Server-Sent Events in Go

Transcript

1. Server-Sent Events
   WARSAW, Feb 2020
   Oleg Kovalov
   Allegro
   https://olegk.dev
   

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2. Me
   - Gopher for ~4 years
   - Open source contributor
   - Engineer at allegro.pl core team
   Website: https://olegk.dev
   Twitter: @oleg_kovalov
   Github: @cristaloleg
   2
   

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3. What is SSE?
   3
   

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4. - Senior Software Engineer
   What is SSE?
   4
   

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5. - Senior Software Engineer
   - Server-Sent Events
   What is SSE?
   5
   

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6. - Senior Software Engineer
   - Server-Sent Events
   - Streaming SIMD Extensions
   What is SSE?
   6
   

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7. - Senior Software Engineer
   - Server-Sent Events
   - Streaming SIMD Extensions
   - Shanghai Stock Exchange
   - Small-scale enterprise
   What is SSE?
   7
   

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8. - Senior Software Engineer
   - Server-Sent Events
   - Streaming SIMD Extensions
   - Shanghai Stock Exchange
   - Small-scale enterprise
   - Skyrim Special Edition
   - ...
   What is SSE?
   8
   

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9. 21st century means real-time
   9
   

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10. 10
    Wikipedia
    

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11. Real-time data delivery
    11
    

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12. - Pull
    - Hey, Server, do you have something?
    Real-time data delivery
    12
    

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13. - Pull
    - Hey, Server, do you have something?
    - Push
    - Hey, Client, I have something!
    Real-time data delivery
    13
    

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14. - Pull
    - Hey, Server, do you have something?
    - Push
    - Hey, Client, I have something!
    - Bidirectional
    - Server <-> Client
    Real-time data delivery
    14
    

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15. - Pull
    - Hey, Server, do you have something?
    - Push
    - Hey, Client, I have something!
    - Bidirectional
    - Server <-> Client
    - Unidirectional
    - Server -> Client or Client -> Server
    Real-time data delivery
    15
    

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16. - Pull
    - Hey, Server, do you have something?
    - Push
    - Hey, Client, I have something!
    - Bidirectional
    - Server <-> Client
    - Unidirectional
    - Server -> Client or Client -> Server
    - ...
    Real-time data delivery
    16
    

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17. There are few ways
    17
    

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18. - Long/short Polling
    There are few ways
    18
    

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19. - Long/short Polling
    - WebSocket
    There are few ways
    19
    

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20. - Long/short Polling
    - WebSocket
    - Server-Sent Events
    There are few ways
    20
    

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21. - Long/short Polling
    - WebSocket
    - Server-Sent Events
    - MQTT and sooooo on...
    There are few ways
    21
    

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22. WebSocket
    22
    

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23. - Made in 2008
    WebSocket
    23
    

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24. - Made in 2008
    - Bidirectional Server-Client protocol
    WebSocket
    24
    

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25. - Made in 2008
    - Bidirectional Server-Client protocol
    - Supported by all browsers (even IE)
    WebSocket
    25
    

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26. WebSocket
    26
    - Made in 2008
    - Bidirectional Server-Client protocol
    - Supported by all browsers (even IE)
    - And binary data
    

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27. Server-Sent Events?
    27
    

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28. - Made in 2006
    Server-Sent Events?
    28
    

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29. - Made in 2006
    - Simple Server-Client protocol over HTTP
    Server-Sent Events?
    29
    

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30. - Made in 2006
    - Simple Server-Client protocol over HTTP
    - Only Server -> Client direction
    Server-Sent Events?
    30
    

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31. - Made in 2006
    - Simple Server-Client protocol over HTTP
    - Only Server -> Client direction
    - Supported by all browsers (sorry, no IE)
    Server-Sent Events?
    31
    

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32. - Made in 2006
    - Simple Server-Client protocol over HTTP
    - Only Server -> Client direction
    - Supported by all browsers (sorry, no IE)
    - No binary data
    Server-Sent Events?
    32
    

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33. - Made in 2006
    - Simple Server-Client protocol over HTTP
    - Only Server -> Client direction
    - Supported by all browsers (sorry, no IE)
    - No binary data
    Debut in Opera, September 1, 2006
    Server-Sent Events?
    33
    

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34. Flow
    34
    

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35. - GET /sse
    Flow
    35
    

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36. - GET /sse
    -
    Flow
    36
    

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37. - GET /sse
    -
    - Content-Type: “text/event-stream”
    Flow
    37
    

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38. Flow
    - GET /sse
    -
    - Content-Type: “text/event-stream”
    -
    38
    

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39. Flow
    - GET /sse
    -
    - Content-Type: “text/event-stream”
    -
    Other checks if you want, it stills a HTTP
    39
    

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40. SSE protocol is simple
    40
    

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41. - ID - uniqueness
    SSE protocol is simple
    41
    

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42. - ID - uniqueness
    - Event - as a type
    SSE protocol is simple
    42
    

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43. - ID - uniqueness
    - Event - as a type
    - Data - main part
    SSE protocol is simple
    43
    

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44. - ID - uniqueness
    - Event - as a type
    - Data - main part
    - Retry - refresh rate
    SSE protocol is simple
    44
    

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45. - ID - uniqueness
    - Event - as a type
    - Data - main part
    - Retry - refresh rate
    id: 54\n
    event: hey-you\n
    data: yes that’s a data\n
    data: \n\n
    SSE protocol is simple
    45
    

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46. - `Last-Event-ID` header
    - A last known ID for client
    - Decide on your own what to do next
    A cozy thing
    46
    

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47. Let’s upgrade to SSE
    47
    

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48. http.HandleFunc("/sse", func(w http.ResponseWriter, r *http.Request) {
    Let’s upgrade to SSE
    48
    

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49. http.HandleFunc("/sse", func(w http.ResponseWriter, r *http.Request) {
    stream, err := sse.UpgradeHTTP(r, w)
    if err != nil {
    http.Error(w, err.Error(), http.StatusBadRequest)
    return
    }
    Let’s upgrade to SSE
    49
    

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50. http.HandleFunc("/sse", func(w http.ResponseWriter, r *http.Request) {
    stream, err := sse.UpgradeHTTP(r, w)
    if err != nil {
    http.Error(w, err.Error(), http.StatusBadRequest)
    return
    }
    var data struct {
    Text string `json:"text"`
    Timestamp int64 `json:"ts"`
    }
    Let’s upgrade to SSE
    50
    

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51. http.HandleFunc("/sse", func(w http.ResponseWriter, r *http.Request) {
    stream, err := sse.UpgradeHTTP(r, w)
    if err != nil {
    http.Error(w, err.Error(), http.StatusBadRequest)
    return
    }
    var data struct {
    Text string `json:"text"`
    Timestamp int64 `json:"ts"`
    }
    for {
    data.Timestamp = time.Now().Unix()
    stream.WriteJSON(data)
    time.Sleep(time.Second)
    }
    })
    Let’s upgrade to SSE
    51
    

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52. func UpgradeHTTP(r *http.Request, w http.ResponseWriter) (*Stream, error) {
    Inside the UpgradeHTTP
    52
    

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53. func UpgradeHTTP(r *http.Request, w http.ResponseWriter) (*Stream, error) {
    hj, ok := w.(http.Hijacker)
    if !ok {
    return nil, ErrNotHijacker
    }
    Inside the UpgradeHTTP
    53
    

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54. func UpgradeHTTP(r *http.Request, w http.ResponseWriter) (*Stream, error) {
    hj, ok := w.(http.Hijacker)
    if !ok {
    return nil, ErrNotHijacker
    }
    // Hijack() (net.Conn, *bufio.ReadWriter, error)
    //
    // The Hijacker interface is implemented by ResponseWriters
    // that allow an HTTP handler to take over the connection.
    Inside the UpgradeHTTP
    54
    

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55. func UpgradeHTTP(r *http.Request, w http.ResponseWriter) (*Stream, error) {
    hj, ok := w.(http.Hijacker)
    if !ok {
    return nil, ErrNotHijacker
    }
    // Hijack() (net.Conn, *bufio.ReadWriter, error)
    //
    // The Hijacker interface is implemented by ResponseWriters
    // that allow an HTTP handler to take over the connection.
    //
    // After a call to Hijack, the original Request.Body must not
    // be used.
    Inside the UpgradeHTTP
    55
    

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56. func UpgradeHTTP(r *http.Request, w http.ResponseWriter) (*Stream, error) {
    hj, ok := w.(http.Hijacker)
    if !ok {
    return nil, ErrNotHijacker
    }
    _, bw, err := hj.Hijack()
    if err != nil {
    retu rn nil, err
    }
    Inside the UpgradeHTTP
    56
    

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57. func UpgradeHTTP(r *http.Request, w http.ResponseWriter) (*Stream, error) {
    hj, ok := w.(http.Hijacker)
    if !ok {
    return nil, ErrNotHijacker
    }
    _, bw, err := hj.Hijack()
    if err != nil {
    retu rn nil, err
    }
    httpWriteResponseUpgrade(bw.Writer)
    Inside the UpgradeHTTP
    57
    

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58. func UpgradeHTTP(r *http.Request, w http.ResponseWriter) (*Stream, error) {
    hj, ok := w.(http.Hijacker)
    if !ok {
    return nil, ErrNotHijacker
    }
    _, bw, err := hj.Hijack()
    if err != nil {
    retu rn nil, err
    }
    httpWriteResponseUpgrade(bw.Writer)
    if err := bw.Flush(); err != nil {
    return nil, err
    }
    return &Stream{bw: bw}, nil
    }
    Inside the UpgradeHTTP
    58
    

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59. Improvise.
    59
    

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60. Improvise. Adopt.
    60
    

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61. Improvise. Adopt. BufferedWriter.
    61
    

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62. const (
    textStatusLine = "HTTP/1.1 200\r\n"
    colonAndSpace = ": "
    )
    Improvise. Adopt. BufferedWriter.
    62
    

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63. const (
    textStatusLine = "HTTP/1.1 200\r\n"
    colonAndSpace = ": "
    )
    func httpWriteResponseUpgrade(bw *bufio.Writer) {
    bw.WriteString(textStatusLine)
    httpWriteHeader(bw, "Cache-Control", "no-cache")
    httpWriteHeader(bw, "Content-Type", "text/event-stream")
    bw.WriteString(crlf)
    }
    Improvise. Adopt. BufferedWriter.
    63
    

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64. const (
    textStatusLine = "HTTP/1.1 200\r\n"
    colonAndSpace = ": "
    )
    func httpWriteResponseUpgrade(bw *bufio.Writer) {
    bw.WriteString(textStatusLine)
    httpWriteHeader(bw, "Cache-Control", "no-cache")
    httpWriteHeader(bw, "Content-Type", "text/event-stream")
    bw.WriteString(crlf)
    }
    func httpWriteHeader(bw *bufio.Writer, key, value string) {
    bw.WriteString(key)
    bw.WriteString(colonAndSpace)
    bw.WriteString(value)
    bw.WriteString(crlf)
    }
    Improvise. Adopt. BufferedWriter.
    64
    

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65. Stream from a user perspective
    65
    

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66. func UpgradeHTTP(*http.Request, http.ResponseWriter) (*Stream, error) {...}
    Stream from a user perspective
    66
    

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67. func UpgradeHTTP(*http.Request, http.ResponseWriter) (*Stream, error) {...}
    type Stream struct {
    bw *bufio.ReadWriter
    }
    Stream from a user perspective
    67
    

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68. func UpgradeHTTP(*http.Request, http.ResponseWriter) (*Stream, error) {...}
    type Stream struct {
    bw *bufio.ReadWriter
    }
    func (s *Stream) SetEvent(event string) error {
    data := []byte("event:" + event + "\n")
    _, err := s.bw.Write(data)
    return err
    }
    Stream from a user perspective
    68
    

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69. func UpgradeHTTP(*http.Request, http.ResponseWriter) (*Stream, error) {...}
    type Stream struct {
    bw *bufio.ReadWriter
    }
    func (s *Stream) SetEvent(event string) error {
    data := []byte("event:" + event + "\n")
    _, err := s.bw.Write(data)
    return err
    }
    func (s *Stream) WriteBytes(data []byte) error {
    return s.writeData(data)
    }
    Stream from a user perspective
    69
    

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70. func UpgradeHTTP(*http.Request, http.ResponseWriter) (*Stream, error) {...}
    type Stream struct {
    bw *bufio.ReadWriter
    }
    func (s *Stream) SetEvent(event string) error {
    data := []byte("event:" + event + "\n")
    _, err := s.bw.Write(data)
    return err
    }
    func (s *Stream) WriteBytes(data []byte) error {
    return s.writeData(data)
    }
    and other methods: SetRetry, WriteJSON, WriteFloat...
    Stream from a user perspective
    70
    

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71. BRUTAL MINIMALISM
    71
    

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72. 
    
    
    SSE Demo
    <br/>// next slide, I promise<br/>
    
    
    Waiting for data…
    
    
    
    BRUTAL MINIMALISM
    72
    

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73. 
    
    
    SSE Demo
    <br/>// next slide, I promise<br/>
    
    
    Waiting for data…
    
    
    
    BRUTAL MINIMALISM
    73
    Google: This is a motherf***ing website.
    

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74. A bit of JavaScript, no node_modules!
    74
    

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75. let contentbox = document.querySelector("#contentbox")
    A bit of JavaScript, no node_modules!
    75
    

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76. let contentbox = document.querySelector("#contentbox")
    let src = new EventSource("http://127.0.0.1:31337/sse")
    src.addEventListener("close", e => {
    src.close();
    contentbox.innerText += "close connection\n";
    });
    A bit of JavaScript, no node_modules!
    76
    

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77. let contentbox = document.querySelector("#contentbox")
    let src = new EventSource("http://127.0.0.1:31337/sse")
    src.addEventListener("close", e => {
    src.close();
    contentbox.innerText += "close connection\n";
    });
    src.addEventListener("message", e => {
    let data = JSON.parse(e.data)
    contentbox.innerText += data.time + "\n";
    });
    A bit of JavaScript, no node_modules!
    77
    

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78. 
    Fingers crossed Demo time
    78
    

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79. Who needs TCP when we’re almost in HTTP3 era?
    79
    

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80. - Better resource control
    Who needs TCP when we’re almost in HTTP3 era?
    80
    

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81. Who needs TCP when we’re almost in HTTP3 era?
    81
    - Better resource control
    - Less allocations
    

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82. Who needs TCP when we’re almost in HTTP3 era?
    82
    - Better resource control
    - Less allocations
    - Mechanical sympathy
    

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83. Who needs TCP when we’re almost in HTTP3 era?
    83
    - Better resource control
    - Less allocations
    - Mechanical sympathy
    See Github:
    - valyala/fasthttp - HTTP/1.1
    - gobwas/ws - WebSocket
    

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84. Simple Go HTTP server
    ...
    func main() {
    http.Handle("/", yoHandler)
    http.ListenAndServe(":31337", nil)
    }
    func yoHandler(w http.ResponseWriter, r *http.Request) {
    io.WriteString(w, "hey ʕ◔ϖ◔ʔ")
    }
    84
    

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85. // Serve accepts incoming connections on the Listener l, creating a
    // new service goroutine for each. The service goroutines read requests and
    // then call srv.Handler to reply to them.
    //
    func (srv *Server) Serve(l net.Listener) error {
    // ...
    for {
    rw, e := l.Accept()
    // ...
    c := srv.newConn(rw)
    go c.serve(connCtx)
    }
    }
    But what happens inside?
    85
    

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86. func main() {
    ln, err := net.Listen("tcp", ":8080")
    if err != nil {
    log.Fatal(err)
    }
    defer ln.Close()
    for {
    conn, err := ln.Accept()
    if err != nil {
    log.Println(err)
    continue
    }
    go handle(conn)
    }
    }
    Well, it’s just a TCP server
    86
    

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87. func main() {
    ln, err := net.Listen("tcp", ":8080")
    if err != nil {
    log.Fatal(err)
    }
    defer ln.Close()
    for {
    conn, err := ln.Accept()
    if err != nil {
    log.Println(err)
    continue
    }
    go handle(conn) // or just an Upgrade!
    }
    }
    Well, it’s just a TCP server
    87
    

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88. func (u Upgrader) Upgrade(conn io.ReadWriter) (*Stream, error) {
    br := bufio.NewReaderSize(conn, 1000)
    bw := bufio.NewWriterSize(conn, 1000)
    rl, err := readLine(br)
    if err != nil {
    return nil, err
    }
    req, err := httpParseRequestLine(rl)
    if err != nil {
    return nil, err
    }
    // ...
    }
    Low-level Upgrader
    88
    

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89. func (u Upgrader) Upgrade(conn io.ReadWriter) (*Stream, error) {
    br := bufio.NewReaderSize(conn, 1000)
    bw := bufio.NewWriterSize(conn, 1000)
    rl, err := readLine(br)
    if err != nil {
    return nil, err
    }
    req, err := httpParseRequestLine(rl)
    if err != nil {
    return nil, err
    }
    // ...
    }
    Low-level Upgrader
    89
    

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90. func (u Upgrader) Upgrade(conn io.ReadWriter) (*Stream, error) {
    // ...
    for err == nil {
    line, errRead := readLine(br)
    if errRead != nil {
    return nil, errRead
    }
    if len(line) == 0 {
    break // Blank line, no more lines to read.
    }
    k, v, ok := httpParseHeaderLine(line)
    if !ok {
    err = errors.New("ErrMalformedRequest"); break
    }
    // ...
    }
    }
    Low-level Upgrader (cont.)
    90
    

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91. Wanna cool thing?
    91
    

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92. - That’s basically all
    Wanna cool thing?
    92
    

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93. - That’s basically all
    - Stream works with bufio.Writer
    Wanna cool thing?
    93
    

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94. - That’s basically all
    - Stream works with bufio.Writer
    - Which is independent of a type of a Writer
    Wanna cool thing?
    94
    

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95. Where is the code Lebowski?
    95
    

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96. - Good question
    Where is the code Lebowski?
    96
    

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97. - Good question
    - Partially available
    - https://github.com/cristalhq/sse
    Where is the code Lebowski?
    97
    

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98. - Good question
    - Partially available
    - https://github.com/cristalhq/sse
    - Eventually everything will be on Github
    Where is the code Lebowski?
    98
    

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99. - Good question
    - Partially available
    - https://github.com/cristalhq/sse
    - Eventually everything will be on Github
    - I mean code...
    Where is the code Lebowski?
    99
    

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100. cristaltech? cristalhq? wut?
     100
     

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101. - Make better open source
     cristaltech? cristalhq? wut?
     101
     

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102. - Make better open source
     - Simple API
     cristaltech? cristalhq? wut?
     102
     

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103. - Make better open source
     - Simple API
     - No dependencies (mostly)
     cristaltech? cristalhq? wut?
     103
     

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104. - Make better open source
     - Simple API
     - No dependencies (mostly)
     - Learn new things & have fun
     cristaltech? cristalhq? wut?
     104
     

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105. - Make better open source
     - Simple API
     - No dependencies (mostly)
     - Learn new things & have fun
     - Don’t forget to rest sometimes
     cristaltech? cristalhq? wut?
     105
     

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106. - Aliaksandr Valialkin (fasthttp)
     - Sergey Kamardin (ws)
     - One of the best Go libraries (IMO, but who cares)
     https://github.com/valyala/fasthttp
     https://github.com/gobwas/ws
     Thanks
     106
     

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107. That’s all folks
     Thank you
     Questions?
     Twitter: @oleg_kovalov
     Github: @cristaloleg
     

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