add Content-Disposition and Filename to the payload of incoming webhooks

for each message part. The ContentDisposition value is the base value without
header key/value parameters. the Filename field is the likely filename of the
part. the different email clients encode filenames differently. there is a
standard mime mechanism from rfc 2231. and there is the q/b-word-encoding from
rfc 2047. instead of letting users of the webhook api deal with those
differences, we provide just the parsed filename.

for issue #258 by morki, thanks for reporting!

webmail/api.go

@@ -904,7 +904,12 @@ func (w Webmail) MessageSubmit(ctx context.Context, m SubmitMessage) {
 							ap = ap.Parts[xp]
 						}
 
-						filename := tryDecodeParam(log, ap.ContentTypeParams["name"])
+						_, filename, err := ap.DispositionFilename()
+						if err != nil && errors.Is(err, message.ErrParamEncoding) {
+							log.Debugx("parsing disposition/filename", err)
+						} else {
+							xcheckf(ctx, err, "reading disposition")
+						}
 						if filename == "" {
 							filename = "unnamed.bin"
 						}

webmail/message.go

@@ -2,6 +2,7 @@ package webmail
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
 	"io"
 	"log/slog"
@@ -275,21 +276,16 @@ func parsedMessage(log mlog.Log, m store.Message, state *msgState, full, msgitem
 		case "TEXT/PLAIN", "/":
 			// Don't include if Content-Disposition attachment.
 			if full || msgitem {
-				// todo: should have this, and perhaps all content-* headers, preparsed in message.Part?
-				h, err := p.Header()
-				log.Check(err, "parsing attachment headers", slog.Int64("msgid", m.ID))
-				cp := h.Get("Content-Disposition")
-				if cp != "" {
-					disp, params, err := mime.ParseMediaType(cp)
-					log.Check(err, "parsing content-disposition", slog.String("cp", cp))
-					if strings.EqualFold(disp, "attachment") {
-						name := tryDecodeParam(log, p.ContentTypeParams["name"])
-						if name == "" {
-							name = tryDecodeParam(log, params["filename"])
-						}
-						addAttachment(Attachment{path, name, p}, parentMixed)
-						return
-					}
+				disp, name, err := p.DispositionFilename()
+				if err != nil && errors.Is(err, message.ErrParamEncoding) {
+					log.Debugx("parsing disposition/filename", err)
+				} else if err != nil {
+					rerr = fmt.Errorf("reading disposition/filename: %v", err)
+					return
+				}
+				if strings.EqualFold(disp, "attachment") {
+					addAttachment(Attachment{path, name, p}, parentMixed)
+					return
 				}
 			}
 

webmail/view.go

@@ -1829,11 +1829,17 @@ func attachmentTypes(log mlog.Log, m store.Message, state *msgState) (map[Attach
 		mt := strings.ToLower(a.Part.MediaType + "/" + a.Part.MediaSubType)
 		if t, ok := attachmentMimetypes[mt]; ok {
 			types[t] = true
-		} else if ext := filepath.Ext(tryDecodeParam(log, a.Part.ContentTypeParams["name"])); ext != "" {
+			continue
+		}
+		_, filename, err := a.Part.DispositionFilename()
+		if err != nil && errors.Is(err, message.ErrParamEncoding) {
+			log.Debugx("parsing disposition/filename", err)
+		} else if err != nil {
+			return nil, fmt.Errorf("reading disposition/filename: %v", err)
+		}
+		if ext := filepath.Ext(filename); ext != "" {
 			if t, ok := attachmentExtensions[strings.ToLower(ext)]; ok {
 				types[t] = true
-			} else {
-				continue
 			}
 		}
 	}

webmail/webmail.go

@@ -521,13 +521,11 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 		names := map[string]bool{}
 		for _, a := range mi.Attachments {
 			ap := a.Part
-			name := tryDecodeParam(log, ap.ContentTypeParams["name"])
-			if name == "" {
-				// We don't check errors, this is all best-effort.
-				h, _ := ap.Header()
-				disposition := h.Get("Content-Disposition")
-				_, params, _ := mime.ParseMediaType(disposition)
-				name = tryDecodeParam(log, params["filename"])
+			_, name, err := ap.DispositionFilename()
+			if err != nil && errors.Is(err, message.ErrParamEncoding) {
+				log.Debugx("parsing disposition header for filename", err)
+			} else {
+				xcheckf(ctx, err, "reading disposition header")
 			}
 			if name != "" {
 				name = filepath.Base(name)
@@ -816,13 +814,11 @@ func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w htt
 		h.Set("Content-Type", ct)
 		h.Set("Cache-Control", "no-store, max-age=0")
 		if t[1] == "download" {
-			name := tryDecodeParam(log, ap.ContentTypeParams["name"])
-			if name == "" {
-				// We don't check errors, this is all best-effort.
-				h, _ := ap.Header()
-				disposition := h.Get("Content-Disposition")
-				_, params, _ := mime.ParseMediaType(disposition)
-				name = tryDecodeParam(log, params["filename"])
+			_, name, err := ap.DispositionFilename()
+			if err != nil && errors.Is(err, message.ErrParamEncoding) {
+				log.Debugx("parsing disposition/filename", err)
+			} else {
+				xcheckf(ctx, err, "reading disposition/filename")
 			}
 			if name == "" {
 				name = "attachment.bin"