blaze822: add blaze822_chdr to search for a header passed as C string

blaze822.c

@@ -441,6 +441,15 @@ blaze822_hdr_(struct message *mesg, const char *hdr, size_t hdrlen)
 	return v;
 }
 
+char *
+blaze822_chdr(struct message *mesg, const char *chdr)
+{
+	char hdr[256];
+	size_t l = snprintf(hdr, sizeof hdr, "%c%s:", 0, chdr);
+
+	return blaze822_hdr_(mesg, hdr, l);
+}
+
 int
 blaze822_loop(int argc, char *argv[], void (*cb)(char *))
 {

blaze822.h

@@ -12,6 +12,7 @@ struct message *blaze822_mem(char *buf, size_t len);  // header + body
 
 char *blaze822_hdr_(struct message *mesg, const char *hdr, size_t len);
 #define blaze822_hdr(mesg, hdr) blaze822_hdr_(mesg, "\0" hdr ":", 2+strlen((hdr)))
+char *blaze822_chdr(struct message *mesg, const char *chdr);
 
 char *blaze822_next_header(struct message *mesg, char *prev);