feat(quic): step 3 of RFC 9002 retransmit — drain SentPacket on ACK

QuicConnectionParser's AckFrame handler now drains state.sentPackets of every entry whose packet number is covered by the ACK's ranges. The drained SentPackets are returned but discarded for now; step 5 will route them to loss detection / RTT. New helper file `connection/recovery/AckedPackets.kt`: - forEachAckedPacketNumber(ack, block): inline iterator over an AckFrame's ranges in RFC 9000 §19.3.1 order. Walks first range [largestAcked - firstAckRange, largestAcked] then each additional range with `nextLargest = previousSmallest - gap - 2`, `nextSmallest = nextLargest - ackRangeLength`. Defensive clamp at PN 0 against malformed peer ACKs. - drainAckedSentPackets(sentPackets, ack): walks via forEachAckedPacketNumber and removes each matching entry from the map. Returns the drained list. Wired into QuicConnectionParser.kt:165 alongside the existing ackTracker.purgeBelow call. Tests added (9, all pass): - simpleRange / multipleRanges / singlePacketAck: range walking for typical ACK shapes - ackForUnsentPn_isNoOp / emptyMap_returnsEmptyDrain: defensive paths - ackBoundary_pn0Inclusive: PN 0 is correctly included, no underflow - forEachAckedPacketNumber_iteratesDescending / forEachAckedPacketNumber_acrossMultipleRanges_descending: iterator semantics - returnedDrain_preservesTokens: drained SentPacket retains its full tokens list — step 5+ will dispatch these to RTT / loss Mirror of neqo's `recovery/mod.rs::remove_acked` (one of the 20 recovery tests we owe per `quic/plans/2026-05-04-control-frame-retransmit.md`). The remaining loss-detection tests land in step 5. Full :quic test suite + nestsClient moq-lite tests pass. https://claude.ai/code/session_01PYYez8a6sjiakyjAxsfCEQ
2026-05-04 22:45:10 +00:00
parent ea15a9afa1
commit 0ced269b27
3 changed files with 334 additions and 5 deletions
@@ -21,6 +21,7 @@
 package com.vitorpamplona.quic.connection

 import com.vitorpamplona.quic.QuicCodecException
+import com.vitorpamplona.quic.connection.recovery.drainAckedSentPackets
 import com.vitorpamplona.quic.frame.AckFrame
 import com.vitorpamplona.quic.frame.ConnectionCloseFrame
 import com.vitorpamplona.quic.frame.CryptoFrame
@@ -163,12 +164,18 @@ private fun dispatchFrames(
    for (frame in frames) {
        when (frame) {
            is AckFrame -> {
-                // We don't currently retransmit, so we just absorb ACKs. But
-                // we DO purge our own ACK tracker below the peer's largest
-                // acknowledged: the peer has confirmed receipt of those ACKs,
-                // so we don't need to keep advertising them — without this
-                // the range list grows unboundedly on long connections.
+                // Purge our own ACK tracker below the peer's largest
+                // acknowledged: the peer has confirmed receipt of those
+                // ACKs, so we don't need to keep advertising them —
+                // without this the range list grows unboundedly on long
+                // connections.
                state.ackTracker.purgeBelow(frame.largestAcknowledged - frame.firstAckRange)
+                // Step 3 of `quic/plans/2026-05-04-control-frame-retransmit.md`:
+                // remove SentPacket entries for the PNs the peer acknowledged.
+                // Returned list is intentionally discarded for now —
+                // step 5 will use it to feed loss detection / RTT
+                // estimation; for step 3 we just drain.
+                drainAckedSentPackets(state.sentPackets, frame)
            }

            is CryptoFrame -> {
@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quic.connection.recovery
+
+import com.vitorpamplona.quic.frame.AckFrame
+
+/**
+ * Walks the ACK ranges of an [AckFrame] in RFC 9000 §19.3.1 form and
+ * yields each ACK'd packet number, descending. The first range covers
+ * `[largestAcked - firstAckRange, largestAcked]`; each additional
+ * range's largest PN is `previousSmallest - gap - 2` and its smallest
+ * is `largest - ackRangeLength`.
+ *
+ * Ranges below packet number 0 are clamped — the spec disallows
+ * negative PNs, but defensive clamping keeps a malformed peer ACK
+ * from blowing up the iterator.
+ *
+ * The function does not allocate per-PN; it iterates by primitive
+ * `Long` and invokes [block] for each ACK'd PN. Hot path on every
+ * inbound ACK frame, so allocation matters.
+ */
+inline fun forEachAckedPacketNumber(
+    ack: AckFrame,
+    block: (Long) -> Unit,
+) {
+    var currentLargest = ack.largestAcknowledged
+    var currentSmallest = currentLargest - ack.firstAckRange
+    if (currentSmallest < 0L) currentSmallest = 0L
+    var pn = currentLargest
+    while (pn >= currentSmallest) {
+        block(pn)
+        pn -= 1L
+    }
+    for (range in ack.additionalRanges) {
+        // Next range's largest = previousSmallest - gap - 2.
+        // Next range's smallest = largest - ackRangeLength.
+        val nextLargest = currentSmallest - range.gap - 2L
+        if (nextLargest < 0L) break
+        val nextSmallest = (nextLargest - range.ackRangeLength).coerceAtLeast(0L)
+        var pn2 = nextLargest
+        while (pn2 >= nextSmallest) {
+            block(pn2)
+            pn2 -= 1L
+        }
+        currentSmallest = nextSmallest
+    }
+}
+
+/**
+ * Drain [sentPackets] of every entry whose packet number is covered
+ * by [ack]. Returns the drained packets so callers can pass their
+ * tokens to congestion-control / RTT estimation layers (step 5+ of
+ * `quic/plans/2026-05-04-control-frame-retransmit.md`).
+ *
+ * Caller must hold the connection lock.
+ */
+fun drainAckedSentPackets(
+    sentPackets: MutableMap<Long, SentPacket>,
+    ack: AckFrame,
+): List<SentPacket> {
+    val drained = mutableListOf<SentPacket>()
+    forEachAckedPacketNumber(ack) { pn ->
+        sentPackets.remove(pn)?.let { drained += it }
+    }
+    return drained
+}
@@ -0,0 +1,238 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quic.connection.recovery
+
+import com.vitorpamplona.quic.frame.AckFrame
+import com.vitorpamplona.quic.frame.AckRange
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+/**
+ * Step 3 of `quic/plans/2026-05-04-control-frame-retransmit.md`:
+ * `drainAckedSentPackets` removes SentPacket entries for every packet
+ * number covered by an inbound `AckFrame`'s ranges (RFC 9000
+ * §19.3.1). Equivalent in scope to the `remove_acked` test in
+ * neqo's `recovery/mod.rs:1262`, plus a few range-walk edge cases.
+ */
+class AckedPacketsTest {
+    private fun sentPacket(pn: Long): SentPacket =
+        SentPacket(
+            packetNumber = pn,
+            sentAtMillis = 0L,
+            ackEliciting = true,
+            sizeBytes = 64,
+            tokens = listOf(RecoveryToken.MaxStreamsUni(maxStreams = pn * 10)),
+        )
+
+    @Test
+    fun simpleRange_drainsAllAckedPns() {
+        val sent = mutableMapOf<Long, SentPacket>()
+        for (pn in 0L..9L) sent[pn] = sentPacket(pn)
+
+        // ACK [3..7]: largest=7, firstRange=4 → covers 3..7.
+        val ack =
+            AckFrame(
+                largestAcknowledged = 7L,
+                ackDelay = 0L,
+                firstAckRange = 4L,
+            )
+
+        val drained = drainAckedSentPackets(sent, ack)
+        assertEquals(5, drained.size, "5 PNs in [3..7]")
+        assertEquals(setOf(3L, 4L, 5L, 6L, 7L), drained.map { it.packetNumber }.toSet())
+        // Map keeps everything outside the range.
+        assertEquals(setOf(0L, 1L, 2L, 8L, 9L), sent.keys)
+    }
+
+    @Test
+    fun multipleRanges_drainsAllAckedPns() {
+        val sent = mutableMapOf<Long, SentPacket>()
+        for (pn in 0L..20L) sent[pn] = sentPacket(pn)
+
+        // ACK ranges: [18..20] then [10..12] then [0..3].
+        // Encoding (descending):
+        //   firstRange covers [18..20] → largest=20, firstRange=2
+        //   gap before next: previousSmallest=18, nextLargest=12 ⇒ gap=18-12-2=4
+        //   nextLength: 12..10 ⇒ length=2
+        //   gap before next: previousSmallest=10, nextLargest=3 ⇒ gap=10-3-2=5
+        //   nextLength: 3..0 ⇒ length=3
+        val ack =
+            AckFrame(
+                largestAcknowledged = 20L,
+                ackDelay = 0L,
+                firstAckRange = 2L,
+                additionalRanges =
+                    listOf(
+                        AckRange(gap = 4L, ackRangeLength = 2L),
+                        AckRange(gap = 5L, ackRangeLength = 3L),
+                    ),
+            )
+
+        val drained = drainAckedSentPackets(sent, ack)
+        val drainedPns = drained.map { it.packetNumber }.toSet()
+        assertEquals(setOf(18L, 19L, 20L, 10L, 11L, 12L, 0L, 1L, 2L, 3L), drainedPns)
+        // Map keeps everything outside the ranges.
+        assertEquals(setOf(4L, 5L, 6L, 7L, 8L, 9L, 13L, 14L, 15L, 16L, 17L), sent.keys)
+    }
+
+    @Test
+    fun ackForUnsentPn_isNoOp() {
+        val sent = mutableMapOf<Long, SentPacket>()
+        sent[5L] = sentPacket(5L)
+
+        // ACK PN 100 (never sent). drainAckedSentPackets should walk the
+        // range, find no matching key, and leave the map untouched.
+        // RFC 9000 §13.1 says ACK for unsent PN is a connection error —
+        // detecting that is the connection-state machine's job; this
+        // helper just drains, doesn't validate.
+        val ack =
+            AckFrame(
+                largestAcknowledged = 100L,
+                ackDelay = 0L,
+                firstAckRange = 0L,
+            )
+
+        val drained = drainAckedSentPackets(sent, ack)
+        assertEquals(0, drained.size)
+        assertEquals(1, sent.size)
+        assertNotNull(sent[5L])
+    }
+
+    @Test
+    fun emptyMap_returnsEmptyDrain() {
+        val sent = mutableMapOf<Long, SentPacket>()
+        val ack =
+            AckFrame(
+                largestAcknowledged = 5L,
+                ackDelay = 0L,
+                firstAckRange = 5L,
+            )
+        val drained = drainAckedSentPackets(sent, ack)
+        assertTrue(drained.isEmpty())
+    }
+
+    @Test
+    fun singlePacketAck_drainsOne() {
+        val sent = mutableMapOf<Long, SentPacket>()
+        sent[42L] = sentPacket(42L)
+
+        val ack =
+            AckFrame(
+                largestAcknowledged = 42L,
+                ackDelay = 0L,
+                firstAckRange = 0L,
+            )
+
+        val drained = drainAckedSentPackets(sent, ack)
+        assertEquals(1, drained.size)
+        assertEquals(42L, drained.single().packetNumber)
+        assertNull(sent[42L])
+    }
+
+    @Test
+    fun ackBoundary_pn0Inclusive() {
+        // First range [0..2] — must include PN 0 and not under-flow.
+        val sent = mutableMapOf<Long, SentPacket>()
+        for (pn in 0L..2L) sent[pn] = sentPacket(pn)
+
+        val ack =
+            AckFrame(
+                largestAcknowledged = 2L,
+                ackDelay = 0L,
+                firstAckRange = 2L,
+            )
+
+        val drained = drainAckedSentPackets(sent, ack)
+        assertEquals(setOf(0L, 1L, 2L), drained.map { it.packetNumber }.toSet())
+        assertTrue(sent.isEmpty())
+    }
+
+    @Test
+    fun forEachAckedPacketNumber_iteratesDescending() {
+        val ack =
+            AckFrame(
+                largestAcknowledged = 5L,
+                ackDelay = 0L,
+                firstAckRange = 2L,
+            )
+        val pns = mutableListOf<Long>()
+        forEachAckedPacketNumber(ack) { pns += it }
+        // First range is [3..5]; iteration order is descending.
+        assertEquals(listOf(5L, 4L, 3L), pns)
+    }
+
+    @Test
+    fun forEachAckedPacketNumber_acrossMultipleRanges_descending() {
+        // ACK [18..20] then [10..12] then [0..3] (same as multipleRanges_).
+        val ack =
+            AckFrame(
+                largestAcknowledged = 20L,
+                ackDelay = 0L,
+                firstAckRange = 2L,
+                additionalRanges =
+                    listOf(
+                        AckRange(gap = 4L, ackRangeLength = 2L),
+                        AckRange(gap = 5L, ackRangeLength = 3L),
+                    ),
+            )
+        val pns = mutableListOf<Long>()
+        forEachAckedPacketNumber(ack) { pns += it }
+        assertEquals(
+            listOf(20L, 19L, 18L, 12L, 11L, 10L, 3L, 2L, 1L, 0L),
+            pns,
+        )
+    }
+
+    @Test
+    fun returnedDrain_preservesTokens() {
+        val sent = mutableMapOf<Long, SentPacket>()
+        sent[7L] =
+            SentPacket(
+                packetNumber = 7L,
+                sentAtMillis = 1_000L,
+                ackEliciting = true,
+                sizeBytes = 100,
+                tokens =
+                    listOf(
+                        RecoveryToken.MaxStreamsUni(maxStreams = 200L),
+                        RecoveryToken.MaxData(maxData = 1_000_000L),
+                    ),
+            )
+
+        val ack =
+            AckFrame(
+                largestAcknowledged = 7L,
+                ackDelay = 0L,
+                firstAckRange = 0L,
+            )
+        val drained = drainAckedSentPackets(sent, ack)
+
+        assertEquals(1, drained.size)
+        val sp = drained.single()
+        assertEquals(7L, sp.packetNumber)
+        assertEquals(2, sp.tokens.size)
+        assertEquals(RecoveryToken.MaxStreamsUni(200L), sp.tokens[0])
+        assertEquals(RecoveryToken.MaxData(1_000_000L), sp.tokens[1])
+    }
+}