add assets.ml

src/util.ml

@@ -0,0 +1,29 @@
+(* TODO Taler documentation
+   markdown mimetype should be the prefered one, and be supported, according to DD
+   we take text/plain as default instead for now *)
+let default_extension = "txt"
+
+let is_valid_filename, media_to_extension =
+  let mimetype_ext_assoc =
+    [
+      (("text", "plain"), "txt"); (("text", "markdown"), "md")
+    ; (("text", "html"), "html"); (("text", "html"), "htm")
+    ; (("application", "pdf"), "pdf"); (("image", "jpeg"), "jpg")
+    ; (("image", "jpeg"), "jpeg"); (("image", "png"), "png")
+    ; (("image", "gif"), "gif")
+    ]
+  in
+  (* <> than the actual set of "supported" extension (depends on config files) *)
+  let all_known_extensions = mimetype_ext_assoc |> List.split |> snd in
+  let is_valid_filename path = Fpath.mem_ext all_known_extensions path in
+  let media_to_extension = function
+    | Cohttp.Accept.MediaType (m, m_sub) ->
+        List.assoc_opt (m, m_sub) mimetype_ext_assoc
+    | AnyMediaSubtype m ->
+        List.find_map
+          (fun ((m', _), ext) ->
+            match String.equal m m' with false -> None | true -> Some ext)
+          mimetype_ext_assoc
+    | AnyMedia -> Some default_extension
+  in
+  (is_valid_filename, media_to_extension)