tvbuff: add tvb_ensure_reported_length_remaining().

It is to tvb_reported_length_remaining() as
tvb_ensure_captured_length_remaining() is to
tvb_captured_length_remaining() - it throws an exception if the offset
is out of range.

(Note that an offset that's just past the end of the {reported,
captured} data is *not* out of range, it just means that there is no
data remaining.  Anything *past* that is out of range and thus invalid.)

debian/libwireshark0.symbols

@@ -1730,6 +1730,7 @@ libwireshark.so.0 libwireshark0 #MINVER#
  tvb_ensure_bytes_exist@Base 1.9.1
  tvb_ensure_bytes_exist64@Base 1.99.0
  tvb_ensure_captured_length_remaining@Base 1.12.0~rc1
+ tvb_ensure_reported_length_remaining@Base 3.5.0
  tvb_get_etsi_ts_102_221_annex_a_string@Base 3.3.1
  tvb_find_guint8@Base 1.9.1
  tvb_find_guint16@Base 2.3.0

epan/tvbuff.c

@@ -539,9 +539,6 @@ tvb_ensure_captured_length_remaining(const tvbuff_t *tvb, const gint offset)
 	return rem_length;
 }
 
-
-
-
 /* Validates that 'length' bytes are available starting from
  * offset (pos/neg). Does not throw an exception. */
 gboolean
@@ -713,6 +710,24 @@ tvb_reported_length_remaining(const tvbuff_t *tvb, const gint offset)
 		return 0;
 }
 
+guint
+tvb_ensure_reported_length_remaining(const tvbuff_t *tvb, const gint offset)
+{
+	guint abs_offset = 0;
+	int   exception;
+
+	DISSECTOR_ASSERT(tvb && tvb->initialized);
+
+	exception = compute_offset(tvb, offset, &abs_offset);
+	if (exception)
+		THROW(exception);
+
+	if (tvb->reported_length >= abs_offset)
+		return tvb->reported_length - abs_offset;
+	else
+		THROW(ReportedBoundsError);
+}
+
 /* Set the reported length of a tvbuff to a given value; used for protocols
  * whose headers contain an explicit length and where the calling
  * dissector's payload may include padding as well as the packet for

epan/tvbuff.h

@@ -252,6 +252,10 @@ WS_DLL_PUBLIC guint tvb_reported_length(const tvbuff_t *tvb);
 WS_DLL_PUBLIC gint tvb_reported_length_remaining(const tvbuff_t *tvb,
     const gint offset);
 
+/** Same as above, but throws an exception if the offset is out of bounds. */
+WS_DLL_PUBLIC guint tvb_ensure_reported_length_remaining(const tvbuff_t *tvb,
+    const gint offset);
+
 /** Set the reported length of a tvbuff to a given value; used for protocols
    whose headers contain an explicit length and where the calling
    dissector's payload may include padding as well as the packet for