http/http_client.hpp

/*
Copyright (c) 2020 Intel Corporation

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#pragma once

#include "async_resolve.hpp"
#include "http_body.hpp"
#include "http_response.hpp"
#include "logging.hpp"
#include "ssl_key_handler.hpp"

#include <boost/asio/connect.hpp>
#include <boost/asio/io_context.hpp>
#include <boost/asio/ip/address.hpp>
#include <boost/asio/ip/basic_endpoint.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/ssl/context.hpp>
#include <boost/asio/ssl/error.hpp>
#include <boost/asio/ssl/stream.hpp>
#include <boost/asio/steady_timer.hpp>
#include <boost/beast/core/flat_static_buffer.hpp>
#include <boost/beast/http/message.hpp>
#include <boost/beast/http/message_generator.hpp>
#include <boost/beast/http/parser.hpp>
#include <boost/beast/http/read.hpp>
#include <boost/beast/http/write.hpp>
#include <boost/container/devector.hpp>
#include <boost/system/error_code.hpp>
#include <boost/url/format.hpp>
#include <boost/url/url.hpp>
#include <boost/url/url_view_base.hpp>

#include <cstdlib>
#include <functional>
#include <memory>
#include <queue>
#include <string>

namespace crow
{
// With Redfish Aggregation it is assumed we will connect to another
// instance of BMCWeb which can handle 100 simultaneous connections.
constexpr size_t maxPoolSize = 20;
constexpr size_t maxRequestQueueSize = 500;
constexpr unsigned int httpReadBodyLimit = 131072;
constexpr unsigned int httpReadBufferSize = 4096;

enum class ConnState
{
    initialized,
    resolveInProgress,
    resolveFailed,
    connectInProgress,
    connectFailed,
    connected,
    handshakeInProgress,
    handshakeFailed,
    sendInProgress,
    sendFailed,
    recvInProgress,
    recvFailed,
    idle,
    closed,
    suspended,
    terminated,
    abortConnection,
    sslInitFailed,
    retry
};

inline boost::system::error_code defaultRetryHandler(unsigned int respCode)
{
    // As a default, assume 200X is alright
    BMCWEB_LOG_DEBUG("Using default check for response code validity");
    if ((respCode < 200) || (respCode >= 300))
    {
        return boost::system::errc::make_error_code(
            boost::system::errc::result_out_of_range);
    }

    // Return 0 if the response code is valid
    return boost::system::errc::make_error_code(boost::system::errc::success);
};

// We need to allow retry information to be set before a message has been
// sent and a connection pool has been created
struct ConnectionPolicy
{
    uint32_t maxRetryAttempts = 5;

    // the max size of requests in bytes.  0 for unlimited
    boost::optional<uint64_t> requestByteLimit = httpReadBodyLimit;

    size_t maxConnections = 1;

    std::string retryPolicyAction = "TerminateAfterRetries";

    std::chrono::seconds retryIntervalSecs = std::chrono::seconds(0);
    std::function<boost::system::error_code(unsigned int respCode)>
        invalidResp = defaultRetryHandler;
};

struct PendingRequest
{
    boost::beast::http::request<bmcweb::HttpBody> req;
    std::function<void(bool, uint32_t, Response&)> callback;
    PendingRequest(
        boost::beast::http::request<bmcweb::HttpBody>&& reqIn,
        const std::function<void(bool, uint32_t, Response&)>& callbackIn) :
        req(std::move(reqIn)), callback(callbackIn)
    {}
};

namespace http = boost::beast::http;
class ConnectionInfo : public std::enable_shared_from_this<ConnectionInfo>
{
  private:
    ConnState state = ConnState::initialized;
    uint32_t retryCount = 0;
    std::string subId;
    std::shared_ptr<ConnectionPolicy> connPolicy;
    boost::urls::url host;
    ensuressl::VerifyCertificate verifyCert;
    uint32_t connId;
    // Data buffers
    http::request<bmcweb::HttpBody> req;
    using parser_type = http::response_parser<bmcweb::HttpBody>;
    std::optional<parser_type> parser;
    boost::beast::flat_static_buffer<httpReadBufferSize> buffer;
    Response res;

    // Ascync callables
    std::function<void(bool, uint32_t, Response&)> callback;

    boost::asio::io_context& ioc;

    using Resolver = std::conditional_t<BMCWEB_DNS_RESOLVER == "systemd-dbus",
                                        async_resolve::Resolver,
                                        boost::asio::ip::tcp::resolver>;
    Resolver resolver;

    boost::asio::ip::tcp::socket conn;
    std::optional<boost::asio::ssl::stream<boost::asio::ip::tcp::socket&>>
        sslConn;

    boost::asio::steady_timer timer;

    friend class ConnectionPool;

    void doResolve()
    {
        state = ConnState::resolveInProgress;
        BMCWEB_LOG_DEBUG("Trying to resolve: {}, id: {}", host, connId);

        resolver.async_resolve(host.encoded_host_address(), host.port(),
                               std::bind_front(&ConnectionInfo::afterResolve,
                                               this, shared_from_this()));
    }

    void afterResolve(const std::shared_ptr<ConnectionInfo>& /*self*/,
                      const boost::system::error_code& ec,
                      const Resolver::results_type& endpointList)
    {
        if (ec || (endpointList.empty()))
        {
            BMCWEB_LOG_ERROR("Resolve failed: {} {}", ec.message(), host);
            state = ConnState::resolveFailed;
            waitAndRetry();
            return;
        }
        BMCWEB_LOG_DEBUG("Resolved {}, id: {}", host, connId);
        state = ConnState::connectInProgress;

        BMCWEB_LOG_DEBUG("Trying to connect to: {}, id: {}", host, connId);

        timer.expires_after(std::chrono::seconds(30));
        timer.async_wait(std::bind_front(onTimeout, weak_from_this()));

        boost::asio::async_connect(
            conn, endpointList,
            std::bind_front(&ConnectionInfo::afterConnect, this,
                            shared_from_this()));
    }

    void afterConnect(const std::shared_ptr<ConnectionInfo>& /*self*/,
                      const boost::beast::error_code& ec,
                      const boost::asio::ip::tcp::endpoint& endpoint)
    {
        // The operation already timed out.  We don't want do continue down
        // this branch
        if (ec && ec == boost::asio::error::operation_aborted)
        {
            return;
        }

        timer.cancel();
        if (ec)
        {
            BMCWEB_LOG_ERROR("Connect {}:{}, id: {} failed: {}",
                             endpoint.address().to_string(), endpoint.port(),
                             connId, ec.message());
            state = ConnState::connectFailed;
            waitAndRetry();
            return;
        }
        BMCWEB_LOG_DEBUG("Connected to: {}:{}, id: {}",
                         endpoint.address().to_string(), endpoint.port(),
                         connId);
        if (sslConn)
        {
            doSslHandshake();
            return;
        }
        state = ConnState::connected;
        sendMessage();
    }

    void doSslHandshake()
    {
        if (!sslConn)
        {
            return;
        }
        state = ConnState::handshakeInProgress;
        timer.expires_after(std::chrono::seconds(30));
        timer.async_wait(std::bind_front(onTimeout, weak_from_this()));
        sslConn->async_handshake(
            boost::asio::ssl::stream_base::client,
            std::bind_front(&ConnectionInfo::afterSslHandshake, this,
                            shared_from_this()));
    }

    void afterSslHandshake(const std::shared_ptr<ConnectionInfo>& /*self*/,
                           const boost::beast::error_code& ec)
    {
        // The operation already timed out.  We don't want do continue down
        // this branch
        if (ec && ec == boost::asio::error::operation_aborted)
        {
            return;
        }

        timer.cancel();
        if (ec)
        {
            BMCWEB_LOG_ERROR("SSL Handshake failed - id: {} error: {}", connId,
                             ec.message());
            state = ConnState::handshakeFailed;
            waitAndRetry();
            return;
        }
        BMCWEB_LOG_DEBUG("SSL Handshake successful - id: {}", connId);
        state = ConnState::connected;
        sendMessage();
    }

    void sendMessage()
    {
        state = ConnState::sendInProgress;

        // Set a timeout on the operation
        timer.expires_after(std::chrono::seconds(30));
        timer.async_wait(std::bind_front(onTimeout, weak_from_this()));
        // Send the HTTP request to the remote host
        if (sslConn)
        {
            boost::beast::http::async_write(
                *sslConn, req,
                std::bind_front(&ConnectionInfo::afterWrite, this,
                                shared_from_this()));
        }
        else
        {
            boost::beast::http::async_write(
                conn, req,
                std::bind_front(&ConnectionInfo::afterWrite, this,
                                shared_from_this()));
        }
    }

    void afterWrite(const std::shared_ptr<ConnectionInfo>& /*self*/,
                    const boost::beast::error_code& ec, size_t bytesTransferred)
    {
        // The operation already timed out.  We don't want do continue down
        // this branch
        if (ec && ec == boost::asio::error::operation_aborted)
        {
            return;
        }

        timer.cancel();
        if (ec)
        {
            BMCWEB_LOG_ERROR("sendMessage() failed: {} {}", ec.message(), host);
            state = ConnState::sendFailed;
            waitAndRetry();
            return;
        }
        BMCWEB_LOG_DEBUG("sendMessage() bytes transferred: {}",
                         bytesTransferred);

        recvMessage();
    }

    void recvMessage()
    {
        state = ConnState::recvInProgress;

        parser_type& thisParser = parser.emplace();

        thisParser.body_limit(connPolicy->requestByteLimit);

        timer.expires_after(std::chrono::seconds(30));
        timer.async_wait(std::bind_front(onTimeout, weak_from_this()));

        // Receive the HTTP response
        if (sslConn)
        {
            boost::beast::http::async_read(
                *sslConn, buffer, thisParser,
                std::bind_front(&ConnectionInfo::afterRead, this,
                                shared_from_this()));
        }
        else
        {
            boost::beast::http::async_read(
                conn, buffer, thisParser,
                std::bind_front(&ConnectionInfo::afterRead, this,
                                shared_from_this()));
        }
    }

    void afterRead(const std::shared_ptr<ConnectionInfo>& /*self*/,
                   const boost::beast::error_code& ec,
                   const std::size_t& bytesTransferred)
    {
        // The operation already timed out.  We don't want do continue down
        // this branch
        if (ec && ec == boost::asio::error::operation_aborted)
        {
            return;
        }

        timer.cancel();
        if (ec && ec != boost::asio::ssl::error::stream_truncated)
        {
            BMCWEB_LOG_ERROR("recvMessage() failed: {} from {}", ec.message(),
                             host);
            state = ConnState::recvFailed;
            waitAndRetry();
            return;
        }
        BMCWEB_LOG_DEBUG("recvMessage() bytes transferred: {}",
                         bytesTransferred);
        if (!parser)
        {
            return;
        }
        BMCWEB_LOG_DEBUG("recvMessage() data: {}", parser->get().body().str());

        unsigned int respCode = parser->get().result_int();
        BMCWEB_LOG_DEBUG("recvMessage() Header Response Code: {}", respCode);

        // Handle the case of stream_truncated.  Some servers close the ssl
        // connection uncleanly, so check to see if we got a full response
        // before we handle this as an error.
        if (!parser->is_done())
        {
            state = ConnState::recvFailed;
            waitAndRetry();
            return;
        }

        // Make sure the received response code is valid as defined by
        // the associated retry policy
        if (connPolicy->invalidResp(respCode))
        {
            // The listener failed to receive the Sent-Event
            BMCWEB_LOG_ERROR(
                "recvMessage() Listener Failed to "
                "receive Sent-Event. Header Response Code: {} from {}",
                respCode, host);
            state = ConnState::recvFailed;
            waitAndRetry();
            return;
        }

        // Send is successful
        // Reset the counter just in case this was after retrying
        retryCount = 0;

        // Keep the connection alive if server supports it
        // Else close the connection
        BMCWEB_LOG_DEBUG("recvMessage() keepalive : {}", parser->keep_alive());

        // Copy the response into a Response object so that it can be
        // processed by the callback function.
        res.response = parser->release();
        callback(parser->keep_alive(), connId, res);
        res.clear();
    }

    static void onTimeout(const std::weak_ptr<ConnectionInfo>& weakSelf,
                          const boost::system::error_code& ec)
    {
        if (ec == boost::asio::error::operation_aborted)
        {
            BMCWEB_LOG_DEBUG(
                "async_wait failed since the operation is aborted");
            return;
        }
        if (ec)
        {
            BMCWEB_LOG_ERROR("async_wait failed: {}", ec.message());
            // If the timer fails, we need to close the socket anyway, same
            // as if it expired.
        }
        std::shared_ptr<ConnectionInfo> self = weakSelf.lock();
        if (self == nullptr)
        {
            return;
        }
        self->waitAndRetry();
    }

    void waitAndRetry()
    {
        if ((retryCount >= connPolicy->maxRetryAttempts) ||
            (state == ConnState::sslInitFailed))
        {
            BMCWEB_LOG_ERROR("Maximum number of retries reached. {}", host);
            BMCWEB_LOG_DEBUG("Retry policy: {}", connPolicy->retryPolicyAction);

            if (connPolicy->retryPolicyAction == "TerminateAfterRetries")
            {
                // TODO: delete subscription
                state = ConnState::terminated;
            }
            if (connPolicy->retryPolicyAction == "SuspendRetries")
            {
                state = ConnState::suspended;
            }

            // We want to return a 502 to indicate there was an error with
            // the external server
            res.result(boost::beast::http::status::bad_gateway);
            callback(false, connId, res);
            res.clear();

            // Reset the retrycount to zero so that client can try
            // connecting again if needed
            retryCount = 0;
            return;
        }

        retryCount++;

        BMCWEB_LOG_DEBUG("Attempt retry after {} seconds. RetryCount = {}",
                         connPolicy->retryIntervalSecs.count(), retryCount);
        timer.expires_after(connPolicy->retryIntervalSecs);
        timer.async_wait(std::bind_front(&ConnectionInfo::onTimerDone, this,
                                         shared_from_this()));
    }

    void onTimerDone(const std::shared_ptr<ConnectionInfo>& /*self*/,
                     const boost::system::error_code& ec)
    {
        if (ec == boost::asio::error::operation_aborted)
        {
            BMCWEB_LOG_DEBUG(
                "async_wait failed since the operation is aborted{}",
                ec.message());
        }
        else if (ec)
        {
            BMCWEB_LOG_ERROR("async_wait failed: {}", ec.message());
            // Ignore the error and continue the retry loop to attempt
            // sending the event as per the retry policy
        }

        // Let's close the connection and restart from resolve.
        shutdownConn(true);
    }

    void restartConnection()
    {
        BMCWEB_LOG_DEBUG("{}, id: {}  restartConnection", host,
                         std::to_string(connId));
        initializeConnection(host.scheme() == "https");
        doResolve();
    }

    void shutdownConn(bool retry)
    {
        boost::beast::error_code ec;
        conn.shutdown(boost::asio::ip::tcp::socket::shutdown_both, ec);
        conn.close();

        // not_connected happens sometimes so don't bother reporting it.
        if (ec && ec != boost::beast::errc::not_connected)
        {
            BMCWEB_LOG_ERROR("{}, id: {} shutdown failed: {}", host, connId,
                             ec.message());
        }
        else
        {
            BMCWEB_LOG_DEBUG("{}, id: {} closed gracefully", host, connId);
        }

        if (retry)
        {
            // Now let's try to resend the data
            state = ConnState::retry;
            restartConnection();
        }
        else
        {
            state = ConnState::closed;
        }
    }

    void doClose(bool retry = false)
    {
        if (!sslConn)
        {
            shutdownConn(retry);
            return;
        }

        sslConn->async_shutdown(
            std::bind_front(&ConnectionInfo::afterSslShutdown, this,
                            shared_from_this(), retry));
    }

    void afterSslShutdown(const std::shared_ptr<ConnectionInfo>& /*self*/,
                          bool retry, const boost::system::error_code& ec)
    {
        if (ec)
        {
            BMCWEB_LOG_ERROR("{}, id: {} shutdown failed: {}", host, connId,
                             ec.message());
        }
        else
        {
            BMCWEB_LOG_DEBUG("{}, id: {} closed gracefully", host, connId);
        }
        shutdownConn(retry);
    }

    void setCipherSuiteTLSext()
    {
        if (!sslConn)
        {
            return;
        }

        if (host.host_type() != boost::urls::host_type::name)
        {
            // Avoid setting SNI hostname if its IP address
            return;
        }
        // Create a null terminated string for SSL
        std::string hostname(host.encoded_host_address());
        // NOTE: The SSL_set_tlsext_host_name is defined in tlsv1.h header
        // file but its having old style casting (name is cast to void*).
        // Since bmcweb compiler treats all old-style-cast as error, its
        // causing the build failure. So replaced the same macro inline and
        // did corrected the code by doing static_cast to viod*. This has to
        // be fixed in openssl library in long run. Set SNI Hostname (many
        // hosts need this to handshake successfully)
        if (SSL_ctrl(sslConn->native_handle(), SSL_CTRL_SET_TLSEXT_HOSTNAME,
                     TLSEXT_NAMETYPE_host_name,
                     static_cast<void*>(hostname.data())) == 0)

        {
            boost::beast::error_code ec{static_cast<int>(::ERR_get_error()),
                                        boost::asio::error::get_ssl_category()};

            BMCWEB_LOG_ERROR("SSL_set_tlsext_host_name {}, id: {} failed: {}",
                             host, connId, ec.message());
            // Set state as sslInit failed so that we close the connection
            // and take appropriate action as per retry configuration.
            state = ConnState::sslInitFailed;
            waitAndRetry();
            return;
        }
    }

    void initializeConnection(bool ssl)
    {
        conn = boost::asio::ip::tcp::socket(ioc);
        if (ssl)
        {
            std::optional<boost::asio::ssl::context> sslCtx =
                ensuressl::getSSLClientContext(verifyCert);

            if (!sslCtx)
            {
                BMCWEB_LOG_ERROR("prepareSSLContext failed - {}, id: {}", host,
                                 connId);
                // Don't retry if failure occurs while preparing SSL context
                // such as certificate is invalid or set cipher failure or
                // set host name failure etc... Setting conn state to
                // sslInitFailed and connection state will be transitioned
                // to next state depending on retry policy set by
                // subscription.
                state = ConnState::sslInitFailed;
                waitAndRetry();
                return;
            }
            sslConn.emplace(conn, *sslCtx);
            setCipherSuiteTLSext();
        }
    }

  public:
    explicit ConnectionInfo(
        boost::asio::io_context& iocIn, const std::string& idIn,
        const std::shared_ptr<ConnectionPolicy>& connPolicyIn,
        const boost::urls::url_view_base& hostIn,
        ensuressl::VerifyCertificate verifyCertIn, unsigned int connIdIn) :
        subId(idIn), connPolicy(connPolicyIn), host(hostIn),
        verifyCert(verifyCertIn), connId(connIdIn), ioc(iocIn), resolver(iocIn),
        conn(iocIn), timer(iocIn)
    {
        initializeConnection(host.scheme() == "https");
    }
};

class ConnectionPool : public std::enable_shared_from_this<ConnectionPool>
{
  private:
    boost::asio::io_context& ioc;
    std::string id;
    std::shared_ptr<ConnectionPolicy> connPolicy;
    boost::urls::url destIP;
    std::vector<std::shared_ptr<ConnectionInfo>> connections;
    boost::container::devector<PendingRequest> requestQueue;
    ensuressl::VerifyCertificate verifyCert;

    friend class HttpClient;

    // Configure a connections's request, callback, and retry info in
    // preparation to begin sending the request
    void setConnProps(ConnectionInfo& conn)
    {
        if (requestQueue.empty())
        {
            BMCWEB_LOG_ERROR(
                "setConnProps() should not have been called when requestQueue is empty");
            return;
        }

        PendingRequest& nextReq = requestQueue.front();
        conn.req = std::move(nextReq.req);
        conn.callback = std::move(nextReq.callback);

        BMCWEB_LOG_DEBUG("Setting properties for connection {}, id: {}",
                         conn.host, conn.connId);

        // We can remove the request from the queue at this point
        requestQueue.pop_front();
    }

    // Gets called as part of callback after request is sent
    // Reuses the connection if there are any requests waiting to be sent
    // Otherwise closes the connection if it is not a keep-alive
    void sendNext(bool keepAlive, uint32_t connId)
    {
        auto conn = connections[connId];

        // Allow the connection's handler to be deleted
        // This is needed because of Redfish Aggregation passing an
        // AsyncResponse shared_ptr to this callback
        conn->callback = nullptr;

        // Reuse the connection to send the next request in the queue
        if (!requestQueue.empty())
        {
            BMCWEB_LOG_DEBUG(
                "{} requests remaining in queue for {}, reusing connection {}",
                requestQueue.size(), destIP, connId);

            setConnProps(*conn);

            if (keepAlive)
            {
                conn->sendMessage();
            }
            else
            {
                // Server is not keep-alive enabled so we need to close the
                // connection and then start over from resolve
                conn->doClose();
                conn->restartConnection();
            }
            return;
        }

        // No more messages to send so close the connection if necessary
        if (keepAlive)
        {
            conn->state = ConnState::idle;
        }
        else
        {
            // Abort the connection since server is not keep-alive enabled
            conn->state = ConnState::abortConnection;
            conn->doClose();
        }
    }

    void sendData(std::string&& data, const boost::urls::url_view_base& destUri,
                  const boost::beast::http::fields& httpHeader,
                  const boost::beast::http::verb verb,
                  const std::function<void(Response&)>& resHandler)
    {
        // Construct the request to be sent
        boost::beast::http::request<bmcweb::HttpBody> thisReq(
            verb, destUri.encoded_target(), 11, "", httpHeader);
        thisReq.set(boost::beast::http::field::host,
                    destUri.encoded_host_address());
        thisReq.keep_alive(true);
        thisReq.body().str() = std::move(data);
        thisReq.prepare_payload();
        auto cb = std::bind_front(&ConnectionPool::afterSendData,
                                  weak_from_this(), resHandler);
        // Reuse an existing connection if one is available
        for (unsigned int i = 0; i < connections.size(); i++)
        {
            auto conn = connections[i];
            if ((conn->state == ConnState::idle) ||
                (conn->state == ConnState::initialized) ||
                (conn->state == ConnState::closed))
            {
                conn->req = std::move(thisReq);
                conn->callback = std::move(cb);
                std::string commonMsg = std::format("{} from pool {}", i, id);

                if (conn->state == ConnState::idle)
                {
                    BMCWEB_LOG_DEBUG("Grabbing idle connection {}", commonMsg);
                    conn->sendMessage();
                }
                else
                {
                    BMCWEB_LOG_DEBUG("Reusing existing connection {}",
                                     commonMsg);
                    conn->restartConnection();
                }
                return;
            }
        }

        // All connections in use so create a new connection or add request
        // to the queue
        if (connections.size() < connPolicy->maxConnections)
        {
            BMCWEB_LOG_DEBUG("Adding new connection to pool {}", id);
            auto conn = addConnection();
            conn->req = std::move(thisReq);
            conn->callback = std::move(cb);
            conn->doResolve();
        }
        else if (requestQueue.size() < maxRequestQueueSize)
        {
            BMCWEB_LOG_DEBUG("Max pool size reached. Adding data to queue {}",
                             id);
            requestQueue.emplace_back(std::move(thisReq), std::move(cb));
        }
        else
        {
            // If we can't buffer the request then we should let the
            // callback handle a 429 Too Many Requests dummy response
            BMCWEB_LOG_ERROR("{} request queue full.  Dropping request.", id);
            Response dummyRes;
            dummyRes.result(boost::beast::http::status::too_many_requests);
            resHandler(dummyRes);
        }
    }

    // Callback to be called once the request has been sent
    static void afterSendData(const std::weak_ptr<ConnectionPool>& weakSelf,
                              const std::function<void(Response&)>& resHandler,
                              bool keepAlive, uint32_t connId, Response& res)
    {
        // Allow provided callback to perform additional processing of the
        // request
        resHandler(res);

        // If requests remain in the queue then we want to reuse this
        // connection to send the next request
        std::shared_ptr<ConnectionPool> self = weakSelf.lock();
        if (!self)
        {
            BMCWEB_LOG_CRITICAL("{} Failed to capture connection",
                                logPtr(self.get()));
            return;
        }

        self->sendNext(keepAlive, connId);
    }

    std::shared_ptr<ConnectionInfo>& addConnection()
    {
        unsigned int newId = static_cast<unsigned int>(connections.size());

        auto& ret = connections.emplace_back(std::make_shared<ConnectionInfo>(
            ioc, id, connPolicy, destIP, verifyCert, newId));

        BMCWEB_LOG_DEBUG("Added connection {} to pool {}",
                         connections.size() - 1, id);

        return ret;
    }

  public:
    explicit ConnectionPool(
        boost::asio::io_context& iocIn, const std::string& idIn,
        const std::shared_ptr<ConnectionPolicy>& connPolicyIn,
        const boost::urls::url_view_base& destIPIn,
        ensuressl::VerifyCertificate verifyCertIn) :
        ioc(iocIn), id(idIn), connPolicy(connPolicyIn), destIP(destIPIn),
        verifyCert(verifyCertIn)
    {
        BMCWEB_LOG_DEBUG("Initializing connection pool for {}", id);

        // Initialize the pool with a single connection
        addConnection();
    }

    // Check whether all connections are terminated
    bool areAllConnectionsTerminated()
    {
        if (connections.empty())
        {
            BMCWEB_LOG_DEBUG("There are no connections for pool id:{}", id);
            return false;
        }
        for (const auto& conn : connections)
        {
            if (conn != nullptr && conn->state != ConnState::terminated)
            {
                BMCWEB_LOG_DEBUG(
                    "Not all connections of pool id:{} are terminated", id);
                return false;
            }
        }
        BMCWEB_LOG_INFO("All connections of pool id:{} are terminated", id);
        return true;
    }
};

class HttpClient
{
  private:
    std::unordered_map<std::string, std::shared_ptr<ConnectionPool>>
        connectionPools;

    // reference_wrapper here makes HttpClient movable
    std::reference_wrapper<boost::asio::io_context> ioc;
    std::shared_ptr<ConnectionPolicy> connPolicy;

    // Used as a dummy callback by sendData() in order to call
    // sendDataWithCallback()
    static void genericResHandler(const Response& res)
    {
        BMCWEB_LOG_DEBUG("Response handled with return code: {}",
                         res.resultInt());
    }

  public:
    HttpClient() = delete;
    explicit HttpClient(boost::asio::io_context& iocIn,
                        const std::shared_ptr<ConnectionPolicy>& connPolicyIn) :
        ioc(iocIn), connPolicy(connPolicyIn)
    {}

    HttpClient(const HttpClient&) = delete;
    HttpClient& operator=(const HttpClient&) = delete;
    HttpClient(HttpClient&& client) = default;
    HttpClient& operator=(HttpClient&& client) = default;
    ~HttpClient() = default;

    // Send a request to destIP where additional processing of the
    // result is not required
    void sendData(std::string&& data, const boost::urls::url_view_base& destUri,
                  ensuressl::VerifyCertificate verifyCert,
                  const boost::beast::http::fields& httpHeader,
                  const boost::beast::http::verb verb)
    {
        const std::function<void(Response&)> cb = genericResHandler;
        sendDataWithCallback(std::move(data), destUri, verifyCert, httpHeader,
                             verb, cb);
    }

    // Send request to destIP and use the provided callback to
    // handle the response
    void sendDataWithCallback(std::string&& data,
                              const boost::urls::url_view_base& destUrl,
                              ensuressl::VerifyCertificate verifyCert,
                              const boost::beast::http::fields& httpHeader,
                              const boost::beast::http::verb verb,
                              const std::function<void(Response&)>& resHandler)
    {
        std::string_view verify = "ssl_verify";
        if (verifyCert == ensuressl::VerifyCertificate::NoVerify)
        {
            verify = "ssl no verify";
        }
        std::string clientKey =
            std::format("{}{}://{}", verify, destUrl.scheme(),
                        destUrl.encoded_host_and_port());
        auto pool = connectionPools.try_emplace(clientKey);
        if (pool.first->second == nullptr)
        {
            pool.first->second = std::make_shared<ConnectionPool>(
                ioc, clientKey, connPolicy, destUrl, verifyCert);
        }
        // Send the data using either the existing connection pool or the
        // newly created connection pool
        pool.first->second->sendData(std::move(data), destUrl, httpHeader, verb,
                                     resHandler);
    }

    // Test whether all connections are terminated (after MaxRetryAttempts)
    bool isTerminated()
    {
        for (const auto& pool : connectionPools)
        {
            if (pool.second != nullptr &&
                !pool.second->areAllConnectionsTerminated())
            {
                BMCWEB_LOG_DEBUG(
                    "Not all of client connections are terminated");
                return false;
            }
        }
        BMCWEB_LOG_DEBUG("All client connections are terminated");
        return true;
    }
};
} // namespace crow