vcc_backend: Initialize undefined timeouts with -1

We can't use NAN in VGC code today, so in order to convey the lack of
timeout setting in a backend definition, only a negative value makes
sense since zero will eventually mean zero instead of undefined.

This is an implicit breakage of the VRT ABI for the meaning of struct
vrt_backend.

bin/varnishd/cache/cache_backend.c

@@ -99,7 +99,7 @@ VBE_Connect_Error(struct VSC_vbe *vsc, int err)
 	do {								\
 		CHECK_OBJ_NOTNULL(bo, BUSYOBJ_MAGIC);			\
 		dst = bo->tmx;						\
-		if (dst == 0.0)						\
+		if (dst == 0.0 && be->tmx >= 0.0)			\
 			dst = be->tmx;					\
 		if (dst == 0.0)						\
 			dst = cache_param->tmx;				\

include/vrt.h

@@ -64,6 +64,8 @@
  *	VRT_u_sess_send_timeout() added
  *	VRT_u_sess_timeout_idle() added
  *	VRT_u_sess_timeout_linger() added
+ *	(struct vrt_backend).*_timeout must be initialized to a negative value
+ *	VRT_BACKEND_INIT() helper macro added
  * 18.1 (2023-12-05)
  *	vbf_objiterate() implementation changed #4013
  * 18.0 (2023-09-15)
@@ -582,6 +584,14 @@ struct vrt_endpoint {
 	unsigned			max_connections;	\
 	unsigned			proxy_header;
 
+#define VRT_BACKEND_INIT(be)					\
+	do {							\
+		INIT_OBJ(be, VRT_BACKEND_MAGIC);		\
+		(be)->connect_timeout = -1.0;			\
+		(be)->first_byte_timeout = -1.0;		\
+		(be)->between_bytes_timeout = -1.0;		\
+	} while(0)
+
 #define VRT_BACKEND_HANDLE()			\
 	do {					\
 		DA(vcl_name);			\

lib/libvcc/vcc_backend.c

@@ -32,6 +32,7 @@
 
 #include "config.h"
 
+#include <math.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
@@ -381,9 +382,11 @@ vcc_ParseHostDef(struct vcc *tl, struct symbol *sym,
 	struct inifin *ifp;
 	struct vsb *vsb1;
 	struct symbol *via = NULL;
+	vtim_dur connect_timeout = NAN;
+	vtim_dur first_byte_timeout = NAN;
+	vtim_dur between_bytes_timeout = NAN;
 	char *p;
 	unsigned u;
-	double t;
 
 	if (tl->t->tok == ID &&
 	    (vcc_IdIs(tl->t, "none") || vcc_IdIs(tl->t, "None"))) {
@@ -480,21 +483,21 @@ vcc_ParseHostDef(struct vcc *tl, struct symbol *sym,
 			SkipToken(tl, ';');
 		} else if (vcc_IdIs(t_field, "connect_timeout")) {
 			Fb(tl, 0, "\t.connect_timeout = ");
-			vcc_Duration(tl, &t);
+			vcc_Duration(tl, &connect_timeout);
 			ERRCHK(tl);
-			Fb(tl, 0, "%g,\n", t);
+			Fb(tl, 0, "%g,\n", connect_timeout);
 			SkipToken(tl, ';');
 		} else if (vcc_IdIs(t_field, "first_byte_timeout")) {
 			Fb(tl, 0, "\t.first_byte_timeout = ");
-			vcc_Duration(tl, &t);
+			vcc_Duration(tl, &first_byte_timeout);
 			ERRCHK(tl);
-			Fb(tl, 0, "%g,\n", t);
+			Fb(tl, 0, "%g,\n", first_byte_timeout);
 			SkipToken(tl, ';');
 		} else if (vcc_IdIs(t_field, "between_bytes_timeout")) {
 			Fb(tl, 0, "\t.between_bytes_timeout = ");
-			vcc_Duration(tl, &t);
+			vcc_Duration(tl, &between_bytes_timeout);
 			ERRCHK(tl);
-			Fb(tl, 0, "%g,\n", t);
+			Fb(tl, 0, "%g,\n", between_bytes_timeout);
 			SkipToken(tl, ';');
 		} else if (vcc_IdIs(t_field, "max_connections")) {
 			u = vcc_UintVal(tl);
@@ -581,6 +584,13 @@ vcc_ParseHostDef(struct vcc *tl, struct symbol *sym,
 	free(fs);
 	ERRCHK(tl);
 
+	if (isnan(connect_timeout))
+		Fb(tl, 0, "\t.connect_timeout = -1.0,\n");
+	if (isnan(first_byte_timeout))
+		Fb(tl, 0, "\t.first_byte_timeout = -1.0,\n");
+	if (isnan(between_bytes_timeout))
+		Fb(tl, 0, "\t.between_bytes_timeout = -1.0,\n");
+
 	ExpectErr(tl, '}');
 
 	if (t_host == NULL && t_path == NULL) {

vmod/vmod_debug_dyn.c

@@ -75,7 +75,7 @@ dyn_dir_init(VRT_CTX, struct xyzzy_debug_dyn *dyn,
 	CHECK_OBJ_ORNULL(via, DIRECTOR_MAGIC);
 
 	INIT_OBJ(&vep, VRT_ENDPOINT_MAGIC);
-	INIT_OBJ(&vrt, VRT_BACKEND_MAGIC);
+	VRT_BACKEND_INIT(&vrt);
 	vrt.endpoint = &vep;
 	vrt.vcl_name = dyn->vcl_name;
 	vrt.hosthdr = addr;
@@ -206,7 +206,7 @@ dyn_uds_init(VRT_CTX, struct xyzzy_debug_dyn_uds *uds, VCL_STRING path)
 	}
 
 	INIT_OBJ(&vep, VRT_ENDPOINT_MAGIC);
-	INIT_OBJ(&vrt, VRT_BACKEND_MAGIC);
+	VRT_BACKEND_INIT(&vrt);
 	vrt.endpoint = &vep;
 	vep.uds_path = path;
 	vrt.vcl_name = uds->vcl_name;