fuzz: split FuzzedSock interface and implementation

Move the `FuzzedSock`'s implementation from `src/test/fuzz/util.h` to
`src/test/fuzz/util.cpp`.

A separate interface and implementation make the code more readable for
consumers who don't need to (better not) know the implementation
details.

1 files changed, 173 insertions, 0 deletions

diff --git a/src/test/fuzz/util.cpp b/src/test/fuzz/util.cpp
index d16c5afac7..f772bc01d8 100644
--- a/src/test/fuzz/util.cpp
+++ b/src/test/fuzz/util.cpp
@@ -7,6 +7,170 @@
 #include <util/rbf.h>
 #include <version.h>
 
+FuzzedSock::FuzzedSock(FuzzedDataProvider& fuzzed_data_provider)
+    : m_fuzzed_data_provider{fuzzed_data_provider}
+{
+    m_socket = fuzzed_data_provider.ConsumeIntegralInRange<SOCKET>(INVALID_SOCKET - 1, INVALID_SOCKET);
+}
+
+FuzzedSock::~FuzzedSock()
+{
+    // Sock::~Sock() will be called after FuzzedSock::~FuzzedSock() and it will call
+    // Sock::Reset() (not FuzzedSock::Reset()!) which will call CloseSocket(m_socket).
+    // Avoid closing an arbitrary file descriptor (m_socket is just a random very high number which
+    // theoretically may concide with a real opened file descriptor).
+    Reset();
+}
+
+FuzzedSock& FuzzedSock::operator=(Sock&& other)
+{
+    assert(false && "Move of Sock into FuzzedSock not allowed.");
+    return *this;
+}
+
+void FuzzedSock::Reset()
+{
+    m_socket = INVALID_SOCKET;
+}
+
+ssize_t FuzzedSock::Send(const void* data, size_t len, int flags) const
+{
+    constexpr std::array send_errnos{
+        EACCES,
+        EAGAIN,
+        EALREADY,
+        EBADF,
+        ECONNRESET,
+        EDESTADDRREQ,
+        EFAULT,
+        EINTR,
+        EINVAL,
+        EISCONN,
+        EMSGSIZE,
+        ENOBUFS,
+        ENOMEM,
+        ENOTCONN,
+        ENOTSOCK,
+        EOPNOTSUPP,
+        EPIPE,
+        EWOULDBLOCK,
+    };
+    if (m_fuzzed_data_provider.ConsumeBool()) {
+        return len;
+    }
+    const ssize_t r = m_fuzzed_data_provider.ConsumeIntegralInRange<ssize_t>(-1, len);
+    if (r == -1) {
+        SetFuzzedErrNo(m_fuzzed_data_provider, send_errnos);
+    }
+    return r;
+}
+
+ssize_t FuzzedSock::Recv(void* buf, size_t len, int flags) const
+{
+    // Have a permanent error at recv_errnos[0] because when the fuzzed data is exhausted
+    // SetFuzzedErrNo() will always return the first element and we want to avoid Recv()
+    // returning -1 and setting errno to EAGAIN repeatedly.
+    constexpr std::array recv_errnos{
+        ECONNREFUSED,
+        EAGAIN,
+        EBADF,
+        EFAULT,
+        EINTR,
+        EINVAL,
+        ENOMEM,
+        ENOTCONN,
+        ENOTSOCK,
+        EWOULDBLOCK,
+    };
+    assert(buf != nullptr || len == 0);
+    if (len == 0 || m_fuzzed_data_provider.ConsumeBool()) {
+        const ssize_t r = m_fuzzed_data_provider.ConsumeBool() ? 0 : -1;
+        if (r == -1) {
+            SetFuzzedErrNo(m_fuzzed_data_provider, recv_errnos);
+        }
+        return r;
+    }
+    std::vector<uint8_t> random_bytes;
+    bool pad_to_len_bytes{m_fuzzed_data_provider.ConsumeBool()};
+    if (m_peek_data.has_value()) {
+        // `MSG_PEEK` was used in the preceding `Recv()` call, return `m_peek_data`.
+        random_bytes.assign({m_peek_data.value()});
+        if ((flags & MSG_PEEK) == 0) {
+            m_peek_data.reset();
+        }
+        pad_to_len_bytes = false;
+    } else if ((flags & MSG_PEEK) != 0) {
+        // New call with `MSG_PEEK`.
+        random_bytes = m_fuzzed_data_provider.ConsumeBytes<uint8_t>(1);
+        if (!random_bytes.empty()) {
+            m_peek_data = random_bytes[0];
+            pad_to_len_bytes = false;
+        }
+    } else {
+        random_bytes = m_fuzzed_data_provider.ConsumeBytes<uint8_t>(
+            m_fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, len));
+    }
+    if (random_bytes.empty()) {
+        const ssize_t r = m_fuzzed_data_provider.ConsumeBool() ? 0 : -1;
+        if (r == -1) {
+            SetFuzzedErrNo(m_fuzzed_data_provider, recv_errnos);
+        }
+        return r;
+    }
+    std::memcpy(buf, random_bytes.data(), random_bytes.size());
+    if (pad_to_len_bytes) {
+        if (len > random_bytes.size()) {
+            std::memset((char*)buf + random_bytes.size(), 0, len - random_bytes.size());
+        }
+        return len;
+    }
+    if (m_fuzzed_data_provider.ConsumeBool() && std::getenv("FUZZED_SOCKET_FAKE_LATENCY") != nullptr) {
+        std::this_thread::sleep_for(std::chrono::milliseconds{2});
+    }
+    return random_bytes.size();
+}
+
+int FuzzedSock::Connect(const sockaddr*, socklen_t) const
+{
+    // Have a permanent error at connect_errnos[0] because when the fuzzed data is exhausted
+    // SetFuzzedErrNo() will always return the first element and we want to avoid Connect()
+    // returning -1 and setting errno to EAGAIN repeatedly.
+    constexpr std::array connect_errnos{
+        ECONNREFUSED,
+        EAGAIN,
+        ECONNRESET,
+        EHOSTUNREACH,
+        EINPROGRESS,
+        EINTR,
+        ENETUNREACH,
+        ETIMEDOUT,
+    };
+    if (m_fuzzed_data_provider.ConsumeBool()) {
+        SetFuzzedErrNo(m_fuzzed_data_provider, connect_errnos);
+        return -1;
+    }
+    return 0;
+}
+
+int FuzzedSock::GetSockOpt(int level, int opt_name, void* opt_val, socklen_t* opt_len) const
+{
+    constexpr std::array getsockopt_errnos{
+        ENOMEM,
+        ENOBUFS,
+    };
+    if (m_fuzzed_data_provider.ConsumeBool()) {
+        SetFuzzedErrNo(m_fuzzed_data_provider, getsockopt_errnos);
+        return -1;
+    }
+    if (opt_val == nullptr) {
+        return 0;
+    }
+    std::memcpy(opt_val,
+                ConsumeFixedLengthByteVector(m_fuzzed_data_provider, *opt_len).data(),
+                *opt_len);
+    return 0;
+}
+
 bool FuzzedSock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occurred) const
 {
     constexpr std::array wait_errnos{
@@ -24,6 +188,15 @@ bool FuzzedSock::Wait(std::chrono::milliseconds timeout, Event requested, Event*
     return true;
 }
 
+bool FuzzedSock::IsConnected(std::string& errmsg) const
+{
+    if (m_fuzzed_data_provider.ConsumeBool()) {
+        return true;
+    }
+    errmsg = "disconnected at random by the fuzzer";
+    return false;
+}
+
 void FillNode(FuzzedDataProvider& fuzzed_data_provider, CNode& node, bool init_version) noexcept
 {
     const ServiceFlags remote_services = ConsumeWeakEnum(fuzzed_data_provider, ALL_SERVICE_FLAGS);