Fix S3 filename header escaping

Use an ASCII-only fallback for Content-Disposition filename and
RFC 5987 path escaping for filename* so presigned S3 responses keep
spaces and Unicode filenames interoperable.

Signed-off-by: Cursor Agent <cursoragent@cursor.com>

Co-authored-by: Ludovic <ludovic@probo.com>

pkg/filemanager/s3.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"io"
 	"net/url"
+	"strings"
 	"time"
 
 	"github.com/aws/aws-sdk-go-v2/service/s3"
@@ -118,11 +119,10 @@ func (s *Service) GeneratePresignedURL(
 ) (string, error) {
 	presignClient := s3.NewPresignClient(s.s3Client)
 
-	encodedFilename := url.QueryEscape(file.FileName)
 	contentDisposition := fmt.Sprintf(
 		"attachment; filename=%q; filename*=UTF-8''%s",
-		encodedFilename,
-		encodedFilename,
+		asciiFilename(file.FileName),
+		url.PathEscape(file.FileName),
 	)
 
 	presignedReq, err := presignClient.PresignGetObject(
@@ -145,6 +145,22 @@ func (s *Service) GeneratePresignedURL(
 	return presignedReq.URL, nil
 }
 
+func asciiFilename(filename string) string {
+	var b strings.Builder
+	b.Grow(len(filename))
+
+	for _, r := range filename {
+		if r < 0x20 || r > 0x7e {
+			b.WriteByte('_')
+			continue
+		}
+
+		b.WriteRune(r)
+	}
+
+	return b.String()
+}
+
 // GetFileSize determines the byte size of a seekable io.Reader by seeking to
 // the end and back. Returns an error if content is not seekable.
 func GetFileSize(content io.Reader) (int64, error) {

pkg/filemanager/url_test.go

@@ -15,9 +15,16 @@
 package filemanager_test
 
 import (
+	"context"
+	"net/url"
 	"testing"
+	"time"
 
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/credentials"
+	awss3 "github.com/aws/aws-sdk-go-v2/service/s3"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"go.probo.inc/probo/pkg/baseurl"
 	"go.probo.inc/probo/pkg/coredata"
 	"go.probo.inc/probo/pkg/filemanager"
@@ -65,3 +72,33 @@ func TestGenerateFileURL_PrivateFile(t *testing.T) {
 		svc.GenerateFileURL(file),
 	)
 }
+
+func TestGeneratePresignedFileURL_EscapesContentDispositionFilename(t *testing.T) {
+	t.Parallel()
+
+	s3Client := awss3.NewFromConfig(
+		aws.Config{
+			Region:      "us-east-1",
+			Credentials: credentials.NewStaticCredentialsProvider("access-key", "secret-key", ""),
+		},
+	)
+	svc := filemanager.NewService(nil, nil, s3Client)
+	file := &coredata.File{
+		BucketName: "uploads",
+		FileKey:    "tenant/file",
+		FileName:   `report "Q2"/résumé 100%.pdf`,
+		MimeType:   "application/pdf",
+	}
+
+	rawURL, err := svc.GeneratePresignedFileURL(context.Background(), file, time.Hour)
+	require.NoError(t, err)
+
+	parsedURL, err := url.Parse(rawURL)
+	require.NoError(t, err)
+
+	assert.Equal(
+		t,
+		`attachment; filename="report \"Q2\"/r_sum_ 100%.pdf"; filename*=UTF-8''report%20%22Q2%22%2Fr%C3%A9sum%C3%A9%20100%25.pdf`,
+		parsedURL.Query().Get("response-content-disposition"),
+	)
+}