git.giacomolli.uk - onechat/blob - telegram_api.go

   1 package main
   2
   3 import (
   4         "bytes"
   5         "context"
   6         "encoding/json"
   7         "errors"
   8         "fmt"
   9         "io"
  10         "net/http"
  11         "net/url"
  12         "strings"
  13         "time"
  14 )
  15
  16 const (
  17         // telegramPollSeconds is how long one getUpdates call waits for an
  18         // update.
  19         telegramPollSeconds = 50
  20
  21         // telegramPollSlack is how much longer than telegramPollSeconds a
  22         // getUpdates call can take before the bot gives it up.
  23         telegramPollSlack = 20 * time.Second
  24
  25         // telegramSendTimeout is how long a sendMessage, sendRichMessage, or
  26         // sendChatAction call can take. A connection that stops without a
  27         // close, such as after a network change, then fails the call, and the
  28         // sender tries again, instead of a wait until TCP gives up. The client
  29         // has no timeout of its own, because the long poll of getUpdates needs
  30         // a longer limit.
  31         telegramSendTimeout = 30 * time.Second
  32
  33         // telegramAnswerBytes is the most bytes of one answer of the Bot API.
  34         telegramAnswerBytes = 16 << 20
  35 )
  36
  37 // errTelegramNetwork tells that a Bot API call got no valid answer, such as
  38 // after a network error. A later call can work.
  39 var errTelegramNetwork = errors.New("no valid answer from the Bot API")
  40
  41 // newTelegramAPI returns the client of the Bot API at base with token.
  42 func newTelegramAPI(base, token string) *TelegramAPI {
  43         return &TelegramAPI{
  44                 base:        base,
  45                 token:       token,
  46                 http:        &http.Client{},
  47                 sendTimeout: telegramSendTimeout,
  48         }
  49 }
  50
  51 // telegramRetryable tells if a later try of a failed Bot API call can work:
  52 // after a network error, HTTP 429, or a server error. It returns the wait that
  53 // the Bot API asks for, or 0.
  54 func telegramRetryable(err error) (bool, time.Duration) {
  55         if errors.Is(err, errTelegramNetwork) {
  56                 return true, 0
  57         }
  58
  59         var answer *TelegramError
  60         if errors.As(err, &answer) {
  61                 return answer.Status == http.StatusTooManyRequests || answer.Status >= 500, answer.RetryAfter
  62         }
  63
  64         return false, 0
  65 }
  66
  67 // telegramRejected tells if the Bot API refused a call with ok false and HTTP
  68 // 400 or 404. Then the call did nothing: 400 refuses the request, and 404 tells
  69 // that the method is not there. An error page with no Bot API answer does not
  70 // tell this, so it is not a refusal.
  71 func telegramRejected(err error) bool {
  72         var answer *TelegramError
  73         return errors.As(err, &answer) && answer.Refused && (answer.Status == http.StatusBadRequest || answer.Status == http.StatusNotFound)
  74 }
  75
  76 // TelegramAPI calls the Telegram Bot API. The bot token is a part of each URL,
  77 // so no error of TelegramAPI holds a URL, a net/http error, or the token. Its
  78 // sendTimeout field limits each sendMessage, sendRichMessage, and
  79 // sendChatAction call.
  80 type TelegramAPI struct {
  81         base        string
  82         token       string
  83         http        *http.Client
  84         sendTimeout time.Duration
  85 }
  86
  87 // GetUpdates waits for the updates from offset on, up to telegramPollSeconds,
  88 // and returns them. Telegram forgets each update before offset. Only new
  89 // messages are asked for.
  90 func (b *TelegramAPI) GetUpdates(ctx context.Context, offset int64) ([]TelegramUpdate, error) {
  91         ctx, cancel := context.WithTimeout(ctx, telegramPollSeconds*time.Second+telegramPollSlack)
  92         defer cancel()
  93
  94         var updates []TelegramUpdate
  95         err := b.call(ctx, "getUpdates", map[string]any{
  96                 "offset":          offset,
  97                 "timeout":         telegramPollSeconds,
  98                 "allowed_updates": []string{"message"},
  99         }, &updates)
 100
 101         return updates, err
 102 }
 103
 104 // SendMessage sends text to chat with the format of entities, with no parse
 105 // mode, so the text needs no escaping. With no entities, the text is plain. A
 106 // call that takes longer than telegramSendTimeout fails with
 107 // errTelegramNetwork.
 108 func (b *TelegramAPI) SendMessage(ctx context.Context, chat int64, text string, entities []TelegramEntity) error {
 109         ctx, cancel := context.WithTimeout(ctx, b.sendTimeout)
 110         defer cancel()
 111
 112         params := map[string]any{
 113                 "chat_id": chat,
 114                 "text":    text,
 115         }
 116
 117         if len(entities) > 0 {
 118                 params["entities"] = entities
 119         }
 120
 121         return b.call(ctx, "sendMessage", params, nil)
 122 }
 123
 124 // SendRichMessage sends markdown to chat as a rich message, which Telegram
 125 // renders itself, tables included. A call that takes longer than
 126 // telegramSendTimeout fails with errTelegramNetwork.
 127 func (b *TelegramAPI) SendRichMessage(ctx context.Context, chat int64, markdown string) error {
 128         ctx, cancel := context.WithTimeout(ctx, b.sendTimeout)
 129         defer cancel()
 130
 131         return b.call(ctx, "sendRichMessage", map[string]any{
 132                 "chat_id": chat,
 133                 "rich_message": map[string]any{
 134                         "markdown": markdown,
 135                 },
 136         }, nil)
 137 }
 138
 139 // SendTyping shows the typing action in chat for about five seconds. A call
 140 // that takes longer than telegramSendTimeout fails with errTelegramNetwork.
 141 func (b *TelegramAPI) SendTyping(ctx context.Context, chat int64) error {
 142         ctx, cancel := context.WithTimeout(ctx, b.sendTimeout)
 143         defer cancel()
 144
 145         return b.call(ctx, "sendChatAction", map[string]any{
 146                 "chat_id": chat,
 147                 "action":  "typing",
 148         }, nil)
 149 }
 150
 151 // call sends one call of method with the JSON params and decodes its result
 152 // into result, when result is not nil.
 153 func (b *TelegramAPI) call(ctx context.Context, method string, params, result any) error {
 154         body, err := json.Marshal(params)
 155         if err != nil {
 156                 return fmt.Errorf("%s: encode request: %w", method, err)
 157         }
 158
 159         request, err := http.NewRequestWithContext(ctx, http.MethodPost, b.base+"/bot"+b.token+"/"+method, bytes.NewReader(body))
 160         if err != nil {
 161                 return fmt.Errorf("%s: make request: %s", method, b.redact(err))
 162         }
 163
 164         request.Header.Set("Content-Type", "application/json")
 165         response, err := b.http.Do(request)
 166         if err != nil {
 167                 return fmt.Errorf("%s: %w: %s", method, errTelegramNetwork, b.redact(err))
 168         }
 169
 170         data, err := io.ReadAll(io.LimitReader(response.Body, telegramAnswerBytes))
 171         err = errors.Join(err, response.Body.Close())
 172         if err != nil {
 173                 return fmt.Errorf("%s: %w: read answer: %s", method, errTelegramNetwork, b.redact(err))
 174         }
 175
 176         var answer TelegramAnswer
 177         err = json.Unmarshal(data, &answer)
 178         if err != nil && response.StatusCode != http.StatusOK {
 179                 return &TelegramError{
 180                         Method:      method,
 181                         Status:      response.StatusCode,
 182                         Description: http.StatusText(response.StatusCode),
 183                 }
 184         }
 185
 186         if err != nil {
 187                 return fmt.Errorf("%s: %w: decode answer: %s", method, errTelegramNetwork, b.redact(err))
 188         }
 189
 190         if !answer.OK {
 191                 return &TelegramError{
 192                         Method:      method,
 193                         Status:      response.StatusCode,
 194                         Description: b.redact(errors.New(answer.Description)),
 195                         RetryAfter:  time.Duration(answer.Parameters.RetryAfter) * time.Second,
 196                         Refused:     true,
 197                 }
 198         }
 199
 200         if result == nil {
 201                 return nil
 202         }
 203
 204         err = json.Unmarshal(answer.Result, result)
 205         if err != nil {
 206                 return fmt.Errorf("%s: %w: decode result: %s", method, errTelegramNetwork, b.redact(err))
 207         }
 208
 209         return nil
 210 }
 211
 212 // redact returns the text of err without a URL and without the token. A
 213 // *url.Error holds the URL of the call, which holds the token, so only its
 214 // cause is kept.
 215 func (b *TelegramAPI) redact(err error) string {
 216         var urlError *url.Error
 217         if errors.As(err, &urlError) {
 218                 err = urlError.Err
 219         }
 220
 221         return strings.ReplaceAll(err.Error(), b.token, "TOKEN")
 222 }
 223
 224 // TelegramError is an answer of the Bot API that tells of a failure. RetryAfter
 225 // is the wait that the Bot API asks for after HTTP 429. Refused tells that the
 226 // answer is a Bot API answer with ok false, not a page of a proxy or of a
 227 // server error.
 228 type TelegramError struct {
 229         Method      string
 230         Status      int
 231         Description string
 232         RetryAfter  time.Duration
 233         Refused     bool
 234 }
 235
 236 func (e *TelegramError) Error() string {
 237         return fmt.Sprintf("%s: Bot API answered %d: %s", e.Method, e.Status, e.Description)
 238 }
 239
 240 // TelegramUpdate is one update of getUpdates. Message is nil for the kinds of
 241 // updates that are not a new message.
 242 type TelegramUpdate struct {
 243         UpdateID int64            `json:"update_id"`
 244         Message  *TelegramMessage `json:"message"`
 245 }
 246
 247 // TelegramEntity is a message entity of sendMessage: a part of the text with a
 248 // format, such as bold or a link. Offset and Length count UTF-16 code units.
 249 // URL is the target of a text_link, and Language the language of a pre.
 250 type TelegramEntity struct {
 251         Type     string `json:"type"`
 252         Offset   int    `json:"offset"`
 253         Length   int    `json:"length"`
 254         URL      string `json:"url,omitempty"`
 255         Language string `json:"language,omitempty"`
 256 }
 257
 258 // TelegramAnswer is the envelope of each answer of the Bot API.
 259 type TelegramAnswer struct {
 260         OK          bool            `json:"ok"`
 261         Result      json.RawMessage `json:"result"`
 262         ErrorCode   int             `json:"error_code"`
 263         Description string          `json:"description"`
 264         Parameters  struct {
 265                 RetryAfter int `json:"retry_after"`
 266         } `json:"parameters"`
 267 }
 268
 269 // TelegramMessage is a message to the bot. Text is empty for a message that is
 270 // not text, such as a photo.
 271 type TelegramMessage struct {
 272         Chat TelegramChat  `json:"chat"`
 273         From *TelegramUser `json:"from"`
 274         Text string        `json:"text"`
 275 }
 276
 277 // TelegramChat is the chat of a message. Type is private for a chat with one
 278 // user.
 279 type TelegramChat struct {
 280         ID   int64  `json:"id"`
 281         Type string `json:"type"`
 282 }
 283
 284 // TelegramUser is the sender of a message.
 285 type TelegramUser struct {
 286         ID int64 `json:"id"`
 287 }