/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
 * Copyright the Collabora Online contributors.
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/*
 * SSL/TLS socket implementation using OpenSSL for encrypted connections.
 * Classes: SslStreamSocket
 */

#pragma once

#include <common/Log.hpp>
#include <net/Ssl.hpp>
#include <net/Socket.hpp>

#include <openssl/ssl.h>
#include <openssl/err.h>

#include <cerrno>
#include <sstream>
#include <string>

/// An SSL/TSL, non-blocking, data streaming socket.
class SslStreamSocket final : public StreamSocket
{
public:
    SslStreamSocket(const std::string& host, const int fd, Type type, bool isClient,
                    HostType hostType, ReadType readType = ReadType::NormalRead,
                    std::chrono::steady_clock::time_point creationTime = std::chrono::steady_clock::now())
        : StreamSocket(host, fd, type, isClient, hostType, readType, creationTime)
        , _bio(nullptr)
        , _ssl(nullptr)
        , _sslWantsTo(SslWantsTo::Neither)
        , _doHandshake(true)
    {
        LOG_TRC("SslStreamSocket ctor #" << fd);

        _bio = BIO_new(BIO_s_socket());
        if (_bio == nullptr)
        {
            throw std::runtime_error("Failed to create SSL BIO.");
        }

        BIO_set_fd(_bio, fd, BIO_NOCLOSE);

        _ssl = isClient ? ssl::Manager::newClientSsl(_verification)
                        : ssl::Manager::newServerSsl(_verification);
        if (!_ssl)
        {
            BIO_free(_bio);
            _bio = nullptr;
            throw std::runtime_error("Failed to create SSL.");
        }

        if (!hostname().empty())
        {
            if (!SSL_set_tlsext_host_name(_ssl, hostname().c_str()))
                LOG_WRN("Failed to set hostname for Server Name Indication [" << hostname() << ']');
            else
                LOG_TRC("Set [" << hostname() << "] as TLS hostname.");
        }

        SSL_set_bio(_ssl, _bio, _bio);

        if (isClient)
        {
            LOG_TRC("Setting SSL into connect state");
            SSL_set_connect_state(_ssl);
            if (SSL_connect(_ssl) == 0)
                LOG_DBG("SslStreamSocket connect #" << getFD() << " failed ");
            // else -1 is quite possibly SSL_ERROR_WANT_READ
        }
        else // We are a server-side socket.
        {
            LOG_TRC("Setting SSL into accept state");
            SSL_set_accept_state(_ssl);
        }
    }

    long getSslVerifyResult() override
    {
        return SSL_get_verify_result(_ssl);
    }

    static std::string getSslVerifyString(long lerr)
    {
        if (lerr != X509_V_OK)
            return X509_verify_cert_error_string(lerr);
        return std::string();
    }

    std::string getSslCert(std::string& subjectHash) override;

    ~SslStreamSocket()
    {
        LOG_TRC("SslStreamSocket dtor #" << getFD());

        if (!isShutdownSignalled())
        {
            setShutdownSignalled();
            SslStreamSocket::shutdownConnection();
        }

        SSL_free(_ssl);
    }

    /// Returns the servername per the SSL, as set by
    /// SSL_set_tlsext_host_name, if called. For testing.
    std::string getSslServername() const
    {
        const int type = SSL_get_servername_type(_ssl);
        if (type != -1)
        {
            const char* name = SSL_get_servername(_ssl, type);
            if (name)
            {
                return std::string(name);
            }
        }

        return std::string();
    }

    /// Shutdown the TLS/SSL connection properly.
    void shutdownConnection() override
    {
        LOG_DBG("SslStreamSocket::shutdownConnection() #" << getFD());
        if (SSL_shutdown(_ssl) == 0)
        {
            // Complete the bidirectional shutdown.
            SSL_shutdown(_ssl);
        }

        // Close the TCP Socket.
        syncShutdown();
    }

    int readIncomingData() override
    {
        ASSERT_CORRECT_SOCKET_THREAD(this);

        const int rc = doHandshake();
        if (rc <= 0)
        {
            // 0 means shutdown.
            return rc;
        }

        // Default implementation.
        return StreamSocket::readIncomingData();
    }

    int writeOutgoingData() override
    {
        ASSERT_CORRECT_SOCKET_THREAD(this);

        const int rc = doHandshake();
        if (rc <= 0)
        {
            // 0 means shutdown.
            return rc;
        }

        // Default implementation.
        return StreamSocket::writeOutgoingData();
    }

    virtual int readData(char* buf, int len) override
    {
        ASSERT_CORRECT_SOCKET_THREAD(this);

        // avoided in readIncomingData
        if (ignoringInput())
            return -1;

#if ENABLE_DEBUG
        if (simulateSocketError(true))
            return -1;
#endif
        return handleSslState(SSL_read(_ssl, buf, len), "read");
    }

    virtual int writeData(const char* buf, const int len) override
    {
        ASSERT_CORRECT_SOCKET_THREAD(this);

        assert (len > 0); // Never write 0 bytes.

#if ENABLE_DEBUG
        if (simulateSocketError(false))
            return -1;
#endif
        return handleSslState(SSL_write(_ssl, buf, len), "write");
    }

    int getPollEvents(std::chrono::steady_clock::time_point now,
                      int64_t & timeoutMaxMicroS) override
    {
        ASSERT_CORRECT_SOCKET_THREAD(this);

        // We cannot communicate with a client when SSL wants
        // to negotiate the handshake. Here, we give priority to
        // SSL's needs. Only when SSL is done negotiating
        // (i.e. wants neither to read, nor to write) do we see
        // what data activity we have.
        if (_doHandshake)
        {
            if (_sslWantsTo == SslWantsTo::Write)
            {
                return POLLOUT;
            }

            if (_sslWantsTo == SslWantsTo::Read)
            {
                return POLLIN;
            }

            // The first call will have SslWantsTo::Neither and
            // we will fall-through and call the base.
        }

        int events = StreamSocket::getPollEvents(now, timeoutMaxMicroS); // Default to base.
        if (_sslWantsTo == SslWantsTo::Write) // If OpenSSL wants to write (and we don't).
            events |= POLLOUT;

        return events;
    }

private:
    /// The possible next I/O operation that SSL want to do.
    enum class SslWantsTo : std::uint8_t
    {
        Neither,
        Read,
        Write
    };

    int doHandshake()
    {
        ASSERT_CORRECT_SOCKET_THREAD(this);

        if (_doHandshake)
        {
            int rc;
            do
            {
                rc = SSL_do_handshake(_ssl);
            }
            while (rc < 0 && errno == EINTR);

            if (rc <= 0)
            {
                rc = handleSslState(rc, "handshake");
                if (rc <= 0)
                {
                    // 0 means shutdown.
                    return rc;
                }
            }

            if (rc == 1)
            {
                // Successful handshake; TLS/SSL connection established.
                LOG_TRC("SSL handshake completed successfully");
                _doHandshake = false;
                _sslWantsTo = SslWantsTo::Neither; // Reset until we are told otherwise.

                if (!verifyCertificate())
                {
                    LOG_WRN("Failed to verify the certificate of [" << hostname() << ']');
                    shutdownConnection();
                    return 0; // Connection is closed.
                }
            }
            else
            {
                LOG_ERR("Unexpected return code from SSL_do_handshake: " << rc);
                return rc;
            }
        }

        // Handshake complete.
        return 1;
    }

    /// Verify the peer's certificate.
    /// Return true iff the certificate matches the hostname.
    bool verifyCertificate();

    /// Handles the state of SSL after read or write.
    int handleSslState(const int rc, const char* context)
    {
        int last_errno = errno; // Capture first thing.

        ASSERT_CORRECT_SOCKET_THREAD(this);

        if (rc > 0)
        {
            const unsigned long bioError = ERR_peek_error();
            if (bioError != 0)
            {
                constexpr size_t errorStringLength = 256;
                char errorString[errorStringLength + 1] = { '\0' };
                ERR_error_string_n(bioError, errorString, errorStringLength);

                LOG_DBG("Unexpected SSL error (" << errorString
                                                 << ") after success implies uncleared earlier "
                                                    "errors or a bug in the SSL library");
                ERR_clear_error();
            }

            // Success: Reset so we can do either.
            _sslWantsTo = SslWantsTo::Neither;
            return rc;
        }

        // Handle errors in the error-queue.
        const int ret = handleSslError(rc, last_errno, context);
        errno = last_errno; // Restore errno.

        ERR_clear_error(); // Make sure we leave no errors in the queue.

        return ret;
    }

    /// Maps SSL Error codes to their respective string form.
    static constexpr std::string_view sslErrorToName(int sslError)
    {
        switch (sslError)
        {
            case SSL_ERROR_NONE:
                return "NONE";
            case SSL_ERROR_SSL:
                return "SSL";
            case SSL_ERROR_WANT_READ:
                return "WANT_READ";
            case SSL_ERROR_WANT_WRITE:
                return "WANT_WRITE";
            case SSL_ERROR_WANT_X509_LOOKUP:
                return "WANT_X509_LOOKUP";
            case SSL_ERROR_SYSCALL:
                return "SYSCALL";
            case SSL_ERROR_ZERO_RETURN:
                return "ZERO_RETURN";
            case SSL_ERROR_WANT_CONNECT:
                return "WANT_CONNECT";
            case SSL_ERROR_WANT_ACCEPT:
                return "WANT_ACCEPT";
            case SSL_ERROR_WANT_ASYNC:
                return "WANT_ASYNC";
            case SSL_ERROR_WANT_ASYNC_JOB:
                return "WANT_ASYNC_JOB";
            case SSL_ERROR_WANT_CLIENT_HELLO_CB:
                return "WANT_CLIENT_HELLO_CB";
            case SSL_ERROR_WANT_RETRY_VERIFY:
                return "WANT_RETRY_VERIFY";
        }

        return "UNKNOWN";
    }

    /// Handle SSL errors after read or write. Called from handleSslState().
    int handleSslError(const int rc, int& last_errno, const char* context)
    {
        assert(rc <= 0 && "Expected SSL failure to handle but have success");

        // Last operation failed. Find out if SSL was trying
        // to do something different that failed, or not.
        const int sslError = SSL_get_error(_ssl, rc);
        LOG_ASSERT_MSG(sslError != SSL_ERROR_NONE, "Expected an SSL error to handle but have none");

        // If the error is coming from BIO, get the code and text.
        const unsigned long bioError = ERR_peek_error();
        const std::string bioErrStr = getBioError(bioError);

        // Having an empty answer is valid, no need to log
        // EAGAIN, SSL_ERROR_WANT_READ/SSL_ERROR_WANT_WRITE are normal business
        if (bioError != SSL_ERROR_ZERO_RETURN && bioError != SSL_ERROR_WANT_READ && bioError != SSL_ERROR_WANT_WRITE) {
            LOG_DBG("SSL error (" << context << "): " << sslErrorToName(sslError) << " (" << sslError
                              << "), rc: " << rc << ", errno: " << last_errno << " ("
                              << Util::symbolicErrno(last_errno) << ": "
                              << std::strerror(last_errno) << "): " << bioErrStr);
        } else {
            LOG_TRC("SSL error (" << context << "): " << sslErrorToName(sslError) << " (" << sslError
                              << "), rc: " << rc << ", errno: " << last_errno << " ("
                              << Util::symbolicErrno(last_errno) << ": "
                              << std::strerror(last_errno) << "): " << bioErrStr);
        }

        // Handle non-fatal cases first.
        switch (sslError)
        {
            // Not an error; should be handled elsewhere.
            case SSL_ERROR_NONE: // 0
                return rc;

            // Peer stopped writing. We have nothing more to read, but can write.
            // This doesn't necessarily signify that we are disconnected.
            case SSL_ERROR_ZERO_RETURN: // 6
                return 0;

            // Retry: Need to read/write data. Effectively, EAGAIN but for a specific operation.
            case SSL_ERROR_WANT_READ: // 2
            case SSL_ERROR_WANT_WRITE: // 3
                LOG_TRC(sslErrorToName(sslError)
                        << " with " << (SSL_has_pending(_ssl) ? "(" : "no(") << SSL_pending(_ssl)
                        << ") pending data to read");
                _sslWantsTo =
                    sslError == SSL_ERROR_WANT_READ ? SslWantsTo::Read : SslWantsTo::Write;
                return rc;

            // Retry.
            case SSL_ERROR_WANT_CONNECT: // 7
            case SSL_ERROR_WANT_ACCEPT: // 8
                return rc;

            // Unexpected: happens only with SSL_CTX_set_client_cert_cb().
            case SSL_ERROR_WANT_X509_LOOKUP: // 4
            case SSL_ERROR_WANT_CLIENT_HELLO_CB: // 11
                LOG_ASSERT_MSG(!"Unhandled use of SSL_CTX_set_client_cert_cb()",
                               "Unhandled " << sslErrorToName(sslError)
                                            << " with SSL_CTX_set_client_cert_cb()");
                return rc;

            case SSL_ERROR_WANT_ASYNC: // 9
            case SSL_ERROR_WANT_ASYNC_JOB: // 10
                LOG_ASSERT_MSG(!"Unhandled use of SSL_MODE_ASYNC",
                               "Unhandled " << sslErrorToName(sslError) << " with SSL_MODE_ASYNC");
                return rc;

            // Non-recoverable, fatal I/O error occurred.
            // Check errno *and* the error queue.
            case SSL_ERROR_SYSCALL: // 5
                if (last_errno != 0)
                {
                    // Posix API error, let the caller handle.
                    return rc;
                }

                [[fallthrough]];

            // Non-recoverable, fatal I/O error occurred.
            // SSL_shutdown() must not be called.
            case SSL_ERROR_SSL: // 1
            default:
            {
                // We should know what errors we handle here.
                LOG_ASSERT_MSG(sslError == SSL_ERROR_SYSCALL || sslError == SSL_ERROR_SSL,
                               "Unexpected SSL error " << sslErrorToName(sslError));

                // Effectively an EAGAIN error at the BIO layer
                if (BIO_should_retry(_bio))
                {
                    LOG_TRC("BIO asks for retry - underlying EAGAIN? with "
                            << (SSL_has_pending(_ssl) ? "(" : "no(") << SSL_pending(_ssl)
                            << ") pending data to read");
                    last_errno = last_errno ? last_errno : EAGAIN; // Set errno if unset.
                    return -1; // poll is used to detect real errors.
                }

                std::ostringstream oss;
                oss << '#' << getFD();

                if (bioError == 0)
                {
                    if (rc == 0)
                    {
                        // Socket closed. Not an error.
                        oss << " (" << context << "): closed. " << bioErrStr;
                    }
                    else if (rc == -1)
                    {
                        oss << " (" << context << "): socket closed unexpectedly. ";
                    }
                    else
                    {
                        oss << " (" << context << "): unknown. ";
                    }
                }
                else
                {
                    oss << " (" << context << "): unknown. ";
                }

                oss << bioErrStr;
                LOG_DBG("SSL Error (" << context << "): " << oss.str());

                handshakeFail();

                std::string sslVerifyResult = getSslVerifyString(SSL_get_verify_result(_ssl));
                // If there is anything useful available from SSL_get_verify_result provide a warning about that.
                if (!sslVerifyResult.empty())
                    LOG_ERR("SSL verification warning (" << context << "): " << sslVerifyResult);

                last_errno = last_errno ? last_errno : EPIPE; // Set errno if unset.
                return 0; // EOF.
            }
            break;
        }

        return rc;
    }

    /// Get the error string for the given error code from OpenSSL.
    static std::string getBioError(const unsigned long bioError)
    {
        std::ostringstream oss;
        oss << "BIO error: " << bioError;

        char buf[512];
        ERR_error_string_n(bioError, buf, sizeof(buf));

        oss << ": " << buf << ':';

        auto cb = [](const char* str, size_t len, void* u) -> int
        {
            std::ostringstream& os = *static_cast<std::ostringstream*>(u);
            os << '\n' << std::string_view(str, len);
            return 1; // Apparently 0 means failure here.
        };

        ERR_print_errors_cb(cb, &oss);
        return oss.str();
    }

private:
    BIO* _bio;
    SSL* _ssl;
    ssl::CertificateVerification _verification; ///< The certificate verification requirement.

    /// During handshake SSL might want to read
    /// on write, or write on read.
    SslWantsTo _sslWantsTo;
    /// We must do the handshake during the first
    /// read or write in non-blocking.
    bool _doHandshake;
};

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