Initial DDC release

internal/fetch/filename.go

@@ -0,0 +1,65 @@
+package fetch
+
+import (
+	"mime"
+	"net/http"
+	"path"
+	"path/filepath"
+	"strings"
+	"unicode/utf8"
+)
+
+const (
+	maxFileNameBytes  = 200
+	maxExtensionBytes = 16
+	fallbackFileName  = "download"
+)
+
+func FileNameFromResponse(response *http.Response) string {
+	if disposition := response.Header.Get("Content-Disposition"); disposition != "" {
+		if _, parameters, err := mime.ParseMediaType(disposition); err == nil {
+			if name := SanitizeFileName(parameters["filename"]); name != "" {
+				return name
+			}
+		}
+	}
+	if response.Request != nil && response.Request.URL != nil {
+		if name := SanitizeFileName(path.Base(response.Request.URL.Path)); name != "" {
+			return name
+		}
+	}
+	return fallbackFileName
+}
+
+func SanitizeFileName(raw string) string {
+	name := path.Base(strings.ReplaceAll(raw, "\\", "/"))
+	name = strings.Map(dropUnsafeRune, name)
+	name = strings.TrimSpace(strings.TrimLeft(name, ". "))
+	if name == "" {
+		return ""
+	}
+	return truncate(name)
+}
+
+func dropUnsafeRune(character rune) rune {
+	if character < 0x20 || character == 0x7f || character == '/' || character == utf8.RuneError {
+		return -1
+	}
+	return character
+}
+
+func truncate(name string) string {
+	if len(name) <= maxFileNameBytes {
+		return name
+	}
+	extension := filepath.Ext(name)
+	if len(extension) > maxExtensionBytes {
+		extension = ""
+	}
+	base := strings.TrimSuffix(name, extension)
+	for len(base)+len(extension) > maxFileNameBytes {
+		_, size := utf8.DecodeLastRuneInString(base)
+		base = base[:len(base)-size]
+	}
+	return base + extension
+}