common/mlstdutils: Add chomp function to remove \n from end of strings.

This is like the Perl chomp function, it removes a single \n from the
end of a string if present, else leaves the string alone.

I believe I found the only (two) places where such a function is used,
but there may be a few more lurking.

common/mlstdutils/std_utils.ml

@@ -229,6 +229,13 @@ module String = struct
     let trim ?(test = Char.isspace) str =
       trimr ~test (triml ~test str)
 
+    let chomp str =
+      let n = String.length str in
+      if n > 0 && str.[n-1] = '\n' then
+        String.sub str 0 (n-1)
+      else
+        str
+
     let count_chars c str =
       let count = ref 0 in
       for i = 0 to String.length str - 1 do

common/mlstdutils/std_utils.mli

@@ -107,6 +107,8 @@ module String : sig
     (** Trim right. *)
     val trim : ?test:(char -> bool) -> string -> string
     (** Trim left and right. *)
+    val chomp : string -> string
+    (** If the string ends with [\n], remove it. *)
     val count_chars : char -> string -> int
     (** Count number of times the character occurs in string. *)
     val explode : string -> char list

common/mlstdutils/std_utils_tests.ml

@@ -110,6 +110,15 @@ let test_string_span ctx =
   assert_equal_int 3 (String.cspan "def" "ab");
   assert_equal_int 0 (String.cspan "" "ab")
 
+(* Test Std_utils.String.chomp. *)
+let test_string_chomp ctx =
+  assert_equal_string "a" (String.chomp "a");
+  assert_equal_string "a" (String.chomp "a\n");
+  assert_equal_string "a\nb" (String.chomp "a\nb");
+  assert_equal_string "" (String.chomp "");
+  assert_equal_string "" (String.chomp "\n");
+  assert_equal_string "\n" (String.chomp "\n\n") (* only removes one *)
+
 (* Suites declaration. *)
 let suite =
   "mllib Std_utils" >:::
@@ -122,6 +131,7 @@ let suite =
       "strings.find" >:: test_string_find;
       "strings.lines_split" >:: test_string_lines_split;
       "strings.span" >:: test_string_span;
+      "strings.chomp" >:: test_string_chomp;
     ]
 
 let () =

mllib/common_utils.ml

@@ -376,14 +376,8 @@ let shell_command ?(echo_cmd = true) cmd =
 let uuidgen () =
   let lines = external_command "uuidgen -r" in
   assert (List.length lines >= 1);
-  let uuid = List.hd lines in
-  let len = String.length uuid in
-  let uuid, len =
-    if len > 0 && uuid.[len-1] = '\n' then
-      String.sub uuid 0 (len-1), len-1
-    else
-      uuid, len in
-  if len < 10 then assert false; (* sanity check on uuidgen *)
+  let uuid = String.chomp (List.hd lines) in
+  if String.length uuid < 10 then assert false; (* sanity check on uuidgen *)
   uuid
 
 (* Remove a temporary directory on exit. *)

v2v/linux_bootloaders.ml

@@ -296,12 +296,8 @@ object (self)
       match res with
       | None -> None
       | Some k ->
-        let len = String.length k in
-        let k =
-          if len > 0 && k.[len-1] = '\n' then
-            String.sub k 0 (len-1)
-          else k in
-        Some (remove_hd_prefix k)
+         let k = String.chomp k in
+         Some (remove_hd_prefix k)
     in
 
     let vmlinuzes =