Crafter.Network/implementations/Crafter.Network-TLS.cpp

//SPDX-License-Identifier: LGPL-3.0-only
//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

module;
#include <poll.h>
#include <arpa/inet.h>
#include <cerrno>
#include <climits>

#include <openssl/bio.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/pem.h>
#include <openssl/ssl.h>
#include <openssl/sslerr.h>
#include <openssl/x509v3.h>

module Crafter.Network:TLS_impl;
import :TLS;
import :Stream;
import std;

using namespace Crafter;

namespace {
    // ── OpenSSL plumbing ─────────────────────────────────────────────────
    template <typename T, void (*Release)(T*)>
    struct Releaser {
        void operator()(T* pointer) const noexcept { if (pointer) Release(pointer); }
    };
    template <typename T, void (*Release)(T*)>
    using Owned = std::unique_ptr<T, Releaser<T, Release>>;

    using OwnedBio = Owned<BIO, BIO_free_all>;
    using OwnedKey = Owned<EVP_PKEY, EVP_PKEY_free>;
    using OwnedCertificate = Owned<X509, X509_free>;

    // Drain OpenSSL's per-thread error queue into a readable message. Without
    // this every TLS failure reads as "handshake failed" with no hint as to
    // whether it was the certificate, the version, or the peer hanging up.
    std::string Describe(std::string_view what) {
        std::string message(what);
        bool first = true;
        while (const unsigned long code = ERR_get_error()) {
            char buffer[256];
            ERR_error_string_n(code, buffer, sizeof(buffer));
            message += first ? ": " : "; ";
            message += buffer;
            first = false;
        }
        return message;
    }

    // True once OpenSSL has told us the peer vanished without a close_notify.
    // For HTTP/1.1 that is an end of connection like any other — the message
    // parser is the thing that decides whether it arrived too early.
    bool UnexpectedEof() {
        const unsigned long code = ERR_peek_error();
        return ERR_GET_LIB(code) == ERR_LIB_SSL
            && ERR_GET_REASON(code) == SSL_R_UNEXPECTED_EOF_WHILE_READING;
    }

    std::string BioToString(BIO* bio) {
        char* data = nullptr;
        const long length = BIO_get_mem_data(bio, &data);
        if (length <= 0 || data == nullptr) return {};
        return std::string(data, static_cast<std::size_t>(length));
    }

    bool IsIpLiteral(const std::string& name) {
        in_addr v4{};
        in6_addr v6{};
        return inet_pton(AF_INET, name.c_str(), &v4) == 1
            || inet_pton(AF_INET6, name.c_str(), &v6) == 1;
    }

    // ── ALPN ─────────────────────────────────────────────────────────────
    // Wire form is a sequence of length-prefixed protocol names.
    std::vector<unsigned char> EncodeAlpn(const std::vector<std::string>& protocols) {
        std::vector<unsigned char> wire;
        for (const std::string& protocol : protocols) {
            if (protocol.empty() || protocol.size() > 255) {
                throw TLSException("ALPN protocol names must be 1..255 bytes: '" + protocol + "'");
            }
            wire.push_back(static_cast<unsigned char>(protocol.size()));
            wire.insert(wire.end(), protocol.begin(), protocol.end());
        }
        return wire;
    }

    // Server-side selection, in *our* preference order rather than the
    // client's: the server is the side that knows what it can actually parse.
    // No overlap is a fatal no_application_protocol alert (RFC 7301 §3.2) —
    // letting the connection through would mean answering HTTP/2 with an
    // HTTP/1.1 response and confusing both ends.
    int SelectAlpn(SSL*, const unsigned char** out, unsigned char* outLength,
                   const unsigned char* in, unsigned int inLength, void* argument) {
        const auto& preferred = *static_cast<const std::vector<std::string>*>(argument);
        for (const std::string& candidate : preferred) {
            for (unsigned int offset = 0; offset < inLength;) {
                const unsigned int length = in[offset];
                if (offset + 1 + length > inLength) break;  // malformed list
                if (length == candidate.size()
                    && std::memcmp(in + offset + 1, candidate.data(), length) == 0) {
                    *out = in + offset + 1;
                    *outLength = static_cast<unsigned char>(length);
                    return SSL_TLSEXT_ERR_OK;
                }
                offset += 1 + length;
            }
        }
        return SSL_TLSEXT_ERR_ALERT_FATAL;
    }

    // ── Self-signed certificate ──────────────────────────────────────────
    void AddExtension(X509* certificate, X509V3_CTX* context, int nid, const char* value) {
        X509_EXTENSION* extension = X509V3_EXT_conf_nid(nullptr, context, nid, value);
        if (extension == nullptr) {
            throw TLSException(Describe("could not build certificate extension"));
        }
        const int added = X509_add_ext(certificate, extension, -1);
        X509_EXTENSION_free(extension);
        if (added != 1) throw TLSException(Describe("could not add certificate extension"));
    }

    TLSCertificatePem MakeSelfSignedCertificate() {
        OwnedKey key(EVP_EC_gen("P-256"));
        if (!key) throw TLSException(Describe("could not generate a P-256 key"));

        OwnedCertificate certificate(X509_new());
        if (!certificate) throw TLSException(Describe("could not allocate a certificate"));

        // X509_set_version takes the zero-based version, so 2 is v3 — which is
        // what the extensions below require.
        X509_set_version(certificate.get(), 2);
        ASN1_INTEGER_set(X509_get_serialNumber(certificate.get()), 1);
        // Backdated an hour so a peer whose clock runs slightly behind ours
        // does not reject a certificate we just minted.
        X509_gmtime_adj(X509_getm_notBefore(certificate.get()), -3600);
        X509_gmtime_adj(X509_getm_notAfter(certificate.get()), 10 * 24 * 60 * 60);
        if (X509_set_pubkey(certificate.get(), key.get()) != 1) {
            throw TLSException(Describe("could not set the certificate public key"));
        }

        X509_NAME* subject = X509_get_subject_name(certificate.get());
        X509_NAME_add_entry_by_txt(subject, "CN", MBSTRING_ASC,
                                   reinterpret_cast<const unsigned char*>("localhost"), -1, -1, 0);
        // Self-signed: issuer is the subject.
        X509_set_issuer_name(certificate.get(), subject);

        X509V3_CTX extensionContext;
        X509V3_set_ctx_nodb(&extensionContext);
        X509V3_set_ctx(&extensionContext, certificate.get(), certificate.get(),
                       nullptr, nullptr, 0);
        AddExtension(certificate.get(), &extensionContext, NID_basic_constraints,
                     "critical,CA:FALSE");
        AddExtension(certificate.get(), &extensionContext, NID_key_usage,
                     "critical,digitalSignature,keyEncipherment");
        AddExtension(certificate.get(), &extensionContext, NID_ext_key_usage, "serverAuth");
        // The SANs are what a verifying client actually matches on; a bare CN
        // has not been accepted by anything for years.
        AddExtension(certificate.get(), &extensionContext, NID_subject_alt_name,
                     "DNS:localhost,IP:127.0.0.1,IP:::1");

        if (X509_sign(certificate.get(), key.get(), EVP_sha256()) == 0) {
            throw TLSException(Describe("could not sign the certificate"));
        }

        TLSCertificatePem pem;
        {
            OwnedBio bio(BIO_new(BIO_s_mem()));
            if (!bio || PEM_write_bio_X509(bio.get(), certificate.get()) != 1) {
                throw TLSException(Describe("could not encode the certificate as PEM"));
            }
            pem.certificate = BioToString(bio.get());
        }
        {
            OwnedBio bio(BIO_new(BIO_s_mem()));
            if (!bio || PEM_write_bio_PrivateKey(bio.get(), key.get(), nullptr, nullptr, 0,
                                                 nullptr, nullptr) != 1) {
                throw TLSException(Describe("could not encode the private key as PEM"));
            }
            pem.privateKey = BioToString(bio.get());
        }
        return pem;
    }

    // ── Credential loading ───────────────────────────────────────────────
    OwnedBio MemoryBio(const std::string& contents) {
        if (contents.size() > static_cast<std::size_t>(INT_MAX)) {
            throw TLSException("PEM blob is implausibly large");
        }
        OwnedBio bio(BIO_new_mem_buf(contents.data(), static_cast<int>(contents.size())));
        if (!bio) throw TLSException(Describe("could not wrap the PEM blob"));
        return bio;
    }

    // Leaf first, then any intermediates, exactly as OpenSSL's own
    // *_chain_file loader treats a PEM bundle.
    void UseCertificateChainPem(SSL_CTX* context, const std::string& pem) {
        OwnedBio bio = MemoryBio(pem);
        OwnedCertificate leaf(PEM_read_bio_X509(bio.get(), nullptr, nullptr, nullptr));
        if (!leaf) throw TLSException(Describe("could not read the certificate PEM"));
        if (SSL_CTX_use_certificate(context, leaf.get()) != 1) {
            throw TLSException(Describe("could not install the certificate"));
        }
        SSL_CTX_clear_chain_certs(context);
        for (;;) {
            OwnedCertificate extra(PEM_read_bio_X509(bio.get(), nullptr, nullptr, nullptr));
            if (!extra) break;
            // add0 takes ownership on success, so the pointer is released.
            if (SSL_CTX_add0_chain_cert(context, extra.get()) != 1) {
                throw TLSException(Describe("could not install a chain certificate"));
            }
            (void)extra.release();
        }
        // PEM_read_bio_X509 leaves a "no start line" error behind when it runs
        // out of certificates; that is the loop's exit condition, not a fault.
        ERR_clear_error();
    }

    void UsePrivateKeyPem(SSL_CTX* context, const std::string& pem) {
        OwnedBio bio = MemoryBio(pem);
        OwnedKey key(PEM_read_bio_PrivateKey(bio.get(), nullptr, nullptr, nullptr));
        if (!key) throw TLSException(Describe("could not read the private key PEM"));
        if (SSL_CTX_use_PrivateKey(context, key.get()) != 1) {
            throw TLSException(Describe("could not install the private key"));
        }
    }

    // A trust anchor path is either a PEM bundle or a hashed directory of
    // them; OpenSSL wants to be told which, so look.
    void LoadTrustAnchorPath(SSL_CTX* context, const std::string& path) {
        std::error_code error;
        const bool directory = std::filesystem::is_directory(path, error);
        const int loaded = directory
            ? SSL_CTX_load_verify_locations(context, nullptr, path.c_str())
            : SSL_CTX_load_verify_locations(context, path.c_str(), nullptr);
        if (loaded != 1) {
            throw TLSException(Describe("could not load trust anchors from '" + path + "'"));
        }
    }

    void LoadTrustAnchorPem(SSL_CTX* context, const std::string& pem) {
        X509_STORE* store = SSL_CTX_get_cert_store(context);
        OwnedBio bio = MemoryBio(pem);
        std::size_t added = 0;
        for (;;) {
            OwnedCertificate anchor(PEM_read_bio_X509(bio.get(), nullptr, nullptr, nullptr));
            if (!anchor) break;
            if (X509_STORE_add_cert(store, anchor.get()) != 1) {
                throw TLSException(Describe("could not add a trust anchor"));
            }
            ++added;
        }
        ERR_clear_error();
        if (added == 0) throw TLSException("caPem contained no certificate");
    }

    void ApplyCommonOptions(SSL_CTX* context) {
        // TLS 1.2 floor: 1.0/1.1 are deprecated (RFC 8996) and nothing we want
        // to talk to needs them.
        if (SSL_CTX_set_min_proto_version(context, TLS1_2_VERSION) != 1) {
            throw TLSException(Describe("could not require TLS 1.2 or newer"));
        }
        // Partial writes plus a moving write buffer: our Write() loops over
        // its own offset, so it must be allowed to make progress a record at a
        // time instead of being forced to re-present a byte-identical buffer.
        SSL_CTX_set_mode(context, SSL_MODE_ENABLE_PARTIAL_WRITE
                                | SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER);
        // Renegotiation buys nothing here and is a cheap way for a peer to
        // make us do asymmetric crypto on demand.
        SSL_CTX_set_options(context, SSL_OP_NO_RENEGOTIATION);
    }
}

// ── TLSContext ───────────────────────────────────────────────────────────
struct TLSContext::Impl {
    SSL_CTX* context = nullptr;
    bool verifyPeer = true;
    std::string serverName;
    // Server preference list; SelectAlpn holds a pointer to it, so it must
    // outlive every SSL made from this context — which it does, being owned
    // by the shared_ptr'd TLSContext.
    std::vector<std::string> alpn;

    ~Impl() { if (context) SSL_CTX_free(context); }
};

TLSContext::TLSContext() : impl(std::make_unique<Impl>()) {}
TLSContext::~TLSContext() = default;

std::shared_ptr<TLSContext> TLSContext::Server(const TLSServerCredentials& credentials) {
    std::shared_ptr<TLSContext> wrapper(new TLSContext());
    Impl& state = *wrapper->impl;

    state.context = SSL_CTX_new(TLS_server_method());
    if (state.context == nullptr) throw TLSException(Describe("could not create a TLS context"));
    ApplyCommonOptions(state.context);

    if (!credentials.certPath.empty()) {
        if (credentials.keyPath.empty()) {
            throw TLSException("certPath was given without a matching keyPath");
        }
        if (SSL_CTX_use_certificate_chain_file(state.context, credentials.certPath.c_str()) != 1) {
            throw TLSException(Describe("could not load the certificate '"
                                        + credentials.certPath + "'"));
        }
        if (SSL_CTX_use_PrivateKey_file(state.context, credentials.keyPath.c_str(),
                                        SSL_FILETYPE_PEM) != 1) {
            throw TLSException(Describe("could not load the private key '"
                                        + credentials.keyPath + "'"));
        }
    } else if (!credentials.certPem.empty()) {
        if (credentials.keyPem.empty()) {
            throw TLSException("certPem was given without a matching keyPem");
        }
        UseCertificateChainPem(state.context, credentials.certPem);
        UsePrivateKeyPem(state.context, credentials.keyPem);
    } else if (credentials.selfSigned) {
        const TLSCertificatePem& pem = GetSelfSignedCertificatePem();
        UseCertificateChainPem(state.context, pem.certificate);
        UsePrivateKeyPem(state.context, pem.privateKey);
    } else {
        throw TLSException("no server certificate: set certPath/keyPath, certPem/keyPem, "
                           "or selfSigned for a development certificate");
    }
    if (SSL_CTX_check_private_key(state.context) != 1) {
        throw TLSException(Describe("the private key does not match the certificate"));
    }

    if (credentials.requireClientCertificate) {
        if (!credentials.clientCaPath.empty()) {
            LoadTrustAnchorPath(state.context, credentials.clientCaPath);
            // Advertise the acceptable issuers so the client can choose a
            // certificate instead of guessing.
            std::error_code error;
            if (!std::filesystem::is_directory(credentials.clientCaPath, error)) {
                if (STACK_OF(X509_NAME)* names =
                        SSL_load_client_CA_file(credentials.clientCaPath.c_str())) {
                    SSL_CTX_set_client_CA_list(state.context, names);
                }
            }
        } else if (SSL_CTX_set_default_verify_paths(state.context) != 1) {
            throw TLSException(Describe("could not load the system trust store"));
        }
        SSL_CTX_set_verify(state.context,
                           SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT, nullptr);
    }

    state.alpn = credentials.alpnProtocols;
    if (!state.alpn.empty()) {
        // Validate the names now rather than inside the handshake callback,
        // where there is nowhere useful to report a bad configuration.
        (void)EncodeAlpn(state.alpn);
        SSL_CTX_set_alpn_select_cb(state.context, SelectAlpn, &state.alpn);
    }
    return wrapper;
}

std::shared_ptr<TLSContext> TLSContext::Client(const TLSClientCredentials& credentials) {
    std::shared_ptr<TLSContext> wrapper(new TLSContext());
    Impl& state = *wrapper->impl;

    state.context = SSL_CTX_new(TLS_client_method());
    if (state.context == nullptr) throw TLSException(Describe("could not create a TLS context"));
    ApplyCommonOptions(state.context);

    state.verifyPeer = !credentials.insecureNoServerValidation;
    state.serverName = credentials.serverName;
    if (state.verifyPeer) {
        if (SSL_CTX_set_default_verify_paths(state.context) != 1) {
            throw TLSException(Describe("could not load the system trust store"));
        }
        if (!credentials.caPath.empty()) LoadTrustAnchorPath(state.context, credentials.caPath);
        if (!credentials.caPem.empty()) LoadTrustAnchorPem(state.context, credentials.caPem);
        SSL_CTX_set_verify(state.context, SSL_VERIFY_PEER, nullptr);
    } else {
        // The handshake still completes and SSL_get_verify_result still
        // reports what it found; nothing acts on it.
        SSL_CTX_set_verify(state.context, SSL_VERIFY_NONE, nullptr);
    }

    if (!credentials.certPath.empty()) {
        if (credentials.keyPath.empty()) {
            throw TLSException("certPath was given without a matching keyPath");
        }
        if (SSL_CTX_use_certificate_chain_file(state.context, credentials.certPath.c_str()) != 1) {
            throw TLSException(Describe("could not load the client certificate '"
                                        + credentials.certPath + "'"));
        }
        if (SSL_CTX_use_PrivateKey_file(state.context, credentials.keyPath.c_str(),
                                        SSL_FILETYPE_PEM) != 1) {
            throw TLSException(Describe("could not load the client private key '"
                                        + credentials.keyPath + "'"));
        }
        if (SSL_CTX_check_private_key(state.context) != 1) {
            throw TLSException(Describe("the client key does not match the client certificate"));
        }
    }

    if (!credentials.alpnProtocols.empty()) {
        const std::vector<unsigned char> wire = EncodeAlpn(credentials.alpnProtocols);
        if (SSL_CTX_set_alpn_protos(state.context, wire.data(),
                                    static_cast<unsigned int>(wire.size())) != 0) {
            throw TLSException(Describe("could not set the ALPN protocol list"));
        }
    }
    return wrapper;
}

// ── TLSStream ────────────────────────────────────────────────────────────
struct TLSStream::Impl {
    std::shared_ptr<TLSContext> context;
    SSL* ssl = nullptr;
    int descriptor = -1;
    std::string protocol;
    bool shutdownSent = false;

    ~Impl() { if (ssl) SSL_free(ssl); }

    // Drive SSL_connect/SSL_accept to completion, polling for whichever
    // direction OpenSSL is waiting on. The deadline covers the whole
    // handshake, not each poll, so a peer that dribbles records cannot
    // stretch it indefinitely.
    void Handshake(bool client, std::chrono::milliseconds timeout) {
        const auto deadline = std::chrono::steady_clock::now() + timeout;
        for (;;) {
            ERR_clear_error();
            const int result = client ? SSL_connect(ssl) : SSL_accept(ssl);
            if (result == 1) break;

            const int error = SSL_get_error(ssl, result);
            if (error == SSL_ERROR_WANT_READ || error == SSL_ERROR_WANT_WRITE) {
                const short events = error == SSL_ERROR_WANT_READ ? POLLIN : POLLOUT;
                if (!PollDescriptor(descriptor, events, deadline)) {
                    throw TLSException("TLS handshake timed out");
                }
                continue;
            }
            // Certificate problems are the failure people actually hit, and
            // OpenSSL's generic queue message for them ("certificate verify
            // failed") does not say which check tripped.
            const long verified = SSL_get_verify_result(ssl);
            if (verified != X509_V_OK) {
                throw TLSException(std::string("TLS certificate rejected: ")
                                   + X509_verify_cert_error_string(verified));
            }
            if (error == SSL_ERROR_ZERO_RETURN
                || (error == SSL_ERROR_SYSCALL && result == 0)
                || (error == SSL_ERROR_SSL && UnexpectedEof())) {
                throw TLSException("the peer closed the connection during the TLS handshake");
            }
            if (error == SSL_ERROR_SYSCALL) {
                throw TLSException(std::string("TLS handshake failed: ") + std::strerror(errno));
            }
            throw TLSException(Describe("TLS handshake failed"));
        }

        const unsigned char* selected = nullptr;
        unsigned int length = 0;
        SSL_get0_alpn_selected(ssl, &selected, &length);
        if (selected != nullptr && length != 0) {
            protocol.assign(reinterpret_cast<const char*>(selected), length);
        }
    }
};

TLSStream::TLSStream() : impl(std::make_unique<Impl>()) {}

TLSStream::~TLSStream() {
    Shutdown();
}

std::unique_ptr<TLSStream> TLSStream::Connect(int descriptor,
                                              std::shared_ptr<TLSContext> context,
                                              const std::string& hostName,
                                              std::chrono::milliseconds timeout) {
    if (!context) throw TLSException("no TLS context");
    SetNonBlocking(descriptor);

    std::unique_ptr<TLSStream> stream(new TLSStream());
    TLSContext::Impl& configuration = *context->impl;
    stream->impl->context = std::move(context);
    stream->impl->descriptor = descriptor;

    SSL* ssl = SSL_new(configuration.context);
    if (ssl == nullptr) throw TLSException(Describe("could not create a TLS session"));
    stream->impl->ssl = ssl;
    if (SSL_set_fd(ssl, descriptor) != 1) {
        throw TLSException(Describe("could not attach the socket to the TLS session"));
    }

    const std::string& name = configuration.serverName.empty()
        ? hostName : configuration.serverName;
    const bool literal = !name.empty() && IsIpLiteral(name);
    // SNI carries host names only — an IP literal there is a protocol
    // violation and some servers reject the handshake outright (RFC 6066 §3).
    if (!name.empty() && !literal && SSL_set_tlsext_host_name(ssl, name.c_str()) != 1) {
        throw TLSException(Describe("could not set the SNI host name"));
    }
    if (configuration.verifyPeer) {
        if (name.empty()) {
            throw TLSException("certificate verification needs a name to check against; "
                               "set serverName or use insecureNoServerValidation");
        }
        SSL_set_hostflags(ssl, X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS);
        const int named = literal
            ? X509_VERIFY_PARAM_set1_ip_asc(SSL_get0_param(ssl), name.c_str())
            : SSL_set1_host(ssl, name.c_str());
        if (named != 1) {
            throw TLSException("could not use '" + name + "' as the name to verify");
        }
    }

    SSL_set_connect_state(ssl);
    stream->impl->Handshake(true, timeout);
    return stream;
}

std::unique_ptr<TLSStream> TLSStream::Accept(int descriptor,
                                             std::shared_ptr<TLSContext> context,
                                             std::chrono::milliseconds timeout) {
    if (!context) throw TLSException("no TLS context");
    SetNonBlocking(descriptor);

    std::unique_ptr<TLSStream> stream(new TLSStream());
    TLSContext::Impl& configuration = *context->impl;
    stream->impl->context = std::move(context);
    stream->impl->descriptor = descriptor;

    SSL* ssl = SSL_new(configuration.context);
    if (ssl == nullptr) throw TLSException(Describe("could not create a TLS session"));
    stream->impl->ssl = ssl;
    if (SSL_set_fd(ssl, descriptor) != 1) {
        throw TLSException(Describe("could not attach the socket to the TLS session"));
    }

    SSL_set_accept_state(ssl);
    stream->impl->Handshake(false, timeout);
    return stream;
}

StreamStatus TLSStream::ReadSome(char* buffer, std::size_t size,
                                 std::chrono::milliseconds timeout,
                                 std::size_t& read) {
    read = 0;
    if (size == 0) return StreamStatus::Data;
    const auto deadline = std::chrono::steady_clock::now() + timeout;
    const int wanted = static_cast<int>(std::min<std::size_t>(size, INT_MAX));
    for (;;) {
        ERR_clear_error();
        const int got = SSL_read(impl->ssl, buffer, wanted);
        if (got > 0) {
            read = static_cast<std::size_t>(got);
            return StreamStatus::Data;
        }
        const int error = SSL_get_error(impl->ssl, got);
        switch (error) {
            case SSL_ERROR_WANT_READ:
                if (!PollDescriptor(impl->descriptor, POLLIN, deadline)) {
                    return StreamStatus::TimedOut;
                }
                continue;
            // A read can need the socket writable: TLS 1.3 key updates and
            // (where allowed) renegotiation both send records mid-read.
            case SSL_ERROR_WANT_WRITE:
                if (!PollDescriptor(impl->descriptor, POLLOUT, deadline)) {
                    return StreamStatus::TimedOut;
                }
                continue;
            case SSL_ERROR_ZERO_RETURN:
                return StreamStatus::Closed;   // close_notify: an orderly end
            case SSL_ERROR_SYSCALL:
                if (errno == EINTR) continue;
                if (got == 0 || errno == 0 || errno == ECONNRESET) return StreamStatus::Closed;
                throw TLSException(std::string("TLS read failed: ") + std::strerror(errno));
            case SSL_ERROR_SSL:
                if (UnexpectedEof()) return StreamStatus::Closed;
                throw TLSException(Describe("TLS read failed"));
            default:
                throw TLSException(Describe("TLS read failed"));
        }
    }
}

void TLSStream::Write(const void* buffer, std::size_t size,
                      std::chrono::milliseconds timeout) {
    const auto deadline = std::chrono::steady_clock::now() + timeout;
    const char* data = reinterpret_cast<const char*>(buffer);
    std::size_t sent = 0;
    while (sent < size) {
        const int wanted = static_cast<int>(std::min<std::size_t>(size - sent, INT_MAX));
        ERR_clear_error();
        const int wrote = SSL_write(impl->ssl, data + sent, wanted);
        if (wrote > 0) {
            sent += static_cast<std::size_t>(wrote);
            continue;
        }
        const int error = SSL_get_error(impl->ssl, wrote);
        switch (error) {
            case SSL_ERROR_WANT_READ:
                if (!PollDescriptor(impl->descriptor, POLLIN, deadline)) {
                    throw TLSException("timed out writing to the TLS peer");
                }
                continue;
            case SSL_ERROR_WANT_WRITE:
                if (!PollDescriptor(impl->descriptor, POLLOUT, deadline)) {
                    throw TLSException("timed out writing to the TLS peer");
                }
                continue;
            case SSL_ERROR_ZERO_RETURN:
                throw TLSException("the TLS peer closed the connection");
            case SSL_ERROR_SYSCALL:
                if (errno == EINTR) continue;
                throw TLSException(std::string("TLS write failed: ")
                                   + (errno == 0 ? "the peer closed the connection"
                                                 : std::strerror(errno)));
            default:
                throw TLSException(Describe("TLS write failed"));
        }
    }
}

void TLSStream::Shutdown() noexcept {
    if (!impl || impl->ssl == nullptr || impl->shutdownSent) return;
    impl->shutdownSent = true;
    // One attempt only: close_notify goes out, and we deliberately do not
    // wait for the peer's. Waiting means blocking a teardown path on a peer
    // that may never answer, and every framing decision has already been made
    // by the time we get here.
    ERR_clear_error();
    SSL_shutdown(impl->ssl);
    ERR_clear_error();
}

int TLSStream::Descriptor() const noexcept {
    return impl ? impl->descriptor : -1;
}

std::string_view TLSStream::Protocol() const noexcept {
    return impl ? std::string_view(impl->protocol) : std::string_view();
}

std::string TLSStream::Version() const {
    if (!impl || impl->ssl == nullptr) return {};
    const char* version = SSL_get_version(impl->ssl);
    return version == nullptr ? std::string() : std::string(version);
}

std::string TLSStream::PeerCertificateSubject() const {
    if (!impl || impl->ssl == nullptr) return {};
    OwnedCertificate peer(SSL_get1_peer_certificate(impl->ssl));
    if (!peer) return {};
    char buffer[512] = {};
    X509_NAME_oneline(X509_get_subject_name(peer.get()), buffer, sizeof(buffer));
    return std::string(buffer);
}

const TLSCertificatePem& Crafter::GetSelfSignedCertificatePem() {
    // Generated once per process so every listener presents the same
    // certificate: a client that was handed it as a trust anchor keeps
    // working across reconnects.
    static std::mutex mutex;
    static std::optional<TLSCertificatePem> cached;
    std::lock_guard lock(mutex);
    if (!cached) cached = MakeSelfSignedCertificate();
    return *cached;
}