[GitHub] [trafficserver] bneradt commented on a change in pull request #8550: TSUserArg: add value type checking

[GitBox <gi...@apache.org>]

bneradt commented on a change in pull request #8550:
URL: https://github.com/apache/trafficserver/pull/8550#discussion_r765226892



##########
File path: include/tscore/PluginUserArgs.h
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@@ -35,6 +35,40 @@ static constexpr std::array<size_t, TS_USER_ARGS_COUNT> MAX_USER_ARGS = {{
   128 /* max number of user arguments for GLB */
 }};
 
+/** Stagger each user argument value so we can detect mismatched
+ * indices.
+ *
+ * For example, say a plugin associates data with both sessions and
+ * transactions and that its session index is 2 and its transaction index is 4.
+ * In this case, we'll hand back to the plugin 2002 for its session index and
+ * 1004 for its transaction index. If it then accidentally uses its session
+ * index to reference its transaction index, it will pass back 2002 instead of
+ * 1004, which we will identify as belonging to the wrong user argument type
+ * because it is in the 2000 session block rather than the expected 1000
+ * transaction block.
+ *
+ * Note that these higher value 1000 block indices are only used when
+ * interfacing with the plugin. Internally the lower valued index is used.
+ * That is, for a transaction, expect internally a value of 3 instead of 1003.
+ */
+static constexpr std::array<size_t, TS_USER_ARGS_COUNT> USER_ARGS_OFFSETS = {{
+  1000, /* max number of user arguments for TXN */
+  2000, /* max number of user arguments for SSN */
+  3000, /* max number of user arguments for VCONN */
+  4000  /* max number of user arguments for GLB */
+}};

Review comment:
       I like this idea.




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