Index: /trunk/include/iprt/string.h
===================================================================
--- /trunk/include/iprt/string.h	(revision 50792)
+++ /trunk/include/iprt/string.h	(revision 50793)
@@ -677,4 +677,9 @@
  * VERR_BUFFER_OVERFLOW will be returned if the check fails. */
 #define RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED     RT_BIT_32(0)
+/** Check that the string is exactly the given length.
+ * If it terminates early, VERR_BUFFER_UNDERFLOW will be returned.  When used
+ * together with RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED, the given length must
+ * include the terminator or VERR_BUFFER_OVERFLOW will be returned. */
+#define RTSTR_VALIDATE_ENCODING_EXACT_LENGTH        RT_BIT_32(1)
 /** @} */
 
@@ -684,5 +689,6 @@
  * @returns iprt status code.
  * @param   psz         The string.
- * @param   cch         The max string length. Use RTSTR_MAX to process the entire string.
+ * @param   cch         The max string length (/ size).  Use RTSTR_MAX to
+ *                      process the entire string.
  * @param   fFlags      Combination of RTSTR_VALIDATE_ENCODING_XXX flags.
  */
@@ -3358,5 +3364,6 @@
  * @returns iprt status code.
  * @param   pwsz        The string.
- * @param   cch         The max string length. Use RTSTR_MAX to process the entire string.
+ * @param   cwc         The max string length (/ size) in UTF-16 units. Use
+ *                      RTSTR_MAX to process the entire string.
  * @param   fFlags      Combination of RTSTR_VALIDATE_ENCODING_XXX flags.
  */
Index: /trunk/src/VBox/Runtime/common/string/utf-16.cpp
===================================================================
--- /trunk/src/VBox/Runtime/common/string/utf-16.cpp	(revision 50792)
+++ /trunk/src/VBox/Runtime/common/string/utf-16.cpp	(revision 50793)
@@ -319,5 +319,6 @@
 RTDECL(int) RTUtf16ValidateEncodingEx(PCRTUTF16 pwsz, size_t cwc, uint32_t fFlags)
 {
-    AssertReturn(!(fFlags & ~(RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED)), VERR_INVALID_PARAMETER);
+    AssertReturn(!(fFlags & ~(RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED | RTSTR_VALIDATE_ENCODING_EXACT_LENGTH)),
+                 VERR_INVALID_PARAMETER);
     AssertPtr(pwsz);
 
@@ -330,6 +331,17 @@
     if (RT_SUCCESS(rc))
     {
-        if (    (fFlags & RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED)
-            &&  cwcActual >= cwc)
+        if (fFlags & RTSTR_VALIDATE_ENCODING_EXACT_LENGTH)
+        {
+            if (fFlags & RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED)
+                cwcActual++;
+            if (cwcActual == cwc)
+                rc = VINF_SUCCESS;
+            else if (cwcActual < cwc)
+                rc = VERR_BUFFER_UNDERFLOW;
+            else
+                rc = VERR_BUFFER_OVERFLOW;
+        }
+        else if (    (fFlags & RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED)
+                 &&  cwcActual >= cwc)
             rc = VERR_BUFFER_OVERFLOW;
     }
Index: /trunk/src/VBox/Runtime/common/string/utf-8.cpp
===================================================================
--- /trunk/src/VBox/Runtime/common/string/utf-8.cpp	(revision 50792)
+++ /trunk/src/VBox/Runtime/common/string/utf-8.cpp	(revision 50793)
@@ -301,5 +301,6 @@
 RTDECL(int) RTStrValidateEncodingEx(const char *psz, size_t cch, uint32_t fFlags)
 {
-    AssertReturn(!(fFlags & ~(RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED)), VERR_INVALID_PARAMETER);
+    AssertReturn(!(fFlags & ~(RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED | RTSTR_VALIDATE_ENCODING_EXACT_LENGTH)),
+                 VERR_INVALID_PARAMETER);
     AssertPtr(psz);
 
@@ -312,6 +313,17 @@
     if (RT_SUCCESS(rc))
     {
-        if (    (fFlags & RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED)
-            &&  cchActual >= cch)
+        if (fFlags & RTSTR_VALIDATE_ENCODING_EXACT_LENGTH)
+        {
+            if (fFlags & RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED)
+                cchActual++;
+            if (cchActual == cch)
+                rc = VINF_SUCCESS;
+            else if (cchActual < cch)
+                rc = VERR_BUFFER_UNDERFLOW;
+            else
+                rc = VERR_BUFFER_OVERFLOW;
+        }
+        else if (    (fFlags & RTSTR_VALIDATE_ENCODING_ZERO_TERMINATED)
+                 &&  cchActual >= cch)
             rc = VERR_BUFFER_OVERFLOW;
     }