Add onerror_continue parameter to pretend onerror="continue" was set

With this change,

	pesi.set(onerror_continue, true);

can be used to restore behavior from before varnish-cache 7.3.

See pesi.set() documentation for details.

The test case is a modified version of the one by Geoff Simmons posted
in https://github.com/varnishcache/varnish-cache/issues/4053#issuecomment-1936000064

src/pesi_flags.h

@@ -2,10 +2,12 @@
 /* vcl-controlled flags */
 #define PF_CFG_SERIAL		(1U<<1)
 #define PF_CFG_THREAD		(1U<<2)
+#define PF_CFG_ONERROR_CONTINUE	(1U<<3)
 
 #define PF_CFG_DEFAULT	PF_CFG_THREAD
 
-#define PF_MASK_CFG		\
-	( PF_CFG_SERIAL	\
-	| PF_CFG_THREAD	\
+#define PF_MASK_CFG			\
+	( PF_CFG_SERIAL			\
+	| PF_CFG_THREAD			\
+	| PF_CFG_ONERROR_CONTINUE	\
 	)

src/tbl_set_parameter.h

 VMODENUM(serial, PF_CFG_SERIAL)
 VMODENUM(thread, PF_CFG_THREAD)
+VMODENUM(onerror_continue, PF_CFG_ONERROR_CONTINUE)
 #undef VMODENUM

src/tests/r04053.vtc

+varnishtest "Parent ESI fails despite setting ESP resp.status = 200"
+
+server s1 {
+	rxreq
+	expect req.url == "/abort"
+	txresp  -hdr {surrogate-control: content="ESI/1.0"} \
+	    -body {before <esi:include src="/fail"/> after}
+
+	rxreq
+	expect req.url == "/fail"
+	txresp -hdr "content-length: 100" -nolen
+	delay 0.1
+} -start
+
+varnish v1 -cliok "param.set feature +esi_disable_xml_check"
+
+## Doesn't matter whether this is turned on.
+# varnish v1 -cliok "param.set feature +esi_include_onerror"
+
+varnish v1 -vcl+backend {
+	import ${vmod_pesi};
+	import ${vmod_pesi_debug};
+	include "debug.inc.vcl";
+
+	sub vcl_backend_response {
+		# Prevent cache hits in the next tests.
+		set beresp.uncacheable = true;
+
+		set beresp.do_esi = beresp.http.surrogate-control ~ "ESI/1.0";
+		unset beresp.http.surrogate-control;
+	}
+
+	sub vcl_deliver {
+		pesi.activate();
+		pesi.set(onerror_continue, true);
+	}
+} -start
+
+
+client c1 {
+	txreq -url "/abort"
+	non_fatal
+	rxresp
+	expect resp.body == "before  after"
+} -run
+
+server s1 -wait
+server s1 -start
+
+varnish v1 -vcl+backend {
+	import ${vmod_pesi};
+	import ${vmod_pesi_debug};
+	include "debug.inc.vcl";
+
+	sub vcl_backend_error {
+		set beresp.body = "GURU";
+		return (deliver);
+	}
+
+	sub vcl_backend_response {
+		# Prevent cache hits in the next tests.
+		set beresp.uncacheable = true;
+
+		set beresp.do_esi = beresp.http.surrogate-control ~ "ESI/1.0";
+		set beresp.do_stream = false;
+	}
+
+	sub vcl_deliver {
+		pesi.activate();
+		pesi.set(onerror_continue, true);
+	}
+}
+
+client c1 {
+	txreq -url "/abort"
+	non_fatal
+	rxresp
+	expect resp.body == "before GURU after"
+} -run
+
+server s1 -wait

src/vdp_pesi.c

@@ -856,7 +856,7 @@ vdp_pesi_bytes(struct vdp_ctx *vdx, enum vdp_action act, void **priv,
 	struct nexus_gzip *parent_gzip = NULL;
 	struct bytes_tree *tree;
 	struct node *node, *child = NULL;
-	int incl_cont, retval = 0, parallel;
+	int incl_cont, incl_cont_override, retval = 0, parallel;
 
 	CHECK_OBJ_NOTNULL(vdx, VDP_CTX_MAGIC);
 
@@ -899,6 +899,8 @@ vdp_pesi_bytes(struct vdp_ctx *vdx, enum vdp_action act, void **priv,
 	if (node->parent != NULL && node->parent->nexus.gzip.is)
 		parent_gzip = &node->parent->nexus.gzip;
 
+	incl_cont_override = (pesi->flags & PF_CFG_ONERROR_CONTINUE) != 0;
+
 	pp = ptr;
 	while (retval == 0 && tree->retval == 0) {
 		incl_cont = 0;
@@ -991,6 +993,8 @@ vdp_pesi_bytes(struct vdp_ctx *vdx, enum vdp_action act, void **priv,
 				    T_NEXUS, ST_PRIVATE);
 				CHECK_OBJ_NOTNULL(child, NODE_MAGIC);
 
+				incl_cont |= incl_cont_override;
+
 				VSLdbgv(vdx, "vped_vdp: call vped_include "
 				       "incl_cont=%d", incl_cont);
 				parallel =

src/vdp_pesi.vcc

@@ -205,7 +205,7 @@ Example::
       pesi.activate()
   }
 
-$Function VOID set(ENUM { serial, thread } parameter, [BOOL bool])
+$Function VOID set(ENUM { serial, thread, onerror_continue } parameter, [BOOL bool])
 
 Set a configuration parameter for the VDP, which holds for the current
 (sub)request, as documented below. The parameter to be set is
@@ -215,7 +215,8 @@ this function may allow for setting other data types).
 
 $Restrict vcl_deliver
 
-The parameters that can be set are currently ``serial`` and ``thread``:
+The parameters that can be set are currently ``serial``, ``thread``
+and ``onerror_continue``.
 
 ``serial``
 ----------
@@ -276,6 +277,27 @@ Whether we always request a new thread for includes, default is
 
 See the detailled discussion in `THREADS`_ for details.
 
+``onerror_continue``
+--------------------
+
+If set to ``true``, makes pESI processing behave as if the
+``onerror="continue"`` attribute was set for all includes of the
+current object. The default is ``false``.
+
+.. _VC#4053: https://github.com/varnishcache/varnish-cache/issues/4053
+
+Issue `VC#4053`_ documents a challenge caused by the changed behavior
+with respect to (lack of) the ``onerror="continue"`` attribute, where
+additional complications in VCL are required to restore the behavior
+from before Varnish-Cache 7.3.
+
+With this parameter set to ``true``, pESI behaves as if all includes
+of the currently processed objects had the ``onerror="continue"``
+attribute set.
+
+This parameter should be considered transitional until a generic
+solution is established for Varnish-Cache.
+
 $Function VOID workspace_prealloc(BYTES min_free=4096, INT max_nodes=32)
 
 Configure the maximum amount of workspace used for pesi internal data

src/vmod_pesi.man.rst

@@ -196,8 +196,15 @@ Example::
 
 .. _pesi.set():
 
-VOID set(ENUM {serial, thread} parameter, [BOOL bool])
-------------------------------------------------------
+VOID set(ENUM parameter, [BOOL bool])
+-------------------------------------
+
+::
+
+   VOID set(
+      ENUM {serial, thread, onerror_continue} parameter,
+      [BOOL bool]
+   )
 
 Set a configuration parameter for the VDP, which holds for the current
 (sub)request, as documented below. The parameter to be set is
@@ -207,7 +214,8 @@ this function may allow for setting other data types).
 
 Restricted to: ``vcl_deliver``.
 
-The parameters that can be set are currently ``serial`` and ``thread``:
+The parameters that can be set are currently ``serial``, ``thread``
+and ``onerror_continue``.
 
 ``serial``
 ----------
@@ -268,6 +276,27 @@ Whether we always request a new thread for includes, default is
 
 See the detailled discussion in `THREADS`_ for details.
 
+``onerror_continue``
+--------------------
+
+If set to ``true``, makes pESI processing behave as if the
+``onerror="continue"`` attribute was set for all includes of the
+current object. The default is ``false``.
+
+.. _VC#4053: https://github.com/varnishcache/varnish-cache/issues/4053
+
+Issue `VC#4053`_ documents a challenge caused by the changed behavior
+with respect to (lack of) the ``onerror="continue"`` attribute, where
+additional complications in VCL are required to restore the behavior
+from before Varnish-Cache 7.3.
+
+With this parameter set to ``true``, pESI behaves as if all includes
+of the currently processed objects had the ``onerror="continue"``
+attribute set.
+
+This parameter should be considered transitional until a generic
+solution is established for Varnish-Cache.
+
 .. _pesi.workspace_prealloc():
 
 VOID workspace_prealloc(BYTES min_free, INT max_nodes)