Save offset for subsequent invocation to reip_iter

Previously, we would only look for the first ever match.
To support multiple matches, we now save the start offset
relative to the ptr argument for the next invocation.

src/vmod_re.c

@@ -515,26 +515,35 @@ reip_iter(struct re_iter_priv *reip, unsigned flush,
     const void *ptr, ssize_t len)
 {
 	VCL_STRING		subject;
+	// where data from ptr starts in subject
+	ssize_t			ptrsubjoff;
 	ov_t			*ov;
 	int			i;
 
 	CHECK_OBJ_NOTNULL(reip, RE_ITER_PRIV_MAGIC);
 
-	if (reip->s == PCRE2_ERROR_NOMATCH) {
+	if (reip->s > PCRE2_ERROR_NOMATCH) {
+		AZ(reip->buf);
+		AZ(reip->len);
+		subject = ptr;
+		ptrsubjoff = 0;
+	}
+	else if (reip->s == PCRE2_ERROR_NOMATCH) {
 		AZ(reip->startoffset);
 		AZ(reip->buf);
 		AZ(reip->len);
 
 		subject = ptr;
+		ptrsubjoff = 0;
 	}
 	else if (reip->s == PCRE2_ERROR_PARTIAL) {
+		ptrsubjoff = reip->len;
 		AN(reip->buf);
 		reip->buf = realloc(reip->buf, reip->len + len);
 		AN(reip->buf);
-		memcpy(reip->buf + reip->len, ptr, len);
-		reip->len += len;
-
-		len = reip->len;
+		memcpy(reip->buf + ptrsubjoff, ptr, len);
+		len += reip->len;
+		reip->len = len;
 		subject = reip->buf;
 	}
 	else {
@@ -548,6 +557,7 @@ reip_iter(struct re_iter_priv *reip, unsigned flush,
 	reip->s = match(reip->ctx, reip->vre, subject, len,
 			reip->startoffset, reip->options, reip->task,
 			reip->vre_limits);
+	assert(reip->s != PCRE2_ERROR_BADOFFSET);
 
 	if ((reip->s < PCRE2_ERROR_NOMATCH && reip->s < reip->ret) ||
 	    reip->s > reip->ret)
@@ -587,6 +597,14 @@ reip_iter(struct re_iter_priv *reip, unsigned flush,
 
 	assert(reip->s > PCRE2_ERROR_NOMATCH);
 
+	// save start offset for next call, relative to ptr
+	if (reip->buf == NULL)
+		reip->startoffset = ov->ovector[1];
+	else if (ov->ovector[1] >= ptrsubjoff)
+		reip->startoffset = ov->ovector[1] - ptrsubjoff;
+	else
+		WRONG("impossible ovector[1]");
+
 	/* no buffer && no flush -> no copy needed */
 	if (reip->buf == NULL && (flush & OBJ_ITER_FLUSH) == 0)
 		return (0);