Merge #21387: p2p: Refactor sock to add I2P fuzz and unit tests

40316a37cb test: add I2P test for a runaway SAM proxy (Vasil Dimov)
2d8ac77970 fuzz: add tests for the I2P Session public interface (Vasil Dimov)
9947e44de0 i2p: use pointers to Sock to accommodate mocking (Vasil Dimov)
82d360b5a8 net: change ConnectSocketDirectly() to take a Sock argument (Vasil Dimov)
b5861100f8 net: add connect() and getsockopt() wrappers to Sock (Vasil Dimov)
5a887d49b2 fuzz: avoid FuzzedSock::Recv() repeated errors with EAGAIN (Vasil Dimov)
3088f83d01 fuzz: extend FuzzedSock::Recv() to support MSG_PEEK (Vasil Dimov)
9b05c49ade fuzz: implement unimplemented FuzzedSock methods (Vasil Dimov)

Pull request description:

  Change the networking code and the I2P code to be fully mockable and use `FuzzedSocket` to fuzz the I2P methods `Listen()`, `Accept()` and `Connect()`.

  Add a mocked `Sock` implementation that returns a predefined data on reads and use it for a regression unit test for the bug fixed in https://github.com/bitcoin/bitcoin/pull/21407.

ACKs for top commit:
  practicalswift:
    Tested ACK 40316a37cb
  MarcoFalke:
    Concept ACK 40316a37cb
  jonatack:
    re-ACK 40316a37cb reviewed `git range-diff 01bb3afb 23c861d 40316a3` and the new unit test commit, debug built, ran unit tests, ran bitcoind with an I2P service and network operation with seven I2P peers (2 in, 5 out) is looking nominal
  laanwj:
    Code review ACK 40316a37cb

Tree-SHA512: 7fc4f129849e16e0c7e16662d9f4d35dfcc369bb31450ee369a2b97bdca95285533bee7787983e881e5a3d248f912afb42b4a2299d5860ace7129b0b19623cc8

src/util/sock.cpp

@@ -66,6 +66,16 @@ ssize_t Sock::Recv(void* buf, size_t len, int flags) const
     return recv(m_socket, static_cast<char*>(buf), len, flags);
 }
 
+int Sock::Connect(const sockaddr* addr, socklen_t addr_len) const
+{
+    return connect(m_socket, addr, addr_len);
+}
+
+int Sock::GetSockOpt(int level, int opt_name, void* opt_val, socklen_t* opt_len) const
+{
+    return getsockopt(m_socket, level, opt_name, static_cast<char*>(opt_val), opt_len);
+}
+
 bool Sock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occurred) const
 {
 #ifdef USE_POLL

src/util/sock.h

@@ -80,16 +80,29 @@ public:
 
     /**
      * send(2) wrapper. Equivalent to `send(this->Get(), data, len, flags);`. Code that uses this
-     * wrapper can be unit-tested if this method is overridden by a mock Sock implementation.
+     * wrapper can be unit tested if this method is overridden by a mock Sock implementation.
      */
     virtual ssize_t Send(const void* data, size_t len, int flags) const;
 
     /**
      * recv(2) wrapper. Equivalent to `recv(this->Get(), buf, len, flags);`. Code that uses this
-     * wrapper can be unit-tested if this method is overridden by a mock Sock implementation.
+     * wrapper can be unit tested if this method is overridden by a mock Sock implementation.
      */
     virtual ssize_t Recv(void* buf, size_t len, int flags) const;
 
+    /**
+     * connect(2) wrapper. Equivalent to `connect(this->Get(), addr, addrlen)`. Code that uses this
+     * wrapper can be unit tested if this method is overridden by a mock Sock implementation.
+     */
+    virtual int Connect(const sockaddr* addr, socklen_t addr_len) const;
+
+    /**
+     * getsockopt(2) wrapper. Equivalent to
+     * `getsockopt(this->Get(), level, opt_name, opt_val, opt_len)`. Code that uses this
+     * wrapper can be unit tested if this method is overridden by a mock Sock implementation.
+     */
+    virtual int GetSockOpt(int level, int opt_name, void* opt_val, socklen_t* opt_len) const;
+
     using Event = uint8_t;
 
     /**
@@ -153,7 +166,7 @@ public:
      */
     virtual bool IsConnected(std::string& errmsg) const;
 
-private:
+protected:
     /**
      * Contained socket. `INVALID_SOCKET` designates the object is empty.
      */