HTTPServer: implement and test AcceptConnection()

diff --git a/src/httpserver.cpp b/src/httpserver.cpp
index 310907ba..0bda2843 100644
--- a/src/httpserver.cpp
+++ b/src/httpserver.cpp
@@ -976,4 +976,36 @@ void HTTPServer::StopListening()
 {
     m_listen.clear();
 }
+
+std::unique_ptr<Sock> HTTPServer::AcceptConnection(const Sock& listen_sock, CService& addr)
+{
+    // Make sure we only operate on our own listening sockets
+    Assume(std::ranges::any_of(m_listen, [&](const auto& sock) { return sock.get() == &listen_sock; }));
+
+    sockaddr_storage storage;
+    socklen_t len{sizeof(storage)};
+    auto sa = reinterpret_cast<sockaddr*>(&storage);
+
+    auto sock{listen_sock.Accept(sa, &len)};
+
+    if (!sock) {
+        const int err{WSAGetLastError()};
+        if (err != WSAEWOULDBLOCK) {
+            LogDebug(BCLog::HTTP,
+                     "Cannot accept new connection: %s",
+                     NetworkErrorString(err));
+        }
+        return {};
+    }
+
+    // The OS handed us a valid socket but we can't determine its source address.
+    // In the unlikely event this occurs, the invalid address will be rejected
+    // by the downstream ClientAllowed() check.
+    if (!addr.SetSockAddr(sa, len)) {
+        LogDebug(BCLog::HTTP,
+                 "Unknown socket family");
+    }
+
+    return sock;
+}
 } // namespace http_bitcoin
diff --git a/src/httpserver.h b/src/httpserver.h
index ba93cbb8..e4dabc63 100644
--- a/src/httpserver.h
+++ b/src/httpserver.h
@@ -323,11 +323,29 @@ public:
      */
     size_t GetListeningSocketCount() const { return m_listen.size(); }
 
+    /**
+     * This is a temporary method used to accept connections from a listening
+     * socket in the unit tests before the I/O loop is implemented.
+     * It will be removed in a future commit.
+     */
+    std::unique_ptr<Sock> AcceptConnectionFromListeningSocket(CService& addr)
+    {
+        return AcceptConnection(*m_listen.front(), addr);
+    }
+
 private:
     /**
      * List of listening sockets.
      */
     std::vector<std::shared_ptr<Sock>> m_listen;
+
+    /**
+     * Accept a connection.
+     * @param[in] listen_sock Socket on which to accept the connection.
+     * @param[out] addr Address of the peer that was accepted.
+     * @return Newly created socket for the accepted connection.
+     */
+    std::unique_ptr<Sock> AcceptConnection(const Sock& listen_sock, CService& addr);
 };
 } // namespace http_bitcoin
 
diff --git a/src/test/httpserver_tests.cpp b/src/test/httpserver_tests.cpp
index 1114df05..22af3981 100644
--- a/src/test/httpserver_tests.cpp
+++ b/src/test/httpserver_tests.cpp
@@ -395,5 +395,15 @@ BOOST_AUTO_TEST_CASE(http_server_socket_tests)
     BOOST_REQUIRE(server.BindAndStartListening(addr_bind));
     // We are bound and listening
     BOOST_REQUIRE_EQUAL(server.GetListeningSocketCount(), 1);
+
+    // Pick up the phone, there's no one there
+    CService addr_connection;
+    BOOST_REQUIRE(!server.AcceptConnectionFromListeningSocket(addr_connection));
+
+    // Create a mock client and add it to the local CreateSock queue
+    ConnectClient();
+    // Accept the connection
+    BOOST_REQUIRE(server.AcceptConnectionFromListeningSocket(addr_connection));
+    BOOST_CHECK_EQUAL(addr_connection.ToStringAddrPort(), "5.5.5.5:6789");
 }
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/test/util/setup_common.cpp b/src/test/util/setup_common.cpp
index 2ba63efd..846f4703 100644
--- a/src/test/util/setup_common.cpp
+++ b/src/test/util/setup_common.cpp
@@ -658,6 +658,21 @@ SocketTestingSetup::~SocketTestingSetup()
     CreateSock = m_create_sock_orig;
 }
 
+void SocketTestingSetup::ConnectClient()
+{
+    // I/O pipes for a mock Connected Socket we can read and write to.
+    auto connected_socket_pipes(std::make_shared<DynSock::Pipes>());
+
+    // TODO: Insert a payload
+
+    // Create the Mock Connected Socket that represents a client.
+    // It needs I/O pipes but its queue can remain empty
+    std::unique_ptr<DynSock> connected_socket{std::make_unique<DynSock>(connected_socket_pipes)};
+
+    // Push into the queue of Accepted Sockets returned by the local CreateSock()
+    m_accepted_sockets.Push(std::move(connected_socket));
+}
+
 /**
  * @returns a real block (0000000000013b8ab2cd513b0261a14096412195a72a0c4827d229dcc7e0f7af)
  *      with 9 txs.
diff --git a/src/test/util/setup_common.h b/src/test/util/setup_common.h
index 7a8f6b70..bf9ec42e 100644
--- a/src/test/util/setup_common.h
+++ b/src/test/util/setup_common.h
@@ -256,6 +256,9 @@ public:
     explicit SocketTestingSetup();
     ~SocketTestingSetup();
 
+    //! Connect to the socket with a mock client (a DynSock)
+    void ConnectClient();
+
 private:
     //! Save the original value of CreateSock here and restore it when the test ends.
     decltype(CreateSock) m_create_sock_orig;