MINOR: applet: add a function to reset the svcctx of an applet

The CLI needs to reset the svcctx between commands, and there was nothing
done to handle this. Let's add appctx_reset_svcctx() to do that, it's the
closing equivalent of appctx_reserve_svcctx().

This will have to be backported to 2.6 as it will be used by a subsequent
patch to fix a bug.

include/haproxy/applet.h

@@ -40,6 +40,7 @@ extern struct pool_head *pool_head_appctx;
 struct task *task_run_applet(struct task *t, void *context, unsigned int state);
 int appctx_buf_available(void *arg);
 void *applet_reserve_svcctx(struct appctx *appctx, size_t size);
+void applet_reset_svcctx(struct appctx *appctx);
 void appctx_shut(struct appctx *appctx);
 
 struct appctx *appctx_new_on(struct applet *applet, struct sedesc *sedesc, int thr);

src/applet.c

@@ -142,6 +142,15 @@ void *applet_reserve_svcctx(struct appctx *appctx, size_t size)
 	return appctx->svcctx;
 }
 
+/* This is used to reset an svcctx and the svc.storage without releasing the
+ * appctx. In fact this is only used by the CLI applet between commands.
+ */
+void applet_reset_svcctx(struct appctx *appctx)
+{
+	memset(&appctx->svc.storage, 0, APPLET_MAX_SVCCTX);
+	appctx->svcctx = NULL;
+}
+
 /* call the applet's release() function if any, and marks the sedesc as shut.
  * Needs to be called upon close().
  */