add the error() method

src/tests/b01.vtc

@@ -46,6 +46,10 @@ varnish v1 -vcl+backend {
 		} else {
 			set beresp.status = 999;
 		}
+
+		set beresp.http.foobarerr = foobar.error();
+		set beresp.http.snafuerr = snafu.error();
+		set beresp.http.barerr = bar.error();
 	}
 
 } -start
@@ -56,4 +60,8 @@ client c1 {
 	expect resp.status == "200"
 	expect resp.http.foo1 == "1"
 	expect resp.http.bar1 == "2"
+
+	expect resp.http.foobarerr == ""
+	expect resp.http.snafuerr == ""
+	expect resp.http.barerr == ""
 } -run

src/tests/b05.vtc

@@ -22,6 +22,9 @@ varnish v1 -vcl+backend {
 		if (paren.match(beresp.http.foo)) {
 			set beresp.http.foo = "baz";
 		}
+		else {
+		     set beresp.http.error = paren.error();
+		}
 	}
 } -start
 
@@ -32,6 +35,8 @@ client c1 {
 	expect resp.http.content-length == 6
 	expect resp.http.foo == "bar"
 	expect resp.http.baz == "quux"
+	expect resp.http.error != <undef>
+	expect resp.http.error != ""
 } -run
 
 logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {

src/tests/c08.vtc

@@ -15,6 +15,7 @@ varnish v1 -vcl+backend {
 
 	sub vcl_deliver {
 	        set resp.http.paren = paren.failed();
+		set resp.http.error = paren.error();
 
 		/* match fails */
 		if (paren.match(resp.http.foo)) {
@@ -34,8 +35,9 @@ varnish v1 -vcl+backend {
 		set resp.http.paren10 = paren.backref(10, "fallback10");
 
 		if (paren.match_dyn("(bar)", resp.http.foo)) {
-		   # dynamic matches do not affect failed()
+		   # dynamic matches do not affect failed() or error()
 		   set resp.http.parend = paren.failed();
+		   set resp.http.errord = paren.error();
 		}
 
 		/* compilation fails */
@@ -63,6 +65,8 @@ client c1 {
 	rxresp
 	expect resp.status == 200
 	expect resp.http.paren == "true"
+	expect resp.http.error != <undef>
+	expect resp.http.error != ""
 	expect resp.http.match == <undef>
 	expect resp.http.paren0 == "fallback0"
 	expect resp.http.paren1 == "fallback1"
@@ -78,6 +82,8 @@ client c1 {
 
 	expect resp.http.parend == "true"
 	expect resp.http.matchd == <undef>
+	expect resp.http.errord != <undef>
+	expect resp.http.errord != ""
 	expect resp.http.paren0d == "fallback0"
 	expect resp.http.paren1d == "fallback1"
 	expect resp.http.paren2d == "fallback2"

src/vmod_re.c

@@ -115,6 +115,25 @@ vmod_regex_failed(const struct vrt_ctx *ctx, struct vmod_re_regex *re)
 	return (re->error != NULL);
 }
 
+VCL_STRING
+vmod_regex_error(const struct vrt_ctx *ctx, struct vmod_re_regex *re)
+{
+	VCL_STRING error;
+
+	CHECK_OBJ_NOTNULL(re, VMOD_RE_REGEX_MAGIC);
+	if (re->error == NULL)
+		return "";
+
+	error = (VCL_STRING) WS_Printf(ctx->ws, "%s (position %d)", re->error,
+				       re->erroffset);
+	if (error == NULL) {
+		VSLb(ctx->vsl, SLT_VCL_Error,
+		     "vmod re: insufficient workspace for error message");
+		return "insufficient workspace for error message";
+	}
+	return(error);
+}
+
 VCL_VOID
 vmod_regex__fini(struct vmod_re_regex **rep)
 {

src/vmod_re.vcc

@@ -121,10 +121,23 @@ $Method BOOL .failed()
 
 Description
 	Returns true if regex compilation in the constructor failed.
+	NOTE: This method only pertains to compilation in the
+	constructor, not to compilation of a regex in ``match_dyn``.
 
 Example
 	``if (myregex.failed()) { # ...``
 
+$Method STRING .error()
+
+Description
+	Returns an error message if regex compilation in the
+	constructor failed, or the empty string if compilation
+	succedded. Like ``failed`` this only pertains to failures of
+	compilation in the constructor, not in ``match_dyn``.
+
+Example
+	``std.log("myregex failed to compile: " + myregex.error());``
+
 $Method BOOL .match(STRING)
 
 Description
@@ -262,8 +275,9 @@ LIMITATIONS
 Regular expressions passed into the constructor and into ``match_dyn``
 are compiled at run-time, so there are no errors at VCL compile-time
 for invalid expressions. If an expression is invalid, then a
-``VCL_error`` message is emitted to the Varnish log, and matches
-always fail.
+``VCL_error`` message is emitted to the Varnish log, matches always
+fail, and errors in the constructor can be inspected with ``failed``
+and ``error``.
 
 The VMOD allocates memory for captured subexpressions from Varnish
 workspaces, whose sizes are determined by the runtime parameters