Add the .backref() method.

README.rst

@@ -63,6 +63,15 @@ regex.match
 
 	BOOL regex.match(PRIV_CALL, PRIV_TASK, STRING subject, INT len=0, BOOL anchored=0, INT match_limit=0, INT offset_limit=0, BOOL notbol=0, BOOL noteol=0, BOOL notempty=0, BOOL notempty_atstart=0, BOOL no_jit=0, BOOL no_utf_check=0, ENUM {HARD,SOFT} partial=0, INT recursion_limit=0)
 
+.. _func_regex.backref:
+
+regex.backref
+-------------
+
+::
+
+	STRING regex.backref(INT ref, STRING fallback="**BACKREF METHOD FAILED**")
+
 .. _func_config_bool:
 
 config_bool

src/tests/backref_basic.vtc

+# looks like -*- vcl -*-
+
+varnishtest "basic backrefs"
+
+varnish v1 -vcl {
+	import pcre2 from "${vmod_topbuild}/src/.libs/libvmod_pcre2.so";
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_init {
+		new barbaz = pcre2.regex("(bar)(baz)");
+		new bazplus = pcre2.regex("(baz)(.+)");
+		new fourdots = pcre2.regex("(.)(.)(.)(.)");
+	}
+
+	sub vcl_recv {
+		return(synth(200));
+	}
+
+	sub vcl_synth {
+		# Tests task scopes for two different objects
+		if (barbaz.match("barbaz") && bazplus.match("bazquux")) {
+			set resp.http.bar0 = barbaz.backref(0, "error0");
+			set resp.http.bar1 = barbaz.backref(1, "error1");
+			set resp.http.bar2 = barbaz.backref(2, "error2");
+			set resp.http.baz0 = bazplus.backref(0, "error0");
+			set resp.http.baz1 = bazplus.backref(1, "error1");
+			set resp.http.baz2 = bazplus.backref(2, "error2");
+		}
+		else {
+			set resp.status = 999;
+		}
+		if (fourdots.match("barf")) {
+			set resp.http.frap
+			    = "_" + fourdots.backref(0, "error0") + "_"
+			      + fourdots.backref(4, "error4")
+			      + fourdots.backref(3, "error3")
+			      + fourdots.backref(2, "error2") + "p_";
+		}
+		else {
+			set resp.status = 999;
+		}
+	}
+} -start
+
+client c1 -repeat 2 {
+	txreq
+	rxresp
+	expect resp.status == "200"
+	expect resp.http.bar0 == "barbaz"
+	expect resp.http.bar1 == "bar"
+	expect resp.http.bar2 == "baz"
+	expect resp.http.baz0 == "bazquux"
+	expect resp.http.baz1 == "baz"
+	expect resp.http.baz2 == "quux"
+	expect resp.http.frap == "_barf_frap_"
+} -run

src/vmod_pcre2.c

@@ -519,6 +519,46 @@ vmod_regex_match(VRT_CTX, struct vmod_pcre2_regex *regex,
 	return 0;
 }
 
+VCL_STRING
+vmod_regex_backref(VRT_CTX, struct vmod_pcre2_regex *regex, VCL_INT ref,
+		   VCL_STRING fallback)
+{
+	struct vmod_priv *match_task;
+	pcre2_match_data *mdata;
+	PCRE2_UCHAR *buf;
+	PCRE2_SIZE len;
+	int ret;
+	char *msg;
+	uintptr_t snap;
+
+	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
+	CHECK_OBJ_NOTNULL(regex, VMOD_PCRE2_REGEX_MAGIC);
+	CHECK_UINT32_RANGE(ref, regex->vcl_name, ".backref()", fallback);
+
+	match_task = VRT_priv_task(ctx, regex);
+	if (match_task == NULL) {
+		VERR(ctx, "%s.backref(%ld) called without prior match",
+		     regex->vcl_name, ref);
+		return fallback;
+	}
+	WS_Assert_Allocated(ctx->ws, match_task->priv, 0);
+	mdata = match_task->priv;
+
+	if ((ret = pcre2_substring_get_bynumber(mdata, (uint32_t)ref, &buf,
+						&len)) == 0) {
+		WS_Assert_Allocated(ctx->ws, buf, len + 1);
+		return (VCL_STRING)buf;
+	}
+
+	snap = WS_Snapshot(ctx->ws);
+	if ((msg = WS_Printf(ctx->ws, "in %s.backref(%ld)", regex->vcl_name,
+			     ref)) == NULL)
+		msg = "";
+	report_pcre2_err(ctx, ret, msg, "");
+	WS_Reset(ctx->ws, snap);
+	return fallback;
+}
+
 /* Functions */
 
 VCL_BOOL

src/vmod_pcre2.vcc

@@ -39,6 +39,8 @@ $Method BOOL .match(PRIV_CALL, PRIV_TASK, STRING subject, INT len=0,
 		    BOOL no_utf_check = 0, ENUM {HARD, SOFT} partial=0,
 		    INT recursion_limit=0)
 
+$Method STRING .backref(INT ref, STRING fallback = "**BACKREF METHOD FAILED**")
+
 $Function BOOL config_bool(ENUM {JIT, STACKRECURSE, UNICODE})
 
 $Function STRING config_str(ENUM {BSR, JITTARGET, NEWLINE, UNICODE_VERSION,