address review feedback

src/Tiny_httpd.ml

@@ -326,22 +326,14 @@ module Headers = struct
            / "`" / "|" / "~" / DIGIT / ALPHA ; any VCHAR, except delimiters
   Reference: https://datatracker.ietf.org/doc/html/rfc7230#section-3.2 *)
   let is_tchar = function
-  | '0' .. '9'
-  | 'a' .. 'z'
-  | 'A' .. 'Z'
-  | '!' | '#' | '$' | '%' | '&' | '\'' | '*' | '+' | '-' | '.' | '^' | '_' | '`'
-  | '|' | '~' ->
-      true
+    | '0' .. '9' | 'a' .. 'z' | 'A' .. 'Z'
+    | '!' | '#' | '$' | '%' | '&' | '\'' | '*' | '+' | '-' | '.' | '^'
+    | '_' | '`'  | '|' | '~' -> true
     | _ -> false
 
   let for_all pred s =
-    let len = String.length s in
-    let rec loop idx =
-      if idx = len then true
-      else if pred (String.unsafe_get s idx) then loop (idx + 1)
-      else false
-    in
-    loop 0
+    try String.iter (fun c->if not (pred c) then raise Exit) s; true
+    with Exit -> false
 
   let parse_ ~buf (bs:byte_stream) : t =
     let rec loop acc =
@@ -354,10 +346,10 @@ let is_tchar = function
           try
             let i = String.index line ':' in
             let k = String.sub line 0 i in
-            if for_all is_tchar k then (
+            if not (for_all is_tchar k) then (
+              invalid_arg (Printf.sprintf "Invalid header key: %S" k));
             let v = String.sub line (i+1) (String.length line-i-1) |> String.trim in
-              k,v)
-            else invalid_arg (Printf.sprintf "Invalid header key: %S" k)
+            k,v
           with _ -> bad_reqf 400 "invalid header line: %S" line
         in
         loop ((String.lowercase_ascii k,v)::acc)