--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libsip/grok_from.c	Wed Sep 07 17:53:10 2022 -0800
@@ -0,0 +1,100 @@
+/*
+ * Here we implement further parsing of the From header,
+ * beyond the preliminary step of uas_get_basic_headers().
+ */
+
+#include <ctype.h>
+#include <string.h>
+#include <strings.h>
+#include "grok_from.h"
+
+grok_from_header(from_hdr, gfr)
+	char *from_hdr;
+	struct grok_from *gfr;
+{
+	char *cp = from_hdr, *bp;
+	int bracketed;
+
+	if (*cp == '<' || !strncasecmp(cp, "sip:", 4)) {
+		gfr->cnam = 0;
+		gfr->cnam_len = 0;
+		gfr->cnam_quoted = 0;
+	} else {
+		if (*cp == '"') {
+			cp++;
+			gfr->cnam = cp;
+			for (;;) {
+				if (!*cp)
+					return(-1);
+				if (*cp == '"')
+					break;
+				if (*cp++ == '\\') {
+					if (!*cp)
+						return(-1);
+					cp++;
+				}
+			}
+			gfr->cnam_len = cp - gfr->cnam;
+			gfr->cnam_quoted = 1;
+			cp++;
+			while (isspace(*cp))
+				cp++;
+			if (*cp != '<')
+				return(-1);
+		} else {
+			gfr->cnam = cp;
+			for (;;) {
+				if (!*cp)
+					return(-1);
+				if (*cp == '<')
+					break;
+				cp++;
+			}
+			for (bp = cp; bp > gfr->cnam && isspace(bp[-1]); bp--)
+				;
+			gfr->cnam_len = bp - gfr->cnam;
+			gfr->cnam_quoted = 0;
+		}
+	}
+	if (*cp == '<') {
+		cp++;
+		bracketed = 1;
+	} else
+		bracketed = 0;
+	gfr->uri = cp;
+	if (strncasecmp(cp, "sip:", 4))
+		return(-1);
+	cp += 4;
+	gfr->user = cp;
+	for (;;) {
+		if (!*cp || *cp == '<' || *cp == '>')
+			return(-1);
+		if (*cp == '@')
+			break;
+		cp++;
+	}
+	if (cp == gfr->user)
+		return(-1);
+	gfr->user_len = cp - gfr->user;
+	cp++;
+	for (;;) {
+		switch (*cp) {
+		case '\0':
+		case ';':
+			if (bracketed)
+				return(-1);
+			else
+				break;
+		case '>':
+			if (bracketed)
+				break;
+			else
+				return(-1);
+		case '<':
+			return(-1);
+		}
+		cp++;
+	}
+	gfr->uri_len = cp - gfr->uri;
+	return(0);
+}