Compile-time inputfile validation (#163)

* Cleanup and improve inputfile interfaces

* Update sample bots to work with new typesafe inputfile logic

* Media should be of type inputfileorstring

* fix lint

* Make sure thumbnails cannot be strings

* Improve inputfile logic to properly handle values json value marshalling

* Add missing thumbnail logic to certain inputmedia types and improve
error messages

* remove unnecessary InputString type which turned out to be unnecessary

* regenerate after merge

bot.go

@@ -90,7 +90,7 @@ func (bot *Bot) UseMiddleware(mw func(client BotClient) BotClient) *Bot {
 
 var ErrNilBotClient = errors.New("nil BotClient")
 
-func (bot *Bot) Request(method string, params map[string]string, data map[string]NamedReader, opts *RequestOpts) (json.RawMessage, error) {
+func (bot *Bot) Request(method string, params map[string]string, data map[string]FileReader, opts *RequestOpts) (json.RawMessage, error) {
 	if bot.BotClient == nil {
 		return nil, ErrNilBotClient
 	}

file.go

@@ -0,0 +1,94 @@
+package gotgbot
+
+import (
+	"encoding/json"
+	"errors"
+	"io"
+)
+
+// InputFile (https://core.telegram.org/bots/api#inputfile)
+//
+// This object represents the contents of a file to be uploaded.
+// Must be posted using multipart/form-data in the usual way that files are uploaded via the browser.
+type InputFile interface {
+	InputFileOrString
+	justFiles()
+}
+
+// InputFileOrString (https://core.telegram.org/bots/api#inputfile)
+//
+// This object represents the contents of a file to be uploaded, or a publicly accessible URL to be reused.
+// Files must be posted using multipart/form-data in the usual way that files are uploaded via the browser.
+type InputFileOrString interface {
+	Attach(name string, data map[string]FileReader) error
+	getValue() string
+}
+
+var (
+	_ InputFileOrString = &FileReader{}
+	_ InputFile         = &FileReader{}
+)
+
+type FileReader struct {
+	Name string
+	Data io.Reader
+
+	value string
+}
+
+func (f *FileReader) MarshalJSON() ([]byte, error) {
+	return json.Marshal(f.getValue())
+}
+
+var ErrAttachmentKeyAlreadyExists = errors.New("key already exists")
+
+func (f *FileReader) justFiles() {}
+
+func (f *FileReader) Attach(key string, data map[string]FileReader) error {
+	if f.Data == nil {
+		// if no data, this must be a string; nothing to "attach".
+		return nil
+	}
+
+	if _, ok := data[key]; ok {
+		return ErrAttachmentKeyAlreadyExists
+	}
+	f.value = "attach://" + key
+	data[key] = *f
+	return nil
+}
+
+// getValue returns the file attach reference for the relevant multipart form.
+// Make sure to only call getValue after having called Attach(), to ensure any files have been included.
+func (f *FileReader) getValue() string {
+	return f.value
+}
+
+// InputFileByURL is used to send a file on the internet via a publicly accessible HTTP URL.
+func InputFileByURL(url string) InputFileOrString {
+	return &FileReader{value: url}
+}
+
+// InputFileByID is used to send a file that is already present on telegram's servers, using its telegram file_id.
+func InputFileByID(fileID string) InputFileOrString {
+	return &FileReader{value: fileID}
+}
+
+// InputFileByReader is used to send a file by a reader interface; such as a filehandle from os.Open(), or from a byte
+// buffer.
+//
+// For example:
+//
+//	f, err := os.Open("some_file.go")
+//	if err != nil {
+//		return fmt.Errorf("failed to open file: %w", err)
+//	}
+//
+//	m, err := b.SendDocument(<chat_id>, gotgbot.InputFileByReader("source.go", f), nil)
+//
+// Or
+//
+//	m, err := b.SendDocument(<chat_id>, gotgbot.InputFileByReader("file.txt", strings.NewReader("Some file contents")), nil)
+func InputFileByReader(name string, r io.Reader) InputFile {
+	return &FileReader{Name: name, Data: r}
+}