IAX2: Fix UTF-8 string encoding

Fixes #18651.

epan/dissectors/packet-iax2.c

@@ -1853,7 +1853,7 @@ dissect_fullpacket(tvbuff_t *tvb, guint32 offset,
     proto_tree_add_item(packet_type_tree, hf_iax2_dtmf_csub, tvb, offset+9, 1, ENC_ASCII);
     offset += 10;
 
-    col_append_fstr(pinfo->cinfo, COL_INFO, " digit %c", csub);
+    col_append_fstr(pinfo->cinfo, COL_INFO, " digit %s", format_char(pinfo->pool, csub));
     break;
 
   case AST_FRAME_CONTROL:

wsutil/str_util.c

@@ -1028,6 +1028,34 @@ format_text_chr(wmem_allocator_t *allocator, const char *string, size_t len, cha
     return wmem_strbuf_finalize(buf);
 }
 
+char *
+format_char(wmem_allocator_t *allocator, char c)
+{
+    char *buf;
+    char r;
+
+    if (g_ascii_isprint(c)) {
+        buf = wmem_alloc_array(allocator, char, 2);
+        buf[0] = c;
+        buf[1] = '\0';
+        return buf;
+    }
+    if (escape_char(c, &r)) {
+        buf = wmem_alloc_array(allocator, char, 3);
+        buf[0] = '\\';
+        buf[1] = r;
+        buf[2] = '\0';
+        return buf;
+    }
+    buf = wmem_alloc_array(allocator, char, 5);
+    buf[0] = '\\';
+    buf[1] = 'x';
+    buf[2] = hex[((uint8_t)c >> 4) & 0xF];
+    buf[3] = hex[((uint8_t)c >> 0) & 0xF];
+    buf[4] = '\0';
+    return buf;
+}
+
 char*
 ws_utf8_truncate(char *string, size_t len)
 {

wsutil/str_util.h

@@ -288,6 +288,24 @@ WS_DLL_PUBLIC
 char *format_text_chr(wmem_allocator_t *allocator,
                         const char *string, size_t len, char chr);
 
+/** Given a wmem scope and an 8-bit character
+ *  generate a valid UTF-8 string from it, allocated in the specified
+ *  wmem scope, that:
+ *
+ *   shows printable Unicode characters as themselves;
+ *
+ *   shows non-printable ASCII characters as C-style escapes (hex
+ *   if not one of the standard ones such as LF -> '\n');
+ *
+ *  and return a pointer to it.
+ *
+ * @param allocator The wmem scope
+ * @param c A character to format
+ * @return A pointer to the formatted string
+ */
+WS_DLL_PUBLIC
+char *format_char(wmem_allocator_t *allocator, char c);
+
 /**
  * Truncate a UTF-8 string in place so that it is no larger than len bytes,
  * ensuring that the string is null terminated and ends with a complete