add an event function to check version compatibility with Varnish

configure.ac

 AC_PREREQ(2.59)
 AC_COPYRIGHT([Copyright (c) 2015-2016 UPLEX - Nils Goroll Systemoptimierung])
-AC_INIT([libvmod-blobcode], [0.1])
+AC_INIT([libvmod-blobcode], [1.0])
 AC_CONFIG_MACRO_DIR([m4])
 m4_ifndef([VARNISH_VMOD_INCLUDES], AC_MSG_ERROR([Need varnish.m4 -- see README.rst]))
 AC_CONFIG_SRCDIR(src/vmod_blobcode.vcc)

src/vmod_blobcode.c

@@ -197,6 +197,23 @@ err_decode(VRT_CTX, const char *enc)
 	}
 }
 
+/* Event function */
+
+int __match_proto__(vmod_event_f)
+event(VRT_CTX, struct vmod_priv *priv, enum vcl_event_e e)
+{
+	if (e != VCL_EVENT_LOAD)
+		return 0;
+	if (VRT_MAJOR_VERSION < 3
+	    || (VRT_MAJOR_VERSION == 3 && VRT_MINOR_VERSION < 2)) {
+		AN(ctx->msg);
+		VSB_cat(ctx->msg,
+		 "vmod blobcode: not compatible with Varnish versions < 4.1.2");
+		return 1;
+	}
+	return 0;
+}
+
 /* Objects */
 
 VCL_VOID __match_proto__(td_blobcode_blob__init)

src/vmod_blobcode.vcc

@@ -10,6 +10,8 @@
 
 $Module blobcode 3 binary-to-text encodings and decodings for the VCL blob type
 
+$Event event
+
 ::
 
   sub vcl_init {
@@ -355,6 +357,10 @@ REQUIREMENTS
 This VMOD requires at least Varnish version 4.1.2, and has been tested
 with versions through 5.0.0.
 
+Later versions of this VMOD are only compatible with Varnish versions
+since 5.0.0, and permit the use of the ``encode``, ``decode`` and
+``transcode`` functions in ``vcl_init``.
+
 Perl 5 is required for the build.
 
 INSTALLATION
@@ -441,6 +447,8 @@ HISTORY
 
 * version 0.1: initial version
 
+* version 1.0: compatible with Varnish versions since 4.1.2.
+
 SEE ALSO
 ========