fail more gracefully for vmods missing

src/Makefile.am

@@ -34,6 +34,7 @@ libvmod_tus_la_SOURCES = \
 	tus_b64.h \
 	tus_blob.c \
 	tus_blob.h \
+	tus_checksums.h \
 	tus_concat.h \
 	tus_file.c \
 	tus_file.h \

src/tus_blob.c

@@ -40,6 +40,7 @@
 #include "vmod_blobdigest.h"
 #include "tus_b64.h"
 #include "tus_blob.h"
+#include "tus_checksums.h"
 
 static const struct Vmod_vmod_blob_Func *vmod_blob = NULL;
 static const struct Vmod_vmod_blobdigest_Func *vmod_blobdigest = NULL;
@@ -154,8 +155,11 @@ tus_b64_decode(VRT_CTX, const char *s, VCL_INT l)
 {
 	struct strands st = {.n = 1, .p = &s};
 
-	if (! enabled)
+	if (! enabled) {
+		VRT_fail(ctx, "base64 decode support not available - "
+			 "vmod_blob was not found");
 		return (NULL);
+	}
 
 	AN(vmod_blob);
 	AN(vmod_blob->decode);

src/tus_response.c

@@ -36,15 +36,13 @@
 
 #include "vcc_tus_if.h"
 
+#include "tus_checksums.h"
 #include "tus_b64.h"
 #include "tus_file.h"
 #include "tus_servers.h"
 #include "tus_hdr.h"
 #include "tus_response.h"
 
-/* tus_blob.c */
-const char * tus_checksums(void);
-
 const unsigned s_MULT = 1000;
 const unsigned s_OPTIONS = 1;
 const unsigned s_HEAD = 2;