fix!: add escaped abspath header

Adds new 'abspath-encoded' header to MultiFileReader.
New server sends both headers. New client prefers
'abspath-encoded' over 'abspath'. Old clients won't
be compatible with new servers.

CHANGELOG.md

@@ -22,6 +22,16 @@ The following emojis are used to highlight certain changes:
 
 ### Fixed
 
+* 🛠 `MultiFileReader` has been updated with a new header with the encoded file
+  name instead of the plain filename, due to a regression found in 
+  [`net/textproto`](https://github.com/golang/go/issues/60674). This only affects
+  files with binary characters in their name. By keeping the old header, we maximize
+  backwards compatibility.
+  |            | New Client | Old Client  |
+  |------------|------------|-------------|
+  | New Server | ✅         | ❌          |
+  | Old Server | ✅         | ✅          |
+
 ### Security
 
 ## [v0.11.0]

files/multifilereader.go

@@ -115,6 +115,7 @@ func (mfr *MultiFileReader) Read(buf []byte) (written int, err error) {
 			header.Set("Content-Type", contentType)
 			if rf, ok := entry.Node().(FileInfo); ok {
 				header.Set("abspath", rf.AbsPath())
+				header.Set("abspath-encoded", url.QueryEscape(rf.AbsPath()))
 			}
 
 			_, err := mfr.mpWriter.CreatePart(header)

files/multipartfile.go

@@ -100,9 +100,19 @@ func (w *multipartWalker) nextFile() (Node, error) {
 
 		return NewLinkFile(string(out), nil), nil
 	default:
+		var absPath string
+		if absPathEncoded := part.Header.Get("abspath-encoded"); absPathEncoded != "" {
+			absPath, err = url.QueryUnescape(absPathEncoded)
+			if err != nil {
+				return nil, err
+			}
+		} else {
+			absPath = part.Header.Get("abspath")
+		}
+
 		return &ReaderFile{
 			reader:  part,
-			abspath: part.Header.Get("abspath"),
+			abspath: absPath,
 		}, nil
 	}
 }