feat(edit): implement EditMessageMedia

Replace a message's media and caption: InputMedia -> tg.InputMedia for
photo and the document family, accepting file_id, URL or upload. Caption
honors explicit entities or a parse mode; reply markup via SendOption.
Drop editMessageMedia from the conformance deferred list.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: ernado

conformance_test.go

@@ -21,7 +21,6 @@ var coveredByOtherMeans = map[string]string{
 // implemented. Each is an acknowledged gap tracked in docs/roadmap.md; the
 // conformance test allows them so it can still catch *unacknowledged* drift.
 var deferredMethods = map[string]string{
-	"editMessageMedia":       "Phase 3 deferred",
 	"answerPreCheckoutQuery": "payments — deferred until payment updates land",
 	"answerShippingQuery":    "payments — deferred until payment updates land",
 	"sendInvoice":            "payments — deferred",

edit_media.go

@@ -0,0 +1,147 @@
+package botapi
+
+import (
+	"context"
+
+	"github.com/gotd/td/tg"
+)
+
+// EditMessageMedia replaces the media (and caption) of a message. The new media
+// may reference an existing file_id, an HTTP URL Telegram fetches, or a local
+// upload.
+func (b *Bot) EditMessageMedia(ctx context.Context, chat ChatID, messageID int, media InputMedia, opts ...SendOption) (*Message, error) {
+	var cfg sendConfig
+	for _, o := range opts {
+		o(&cfg)
+	}
+
+	peer, err := b.resolveInputPeer(ctx, chat)
+	if err != nil {
+		return nil, err
+	}
+
+	tgMedia, capt, err := b.inputMediaToTg(ctx, media)
+	if err != nil {
+		return nil, err
+	}
+
+	req := &tg.MessagesEditMessageRequest{Peer: peer, ID: messageID}
+	req.SetMedia(tgMedia)
+
+	msg, entities, err := b.caption(ctx, capt)
+	if err != nil {
+		return nil, err
+	}
+	if msg != "" {
+		req.Message = msg
+	}
+	if len(entities) > 0 {
+		req.Entities = entities
+	}
+	if cfg.markup != nil {
+		mkp, err := replyMarkupToTg(cfg.markup)
+		if err != nil {
+			return nil, err
+		}
+		req.SetReplyMarkup(mkp)
+	}
+
+	resp, err := b.raw.MessagesEditMessage(ctx, req)
+	return b.sentMessage(ctx, peer, resp, err)
+}
+
+// captionData is the caption text and how to format it, extracted from an
+// InputMedia.
+type captionData struct {
+	text      string
+	parseMode ParseMode
+	entities  []MessageEntity
+}
+
+// caption resolves a caption into a message string and MTProto entities,
+// honoring explicit entities or a parse mode.
+func (b *Bot) caption(ctx context.Context, c captionData) (string, []tg.MessageEntityClass, error) {
+	if len(c.entities) > 0 {
+		return c.text, entitiesToTg(c.entities), nil
+	}
+	if c.parseMode != ParseModeNone && c.text != "" {
+		return b.styledMessage(ctx, c.text, c.parseMode)
+	}
+	return c.text, nil, nil
+}
+
+// inputMediaToTg converts a Bot API InputMedia into the MTProto media and its
+// caption. The switch over the sealed InputMedia union is exhaustive.
+func (b *Bot) inputMediaToTg(ctx context.Context, m InputMedia) (tg.InputMediaClass, captionData, error) {
+	switch m := m.(type) {
+	case *InputMediaPhoto:
+		media, err := b.photoInputMedia(ctx, m.Media)
+		return media, captionData{m.Caption, m.ParseMode, m.CaptionEntities}, err
+	case *InputMediaVideo:
+		media, err := b.documentInputMedia(ctx, m.Media, "video/mp4")
+		return media, captionData{m.Caption, m.ParseMode, m.CaptionEntities}, err
+	case *InputMediaAnimation:
+		media, err := b.documentInputMedia(ctx, m.Media, "video/mp4")
+		return media, captionData{m.Caption, m.ParseMode, m.CaptionEntities}, err
+	case *InputMediaAudio:
+		media, err := b.documentInputMedia(ctx, m.Media, "audio/mpeg")
+		return media, captionData{m.Caption, m.ParseMode, m.CaptionEntities}, err
+	case *InputMediaDocument:
+		media, err := b.documentInputMedia(ctx, m.Media, "application/octet-stream")
+		return media, captionData{m.Caption, m.ParseMode, m.CaptionEntities}, err
+	default:
+		return nil, captionData{}, &Error{Code: 400, Description: "Bad Request: unsupported input media type"}
+	}
+}
+
+// photoInputMedia resolves an InputFile into MTProto photo media.
+//
+// The switch over the sealed InputFile union is exhaustive.
+func (b *Bot) photoInputMedia(ctx context.Context, file InputFile) (tg.InputMediaClass, error) {
+	switch f := file.(type) {
+	case InputFileID:
+		photo, err := inputPhotoFromFileID(string(f))
+		if err != nil {
+			return nil, err
+		}
+		return &tg.InputMediaPhoto{ID: photo}, nil
+	case InputFileURL:
+		return &tg.InputMediaPhotoExternal{URL: string(f)}, nil
+	case *InputFileUpload:
+		uploaded, err := b.uploadInputFile(ctx, f)
+		if err != nil {
+			return nil, err
+		}
+		return &tg.InputMediaUploadedPhoto{File: uploaded}, nil
+	default:
+		return nil, &Error{Code: 400, Description: descInvalidFile}
+	}
+}
+
+// documentInputMedia resolves an InputFile into MTProto document media.
+//
+// The switch over the sealed InputFile union is exhaustive.
+func (b *Bot) documentInputMedia(ctx context.Context, file InputFile, mimeType string) (tg.InputMediaClass, error) {
+	switch f := file.(type) {
+	case InputFileID:
+		doc, err := inputDocumentFromFileID(string(f))
+		if err != nil {
+			return nil, err
+		}
+		return &tg.InputMediaDocument{ID: doc}, nil
+	case InputFileURL:
+		return &tg.InputMediaDocumentExternal{URL: string(f)}, nil
+	case *InputFileUpload:
+		uploaded, err := b.uploadInputFile(ctx, f)
+		if err != nil {
+			return nil, err
+		}
+		media := &tg.InputMediaUploadedDocument{File: uploaded, MimeType: mimeType}
+		if f.Name != "" {
+			media.Attributes = []tg.DocumentAttributeClass{&tg.DocumentAttributeFilename{FileName: f.Name}}
+		}
+		return media, nil
+	default:
+		return nil, &Error{Code: 400, Description: descInvalidFile}
+	}
+}

errors_map.go

@@ -15,6 +15,7 @@ const (
 	descChatNotFound = "Bad Request: chat not found"
 	descWrongFileID  = "Bad Request: wrong file identifier/HTTP URL specified"
 	descUnauthorized = "Unauthorized"
+	descInvalidFile  = "Bad Request: invalid file"
 
 	descNotModified = "Bad Request: message is not modified: specified new message content " +
 		"and reply markup are exactly the same as a current content and reply markup of the message"

media.go

@@ -59,7 +59,7 @@ func (b *Bot) photoMedia(ctx context.Context, file InputFile, caption []styling.
 		}
 		return message.UploadedPhoto(upFile, caption...), nil
 	default:
-		return nil, &Error{Code: 400, Description: "Bad Request: invalid file"}
+		return nil, &Error{Code: 400, Description: descInvalidFile}
 	}
 }
 
@@ -92,7 +92,7 @@ func (b *Bot) documentMedia(ctx context.Context, file InputFile, caption []styli
 		}
 		return b, nil
 	default:
-		return nil, &Error{Code: 400, Description: "Bad Request: invalid file"}
+		return nil, &Error{Code: 400, Description: descInvalidFile}
 	}
 }