Respect expires header when checking for new version

It was called to many times and acted similar to a DOS attack.

app/src/test/java/org/schabi/newpipe/NewVersionManagerTest.kt

@@ -0,0 +1,72 @@
+package org.schabi.newpipe
+
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+import java.time.Instant
+import java.time.ZoneId
+import java.time.format.DateTimeFormatter
+import kotlin.math.abs
+
+class NewVersionManagerTest {
+
+    private lateinit var manager: NewVersionManager
+
+    @Before
+    fun setup() {
+        manager = NewVersionManager()
+    }
+
+    @Test
+    fun `Expiry is reached`() {
+        val oneHourEarlier = Instant.now().atZone(ZoneId.of("GMT")).minusHours(1)
+
+        val expired = manager.isExpired(oneHourEarlier.toEpochSecond())
+
+        assertTrue(expired)
+    }
+
+    @Test
+    fun `Expiry is not reached`() {
+        val oneHourLater = Instant.now().atZone(ZoneId.of("GMT")).plusHours(1)
+
+        val expired = manager.isExpired(oneHourLater.toEpochSecond())
+
+        assertFalse(expired)
+    }
+
+    /**
+     * Equal within a range of 5 seconds
+     */
+    private fun assertNearlyEqual(a: Long, b: Long) {
+        assertTrue(abs(a - b) < 5)
+    }
+
+    @Test
+    fun `Expiry must be returned as is because it is inside the acceptable range of 6-72 hours`() {
+        val sixHoursLater = Instant.now().atZone(ZoneId.of("GMT")).plusHours(6)
+
+        val coerced = manager.coerceExpiry(DateTimeFormatter.RFC_1123_DATE_TIME.format(sixHoursLater))
+
+        assertNearlyEqual(sixHoursLater.toEpochSecond(), coerced)
+    }
+
+    @Test
+    fun `Expiry must be increased to 6 hours if below`() {
+        val tooLow = Instant.now().atZone(ZoneId.of("GMT")).plusHours(5)
+
+        val coerced = manager.coerceExpiry(DateTimeFormatter.RFC_1123_DATE_TIME.format(tooLow))
+
+        assertNearlyEqual(tooLow.plusHours(1).toEpochSecond(), coerced)
+    }
+
+    @Test
+    fun `Expiry must be decreased to 72 hours if above`() {
+        val tooHigh = Instant.now().atZone(ZoneId.of("GMT")).plusHours(73)
+
+        val coerced = manager.coerceExpiry(DateTimeFormatter.RFC_1123_DATE_TIME.format(tooHigh))
+
+        assertNearlyEqual(tooHigh.minusHours(1).toEpochSecond(), coerced)
+    }
+}