handle etag header

src/mte.ml

@@ -14,24 +14,6 @@
     along with this program.  If not, see <https://www.gnu.org/licenses/>. *)
 
 module Static = struct
-  (* /terms + /privacy
-
-     - try to find a response with an acceptable mime-type,
-     - then pick the version in the most preferred language of the user,
-     - and finally apply compression if that is allowed by the client
-     - set ETAG header
-
-     TODO:
-       - subsequent requests of the client should provide the tag in an "If-None-Match" header
-         to detect if the terms of service have changed
-       - If it did not change, a "304 Not Modified" response will be returned
-       - The ETAG is encoded in Crockford base-32
-       - A "Taler-Terms-Version" header is generated to indicate the legal version of the terms
-       - When returning a full response (not a "304 Not Modified"), the server
-         should also include a "Avail-Languages" header which includes a
-         comma-separated list of the languages in which the terms of service are available in
-  *)
-
   let select_file headers kind =
     let open Syntax in
     let* ext =
@@ -45,25 +27,55 @@ module Static = struct
     let content = Assets.get_content ~lang ~ext kind in
     content
 
-  (* TODO add headers, handle errors etc
-     think on how to (not) mix error and vif monade well *)
+  (* /terms + /privacy
+
+     - try to find a response with an acceptable mime-type,
+     - then pick the version in the most preferred language of the user,
+     - and finally apply compression if that is allowed by the client
+     - set ETAG header
+     - If it did not change, a "304 Not Modified" response will be returned
+
+     TODO:
+       - The ETAG is encoded in Crockford base-32
+       - A "Taler-Terms-Version" header is generated to indicate the legal version of the terms
+       - When returning a full response (not a "304 Not Modified"), the server
+         should also include a "Avail-Languages" header which includes a
+         comma-separated list of the languages in which the terms of service are available in
+  *)
   let static kind req _server _env =
-    let open Vif.Response.Syntax in
-    let headers = Vif.Request.headers req in
-    (* TODO(etag) *)
-    let _if_none_match = Vif.Headers.get headers "if-none-match" in
-    let data =
-      match select_file headers kind with
-      | Error e -> Fmt.failwith "%s" e
-      | Ok content -> content
+    let get_ok = function
+      | Error e -> Fmt.failwith "TODO handle me, %s" e
+      | Ok v -> v
     in
-    let compression = Headers.select_encoding headers in
-    let* () = Vif.Response.with_string ?compression req data in
-    (* TODO(etag) *)
-    let* () = Vif.Response.add ~field:"etag" (Assets.etag kind) in
-    (* TODO content-type *)
-    let* () = Vif.Response.add ~field:"content-type" "html; charset=utf-8" in
-    Vif.Response.respond `OK
+    let etag =
+      (* TODO keep our static asset etag as Etag.t in Config? *)
+      Assets.etag kind |> Headers.Etag.of_crockford32 |> Result.get_ok
+    in
+    let headers = Vif.Request.headers req in
+    let has_matching_etag =
+      get_ok
+      @@
+      match Vif.Headers.get headers "if-none-match" with
+      | None -> Ok false
+      | Some s ->
+          Headers.Etag.parse s |> Result.map (Headers.Etag.evaluate etag)
+    in
+    let open Vif.Response.Syntax in
+    match has_matching_etag with
+    | true ->
+        let* () = Vif.Response.empty in
+        Vif.Response.respond `Not_modified
+    | false ->
+        let data = select_file headers kind |> get_ok in
+        let compression = Headers.select_encoding headers in
+        let* () = Vif.Response.with_string ?compression req data in
+        let etag_field_value = Headers.Etag.to_field_value etag in
+        let* () = Vif.Response.add ~field:"etag" etag_field_value in
+        (* TODO content-type *)
+        let* () =
+          Vif.Response.add ~field:"content-type" "html; charset=utf-8"
+        in
+        Vif.Response.respond `OK
 
   let terms = static Assets.Terms
   let privacy = static Assets.Privacy