cohttp: revert change to Header.replace, add Header.update

CHANGES.md

@@ -1,3 +1,9 @@
+## Unreleased
+
+- cohttp: a change in #694 modified the semantics of Header.replace.
+  The semantics change is reverted, and a new Header.update function
+  is introduced which changes a header value only when present. (@mseri)
+
 ## v2.5.3 (2020-06-27)
 
 - cohttp-async: adapt to async >= v0.14 (#699 @copy)

cohttp/src/header.ml

@@ -77,8 +77,12 @@ let remove h k =
 
 let replace h k v =
   let k = LString.of_string k in
-  if StringMap.mem k h
-  then StringMap.add k [v] h
+  StringMap.add k [v] h
+
+let update h k v =
+  let k' = LString.of_string k in
+  if StringMap.mem k' h
+  then replace h k v
   else h
 
 let get h k =

cohttp/src/header.mli

@@ -56,10 +56,14 @@ val add_opt_unless_exists : t option -> string -> string -> t
     original header parameter is not modified. *)
 val remove : t -> string -> t
 
-(** Replace the value of a key from the header map if it exists. The
-   original header parameter is not modified. *)
+(** Replace the value of a key from the header map if it exists, otherwise it
+    adds it to the header map. The original header parameter is not modified. *)
 val replace : t -> string -> string -> t
 
+(** Replace the value of a key from the header map if it exists, otherwise
+    return the header map unmodified. The original header parameter is not modified. *)
+val update: t -> string -> string -> t
+
 (** Check if a key exists in the header. *)
 val mem : t -> string -> bool