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         // telegramPollTimeout is how long one getUpdates call can take.
  26         telegramPollTimeout = telegramPollSeconds*time.Second + telegramPollSlack
  27
  28         // telegramSendTimeout is how long a sendMessage, sendRichMessage, or
  29         // sendChatAction call can take. A connection that stops without a
  30         // close, such as after a network change, then fails the call, and the
  31         // sender tries again, instead of a wait until TCP gives up. The client
  32         // has no timeout of its own, because the long poll of getUpdates needs
  33         // a longer limit.
  34         telegramSendTimeout = 30 * time.Second
  35
  36         // telegramAnswerBytes is the most bytes of one answer of the Bot API.
  37         telegramAnswerBytes = 16 << 20
  38 )
  39
  40 // newTelegramAPI returns the client of the Bot API at base with token.
  41 func newTelegramAPI(base, token string) *TelegramAPI {
  42         return &TelegramAPI{
  43                 base:        base,
  44                 token:       token,
  45                 http:        &http.Client{},
  46                 sendTimeout: telegramSendTimeout,
  47         }
  48 }
  49
  50 // telegramRetryable tells if a later try of a failed Bot API call can work:
  51 // after a network error, HTTP 429, or a server error. It returns the wait that
  52 // the Bot API asks for, or 0.
  53 func telegramRetryable(err error) (bool, time.Duration) {
  54         var network *TelegramNetworkError
  55         if errors.As(err, &network) {
  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         var updates []TelegramUpdate
  92         err := b.call(ctx, telegramPollTimeout, "getUpdates", map[string]any{
  93                 "offset":          offset,
  94                 "timeout":         telegramPollSeconds,
  95                 "allowed_updates": []string{"message"},
  96         }, &updates)
  97
  98         return updates, err
  99 }
 100
 101 // SendMessage sends text to chat with the format of entities, with no parse
 102 // mode, so the text needs no escaping. With no entities, the text is plain. A
 103 // call that takes longer than telegramSendTimeout fails with a
 104 // TelegramNetworkError.
 105 func (b *TelegramAPI) SendMessage(ctx context.Context, chat int64, text string, entities []TelegramEntity) error {
 106         params := map[string]any{
 107                 "chat_id": chat,
 108                 "text":    text,
 109         }
 110
 111         if len(entities) > 0 {
 112                 params["entities"] = entities
 113         }
 114
 115         return b.call(ctx, b.sendTimeout, "sendMessage", params, nil)
 116 }
 117
 118 // SendRichMessage sends markdown to chat as a rich message, which Telegram
 119 // renders itself, tables included. A call that takes longer than
 120 // telegramSendTimeout fails with a TelegramNetworkError.
 121 func (b *TelegramAPI) SendRichMessage(ctx context.Context, chat int64, markdown string) error {
 122         return b.call(ctx, b.sendTimeout, "sendRichMessage", map[string]any{
 123                 "chat_id": chat,
 124                 "rich_message": map[string]any{
 125                         "markdown": markdown,
 126                 },
 127         }, nil)
 128 }
 129
 130 // SendTyping shows the typing action in chat for about five seconds. A call
 131 // that takes longer than telegramSendTimeout fails with a TelegramNetworkError.
 132 func (b *TelegramAPI) SendTyping(ctx context.Context, chat int64) error {
 133         return b.call(ctx, b.sendTimeout, "sendChatAction", map[string]any{
 134                 "chat_id": chat,
 135                 "action":  "typing",
 136         }, nil)
 137 }
 138
 139 // call sends one call of method with the JSON params and decodes its result
 140 // into result, when result is not nil. The call can take up to timeout. Its
 141 // errors tell the cause in plain words, with no method name, so that a log line
 142 // can say first what the call was for.
 143 func (b *TelegramAPI) call(ctx context.Context, timeout time.Duration, method string, params, result any) error {
 144         ctx, cancel := context.WithTimeout(ctx, timeout)
 145         defer cancel()
 146
 147         body, err := json.Marshal(params)
 148         if err != nil {
 149                 return fmt.Errorf("%s: encode request: %w", method, err)
 150         }
 151
 152         request, err := http.NewRequestWithContext(ctx, http.MethodPost, b.base+"/bot"+b.token+"/"+method, bytes.NewReader(body))
 153         if err != nil {
 154                 return fmt.Errorf("%s: make request: %s", method, b.redact(err))
 155         }
 156
 157         request.Header.Set("Content-Type", "application/json")
 158         response, err := b.http.Do(request)
 159         if err != nil {
 160                 return b.networkError("no answer", err, timeout)
 161         }
 162
 163         data, err := io.ReadAll(io.LimitReader(response.Body, telegramAnswerBytes))
 164         err = errors.Join(err, response.Body.Close())
 165         if err != nil {
 166                 return b.networkError("answer cut off", err, timeout)
 167         }
 168
 169         var answer TelegramAnswer
 170         err = json.Unmarshal(data, &answer)
 171         if err != nil && response.StatusCode != http.StatusOK {
 172                 return &TelegramError{
 173                         Status:      response.StatusCode,
 174                         Description: http.StatusText(response.StatusCode),
 175                 }
 176         }
 177
 178         if err != nil {
 179                 return b.networkError("invalid JSON", err, timeout)
 180         }
 181
 182         if !answer.OK {
 183                 return &TelegramError{
 184                         Status:      response.StatusCode,
 185                         Description: b.redact(errors.New(answer.Description)),
 186                         RetryAfter:  time.Duration(answer.Parameters.RetryAfter) * time.Second,
 187                         Refused:     true,
 188                 }
 189         }
 190
 191         if result == nil {
 192                 return nil
 193         }
 194
 195         err = json.Unmarshal(answer.Result, result)
 196         if err != nil {
 197                 return b.networkError("invalid result", err, timeout)
 198         }
 199
 200         return nil
 201 }
 202
 203 // networkError returns the TelegramNetworkError of err, which happened at the
 204 // step that what names. When the call used all of its time timeout, the cause
 205 // is "no answer in TIMEOUT", because the Go text of a deadline does not tell
 206 // how long the wait was.
 207 func (b *TelegramAPI) networkError(what string, err error, timeout time.Duration) error {
 208         if errors.Is(err, context.DeadlineExceeded) {
 209                 return &TelegramNetworkError{
 210                         Cause: "no answer in " + timeout.String(),
 211                 }
 212         }
 213
 214         return &TelegramNetworkError{
 215                 Cause: what + ": " + b.redact(err),
 216         }
 217 }
 218
 219 // redact returns the text of err without a URL and without the token. A
 220 // *url.Error holds the URL of the call, which holds the token, so only its
 221 // cause is kept.
 222 func (b *TelegramAPI) redact(err error) string {
 223         var urlError *url.Error
 224         if errors.As(err, &urlError) {
 225                 err = urlError.Err
 226         }
 227
 228         return strings.ReplaceAll(err.Error(), b.token, "TOKEN")
 229 }
 230
 231 // TelegramNetworkError tells that a Bot API call got no valid answer, such as
 232 // after a network error. A later call can work. Cause tells why in plain words,
 233 // with no URL and no token.
 234 type TelegramNetworkError struct {
 235         Cause string
 236 }
 237
 238 func (e *TelegramNetworkError) Error() string {
 239         return e.Cause
 240 }
 241
 242 // TelegramError is an answer of the Bot API that tells of a failure. Its text
 243 // gives the HTTP status and the description, such as "502 Bad Gateway".
 244 // RetryAfter is the wait that the Bot API asks for after HTTP 429. Refused
 245 // tells that the answer is a Bot API answer with ok false, not a page of a
 246 // proxy or of a server error.
 247 type TelegramError struct {
 248         Status      int
 249         Description string
 250         RetryAfter  time.Duration
 251         Refused     bool
 252 }
 253
 254 func (e *TelegramError) Error() string {
 255         return fmt.Sprintf("%d %s", e.Status, e.Description)
 256 }
 257
 258 // TelegramUpdate is one update of getUpdates. Message is nil for the kinds of
 259 // updates that are not a new message.
 260 type TelegramUpdate struct {
 261         UpdateID int64            `json:"update_id"`
 262         Message  *TelegramMessage `json:"message"`
 263 }
 264
 265 // TelegramEntity is a message entity of sendMessage: a part of the text with a
 266 // format, such as bold or a link. Offset and Length count UTF-16 code units.
 267 // URL is the target of a text_link, and Language the language of a pre.
 268 type TelegramEntity struct {
 269         Type     string `json:"type"`
 270         Offset   int    `json:"offset"`
 271         Length   int    `json:"length"`
 272         URL      string `json:"url,omitempty"`
 273         Language string `json:"language,omitempty"`
 274 }
 275
 276 // TelegramAnswer is the envelope of each answer of the Bot API.
 277 type TelegramAnswer struct {
 278         OK          bool            `json:"ok"`
 279         Result      json.RawMessage `json:"result"`
 280         ErrorCode   int             `json:"error_code"`
 281         Description string          `json:"description"`
 282         Parameters  struct {
 283                 RetryAfter int `json:"retry_after"`
 284         } `json:"parameters"`
 285 }
 286
 287 // TelegramMessage is a message to the bot. Text is empty for a message that is
 288 // not text, such as a photo.
 289 type TelegramMessage struct {
 290         Chat TelegramChat  `json:"chat"`
 291         From *TelegramUser `json:"from"`
 292         Text string        `json:"text"`
 293 }
 294
 295 // TelegramChat is the chat of a message. Type is private for a chat with one
 296 // user.
 297 type TelegramChat struct {
 298         ID   int64  `json:"id"`
 299         Type string `json:"type"`
 300 }
 301
 302 // TelegramUser is the sender of a message.
 303 type TelegramUser struct {
 304         ID int64 `json:"id"`
 305 }