test-lib-functions.sh: add generate_zero_bytes function

t5318 and t5562 used /dev/zero, which is not portable. This function
provides both a fixed block of NUL bytes and an infinite stream of NULs.

Signed-off-by: Randall S. Becker <rsbecker@nexbridge.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib-functions.sh

@@ -116,6 +116,19 @@ remove_cr () {
 	tr '\015' Q | sed -e 's/Q$//'
 }
+# Generate an output of $1 bytes of all zeroes (NULs, not ASCII zeroes).
+# If $1 is 'infinity', output forever or until the receiving pipe stops reading,
+# whichever comes first.
+generate_zero_bytes () {
+	perl -e 'if ($ARGV[0] == "infinity") {
+		while (-1) {
+			print "\0"
+		}
+	} else {
+		print "\0" x $ARGV[0]
+	}' "$@"
+}
+
 # In some bourne shell implementations, the "unset" builtin returns
 # nonzero status when a variable to be unset was not set in the first
 # place.