Use IndexOfAnyValues in MultipartContent (#79788)

Author: MihaZupan

src/libraries/System.Net.Http/src/System/Net/Http/MultipartContent.cs

@@ -23,6 +23,9 @@ public class MultipartContent : HttpContent, IEnumerable<HttpContent>
         private const int ColonSpaceLength = 2;
         private const int CommaSpaceLength = 2;
 
+        private static readonly IndexOfAnyValues<char> s_allowedBoundaryChars =
+            IndexOfAnyValues.Create(" '()+,-./0123456789:=?ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz");
+
         private readonly List<HttpContent> _nestedContent;
         private readonly string _boundary;
 
@@ -85,15 +88,9 @@ private static void ValidateBoundary(string boundary)
                 throw new ArgumentException(SR.Format(System.Globalization.CultureInfo.InvariantCulture, SR.net_http_headers_invalid_value, boundary), nameof(boundary));
             }
 
-            const string AllowedMarks = @"'()+_,-./:=? ";
-
-            foreach (char ch in boundary)
+            if (boundary.AsSpan().IndexOfAnyExcept(s_allowedBoundaryChars) >= 0)
             {
-                if (!char.IsAsciiLetterOrDigit(ch) &&
-                    !AllowedMarks.Contains(ch)) // Marks.
-                {
-                    throw new ArgumentException(SR.Format(System.Globalization.CultureInfo.InvariantCulture, SR.net_http_headers_invalid_value, boundary), nameof(boundary));
-                }
+                throw new ArgumentException(SR.Format(System.Globalization.CultureInfo.InvariantCulture, SR.net_http_headers_invalid_value, boundary), nameof(boundary));
             }
         }