1. Architecture

《Network Programming With Go》不是很深入。

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.

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/1.0rnrn”)) 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/1.0rnrn”)) 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 }

• ASN.1
• JSON
• gob
• base64

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

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.

Data integrity (数据完整性)

// MD5 Has package main import ( “crypto/md5” “fmt” ) func main() { hash := md5.New() bytes := []byte(“hellon”) 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

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))

• html/template, text/template
• pipelines: {{. | html}}
• template.FuncMap{“emailExpand”: EmailExpand}
• variables in templates are prefixed by ‘$’
• conditional