tolerate case changes in X-TUID header name

it is legal for an email system to simply change the case of rfc2822
headers, and at least one imap server apparently does just that.
this would lead to us not finding our own header, which is obviously not
helpful.

REFMAIL: CA+fD2U3hJEszmvwBsXEpTsaWgJ2Dh373mCESM3M0kg3ZwAYjaw@mail.gmail.com

src/common.h

@@ -116,6 +116,7 @@ void *memrchr( const void *s, int c, size_t n );
 #endif
 
 int starts_with( const char *str, int strl, const char *cmp, int cmpl );
+int starts_with_upper( const char *str, int strl, const char *cmp, int cmpl );
 int equals( const char *str, int strl, const char *cmp, int cmpl );
 
 #ifndef HAVE_TIMEGM

src/drv_imap.c

@@ -967,7 +967,7 @@ parse_fetch_rsp( imap_store_t *ctx, list_t *list, char *s ATTR_UNUSED )
 					tmp = tmp->next;
 					if (!is_atom( tmp ))
 						goto bfail;
-					if (starts_with( tmp->val, tmp->len, "X-TUID: ", 8 ))
+					if (starts_with_upper( tmp->val, tmp->len, "X-TUID: ", 8 ))
 						tuid = tmp->val + 8;
 				} else {
 				  bfail:

src/sync.c

@@ -338,7 +338,7 @@ msg_fetched( int sts, void *aux )
 					if (c == '\r')
 						lcrs++;
 					else if (c == '\n') {
-						if (starts_with( fmap + start, len - start, "X-TUID: ", 8 )) {
+						if (starts_with_upper( fmap + start, len - start, "X-TUID: ", 8 )) {
 							extra = (sbreak = start) - (ebreak = i);
 							goto oke;
 						}

src/util.c

@@ -27,6 +27,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <string.h>
+#include <ctype.h>
 #include <pwd.h>
 
 static int need_nl;
@@ -241,6 +242,21 @@ starts_with( const char *str, int strl, const char *cmp, int cmpl )
 	return (strl >= cmpl) && !memcmp( str, cmp, cmpl );
 }
 
+int
+starts_with_upper( const char *str, int strl, const char *cmp, int cmpl )
+{
+	int i;
+
+	if (strl < 0)
+		strl = strnlen( str, cmpl + 1 );
+	if (strl < cmpl)
+		return 0;
+	for (i = 0; i < cmpl; i++)
+		if (str[i] != cmp[i] && toupper( str[i] ) != cmp[i])
+			return 0;
+	return 1;
+}
+
 int
 equals( const char *str, int strl, const char *cmp, int cmpl )
 {