feat: set canonical header for file

news/163.feature

@@ -0,0 +1 @@
+Set `Link` header with `rel="canonical"` for file downloads. @mamico

plone/namedfile/browser.py

@@ -127,6 +127,13 @@ def handle_request_range(self, file):
         except ValueError:
             return default
 
+    def get_canonical(self, file):
+        filename = getattr(file, "filename", None)
+        if filename is None:
+            return f"{self.context.absolute_url()}/@@download/{self.fieldname}"
+        else:
+            return f"{self.context.absolute_url()}/@@download/{self.fieldname}/{filename}"
+
     def set_headers(self, file):
         # With filename None, set_headers will not add the download headers.
         if not self.filename:
@@ -135,7 +142,8 @@ def set_headers(self, file):
                 self.filename = self.fieldname
                 if self.filename is None:
                     self.filename = "file.ext"
-        set_headers(file, self.request.response, filename=self.filename)
+        canonical =  self.get_canonical(file)
+        set_headers(file, self.request.response, filename=self.filename, canonical=canonical)
 
     def _getFile(self):
         if not self.fieldname:
@@ -185,4 +193,5 @@ def set_headers(self, file):
                 if mimetype not in self.allowed_inline_mimetypes:
                     # Let the Download view handle this.
                     return super().set_headers(file)
-        set_headers(file, self.request.response)
+        canonical =  self.get_canonical(file)
+        set_headers(file, self.request.response, canonical=canonical)

plone/namedfile/usage.rst

@@ -32,6 +32,9 @@ These store data with the following types::
     ...         self.image = namedfile.NamedImage()
     ...         self.blob = namedfile.NamedBlobFile()
     ...         self.blobimage = namedfile.NamedBlobImage()
+    ...
+    ...     def absolute_url(self):
+    ...         return "http://foo/bar"
 
 
 File data and content type
@@ -226,6 +229,8 @@ We will test this with a dummy request, faking traversal::
     'text/plain'
     >>> request.response.getHeader('Content-Disposition')
     "attachment; filename*=UTF-8''test.txt"
+    >>> request.response.getHeader('Link')
+    '<http://foo/bar/@@download/simple/test.txt>; rel="canonical"'
 
     >>> request = TestRequest()
     >>> download = Download(container, request).publishTraverse(request, 'blob')
@@ -238,6 +243,8 @@ We will test this with a dummy request, faking traversal::
     'text/plain'
     >>> request.response.getHeader('Content-Disposition')
     "attachment; filename*=UTF-8''test.txt"
+    >>> request.response.getHeader('Link')
+    '<http://foo/bar/@@download/blob/test.txt>; rel="canonical"'
 
     >>> request = TestRequest()
     >>> download = Download(container, request).publishTraverse(request, 'image')
@@ -250,6 +257,8 @@ We will test this with a dummy request, faking traversal::
     'image/foo'
     >>> request.response.getHeader('Content-Disposition')
     "attachment; filename*=UTF-8''zpt.gif"
+    >>> request.response.getHeader('Link')
+    '<http://foo/bar/@@download/image/zpt.gif>; rel="canonical"'
 
     >>> request = TestRequest()
     >>> download = Download(container, request).publishTraverse(request, 'blobimage')
@@ -262,6 +271,8 @@ We will test this with a dummy request, faking traversal::
     'image/foo'
     >>> request.response.getHeader('Content-Disposition')
     "attachment; filename*=UTF-8''zpt.gif"
+    >>> request.response.getHeader('Link')
+    '<http://foo/bar/@@download/blobimage/zpt.gif>; rel="canonical"'
 
 Range support
 -------------

plone/namedfile/utils/__init__.py

@@ -130,7 +130,7 @@ def get_contenttype(file=None, filename=None, default="application/octet-stream"
     return default
 
 
-def set_headers(file, response, filename=None):
+def set_headers(file, response, filename=None, canonical=None):
     """Set response headers for the given file. If filename is given, set
     the Content-Disposition to attachment.
     """
@@ -149,6 +149,8 @@ def set_headers(file, response, filename=None):
             "Content-Disposition", f"attachment; filename*=UTF-8''{filename}"
         )
 
+    if canonical is not None:
+        response.setHeader("Link", f'<{canonical}>; rel="canonical"')
 
 def stream_data(file, start=0, end=None):
     """Return the given file as a stream if possible."""