Merge bitcoin/bitcoin#21879: refactor: wrap accept() and extend usage of Sock

6bf6e9fd9dece67878595a5f3361851c25833c49 net: change CreateNodeFromAcceptedSocket() to take Sock (Vasil Dimov)
9e3cbfca7c9efa620c0cce73503772805cc1fa82 net: use Sock in CConnman::ListenSocket (Vasil Dimov)
f8bd13f85ae5404adef23a52719d804a5c36b1e8 net: add new method Sock::Accept() that wraps accept() (Vasil Dimov)

Pull request description:

  _This is a piece of https://github.com/bitcoin/bitcoin/pull/21878, chopped off to ease review._

  Introduce an `accept(2)` wrapper `Sock::Accept()` and extend the usage of `Sock` in `CConnman::ListenSocket` and `CreateNodeFromAcceptedSocket()`.

ACKs for top commit:
  laanwj:
    Code review ACK 6bf6e9fd9dece67878595a5f3361851c25833c49
  jamesob:
    ACK 6bf6e9fd9dece67878595a5f3361851c25833c49 ([`jamesob/ackr/21879.2.vasild.wrap_accept_and_extend_u`](https://github.com/jamesob/bitcoin/tree/ackr/21879.2.vasild.wrap_accept_and_extend_u))
  jonatack:
    ACK 6bf6e9fd9dece67878595a5f3361851c25833c49 per `git range-diff ea989de 976f6e8 6bf6e9f` -- only change since my last review was `s/listen_socket.socket/listen_socket.sock->Get()/` in `src/net.cpp: CConnman::SocketHandlerListening()` -- re-read the code changes, rebase/debug build/ran units following my previous full review (https://github.com/bitcoin/bitcoin/pull/21879#pullrequestreview-761251278)
  w0xlt:
    tACK 6bf6e9f

Tree-SHA512: dc6d1acc4f255f1f7e8cf6dd74e97975cf3d5959e9fc2e689f74812ac3526d5ee8b6a32eca605925d10a4f7b6ff1ce5e900344311e587d19786b48c54d021b64

7 files changed, 93 insertions, 30 deletions

diff --git a/src/net.cpp b/src/net.cpp
index 019e77fd7a..89a4aee5d9 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -1099,10 +1099,10 @@ bool CConnman::AttemptToEvictConnection()
 void CConnman::AcceptConnection(const ListenSocket& hListenSocket) {
     struct sockaddr_storage sockaddr;
     socklen_t len = sizeof(sockaddr);
-    SOCKET hSocket = accept(hListenSocket.socket, (struct sockaddr*)&sockaddr, &len);
+    auto sock = hListenSocket.sock->Accept((struct sockaddr*)&sockaddr, &len);
     CAddress addr;
 
-    if (hSocket == INVALID_SOCKET) {
+    if (!sock) {
         const int nErr = WSAGetLastError();
         if (nErr != WSAEWOULDBLOCK) {
             LogPrintf("socket error accept failed: %s\n", NetworkErrorString(nErr));
@@ -1116,15 +1116,15 @@ void CConnman::AcceptConnection(const ListenSocket& hListenSocket) {
         addr = CAddress{MaybeFlipIPv6toCJDNS(addr), NODE_NONE};
     }
 
-    const CAddress addr_bind{MaybeFlipIPv6toCJDNS(GetBindAddress(hSocket)), NODE_NONE};
+    const CAddress addr_bind{MaybeFlipIPv6toCJDNS(GetBindAddress(sock->Get())), NODE_NONE};
 
     NetPermissionFlags permissionFlags = NetPermissionFlags::None;
     hListenSocket.AddSocketPermissionFlags(permissionFlags);
 
-    CreateNodeFromAcceptedSocket(hSocket, permissionFlags, addr_bind, addr);
+    CreateNodeFromAcceptedSocket(std::move(sock), permissionFlags, addr_bind, addr);
 }
 
-void CConnman::CreateNodeFromAcceptedSocket(SOCKET hSocket,
+void CConnman::CreateNodeFromAcceptedSocket(std::unique_ptr<Sock>&& sock,
                                             NetPermissionFlags permissionFlags,
                                             const CAddress& addr_bind,
                                             const CAddress& addr)
@@ -1150,27 +1150,24 @@ void CConnman::CreateNodeFromAcceptedSocket(SOCKET hSocket,
 
     if (!fNetworkActive) {
         LogPrint(BCLog::NET, "connection from %s dropped: not accepting new connections\n", addr.ToString());
-        CloseSocket(hSocket);
         return;
     }
 
-    if (!IsSelectableSocket(hSocket))
+    if (!IsSelectableSocket(sock->Get()))
     {
         LogPrintf("connection from %s dropped: non-selectable socket\n", addr.ToString());
-        CloseSocket(hSocket);
         return;
     }
 
     // According to the internet TCP_NODELAY is not carried into accepted sockets
     // on all platforms.  Set it again here just to be sure.
-    SetSocketNoDelay(hSocket);
+    SetSocketNoDelay(sock->Get());
 
     // Don't accept connections from banned peers.
     bool banned = m_banman && m_banman->IsBanned(addr);
     if (!NetPermissions::HasFlag(permissionFlags, NetPermissionFlags::NoBan) && banned)
     {
         LogPrint(BCLog::NET, "connection from %s dropped (banned)\n", addr.ToString());
-        CloseSocket(hSocket);
         return;
     }
 
@@ -1179,7 +1176,6 @@ void CConnman::CreateNodeFromAcceptedSocket(SOCKET hSocket,
     if (!NetPermissions::HasFlag(permissionFlags, NetPermissionFlags::NoBan) && nInbound + 1 >= nMaxInbound && discouraged)
     {
         LogPrint(BCLog::NET, "connection from %s dropped (discouraged)\n", addr.ToString());
-        CloseSocket(hSocket);
         return;
     }
 
@@ -1188,7 +1184,6 @@ void CConnman::CreateNodeFromAcceptedSocket(SOCKET hSocket,
         if (!AttemptToEvictConnection()) {
             // No connection to evict, disconnect the new connection
             LogPrint(BCLog::NET, "failed to find an eviction candidate - connection dropped (full)\n");
-            CloseSocket(hSocket);
             return;
         }
     }
@@ -1202,7 +1197,7 @@ void CConnman::CreateNodeFromAcceptedSocket(SOCKET hSocket,
     }
 
     const bool inbound_onion = std::find(m_onion_binds.begin(), m_onion_binds.end(), addr_bind) != m_onion_binds.end();
-    CNode* pnode = new CNode(id, nodeServices, hSocket, addr, CalculateKeyedNetGroup(addr), nonce, addr_bind, "", ConnectionType::INBOUND, inbound_onion);
+    CNode* pnode = new CNode(id, nodeServices, sock->Release(), addr, CalculateKeyedNetGroup(addr), nonce, addr_bind, "", ConnectionType::INBOUND, inbound_onion);
     pnode->AddRef();
     pnode->m_permissionFlags = permissionFlags;
     pnode->m_prefer_evict = discouraged;
@@ -1364,7 +1359,7 @@ bool CConnman::GenerateSelectSet(const std::vector<CNode*>& nodes,
                                  std::set<SOCKET>& error_set)
 {
     for (const ListenSocket& hListenSocket : vhListenSocket) {
-        recv_set.insert(hListenSocket.socket);
+        recv_set.insert(hListenSocket.sock->Get());
     }
 
     for (CNode* pnode : nodes) {
@@ -1646,7 +1641,7 @@ void CConnman::SocketHandlerListening(const std::set<SOCKET>& recv_set)
         if (interruptNet) {
             return;
         }
-        if (recv_set.count(listen_socket.socket) > 0) {
+        if (recv_set.count(listen_socket.sock->Get()) > 0) {
             AcceptConnection(listen_socket);
         }
     }
@@ -2335,7 +2330,7 @@ void CConnman::ThreadI2PAcceptIncoming()
             continue;
         }
 
-        CreateNodeFromAcceptedSocket(conn.sock->Release(), NetPermissionFlags::None,
+        CreateNodeFromAcceptedSocket(std::move(conn.sock), NetPermissionFlags::None,
                                      CAddress{conn.me, NODE_NONE}, CAddress{conn.peer, NODE_NONE});
     }
 }
@@ -2397,7 +2392,7 @@ bool CConnman::BindListenPort(const CService& addrBind, bilingual_str& strError,
         return false;
     }
 
-    vhListenSocket.push_back(ListenSocket(sock->Release(), permissions));
+    vhListenSocket.emplace_back(std::move(sock), permissions);
     return true;
 }
 
@@ -2706,15 +2701,6 @@ void CConnman::StopNodes()
         DeleteNode(pnode);
     }
 
-    // Close listening sockets.
-    for (ListenSocket& hListenSocket : vhListenSocket) {
-        if (hListenSocket.socket != INVALID_SOCKET) {
-            if (!CloseSocket(hListenSocket.socket)) {
-                LogPrintf("CloseSocket(hListenSocket) failed with error %s\n", NetworkErrorString(WSAGetLastError()));
-            }
-        }
-    }
-
     for (CNode* pnode : m_nodes_disconnected) {
         DeleteNode(pnode);
     }
diff --git a/src/net.h b/src/net.h
index 977e6502ce..80fc93a5d0 100644
--- a/src/net.h
+++ b/src/net.h
@@ -25,6 +25,7 @@
 #include <threadinterrupt.h>
 #include <uint256.h>
 #include <util/check.h>
+#include <util/sock.h>
 
 #include <atomic>
 #include <condition_variable>
@@ -947,9 +948,13 @@ public:
 private:
     struct ListenSocket {
     public:
-        SOCKET socket;
+        std::shared_ptr<Sock> sock;
         inline void AddSocketPermissionFlags(NetPermissionFlags& flags) const { NetPermissions::AddFlag(flags, m_permissions); }
-        ListenSocket(SOCKET socket_, NetPermissionFlags permissions_) : socket(socket_), m_permissions(permissions_) {}
+        ListenSocket(std::shared_ptr<Sock> sock_, NetPermissionFlags permissions_)
+            : sock{sock_}, m_permissions{permissions_}
+        {
+        }
+
     private:
         NetPermissionFlags m_permissions;
     };
@@ -969,12 +974,12 @@ private:
     /**
      * Create a `CNode` object from a socket that has just been accepted and add the node to
      * the `m_nodes` member.
-     * @param[in] hSocket Connected socket to communicate with the peer.
+     * @param[in] sock Connected socket to communicate with the peer.
      * @param[in] permissionFlags The peer's permissions.
      * @param[in] addr_bind The address and port at our side of the connection.
      * @param[in] addr The address and port at the peer's side of the connection.
      */
-    void CreateNodeFromAcceptedSocket(SOCKET hSocket,
+    void CreateNodeFromAcceptedSocket(std::unique_ptr<Sock>&& sock,
                                       NetPermissionFlags permissionFlags,
                                       const CAddress& addr_bind,
                                       const CAddress& addr);
diff --git a/src/test/fuzz/util.cpp b/src/test/fuzz/util.cpp
index 5520eee758..f89b597eed 100644
--- a/src/test/fuzz/util.cpp
+++ b/src/test/fuzz/util.cpp
@@ -13,6 +13,8 @@
 #include <util/time.h>
 #include <version.h>
 
+#include <memory>
+
 FuzzedSock::FuzzedSock(FuzzedDataProvider& fuzzed_data_provider)
     : m_fuzzed_data_provider{fuzzed_data_provider}
 {
@@ -158,6 +160,20 @@ int FuzzedSock::Connect(const sockaddr*, socklen_t) const
     return 0;
 }
 
+std::unique_ptr<Sock> FuzzedSock::Accept(sockaddr* addr, socklen_t* addr_len) const
+{
+    constexpr std::array accept_errnos{
+        ECONNABORTED,
+        EINTR,
+        ENOMEM,
+    };
+    if (m_fuzzed_data_provider.ConsumeBool()) {
+        SetFuzzedErrNo(m_fuzzed_data_provider, accept_errnos);
+        return std::unique_ptr<FuzzedSock>();
+    }
+    return std::make_unique<FuzzedSock>(m_fuzzed_data_provider);
+}
+
 int FuzzedSock::GetSockOpt(int level, int opt_name, void* opt_val, socklen_t* opt_len) const
 {
     constexpr std::array getsockopt_errnos{
diff --git a/src/test/fuzz/util.h b/src/test/fuzz/util.h
index f4f8e9e70d..fd7f40c01d 100644
--- a/src/test/fuzz/util.h
+++ b/src/test/fuzz/util.h
@@ -401,6 +401,8 @@ public:
 
     int Connect(const sockaddr*, socklen_t) const override;
 
+    std::unique_ptr<Sock> Accept(sockaddr* addr, socklen_t* addr_len) const override;
+
     int GetSockOpt(int level, int opt_name, void* opt_val, socklen_t* opt_len) const override;
 
     bool Wait(std::chrono::milliseconds timeout, Event requested, Event* occurred = nullptr) const override;
diff --git a/src/test/util/net.h b/src/test/util/net.h
index 006e876c1a..20c45058a1 100644
--- a/src/test/util/net.h
+++ b/src/test/util/net.h
@@ -13,6 +13,7 @@
 #include <array>
 #include <cassert>
 #include <cstring>
+#include <memory>
 #include <string>
 
 struct ConnmanTestMsg : public CConnman {
@@ -126,6 +127,23 @@ public:
 
     int Connect(const sockaddr*, socklen_t) const override { return 0; }
 
+    std::unique_ptr<Sock> Accept(sockaddr* addr, socklen_t* addr_len) const override
+    {
+        if (addr != nullptr) {
+            // Pretend all connections come from 5.5.5.5:6789
+            memset(addr, 0x00, *addr_len);
+            const socklen_t write_len = static_cast<socklen_t>(sizeof(sockaddr_in));
+            if (*addr_len >= write_len) {
+                *addr_len = write_len;
+                sockaddr_in* addr_in = reinterpret_cast<sockaddr_in*>(addr);
+                addr_in->sin_family = AF_INET;
+                memset(&addr_in->sin_addr, 0x05, sizeof(addr_in->sin_addr));
+                addr_in->sin_port = htons(6789);
+            }
+        }
+        return std::make_unique<StaticContentsSock>("");
+    };
+
     int GetSockOpt(int level, int opt_name, void* opt_val, socklen_t* opt_len) const override
     {
         std::memset(opt_val, 0x0, *opt_len);
diff --git a/src/util/sock.cpp b/src/util/sock.cpp
index 1a4d67a65e..2029d70a37 100644
--- a/src/util/sock.cpp
+++ b/src/util/sock.cpp
@@ -10,6 +10,7 @@
 #include <util/system.h>
 #include <util/time.h>
 
+#include <memory>
 #include <stdexcept>
 #include <string>
 
@@ -73,6 +74,32 @@ int Sock::Connect(const sockaddr* addr, socklen_t addr_len) const
     return connect(m_socket, addr, addr_len);
 }
 
+std::unique_ptr<Sock> Sock::Accept(sockaddr* addr, socklen_t* addr_len) const
+{
+#ifdef WIN32
+    static constexpr auto ERR = INVALID_SOCKET;
+#else
+    static constexpr auto ERR = SOCKET_ERROR;
+#endif
+
+    std::unique_ptr<Sock> sock;
+
+    const auto socket = accept(m_socket, addr, addr_len);
+    if (socket != ERR) {
+        try {
+            sock = std::make_unique<Sock>(socket);
+        } catch (const std::exception&) {
+#ifdef WIN32
+            closesocket(socket);
+#else
+            close(socket);
+#endif
+        }
+    }
+
+    return sock;
+}
+
 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);
diff --git a/src/util/sock.h b/src/util/sock.h
index 59cc8c0b1d..7510482857 100644
--- a/src/util/sock.h
+++ b/src/util/sock.h
@@ -10,6 +10,7 @@
 #include <util/time.h>
 
 #include <chrono>
+#include <memory>
 #include <string>
 
 /**
@@ -97,6 +98,14 @@ public:
     [[nodiscard]] virtual int Connect(const sockaddr* addr, socklen_t addr_len) const;
 
     /**
+     * accept(2) wrapper. Equivalent to `std::make_unique<Sock>(accept(this->Get(), addr, addr_len))`.
+     * Code that uses this wrapper can be unit tested if this method is overridden by a mock Sock
+     * implementation.
+     * The returned unique_ptr is empty if `accept()` failed in which case errno will be set.
+     */
+    [[nodiscard]] virtual std::unique_ptr<Sock> Accept(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.