Prefer code-duplication for clarity

src/main/java/io/vertx/core/http/impl/HttpUtils.java

@@ -880,10 +880,30 @@ private static void validateAsciiHeaderValue(AsciiString value) {
     }
     byte[] asciiChars = value.array();
     int off = value.arrayOffset();
-    int end = off + length;
+    if (off == 0 && length == asciiChars.length) {
+      for (int index = 0; index < asciiChars.length; index++) {
+        int latinChar = asciiChars[index] & 0xFF;
+        if (latinChar == 0x7F) {
+          throw new IllegalArgumentException("a header value contains a prohibited character '127': " + value);
+        }
+        // non-printable chars are rare so let's make it a fall-back method, whilst still accepting HTAB
+        if (latinChar < 32 && latinChar != 0x09) {
+          validateSequenceHeaderValue(value, index - off);
+          break;
+        }
+      }
+    } else {
+      validateAsciiRangeHeaderValue(value, off, length, asciiChars);
+    }
+  }
 
-    // DON'T REMOVE THE OPTIMIZATION off == 0? ..: it's meant to reduce computation to perform bound checks
-    for (int index = off == 0? 0 : off; index < end; index++) {
+  /**
+   * This method is the slow-path generic version of {@link #validateAsciiHeaderValue(AsciiString)} which
+   * is optimized for {@link AsciiString} instances which are backed by a 0-offset full-blown byte array.
+   */
+  private static void validateAsciiRangeHeaderValue(AsciiString value, int off, int length, byte[] asciiChars) {
+    int end = off + length;
+    for (int index = off; index < end; index++) {
       int latinChar = asciiChars[index] & 0xFF;
       if (latinChar == 0x7F) {
         throw new IllegalArgumentException("a header value contains a prohibited character '127': " + value);