简化

func Listen(net, laddr string) (l Listener, err os.Error)
func (l Listener) Accept() (c Conn, err os.Error)

Raw sockets and the type IPConn

IP 协议基础上自定义。按照 ping 发送格式模仿写一个 ping

• The first byte is 8, standing for the echo message
• The second byte is zero
• The third and fourth bytes are a checksum on the entire message
• The fifth and sixth bytes are an arbitrary identifier
• The seventh and eight bytes are an arbitrary sequence number
• The rest of the packet is user data

// Ping，使用 root 运行
package main

import (
    "fmt"
    "net"
    "os"
)

func checkError(err error) {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
        os.Exit(1)
    }
}
func main() {
    if len(os.Args) != 2 {
        fmt.Println("Usage: ", os.Args[0], "host")
        os.Exit(1)
    }
    addr, err := net.ResolveIPAddr("ip", os.Args[1])
    if err != nil {
        fmt.Println("Resolution error", err.Error())
        os.Exit(1)
    }

    fmt.Println(addr)
    conn, err := net.DialIP("ip4:icmp", addr, addr)
    checkError(err)

    var msg [512]byte
    msg[0] = 8  //echo
    msg[1] = 0  //code 0
    msg[2] = 0  //checksum, fix later
    msg[3] = 0  //checksum, fix later
    msg[4] = 0  //identifier[0]
    msg[5] = 13 //identifier[1]
    msg[6] = 0  // sequence[0]
    msg[7] = 37 //sequence[1]
    len := 8

    check := checkSum(msg[0:len])
    msg[2] = byte(check >> 8)
    msg[3] = byte(check & 255)

    _, err = conn.Write(msg[0:len])
    checkError(err)

    _, err = conn.Read(msg[0:])
    checkError(err)

    fmt.Println("Got response")
    if msg[5] == 13 {
        fmt.Println("identifier matches")
    }
    if msg[7] == 37 {
        fmt.Println("Sequence matches")
    }
}

func checkSum(msg []byte) uint16 {
    sum := 0
    for n := 1; n < len(msg)-1; n += 2 {
        sum += int(msg[n])*256 + int(msg[n+1])
    }
    sum = (sum >> 16) + (sum & 0xffff)
    sum += (sum >> 16)
    answer := uint16(^sum)
    return answer
}

4. Data serialisation

• ASN.1
• JSON
• gob
• base64

5. Application Level Protocols

• version control
• message format
• data format: byte encoded or character encoded
• state

6. Managing character sets and encodings

Go use utf8 encoded characters in its strings. Each character is of type rune(alias for int32) as a Unicode character can be 1,2 or 4 bytes in UTF8 encoding. A string is an array of rune.

7. Security

Data integrity (数据完整性)

// MD5 Has
package main

import (
    "crypto/md5"
    "fmt"
)

func main() {
    hash := md5.New()
    bytes := []byte("hello\n")
    hash.Write(bytes)
    hashValue := hash.Sum(nil)
    hashSize := hash.Size()
    // print out in ASCII from as four hexadcimal numbers
    for n := 0; n < hashSize; n += 4 {
        var val uint32
        val = uint32(hashValue[n])<<24 +
            uint32(hashValue[n+1])<<16 +
            uint32(hashValue[n+2])<<8 +
            uint32(hashValue[n+3])
        fmt.Printf("%x ", val)
    }
}

Symmetric key encryption

• Blowfish
• DES

Public key encryption

• crypto/rsa

X.509 certificates

A public key infrastructure(PKI) is a framework for a collections of public keys, along with additional information such as owner name and location.

TLS

• crypto/tls

8. HTTP

HTTP client

package main

import (
    "fmt"
    "net/http"
    "os"
)

func main() {
    url := "http://127.0.0.1:8000"
    response, err := http.Get(url)
    if err != nil {
        fmt.Println(err.Error())
        os.Exit(2)
    }
    if response.Status != "200 OK" {
        fmt.Println(response.Status)
        os.Exit(2)
    }
    // b, _ := httputil.DumpResponse(response, false)
    // fmt.Print(string(b))

    var buf [512]byte
    reader := response.Body
    for {
        n, err := reader.Read(buf[0:])
        if err != nil {
            fmt.Println(err)
            os.Exit(0)
        }
        fmt.Print(string(buf[0:n]))
    }

}

Proxy handling:

proxyURL, err := url.Parse(proxyString) // http://proxy-host:port
transport := &http.Transport{Proxy: http.ProxyURL(proxyURL)}
client := &http.Client{Transport: transport}
// func ProxyFromEnvironment(req *Request) (*url.URL, error)

Servers

• File server

package main

import "net/http"

func main() {
    fileServer := http.FileServer(http.Dir("/home/httpd/html"))
    err := http.ListenAndServe(":8000", fileServer)
    checkError(err)
}

• Handler function

func Handle(pattern string, handler Handler)
func HandleFunc(pattern string, handler func(*Conn, *Request))

9. Templates

• html/template, text/template
• pipelines: {{. | html}}
• template.FuncMap{"emailExpand": EmailExpand}
• variables in templates are prefixed by '$'
• conditional