fuzz: add tests for the I2P Session public interface

src/Makefile.test.include

@@ -239,6 +239,7 @@ test_fuzz_fuzz_SOURCES = \
  test/fuzz/golomb_rice.cpp \
  test/fuzz/hex.cpp \
  test/fuzz/http_request.cpp \
+ test/fuzz/i2p.cpp \
  test/fuzz/integer.cpp \
  test/fuzz/key.cpp \
  test/fuzz/key_io.cpp \

src/test/fuzz/i2p.cpp

@@ -0,0 +1,57 @@
+// Copyright (c) 2020-2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <i2p.h>
+#include <netaddress.h>
+#include <netbase.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+#include <test/util/setup_common.h>
+#include <threadinterrupt.h>
+#include <util/system.h>
+
+void initialize_i2p()
+{
+    static const auto testing_setup = MakeNoLogFileContext<>();
+}
+
+FUZZ_TARGET_INIT(i2p, initialize_i2p)
+{
+    FuzzedDataProvider fuzzed_data_provider{buffer.data(), buffer.size()};
+
+    // Mock CreateSock() to create FuzzedSock.
+    auto CreateSockOrig = CreateSock;
+    CreateSock = [&fuzzed_data_provider](const CService&) {
+        return std::make_unique<FuzzedSock>(fuzzed_data_provider);
+    };
+
+    const CService sam_proxy;
+    CThreadInterrupt interrupt;
+
+    i2p::sam::Session sess{GetDataDir() / "fuzzed_i2p_private_key", sam_proxy, &interrupt};
+
+    i2p::Connection conn;
+
+    if (sess.Listen(conn)) {
+        if (sess.Accept(conn)) {
+            try {
+                conn.sock->RecvUntilTerminator('\n', 10ms, interrupt, i2p::sam::MAX_MSG_SIZE);
+            } catch (const std::runtime_error&) {
+            }
+        }
+    }
+
+    const CService to;
+    bool proxy_error;
+
+    if (sess.Connect(to, conn, proxy_error)) {
+        try {
+            conn.sock->SendComplete("verack\n", 10ms, interrupt);
+        } catch (const std::runtime_error&) {
+        }
+    }
+
+    CreateSock = CreateSockOrig;
+}