Firo I2P support

[reubenyap]

PR intention

This PR adds I2P (Invisible Internet Project) support to Firo, allowing nodes to connect to and accept connections from I2P peers via a SAM (Simple Anonymous Messaging) proxy. This enhances network privacy and censorship resistance for Firo users.

Code changes brief

• New Files (src/i2p.h, src/i2p.cpp): Implement I2P SAM 3.1 protocol for session management, including private key handling, destination generation, and socket communication with the SAM proxy.
• Network Integration (src/netbase.cpp, src/net.h, src/net.cpp): Introduce NET_I2P for address recognition, integrate i2p::sam::Session into CConnman, and modify ConnectNode to handle I2P connections.
• Configuration (src/init.cpp): Add -i2psam=<ip:port> and -i2pacceptincoming options, along with initialization logic for the I2P SAM session.
• Unit Tests (src/test/i2p_tests.cpp): Provide tests for I2P address parsing, network type identification, and ADDRv2 serialization.
• Build System (CMakeLists.txt): Update build configurations to include new I2P source and test files.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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[coderabbitai]

Walkthrough

Adds native I2P (SAM v3.1) support: new i2p header/implementation, SAM session and key management, wiring into init and CConnman for outgoing/incoming I2P connections, new network type handling, and tests + build entries for I2P.

Changes

Cohort / File(s)	Summary
I2P Core Implementation src/i2p.h, src/i2p.cpp	New i2p::sam::Session and helpers: Base64/base32 utilities, destination derivation, SAM request/response parsing, session lifecycle (create/listen/accept/connect/disconnect), private key generation/storage, safe SAM-value checks, and robust socket I/O with timeouts.
Connman & Init Integration src/net.h, src/net.cpp, src/init.cpp	Adds CConnman::m_i2p_sam_session, InitI2P, CLI options -i2psam and -i2pacceptincoming, routes I2P connects via SAM, starts ThreadI2PAcceptIncoming for inbound I2P peers, and integrates incoming I2P peers into node/dandelion flows.
Network Types & Addressing src/netbase.cpp, src/netaddress.cpp	Adds NET_I2P parsing/name mapping, updates GetNetworkName, and adjusts .b32.i2p decoding (padding before base32 decode) and routability checks.
Build & Tests src/CMakeLists.txt, src/test/CMakeLists.txt, src/test/i2p_tests.cpp	Adds i2p.cpp to build and i2p_tests.cpp to tests; new Boost.Test cases covering I2P address parsing, serialization, reachability, and CService behavior.

Sequence Diagram(s)

sequenceDiagram
    participant App as Application (init)
    participant Conn as CConnman
    participant SAM as i2p::sam::Session
    participant Proxy as SAM Proxy
    participant Peer as I2P Peer

    App->>Conn: Start with -i2psam / InitI2P(...)
    Conn->>SAM: Construct Session(control_host[, keyfile])
    Conn->>SAM: CreateIfNotCreatedAlready()
    SAM->>Proxy: HELLO (open control connection)
    Proxy-->>SAM: Reply (OK / session id)
    SAM->>Proxy: DEST GENERATE / IMPORT (key handling)
    Proxy-->>SAM: DESTINATION (public/private)
    Conn->>SAM: Connect(i2p_peer_address)
    SAM->>Proxy: STREAM CONNECT dest=...
    Proxy-->>SAM: RESULT=OK + stream/socket
    SAM-->>Conn: Return connected socket
    Conn->>Peer: Exchange data via I2P tunnel

Loading

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related issues

• [Feature] Add native I2P support #1641 — Requests native I2P support; this PR implements a SAM client and integration addressing that request.

Possibly related PRs

• bip155 torv3 #1733 — Overlapping I2P/addressing and network-layer integration changes.

Suggested reviewers

• levonpetrosyan93
• firstcryptoman
• psolstice

Poem

"🐇 I nibble keys beneath the moonlit code,
Tunnels stitch softly where new sessions grow,
Packets hop along a secret, starlit trail,
Destinations bloom and friendly peers set sail,
Hooray — the rabbit hops, I2P's on the road!"

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 15.38% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Firo I2P support' clearly and concisely describes the main feature being added—I2P protocol support for Firo—making it specific and relevant to the changeset.
Description check	✅ Passed	The PR description fully addresses both required template sections: 'PR intention' explains the feature's purpose and benefits, and 'Code changes brief' details architectural changes across multiple components with clear organization.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch cursor/firo-i2p-support-a07e

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[coderabbitai]

Actionable comments posted: 3

🤖 Fix all issues with AI agents

In `@src/i2p.cpp`:
- Around line 508-527: The code only regenerates when m_private_key is empty but
not when it is corrupted; update the load/validation flow to detect invalid keys
by attempting to construct/validate the destination and regenerate on failure:
after reading m_private_key from m_private_key_file, try to create/validate the
MyDestination (or call whatever validate method you have) inside a try/catch (or
check return/error) and if it throws or fails log via LogPrintf including the
file name and error, call GenerateAndSavePrivateKey(sock) to regenerate, and
continue; reference m_private_key, m_private_key_file, MyDestination(),
LogPrintf, and GenerateAndSavePrivateKey(sock) when implementing the change so
corrupted/truncated files are regenerated in place.

In `@src/net.cpp`:
- Around line 399-422: The I2P SAM path is being skipped when callers pass
pszDest because addrConnect isn't populated before the IsI2P() check; update the
logic so pszDest is parsed/resolved into addrConnect prior to checking
addrConnect.IsI2P() (or alternatively ensure ConnectSocketByName/ConnectSocket
consult NET_I2P and m_i2p_sam_session for proxy routing), so that .b32.i2p
destinations hit the m_i2p_sam_session branch; modify the code paths around
pszDest, addrConnect, IsI2P(), ConnectSocketByName and ConnectSocket to populate
addrConnect (or route NET_I2P to SAM) before deciding to call the SAM session.

In `@src/test/i2p_tests.cpp`:
- Around line 109-124: The test i2p_service has a mismatch between its comment
and assertions: decide whether I2P ports should be normalized to 0 or preserved;
if ports are intentionally preserved, update the comment to state that CService
preserves a supplied port for I2P addresses (leave the assertions as-is using
service.GetPort()==0 for the zero-case and service2.GetPort()==8333 for the
preserved-case); otherwise, change the second assertion to expect 0
(service2.GetPort()==0) and adjust the comment to state I2P ports are normalized
to 0. Locate the test in i2p_service, and modify the comment or the second
BOOST_CHECK_EQUAL accordingly (references: CService constructor,
CNetAddr::SetSpecial, service, service2, IsI2P, GetPort).

🧹 Nitpick comments (3)

src/net.h (1)

24-24: Optional: forward declare i2p::sam::Session to slim net.h dependencies.
net.h is widely included; a forward declaration with the include moved to net.cpp can reduce rebuilds.

src/test/i2p_tests.cpp (1)

126-140: Consider asserting the exact reachability level.
If a constant like REACH_PRIVATE is available, asserting equality will make this test more regression‑resistant.

💡 Example

-    int reachability = addr.GetReachabilityFrom(&addr2);
-    BOOST_CHECK(reachability > 0);
+    int reachability = addr.GetReachabilityFrom(&addr2);
+    BOOST_CHECK_EQUAL(reachability, REACH_PRIVATE);

src/init.cpp (1)

1615-1643: Consider defaulting I2P inbound behavior to -listen.
Right now -i2psam + default -i2pacceptincoming enables inbound I2P even when users set -listen=0. For consistency with other networks, consider defaulting -i2pacceptincoming to the -listen value unless explicitly set, and update help text if the default changes.

♻️ Suggested change

-        const bool i2p_accept_incoming = GetBoolArg("-i2pacceptincoming", true);
+        const bool i2p_accept_incoming =
+            GetBoolArg("-i2pacceptincoming", GetBoolArg("-listen", DEFAULT_LISTEN));

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@src/i2p.cpp`:
- Around line 207-211: The loop that calls Wait(conn.sock, MAX_WAIT_FOR_IO,
true) treats any false as a harmless timeout and can busy-loop if select()
errors; update the loop in the accept/IO routine that checks *m_interrupt to
distinguish timeout vs error by calling IsConnected() (or equivalent) on the
socket when Wait(...) returns false and, if the socket is not connected or
reports an error, break/return to avoid spinning; keep the existing continue
only for genuine timeouts and ensure you reference conn.sock, MAX_WAIT_FOR_IO,
m_interrupt, Wait(), and IsConnected() when making the change.

🧹 Nitpick comments (1)

src/i2p.cpp (1)

755-827: Consider reusing the existing ConnectSocketDirectly to avoid drift.
This helper largely duplicates netbase.cpp logic (and differs on socket options), which can lead to subtle behavior divergence. Exposing a shared utility would reduce maintenance overhead.

[coderabbitai]

Actionable comments posted: 2

🤖 Fix all issues with AI agents

In `@src/net.cpp`:
- Around line 2483-2501: Inbound I2P connection handling in the block around
fNetworkActive/IsSelectableSocket/AttemptToEvictConnection skips ban checks, so
manual bans are ignored; update the path to consult IsBanned just like
AcceptConnection does: before accepting the peer (using conn.peer / conn.addr
and conn.sock), call IsBanned(peer) and if banned log the ban and
CloseSocket(conn.sock) and continue, mirroring AcceptConnection’s ban handling
(including any banlist reason/logging) so I2P connections cannot bypass manual
bans.
- Around line 409-425: The suffix check for .b32.i2p fails when pszDest contains
a port (e.g. .b32.i2p:0); update the block that examines pszDest (the code that
currently uses dest, suffix, CNetAddr::SetSpecial, CService and sets
i2pDest/isI2P) to first strip an optional ":port" tail before doing the
case‑insensitive ".b32.i2p" detection and before calling CNetAddr::SetSpecial so
SAM path is used instead of falling back to ConnectSocketByName; ensure the
stripped value is what you pass into SetSpecial and constructing i2pDest (but
preserve original pszDest elsewhere if needed).

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@src/i2p.cpp`:
- Around line 763-835: The ConnectSocketDirectly function is missing the same
socket options used in netbase.cpp; after creating hSocket in
ConnectSocketDirectly, set SO_NOSIGPIPE when defined and enable TCP_NODELAY
(disable Nagle) before calling SetSocketNonBlocking; use conditional compilation
like `#ifdef` SO_NOSIGPIPE to call setsockopt(hSocket, SOL_SOCKET, SO_NOSIGPIPE,
...) and use a WIN32 vs non-WIN32 variant for setsockopt(hSocket, IPPROTO_TCP,
TCP_NODELAY, ...) so the socket behavior matches the original implementation.