Add "error" state to backend fetch and response

bin/varnishd/cache/cache.h

@@ -407,6 +407,9 @@ struct busyobj {
 
 	struct http_conn	*htc;
 
+	uint16_t		err_code;
+	const char		*err_reason;
+
 	struct pool_task	fetch_task;
 
 #define BO_FLAG(l, r, w, d) unsigned	l:1;

bin/varnishd/cache/cache_fetch.c

@@ -277,7 +277,7 @@ vbf_stp_startfetch(struct worker *wrk, struct busyobj *bo)
 	if (wrk->handling == VCL_RET_ABANDON || wrk->handling == VCL_RET_FAIL)
 		return (F_STP_FAIL);
 
-	assert (wrk->handling == VCL_RET_FETCH);
+	assert (wrk->handling == VCL_RET_FETCH || wrk->handling == VCL_RET_ERROR);
 
 	HTTP_Setup(bo->beresp, bo->ws, bo->vsl, SLT_BerespMethod);
 
@@ -290,6 +290,9 @@ vbf_stp_startfetch(struct worker *wrk, struct busyobj *bo)
 	bo->vfc->resp = bo->beresp;
 	bo->vfc->req = bo->bereq;
 
+	if (wrk->handling == VCL_RET_ERROR)
+		return (F_STP_ERROR);
+
 	i = VDI_GetHdr(wrk, bo);
 
 	now = W_TIM_real(wrk);
@@ -383,10 +386,15 @@ vbf_stp_startfetch(struct worker *wrk, struct busyobj *bo)
 
 	VCL_backend_response_method(bo->vcl, wrk, NULL, bo, NULL);
 
-	if (wrk->handling == VCL_RET_ABANDON || wrk->handling == VCL_RET_FAIL) {
+	if (wrk->handling == VCL_RET_ABANDON || wrk->handling == VCL_RET_FAIL ||
+	    wrk->handling == VCL_RET_ERROR) {
 		bo->htc->doclose = SC_RESP_CLOSE;
+
 		VDI_Finish(bo->wrk, bo);
-		return (F_STP_FAIL);
+		if (wrk->handling == VCL_RET_ERROR)
+			return (F_STP_ERROR);
+		else
+			return (F_STP_FAIL);
 	}
 
 	if (wrk->handling == VCL_RET_RETRY) {
@@ -756,7 +764,8 @@ vbf_stp_error(struct worker *wrk, struct busyobj *bo)
 	AN(bo->fetch_objcore->flags & OC_F_BUSY);
 	assert(bo->director_state == DIR_S_NULL);
 
-	wrk->stats->fetch_failed++;
+	if (wrk->handling !=  VCL_RET_ERROR)
+		wrk->stats->fetch_failed++;
 
 	now = W_TIM_real(wrk);
 	VSLb_ts_busyobj(bo, "Error", now);
@@ -770,7 +779,11 @@ vbf_stp_error(struct worker *wrk, struct busyobj *bo)
 	// XXX: reset all beresp flags ?
 
 	HTTP_Setup(bo->beresp, bo->ws, bo->vsl, SLT_BerespMethod);
-	http_PutResponse(bo->beresp, "HTTP/1.1", 503, "Backend fetch failed");
+	if (bo->err_code > 0)
+		http_PutResponse(bo->beresp, "HTTP/1.1", bo->err_code, bo->err_reason);
+	else
+		http_PutResponse(bo->beresp, "HTTP/1.1", 503, "Backend fetch failed");
+
 	http_TimeHeader(bo->beresp, "Date: ", now);
 	http_SetHeader(bo->beresp, "Server: Varnish");
 

bin/varnishd/cache/cache_vrt.c

@@ -55,9 +55,18 @@ VRT_synth(VRT_CTX, VCL_INT code, VCL_STRING reason)
 {
 
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
-	CHECK_OBJ_NOTNULL(ctx->req, REQ_MAGIC);
+	assert(ctx->req != NULL || ctx->bo != NULL);
 	if (code < 100 || code > 65535)
 		code = 503;
+
+	if (ctx->req == NULL) {
+		CHECK_OBJ_NOTNULL(ctx->bo, BUSYOBJ_MAGIC);
+		ctx->bo->err_code = (uint16_t)code;
+		ctx->bo->err_reason = reason ? reason
+		    : http_Status2Reason(ctx->bo->err_code % 1000, NULL);
+		return;
+	}
+
 	ctx->req->err_code = (uint16_t)code;
 	ctx->req->err_reason = reason ? reason
 	    : http_Status2Reason(ctx->req->err_code % 1000, NULL);

bin/varnishtest/tests/v00062.vtc

+varnishtest "backend_(fetch|response) error state with custom status/reason"
+
+server s1 -repeat 3 {
+	rxreq
+	txresp
+} -start
+
+varnish v1 -vcl+backend {
+	sub vcl_backend_fetch {
+		if (bereq.url == "/errorsynth") {
+			return (error(403));
+		}
+
+		if (bereq.url == "/errorsynthbody") {
+			return (error(403, "Steven has no cookies"));
+		}
+
+		if (bereq.url == "/error") {
+			return (error);
+		}
+	}
+
+	sub vcl_backend_response {
+		if (bereq.url == "/resperrorsynth") {
+			return (error(403));
+		}
+
+		if (bereq.url == "/resperrorsynthbody") {
+			return (error(403, "Steven has no cookies"));
+		}
+
+		if (bereq.url == "/resperror") {
+			return (error);
+		}
+	}
+
+	sub vcl_backend_error {
+		set beresp.http.error = "visited";
+	}
+} -start
+
+client c1 {
+	txreq -url /error
+	rxresp
+	expect resp.status == 503
+	expect resp.http.error == visited
+
+	txreq -url /errorsynth
+	rxresp
+	expect resp.status == 403
+	expect resp.http.error == visited
+
+	txreq -url /errorsynthbody
+	rxresp
+	expect resp.status == 403
+	expect resp.reason == "Steven has no cookies"
+	expect resp.http.error == visited
+
+	txreq -url /resperror
+	rxresp
+	expect resp.status == 503
+	expect resp.http.error == visited
+
+	txreq -url /resperrorsynth
+	rxresp
+	expect resp.status == 403
+	expect resp.http.error == visited
+
+	txreq -url /resperrorsynthbody
+	rxresp
+	expect resp.status == 403
+	expect resp.reason == "Steven has no cookies"
+	expect resp.http.error == visited
+} -run
+
+# Make sure we don't increment the failed fetch counter
+
+varnish v1 -expect fetch_failed == 0

doc/graphviz/cache_fetch.dot

@@ -39,16 +39,18 @@ digraph cache_fetch {
 		/* vbf_stp_startfetch() */
 		v_b_f [
 			    shape=record
-			    label="{vbf_stp_startfetch:|{vcl_backend_fetch\{\}|bereq.*}|{fail|abandon|<fetch>fetch}}"
+			    label="{vbf_stp_startfetch:|{vcl_backend_fetch\{\}|bereq.*}|{<error>error|fail|abandon|<fetch>fetch}}"
 		]
+		v_b_f:error:s -> v_b_e
 		v_b_f:fetch:s -> v_b_hdrs [style=bold]
 		v_b_hdrs [ label="send bereq,\nread beresp (headers)"]
 		v_b_hdrs -> v_b_r [style=bold]
 		v_b_hdrs -> v_b_e
 		v_b_r [
 			    shape=record
-			    label="{vbf_stp_startfetch:|{vcl_backend_response\{\}|{bereq.*|beresp.*}}|{fail|{retry|{<max>max?|<retry>ok?}}|abandon|{deliver or pass|{<fetch_304>304?|<non_304>other?}}}}"
+			    label="{vbf_stp_startfetch:|{vcl_backend_response\{\}|{bereq.*|beresp.*}}|{<error>error|fail|{retry|{<max>max?|<retry>ok?}}|abandon|{deliver or pass|{<fetch_304>304?|<non_304>other?}}}}"
 		]
+		v_b_r:error:s -> v_b_e
 		v_b_r:retry -> v_b_r_retry [color=purple]
 		v_b_r:max -> v_b_e
 		v_b_r:fetch_304:s -> vbf_stp_condfetch
@@ -90,8 +92,8 @@ digraph cache_fetch {
 		]
 		vbf_stp_condfetch:ok:s -> vbf_stp_fetchend
 
-		error [shape=plaintext]
-		error -> FETCH_FAIL
+		fail [shape=plaintext]
+		fail -> FETCH_FAIL
 
 		/* vbf_stp_error */
 		v_b_e [

doc/sphinx/users-guide/vcl-built-in-subs.rst

@@ -345,7 +345,12 @@ The `vcl_backend_fetch` subroutine may terminate with calling
     background fetch, control is passed to :ref:`vcl_synth` on the
     client side with ``resp.status`` preset to 503.
 
-Before calling `vcl_backend_fetch`, varnish core prepares the `bereq`
+  ``error(status code, reason)``
+    Transition to :ref:`vcl_backend_error` with ``beresp.status`` and
+    ``beresp.reason`` being preset to the arguments of ``error()`` if
+    arguments are provided.
+
+Before calling `vcl_backend_fetch`, Varnish core prepares the `bereq`
 backend request as follows:
 
 * Unless the request is a `pass`,
@@ -408,6 +413,11 @@ The `vcl_backend_response` subroutine may terminate with calling
     lookups hitting this object will be turned into passed transactions,
     as if ``vcl_recv`` had returned ``pass``.
 
+  ``error(status code, reason)``
+    Transition to :ref:`vcl_backend_error` with ``beresp.status`` and
+    ``beresp.reason`` being preset to the arguments of ``error()`` if
+    arguments are provided.
+
 304 handling
 ~~~~~~~~~~~~
 

lib/libvcc/generate.py

@@ -131,11 +131,11 @@ returns = (
 
     ('backend_fetch',
      "B",
-     ('fail', 'fetch', 'abandon')
+     ('fail', 'fetch', 'abandon', 'error')
     ),
     ('backend_response',
      "B",
-     ('fail', 'deliver', 'retry', 'abandon', 'pass')
+     ('fail', 'deliver', 'retry', 'abandon', 'pass', 'error')
     ),
     ('backend_error',
      "B",

lib/libvcc/vcc_action.c

@@ -331,7 +331,7 @@ vcc_act_return(struct vcc *tl, struct token *t, struct symbol *sym)
 	vcc_ProcAction(tl->curproc, hand, tl->t);
 	vcc_NextToken(tl);
 	if (tl->t->tok == '(') {
-		if (hand == VCL_RET_SYNTH)
+		if (hand == VCL_RET_SYNTH || hand == VCL_RET_ERROR)
 			vcc_act_return_synth(tl);
 		else if (hand == VCL_RET_VCL)
 			vcc_act_return_vcl(tl);