.synth() may also be called in vcl_backend_error.

README.rst

@@ -312,10 +312,11 @@ message.
 VOID xreader.synth()
 --------------------
 
-Generate a synthetic client response body from the file contents. This
-method may only be called in ``vcl_synth``. Invokes VCL failure if the
-most recent update check encountered an error, or if invoked in any
-other VCL subroutine besides ``vcl_synth``.
+Generate a synthetic response body from the file contents. This method
+may only be called in ``vcl_synth`` or ``vcl_backend_error``. Invokes
+VCL failure if the most recent update check encountered an error, or
+if invoked in any other VCL subroutine besides the two that are
+permitted.
 
 Example::
 
@@ -323,6 +324,10 @@ Example::
 	synth_body.synth();
   }
 
+  sub vcl_backend_error {
+	synth_body.synth();
+  }
+
 .. _xreader.blob():
 
 BLOB xreader.blob()

src/tests/synth.vtc

@@ -2,22 +2,34 @@
 
 varnishtest "reader.synth()"
 
-shell {echo -n "foo bar baz quux" > ${tmpdir}/synth}
+shell {
+	echo -n "foo bar baz quux" > ${tmpdir}/synth
+	echo -n "ouch" > ${tmpdir}/backend_error
+}
 
 varnish v1 -vcl {
 	import ${vmod_file};
 	backend b { .host = "${bad_ip}"; }
 
 	sub vcl_init {
-		new rdr = file.reader("${tmpdir}/synth", ttl=0.1s);
+		new synth = file.reader("${tmpdir}/synth", ttl=0.1s);
+		new backend_err = file.reader("${tmpdir}/backend_error");
 	}
 
 	sub vcl_recv {
+		if (req.url == "/backend") {
+			return (pass);
+		}
 		return (synth(200));
 	}
 
 	sub vcl_synth {
-		rdr.synth();
+		synth.synth();
+		return (deliver);
+	}
+
+	sub vcl_backend_error {
+		backend_err.synth();
 		return (deliver);
 	}
 } -start
@@ -39,6 +51,13 @@ client c1 {
 	expect resp.body == "quux baz bar foo"
 } -run
 
+client c1 {
+	txreq -url /backend
+	rxresp
+	expect resp.status == 503
+	expect resp.body == "ouch"
+} -run
+
 shell {chmod a-r ${tmpdir}/synth}
 delay .1
 
@@ -49,7 +68,7 @@ client c1 {
 
 logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {
 	expect 0 * Begin	req
-	expect * = VCL_Error	{^rdr\.synth\(\): vmod file failure: vcl1\.rdr: cannot open}
+	expect * = VCL_Error	{^synth\.synth\(\): vmod file failure: vcl1\.synth: cannot open}
 	expect * = End
 } -run
 
@@ -73,7 +92,7 @@ varnish v1 -vcl {
 
 logexpect l1 -v v1 -d 0 -g vxid -q "VCL_Error" {
 	expect 0 * Begin	req
-	expect * = VCL_Error	{^rdr\.synth\(\) may only be called in vcl_synth$}
+	expect * = VCL_Error	{^rdr\.synth\(\) may only be called in vcl_synth or vcl_backend_error$}
 	expect * = End
 } -start
 

src/vmod_file.c

@@ -531,9 +531,9 @@ vmod_reader_synth(VRT_CTX, struct VPFX(file_reader) *rdr)
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
 	CHECK_OBJ_NOTNULL(rdr, FILE_READER_MAGIC);
 
-	if ((ctx->method & VCL_MET_SYNTH) == 0) {
-		VRT_fail(ctx, "%s.synth() may only be called in vcl_synth",
-			 rdr->obj_name);
+	if ((ctx->method & (VCL_MET_SYNTH | VCL_MET_BACKEND_ERROR)) == 0) {
+		VRT_fail(ctx, "%s.synth() may only be called in vcl_synth or "
+			 "vcl_backend_error", rdr->obj_name);
 		return;
 	}
 

src/vmod_file.vcc

@@ -292,10 +292,11 @@ message.
 
 $Method VOID .synth()
 
-Generate a synthetic client response body from the file contents. This
-method may only be called in ``vcl_synth``. Invokes VCL failure if the
-most recent update check encountered an error, or if invoked in any
-other VCL subroutine besides ``vcl_synth``.
+Generate a synthetic response body from the file contents. This method
+may only be called in ``vcl_synth`` or ``vcl_backend_error``. Invokes
+VCL failure if the most recent update check encountered an error, or
+if invoked in any other VCL subroutine besides the two that are
+permitted.
 
 Example::
 
@@ -303,6 +304,10 @@ Example::
 	synth_body.synth();
   }
 
+  sub vcl_backend_error {
+	synth_body.synth();
+  }
+
 $Method BLOB .blob()
 
 Return the file's contents as a BLOB. Invokes VCL failure if the most