sid.ml: give hex ia reader enough leeway for sloppy parsing

In MS mode we need for much shorter strings to pass through to the
hex parser.

1 files changed, 12 insertions, 2 deletions

diff --git a/sid.ml b/sid.ml
index 17c8124..0bcba50 100644
--- a/sid.ml
+++ b/sid.ml
@@ -92,7 +92,12 @@ module Con_strict = struct
   let name = "strict"
 
   let parse_hex_ia s p =
-    assert (p <= String.length s - ident_auth_hexlen);
+    if p > String.length s - ident_auth_hexlen then
+      raise (Invalid_argument
+               (Printf.sprintf
+                  "Invalid SID [%s]: conformant string encoding mandates \
+                   exactly 12 hex digits"
+                  s)) else
     let e = p + ident_auth_hexlen - 1 in
     let b = Bytes.make ident_auth_hexlen '\x2a' in
     Bytes.set b 0 '0'; (* hex indicator for U64.of_string *)
@@ -240,9 +245,14 @@ module MkStringFmt (Con : Conformance) = struct
               Con.name (U64.to_string ia))) else
     p, ia
 
+  (* Below constant determines the lowest length at which it is sensible
+     to test for the “-0x…” component that indicates a hex encoded ia. We
+     require at least one hex digit to allow non-conformant parsing modes. *)
+  let min_hexlen = String.length "S-1-0xf"
+
   let read_ident_auth s p =
     let r = String.length s - p in
-    if r < ident_auth_hexlen then ident_auth_decimal s p else (* hex can’t fit *)
+    if r < min_hexlen then ident_auth_decimal s p else
     match s.[p], s.[p+1] with
       | '0', 'x' -> read_ident_auth_hex s p
       | _ -> ident_auth_decimal s p