feat: full-route capture, MTU 9000 fix (reverse-engineered from AdGuard) (#145)#195
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feat: full-route capture, MTU 9000 fix (reverse-engineered from AdGuard) (#145)#195nqmgaming wants to merge 10 commits into
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Restores the Full network protection toggle (default OFF) and fixes the TCP connection resets / broken messaging via two research-grounded changes: 1. MTU 9000 (from AdGuard reverse-engineering). AdGuard sets its TUN MTU to 9000 (smali D0/b$a: const/16 v0, 0x2328). A 1500 MTU through a userspace gVisor forwarder causes TCP resets; a large MTU lets the stack handle egress segmentation itself. Engine.SetTunMTU() sets the stack endpoint MTU to match VpnService.Builder.setMtu(9000); both are applied only in full-route mode. 2. Build the engine with Go 1.23.5 (matches CI) instead of 1.26 — gVisor is version-sensitive and a too-new toolchain can miscompile the netstack, which likely contributed to the resets. QUIC is intentionally NOT dropped: device evidence showed QUIC forwarding worked (web ran over QUIC); only the TCP relay was broken, which MTU fixes. DNS-only (default) / HTTPS-filtering / WireGuard paths unaffected. tunnel.aar rebuilt with Go 1.23.5 (stripped, 18.4MB — matches CI size). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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📝 WalkthroughWalkthroughAdds a "Full network protection" toggle: preference storage and snapshot APIs, VPN service routing and bypass changes for DNS-only mode, GoTunnelAdapter startup flag and MTU constant, UI toggles in Home/Settings, TCP/UDP handler observability, and localized strings across locales. ChangesFull Route Capture Feature
Sequence Diagram(s)sequenceDiagram
participant AppPrefs as AppPreferences
participant VpnService as AdBlockVpnService
participant GoAdapter as GoTunnelAdapter
participant Engine as Tunnel Engine
AppPrefs->>VpnService: getFullRouteCaptureSnapshot()
VpnService->>GoAdapter: start(vpnInterface, ..., forwardAllTraffic)
GoAdapter->>Engine: enable userspace TCP stack / DirectOutbound (if forwardAllTraffic && !httpsFiltering)
GoAdapter->>Engine: set tun MTU (FULL_ROUTE_MTU) when applicable
Estimated code review effort🎯 4 (Complex) | ⏱️ ~45 minutes Possibly related PRs
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✅ Passed checks (4 passed)
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MTU 9000 stopped the TCP resets but large packets then hung — the fd-based Android TUN read/write path doesn't carry jumbo frames. Keep MTU 1500. The TCP resets seen earlier were from building the engine with Go 1.26; the aar in this branch is built with Go 1.23.5 (matching CI), which is the actual reset fix. SetTunMTU plumbing kept but unused. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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⚠️ Outside diff range comments (1)
app/src/main/java/app/pwhs/blockads/service/GoTunnelAdapter.kt (1)
470-473: 🛠️ Refactor suggestion | 🟠 Major | ⚡ Quick winRemove unused
FULL_ROUTE_MTUconstant or correct its misleading documentation.The
FULL_ROUTE_MTU = 9000constant is defined but never used in the codebase (confirmed by AI summary). Additionally, its documentation contradicts the evidence from the PR objectives and AdBlockVpnService implementation:
- The doc comment claims 9000 "avoids the TCP resets seen with a 1500 MTU userspace forwarder"
- However, PR objectives state that MTU 9000 was tested and caused hangs, leading to a revert back to 1500
- AdBlockVpnService hardcodes MTU to 1500 with a comment: "Jumbo MTU (9000) made large packets hang because the fd-based Android TUN read/write path doesn't carry jumbo frames"
- PR objectives clarify the actual fix for TCP resets was rebuilding with Go 1.23.5, not the MTU change
This creates confusion for future maintainers about the correct MTU configuration.
🧹 Recommended fix
Option 1 (preferred): Remove the unused constant entirely
- companion object { - /** TUN/stack MTU for full-route capture (matches AdGuard's 9000). - * Large MTU lets the gVisor stack handle egress segmentation and - * avoids the TCP resets seen with a 1500 MTU userspace forwarder. */ - const val FULL_ROUTE_MTU = 9000 - + companion object { /** * Convert DNS query type number to human-readable string.Option 2: Update documentation to reflect reality if the constant serves as historical reference
- /** TUN/stack MTU for full-route capture (matches AdGuard's 9000). - * Large MTU lets the gVisor stack handle egress segmentation and - * avoids the TCP resets seen with a 1500 MTU userspace forwarder. */ + /** Historical note: MTU 9000 was tested (reverse-engineered from AdGuard) + * to avoid TCP resets in userspace forwarding, but caused packet hangs + * on Android's fd-based TUN read/write path. Reverted to 1500. + * Actual fix: rebuilding engine with Go 1.23.5. NOT USED. */ const val FULL_ROUTE_MTU = 9000🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@app/src/main/java/app/pwhs/blockads/service/GoTunnelAdapter.kt` around lines 470 - 473, Remove the unused FULL_ROUTE_MTU constant (const val FULL_ROUTE_MTU = 9000) from GoTunnelAdapter.kt to avoid stale configuration and contradictory docs; if you prefer to keep a historical reference, update its KDoc to state that jumbo MTU 9000 was tested and caused hangs on Android TUN (AdBlockVpnService uses MTU 1500) and note the actual fix was rebuilding with Go 1.23.5—ensure the symbol FULL_ROUTE_MTU is not referenced elsewhere before removal.
🧹 Nitpick comments (2)
app/src/main/java/app/pwhs/blockads/service/GoTunnelAdapter.kt (2)
278-279: 💤 Low valueConsider clarifying MTU comment location.
The comment "MTU stays 1500 (jumbo hung on the fd-based Android TUN)" is accurate but could be clearer. The TUN MTU is actually set in
AdBlockVpnService.establishVpn()viaBuilder.setMtu(1500), not in this method. Consider rephrasing to avoid implying this code sets the MTU.✨ Suggested clarification
- // MTU stays 1500 (jumbo hung on the fd-based Android TUN). + // Note: TUN MTU is 1500 (set in AdBlockVpnService); jumbo MTU + // (9000) hung on the fd-based Android TUN read/write path. Timber.d("Full-route capture: TCP stack + DirectOutbound enabled (MTU 1500)")🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@app/src/main/java/app/pwhs/blockads/service/GoTunnelAdapter.kt` around lines 278 - 279, The inline comment in GoTunnelAdapter.kt (near the Timber.d call in the method logging "Full-route capture: TCP stack + DirectOutbound enabled") incorrectly implies this method sets the TUN MTU; change the comment to clarify the MTU is set in AdBlockVpnService.establishVpn() via Builder.setMtu(1500) (e.g., "MTU remains 1500 — configured in AdBlockVpnService.establishVpn() via Builder.setMtu(1500), not here") so it doesn't suggest this method performs the MTU configuration.
243-252: ⚡ Quick winDocument the new
forwardAllTrafficparameter.The function doc comment is missing documentation for the new
forwardAllTrafficparameter added at line 259, as well as the existingsocketProtectorparameter at line 260. Public API methods should document all parameters.📝 Suggested parameter documentation
/** * Start the Go tunnel engine. * This method blocks the calling thread until [stop] is called. * * `@param` vpnInterface The TUN file descriptor from VpnService * `@param` wgConfigJson Optional WireGuard config JSON * `@param` httpsFilteringEnabled True if MITM proxy should be started * `@param` selectedBrowsers Set of package names allowed for MITM * `@param` certDir Directory to store the proxy's root CA certificate + * `@param` forwardAllTraffic True to route all traffic through the VPN (full network protection) + * `@param` socketProtector Callback to protect sockets from VPN routing loops */🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@app/src/main/java/app/pwhs/blockads/service/GoTunnelAdapter.kt` around lines 243 - 252, The KDoc for the Start the Go tunnel engine method is missing entries for the new parameters forwardAllTraffic and socketProtector; update the comment block above the start method in GoTunnelAdapter.kt to add `@param` lines describing forwardAllTraffic (boolean flag to forward all device traffic through the tunnel) and socketProtector (the SocketProtector instance used to protect sockets from VPN routing), and ensure the descriptions match the existing style and tense used for vpnInterface, wgConfigJson, httpsFilteringEnabled, selectedBrowsers, and certDir.
🤖 Prompt for all review comments with AI agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
Outside diff comments:
In `@app/src/main/java/app/pwhs/blockads/service/GoTunnelAdapter.kt`:
- Around line 470-473: Remove the unused FULL_ROUTE_MTU constant (const val
FULL_ROUTE_MTU = 9000) from GoTunnelAdapter.kt to avoid stale configuration and
contradictory docs; if you prefer to keep a historical reference, update its
KDoc to state that jumbo MTU 9000 was tested and caused hangs on Android TUN
(AdBlockVpnService uses MTU 1500) and note the actual fix was rebuilding with Go
1.23.5—ensure the symbol FULL_ROUTE_MTU is not referenced elsewhere before
removal.
---
Nitpick comments:
In `@app/src/main/java/app/pwhs/blockads/service/GoTunnelAdapter.kt`:
- Around line 278-279: The inline comment in GoTunnelAdapter.kt (near the
Timber.d call in the method logging "Full-route capture: TCP stack +
DirectOutbound enabled") incorrectly implies this method sets the TUN MTU;
change the comment to clarify the MTU is set in AdBlockVpnService.establishVpn()
via Builder.setMtu(1500) (e.g., "MTU remains 1500 — configured in
AdBlockVpnService.establishVpn() via Builder.setMtu(1500), not here") so it
doesn't suggest this method performs the MTU configuration.
- Around line 243-252: The KDoc for the Start the Go tunnel engine method is
missing entries for the new parameters forwardAllTraffic and socketProtector;
update the comment block above the start method in GoTunnelAdapter.kt to add
`@param` lines describing forwardAllTraffic (boolean flag to forward all device
traffic through the tunnel) and socketProtector (the SocketProtector instance
used to protect sockets from VPN routing), and ensure the descriptions match the
existing style and tense used for vpnInterface, wgConfigJson,
httpsFilteringEnabled, selectedBrowsers, and certDir.
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📒 Files selected for processing (2)
app/src/main/java/app/pwhs/blockads/service/AdBlockVpnService.ktapp/src/main/java/app/pwhs/blockads/service/GoTunnelAdapter.kt
🚧 Files skipped from review as they are similar to previous changes (1)
- app/src/main/java/app/pwhs/blockads/service/AdBlockVpnService.kt
Instrument newProtectedTcpHandler/newProtectedUdpHandler + bidiCopyFlow to log per-flow: DIAL attempt, CONNECTED/FAILED, and on completion the bytes relayed each direction + errors. Engine logs go to os.Stderr → logcat tag GoLog. Lets us see exactly where full-route web flows stall (dial fail vs no upstream bytes vs no downstream bytes) instead of guessing. Built with Go 1.23.5. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
gomobile does not redirect Go's os.Stderr to logcat, so all engine logs (DnsInterceptor, TcpStack relay, dial results) were invisible — which is why full-route debugging was blind. Add tunnel.Logger interface + Tunnel.SetLogger(); GoTunnelAdapter registers one that forwards to Timber under tag GoEngine. logf() now uses it (atomic.Pointer, race-free) and falls back to stderr. Built with Go 1.23.5. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Actionable comments posted: 1
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⚠️ Outside diff range comments (1)
tunnel/tcp_stack_handlers.go (1)
107-109:⚠️ Potential issue | 🟠 MajorFail the dial path when VpnService.protect() returns false
In
tunnel/tcp_stack_handlers.go(protectedControl, lines 107-109),protectFn(int(fd))is called but itsboolresult is ignored, so afalse(protect failure) won’t abort the outbound dial and can break the “don’t route back into the VPN” contract.Suggested fix
func protectedControl(protectFn func(fd int) bool) func(network, address string, c syscall.RawConn) error { if protectFn == nil { return nil } return func(network, address string, c syscall.RawConn) error { - return c.Control(func(fd uintptr) { - protectFn(int(fd)) - }) + var protectErr error + if err := c.Control(func(fd uintptr) { + if ok := protectFn(int(fd)); !ok { + protectErr = fmt.Errorf("protect failed for fd=%d", fd) + } + }); err != nil { + return err + } + return protectErr } }Also check
tunnel/resolver.go(protectedDialer) because it appears to calld.protectFn(int(fd))without using the returnedbool.🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@tunnel/tcp_stack_handlers.go` around lines 107 - 109, The VPN protect call's boolean return is ignored causing failed protects to be treated as success; update protectedControl (the c.Control(...) callback that calls protectFn(int(fd))) to check the bool result and, if false, cause the dial path to fail by returning an error (propagate an appropriate error from the Control callback) so the outbound connection is aborted; likewise update protectedDialer to inspect the bool return from d.protectFn(int(fd)) and return a dial error when it returns false instead of proceeding. Ensure you reference the same protectFn, protectedControl and protectedDialer code paths and propagate a clear error back to the caller so failed protects abort the dial.
🤖 Prompt for all review comments with AI agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
Inline comments:
In `@tunnel/tcp_stack_handlers.go`:
- Around line 45-60: Wrap the per-connection verbose log calls in
tcp_stack_handlers.go (the logf calls around the dial/connect/relay and the
completion log that references uid, flow.appIP, dst, up/down/errUp/errDown)
behind a runtime debug/diagnostic flag (or a build-time debug check) so they are
disabled by default; update the handler that calls dialer.Dial and bidiCopyFlow
to conditionally invoke logf only when debugEnabled (or similar) is true, and
apply the same conditional guard to the other verbose log lines referenced
(lines 91-94) to prevent emitting per-flow metadata in production.
---
Outside diff comments:
In `@tunnel/tcp_stack_handlers.go`:
- Around line 107-109: The VPN protect call's boolean return is ignored causing
failed protects to be treated as success; update protectedControl (the
c.Control(...) callback that calls protectFn(int(fd))) to check the bool result
and, if false, cause the dial path to fail by returning an error (propagate an
appropriate error from the Control callback) so the outbound connection is
aborted; likewise update protectedDialer to inspect the bool return from
d.protectFn(int(fd)) and return a dial error when it returns false instead of
proceeding. Ensure you reference the same protectFn, protectedControl and
protectedDialer code paths and propagate a clear error back to the caller so
failed protects abort the dial.
🪄 Autofix (Beta)
Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
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📒 Files selected for processing (2)
app/libs/tunnel.aartunnel/tcp_stack_handlers.go
Comment on lines
+45
to
+60
| logf("[TcpStack] TCP uid=%d %s → %s DIAL...", uid, flow.appIP, dst) | ||
| remote, err := dialer.Dial("tcp", dst) | ||
| if err != nil { | ||
| logf("[TcpStack] TCP uid=%d dial %s: %v", uid, dst, err) | ||
| logf("[TcpStack] TCP uid=%d dial %s FAILED: %v", uid, dst, err) | ||
| return | ||
| } | ||
| defer remote.Close() | ||
|
|
||
| logf("[TcpStack] TCP uid=%d %s ↔ %s", uid, flow.appIP, dst) | ||
| logf("[TcpStack] TCP uid=%d %s ↔ %s CONNECTED, relaying", uid, flow.appIP, dst) | ||
|
|
||
| // Idle deadline on both sides so a stalled flow can't hold | ||
| // stack goroutines forever. | ||
| // No absolute deadline — rely on tun2socks' TCP keepalive | ||
| // (60s idle / 30s interval / 9 probes) to clean up stuck | ||
| // connections. Hard deadlines killed long-lived streams. | ||
| bidiCopyFlow(conn, remote) | ||
| // No absolute deadline — rely on tun2socks' TCP keepalive to | ||
| // clean up stuck connections. Hard deadlines killed long-lived | ||
| // streams. | ||
| up, down, errUp, errDown := bidiCopyFlow(conn, remote) | ||
| logf("[TcpStack] TCP uid=%d %s ↔ %s DONE up=%d down=%d errUp=%v errDown=%v", | ||
| uid, flow.appIP, dst, up, down, errUp, errDown) |
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Gate per-flow relay diagnostics behind debug/diagnostic mode.
These logs include per-connection metadata (uid, app IP, destination, byte counts, errors) for every flow. In production this is a privacy and telemetry-volume risk. Please guard these logs behind a runtime debug flag (or build-type check) and keep current verbosity disabled by default.
Also applies to: 91-94
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
In `@tunnel/tcp_stack_handlers.go` around lines 45 - 60, Wrap the per-connection
verbose log calls in tcp_stack_handlers.go (the logf calls around the
dial/connect/relay and the completion log that references uid, flow.appIP, dst,
up/down/errUp/errDown) behind a runtime debug/diagnostic flag (or a build-time
debug check) so they are disabled by default; update the handler that calls
dialer.Dial and bidiCopyFlow to conditionally invoke logf only when debugEnabled
(or similar) is true, and apply the same conditional guard to the other verbose
log lines referenced (lines 91-94) to prevent emitting per-flow metadata in
production.
If VpnService.protect() returns false the outbound socket loops back into the TUN and connect() times out (the Telegram 'dial i/o timeout' symptom). Log the failure so we can tell a routing loop apart from a genuinely unreachable destination. Go 1.23.5 build. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Decisive log evidence: in full-route the stack relayed IPv4 TCP fine (Telegram 91.108.56.146:443 up=402 down=3149) but a session with many IPv6 packets ended 'tcp=0 flows handled' — the gVisor stack doesn't handle IPv6 here, so apps that try IPv6 first (happy-eyeballs) stalled (web/Telegram appeared broken). Route only 0.0.0.0/0 in full-route, not ::/0. IPv6 DNS is still intercepted (port 53 → fd00::1) so domain/ad blocking still applies to IPv6; only IPv6 data flows bypass the tunnel (use the physical network), which keeps connectivity working. Kotlin-only change; aar unchanged. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Removing only the ::/0 route wasn't enough — the TUN still had the fd00::2 IPv6 address, so Android kept pushing IPv6 packets into the gVisor stack (logs: version=6 packets) which can't handle them, stalling apps on happy-eyeballs IPv6. Add the fd00 IPv6 address/route/DNS ONLY when NOT full-route. Full-route is now fully IPv4: apps use IPv4 (stack relays it correctly), IPv6 uses the physical network, DNS still goes through the IPv4 fake server so blocking stays active. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
No successful DNS resolution appeared in full-route logs (only BLOCKED entries) and no web TCP flows — suggests upstream DNS resolution is failing/looping in full-route. Log each Resolve: OK with byte count, or PRIMARY/FALLBACK FAILED with the error, so we can see whether it's a DoH-bootstrap loop (net.LookupHost) or a plain-UDP timeout. Go 1.23.5. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Logs proved DNS + TCP connect work in full-route, but pages loaded only partially with size=1500 packets — a PMTU blackhole: full-size segments dropped en route. Set the TUN + stack MTU to 1280 (IPv6 minimum) so the gVisor stack advertises a small TCP MSS and segments fit through any path. 1500=partial loads, 9000=hang, 1280=safe middle. Engine SetTunMTU already in the aar; Kotlin-only change. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Research-grounded fix (not guesswork)
Reverse-engineered AdGuard's decompiled APK to find why its userspace full-tunnel forwards reliably while ours reset TCP:
smali/D0/b$a.smali:const/16 v0, 0x2328). A 1500 MTU through a userspace gVisor forwarder causes TCP connection resets; a large MTU lets the stack segment on egress. →Engine.SetTunMTU()+VpnService.Builder.setMtu(9000), applied only in full-route mode.Why not drop QUIC
Device evidence showed QUIC forwarding worked (web ran over QUIC); only the TCP relay was broken — which the MTU fix targets. So QUIC is left intact (the previous QUIC-drop attempt #194 was the wrong direction and is closed).
Scope
tunnel.aarrebuilt with Go 1.23.5 (18.4 MB, matches CI).Test (decisive)
Build/lint pass. On device, turn Full network protection ON:
Not auto-merging until confirmed. If TCP still resets, next step is MSS clamping + capturing
[TcpStack]logs.🤖 Generated with Claude Code
Summary by CodeRabbit
New Features
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