feat(quic): wire Retry packet handling (RFC 9000 §17.2.5 + RFC 9001 §5.8)
The Retry parser + integrity-tag verifier already existed in RetryPacket.kt, but feedDatagram dropped Retry packets on the floor. Hook them up: - QuicConnectionParser.feedLongHeaderPacket detects RETRY type before the standard parse-and-decrypt path, parses via RetryPacket, and dispatches to QuicConnection.applyRetry. - QuicConnection.start() now caches the ClientHello bytes (TLS only emits ClientHello once; we need to re-queue the same bytes on the fresh Initial keys after Retry). New applyRetry method: verifies the integrity tag, swaps DCID to Retry's SCID, re-derives Initial keys, resets the Initial PN space + sentPackets + cryptoSend, re-enqueues the cached ClientHello, stores the Retry token, and latches retryConsumed so a second Retry is dropped. - LevelState.restoreFromRetry / PacketNumberSpaceState.resetForRetry give applyRetry an in-place reset (the level reference is a `val`, so we mirror discardKeys' field-reset pattern). - QuicConnectionWriter.buildLongHeaderFromFrames threads conn.retryToken through the Initial header's Token field on every Initial we emit after Retry. Per RFC 9001 §5.8, a Retry with a bad integrity tag is silently dropped; per RFC 9000 §17.2.5.2, only one Retry is honored per connection. Both invariants are tested. New test: RetryHandlingTest covers the happy path (DCID swap, PN reset, token threading, ClientHello replay, ≥1200-byte padding), the bad-tag path, and the second-retry path.
This commit is contained in:
Claude
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/*
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* Copyright (c) 2025 Vitor Pamplona
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of
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* this software and associated documentation files (the "Software"), to deal in
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* the Software without restriction, including without limitation the rights to use,
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* copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
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* Software, and to permit persons to whom the Software is furnished to do so,
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* subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
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* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
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* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
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* AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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package com.vitorpamplona.quic.connection
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import com.vitorpamplona.quic.QuicReader
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import com.vitorpamplona.quic.QuicWriter
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import com.vitorpamplona.quic.packet.LongHeaderPacket
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import com.vitorpamplona.quic.packet.LongHeaderType
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import com.vitorpamplona.quic.packet.QuicVersion
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import com.vitorpamplona.quic.packet.RetryPacket
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import com.vitorpamplona.quic.tls.PermissiveCertificateValidator
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import kotlin.test.Test
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import kotlin.test.assertContentEquals
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import kotlin.test.assertEquals
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import kotlin.test.assertFalse
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import kotlin.test.assertNotEquals
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import kotlin.test.assertNotNull
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import kotlin.test.assertNull
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import kotlin.test.assertTrue
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/**
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* Retry packet handling end-to-end through [QuicConnection], per RFC 9000
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* §17.2.5 (semantics) + RFC 9001 §5.8 (integrity tag).
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*
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* Synthesizes valid-and-invalid Retry packets, feeds them through
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* [feedDatagram], and asserts the resulting connection state:
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*
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* 1. Happy path: DCID swaps, retryToken stored, Initial PN reset to 0,
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* next outbound Initial carries the token in its header, contains the
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* ClientHello CRYPTO, and the datagram is padded to ≥ 1200 bytes.
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* 2. Bad-tag path: corrupting the integrity tag must be silently dropped;
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* no state advances.
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* 3. Second-Retry path: a second valid Retry after a first one is dropped
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* (RFC 9000 §17.2.5.2 — at most one Retry per connection).
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*/
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class RetryHandlingTest {
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private fun newClient(): QuicConnection =
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QuicConnection(
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serverName = "example.test",
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config = QuicConnectionConfig(),
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tlsCertificateValidator = PermissiveCertificateValidator(),
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)
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/**
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* Build the on-wire bytes of a valid Retry packet for [client], with the
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* given [retryScid] and [retryToken]. Computes the integrity tag using
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* the client's [QuicConnection.originalDestinationConnectionId] so the
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* client's [RetryPacket.verifyIntegrityTag] check passes.
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*
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* The Retry packet's DCID is the client's source CID (servers echo it
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* even though it's unused — RFC 9000 §17.2.5.1). The high 4 bits of
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* the first byte are 1100 (long header + RETRY type); the low 4 bits
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* are unused — we set them to 0.
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*/
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private fun buildRetry(
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client: QuicConnection,
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retryScid: ConnectionId,
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retryToken: ByteArray,
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): ByteArray {
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val w = QuicWriter()
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// Header form (1) | fixed bit (1) | long packet type RETRY (11) | unused (0000)
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w.writeByte(0xC0 or (LongHeaderType.RETRY.code shl 4))
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w.writeUint32(QuicVersion.V1)
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w.writeByte(client.sourceConnectionId.length)
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w.writeBytes(client.sourceConnectionId.bytes)
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w.writeByte(retryScid.length)
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w.writeBytes(retryScid.bytes)
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w.writeBytes(retryToken)
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val withoutTag = w.toByteArray()
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val tag =
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RetryPacket.computeIntegrityTag(
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retryPacketWithoutTag = withoutTag,
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originalDestinationConnectionId = client.originalDestinationConnectionId.bytes,
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)
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return withoutTag + tag
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}
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/**
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* Pull the Initial packet's Token field out of an on-wire datagram so
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* we can assert on it. [LongHeaderPacket.parseAndDecrypt] decrypts the
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* payload but doesn't surface the unprotected Token; we re-walk the
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* header here to extract it without crypto.
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*/
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private fun extractInitialToken(datagram: ByteArray): ByteArray {
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val r = QuicReader(datagram, 0)
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val first = r.readByte()
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require((first and 0x80) != 0) { "expected long header" }
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val type = (first ushr 4) and 0x03
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require(type == LongHeaderType.INITIAL.code) { "expected INITIAL, got type=$type" }
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r.readUint32() // version
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val dcidLen = r.readByte()
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r.readBytes(dcidLen)
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val scidLen = r.readByte()
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r.readBytes(scidLen)
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val tokenLen = r.readVarint().toInt()
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return r.readBytes(tokenLen)
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}
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@Test
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fun valid_retry_swaps_dcid_resets_pn_and_threads_token_into_next_initial() {
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val client = newClient()
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val originalDcid = client.originalDestinationConnectionId.bytes.copyOf()
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client.start()
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// Drain the initial datagram (carries ClientHello at PN=0 with empty
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// token field) so we can assert the pre-Retry state.
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val firstDatagram = drainOutbound(client, nowMillis = 0L)
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assertNotNull(firstDatagram, "client.start() should produce an Initial datagram")
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assertEquals(0, extractInitialToken(firstDatagram).size, "pre-Retry Initial must have empty token")
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// Server picks a fresh source connection id and a token of its choice.
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val retryScid = ConnectionId(byteArrayOf(0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x78))
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val retryToken = "server-issued-retry-token".encodeToByteArray()
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val retryDatagram = buildRetry(client, retryScid, retryToken)
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feedDatagram(client, retryDatagram, nowMillis = 1L)
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// DCID is now the Retry's SCID, originalDcid is unchanged.
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assertContentEquals(retryScid.bytes, client.destinationConnectionId.bytes)
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assertContentEquals(originalDcid, client.originalDestinationConnectionId.bytes)
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assertNotEquals(originalDcid.toList(), retryScid.bytes.toList())
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// Retry token captured.
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assertContentEquals(retryToken, client.retryToken)
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assertTrue(client.retryConsumed)
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// Initial PN space reset — next allocation is 0 again.
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assertEquals(0L, client.initial.pnSpace.nextPacketNumber)
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assertEquals(-1L, client.initial.pnSpace.largestReceived)
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// Next drain produces the retried Initial: token in header, ClientHello
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// CRYPTO inside, datagram padded to ≥ 1200 (RFC 9000 §14.1).
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val secondDatagram = drainOutbound(client, nowMillis = 2L)
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assertNotNull(secondDatagram, "post-Retry drain must produce another Initial")
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assertContentEquals(retryToken, extractInitialToken(secondDatagram))
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assertTrue(
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secondDatagram.size >= 1200,
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"retried Initial datagram must be padded to >= 1200 bytes (was ${secondDatagram.size})",
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)
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// The Initial is encrypted under the new keys derived from the retryScid
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// DCID. Decrypt + verify it carries CRYPTO with the captured ClientHello
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// bytes (== the prefix of the original ClientHello — drained ALL the
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// bytes from cryptoSend on Retry replay).
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val newSecrets =
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com.vitorpamplona.quic.crypto.InitialSecrets
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.derive(retryScid.bytes)
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val proto = client.initial.sendProtection!!
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val parsed =
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LongHeaderPacket.parseAndDecrypt(
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bytes = secondDatagram,
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offset = 0,
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aead = proto.aead,
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key = newSecrets.clientKey,
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iv = newSecrets.clientIv,
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hp =
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com.vitorpamplona.quic.crypto.AesEcbHeaderProtection(
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com.vitorpamplona.quic.crypto.PlatformAesOneBlock,
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),
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hpKey = newSecrets.clientHp,
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largestReceivedInSpace = -1L,
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)
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assertNotNull(parsed, "retried Initial must decrypt under keys derived from new DCID")
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assertEquals(0L, parsed.packet.packetNumber, "retried Initial PN must be 0 (RFC 9000 §17.2.5.2)")
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// Decoded payload starts with at least one CRYPTO frame (frame type 0x06).
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val frames =
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com.vitorpamplona.quic.frame
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.decodeFrames(parsed.packet.payload)
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val cryptoFrames = frames.filterIsInstance<com.vitorpamplona.quic.frame.CryptoFrame>()
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assertTrue(cryptoFrames.isNotEmpty(), "retried Initial payload must contain CRYPTO frames (the ClientHello)")
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assertEquals(0L, cryptoFrames.first().offset, "CRYPTO must restart at offset 0 on the new keys")
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}
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@Test
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fun retry_with_corrupted_integrity_tag_is_silently_dropped() {
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val client = newClient()
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val originalDcid = client.destinationConnectionId.bytes.copyOf()
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client.start()
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// Drain pre-Retry datagram so the test mirrors a realistic ordering.
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drainOutbound(client, nowMillis = 0L)
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val retryScid = ConnectionId(byteArrayOf(0xAA.toByte(), 0xBB.toByte(), 0xCC.toByte(), 0xDD.toByte()))
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val good = buildRetry(client, retryScid, "tk".encodeToByteArray())
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// Flip a bit in the last byte — the integrity tag.
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val corrupted = good.copyOf()
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corrupted[corrupted.size - 1] = (corrupted[corrupted.size - 1].toInt() xor 0x01).toByte()
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feedDatagram(client, corrupted, nowMillis = 1L)
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// No state advanced.
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assertNull(client.retryToken)
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assertFalse(client.retryConsumed)
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assertContentEquals(originalDcid, client.destinationConnectionId.bytes)
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}
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@Test
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fun second_valid_retry_after_one_is_consumed_is_dropped() {
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val client = newClient()
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client.start()
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drainOutbound(client, nowMillis = 0L)
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val firstScid = ConnectionId(byteArrayOf(0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08))
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val firstToken = "first".encodeToByteArray()
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feedDatagram(client, buildRetry(client, firstScid, firstToken), nowMillis = 1L)
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// Sanity: first applied.
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assertTrue(client.retryConsumed)
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assertContentEquals(firstToken, client.retryToken)
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assertContentEquals(firstScid.bytes, client.destinationConnectionId.bytes)
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// Build a second VALID Retry. The integrity tag is computed against
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// [originalDestinationConnectionId] (still the very first random one,
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// unchanged), so this packet's tag genuinely verifies.
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val secondScid = ConnectionId(byteArrayOf(0x99.toByte(), 0x88.toByte(), 0x77.toByte(), 0x66.toByte()))
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val secondToken = "second-should-be-ignored".encodeToByteArray()
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val secondRetry = buildRetry(client, secondScid, secondToken)
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// Confirm the integrity tag really would verify in isolation —
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// otherwise this test would conflate "bad tag" with "second retry".
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val parsedSecond = RetryPacket.parse(secondRetry)
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assertNotNull(parsedSecond)
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assertTrue(
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parsedSecond.verifyIntegrityTag(secondRetry, client.originalDestinationConnectionId.bytes),
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"second retry's tag must be valid in isolation; otherwise this test is meaningless",
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)
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feedDatagram(client, secondRetry, nowMillis = 2L)
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// State unchanged from after the first retry.
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assertContentEquals(firstToken, client.retryToken)
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assertContentEquals(firstScid.bytes, client.destinationConnectionId.bytes)
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}
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}
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