/*
 * This file is part of the Flowee project
 * Copyright (c) 2015 The Bitcoin Core developers
 * Copyright (c) 2024 Tom Zander <tom@flowee.org>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "httpserver.h"

#include <SettingsDefaults.h>
#include "chainparamsbase.h"
#include <policy/policy.h>
#include "compat.h"
#include "util.h"
#include "netbase.h"
#include "rpcprotocol.h" // For HTTP status codes
#include "sync.h"
#include "UiInterface.h"
#include <utils/utilstrencodings.h>

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>

#include <sys/types.h>
#include <sys/stat.h>
#include <csignal>

#include <event2/event.h>
#include <event2/http.h>
#include <event2/thread.h>
#include <event2/buffer.h>
#include <event2/util.h>
#include <event2/keyvalq_struct.h>

#ifdef EVENT__HAVE_NETINET_IN_H
#include <netinet/in.h>
#ifdef _XOPEN_SOURCE_EXTENDED
#include <arpa/inet.h>
#endif
#endif

#include <boost/algorithm/string/case_conv.hpp> // for to_lower()
#include <boost/foreach.hpp>
#include <boost/scoped_ptr.hpp>

/** Maximum size of http request (request line + headers) */
static constexpr size_t MAX_HEADERS_SIZE = 8192;

/**
 * Maximum HTTP post body size. Twice the maximum block size is added to this
 * value in practice.
 */
static constexpr size_t MIN_SUPPORTED_BODY_SIZE = 0x02000000;

/** HTTP request work item */
class HTTPWorkItem : public HTTPClosure
{
public:
    HTTPWorkItem(HTTPRequest* req, const std::string &path, const HTTPRequestHandler& func):
        req(req), path(path), func(func)
    {
    }
    void operator()()
    {
        func(req.get(), path);
    }

    boost::scoped_ptr<HTTPRequest> req;

private:
    std::string path;
    HTTPRequestHandler func;
};

/** Simple work queue for distributing work over multiple threads.
 * Work items are simply callable objects.
 */
template <typename WorkItem>
class WorkQueue
{
private:
    /** Mutex protects entire object */
    CWaitableCriticalSection cs;
    CConditionVariable cond;
    /* XXX in C++11 we can use std::unique_ptr here and avoid manual cleanup */
    std::deque<WorkItem*> queue;
    bool running;
    size_t maxDepth;
    int numThreads;

    /** RAII object to keep track of number of running worker threads */
    class ThreadCounter
    {
    public:
        WorkQueue &wq;
        ThreadCounter(WorkQueue &w): wq(w)
        {
            boost::lock_guard<boost::mutex> lock(wq.cs);
            wq.numThreads += 1;
        }
        ~ThreadCounter()
        {
            boost::lock_guard<boost::mutex> lock(wq.cs);
            wq.numThreads -= 1;
            wq.cond.notify_all();
        }
    };

public:
    WorkQueue(size_t maxDepth) : running(true),
                                 maxDepth(maxDepth),
                                 numThreads(0)
    {
    }
    /*( Precondition: worker threads have all stopped
     * (call WaitExit)
     */
    ~WorkQueue()
    {
        while (!queue.empty()) {
            delete queue.front();
            queue.pop_front();
        }
    }
    /** Enqueue a work item */
    bool Enqueue(WorkItem* item)
    {
        boost::unique_lock<boost::mutex> lock(cs);
        if (queue.size() >= maxDepth) {
            return false;
        }
        queue.push_back(item);
        cond.notify_one();
        return true;
    }
    /** Thread function */
    void Run()
    {
        ThreadCounter count(*this);
        while (running) {
            WorkItem* i = 0;
            {
                boost::unique_lock<boost::mutex> lock(cs);
                while (running && queue.empty())
                    cond.wait(lock);
                if (!running)
                    break;
                i = queue.front();
                queue.pop_front();
            }
            (*i)();
            delete i;
        }
    }
    /** Interrupt and exit loops */
    void Interrupt()
    {
        boost::unique_lock<boost::mutex> lock(cs);
        running = false;
        cond.notify_all();
    }
    /** Wait for worker threads to exit */
    void WaitExit()
    {
        boost::unique_lock<boost::mutex> lock(cs);
        while (numThreads > 0)
            cond.wait(lock);
    }

    /** Return current depth of queue */
    size_t Depth()
    {
        boost::unique_lock<boost::mutex> lock(cs);
        return queue.size();
    }
};

struct HTTPPathHandler
{
    HTTPPathHandler() {}
    HTTPPathHandler(std::string prefix, bool exactMatch, HTTPRequestHandler handler):
        prefix(prefix), exactMatch(exactMatch), handler(handler)
    {
    }
    std::string prefix;
    bool exactMatch;
    HTTPRequestHandler handler;
};

/** HTTP module state */

//! libevent event loop
static struct event_base* eventBase = 0;
//! HTTP server
struct evhttp* eventHTTP = 0;
//! List of subnets to allow RPC connections from
static std::vector<CSubNet> rpc_allow_subnets;
//! Work queue for handling longer requests off the event loop thread
static WorkQueue<HTTPClosure>* workQueue = 0;
//! Handlers for (sub)paths
std::vector<HTTPPathHandler> pathHandlers;
//! Bound listening sockets
std::vector<evhttp_bound_socket *> boundSockets;

/** Check if a network address is allowed to access the HTTP server */
static bool ClientAllowed(const CNetAddr& netaddr)
{
    if (!netaddr.IsValid())
        return false;
    BOOST_FOREACH (const CSubNet& subnet, rpc_allow_subnets)
        if (subnet.Match(netaddr))
            return true;
    return false;
}

/** Initialize ACL list for HTTP server */
static bool InitHTTPAllowList()
{
    rpc_allow_subnets.clear();
    rpc_allow_subnets.push_back(CSubNet("127.0.0.0/8")); // always allow IPv4 local subnet
    rpc_allow_subnets.push_back(CSubNet("::1"));         // always allow IPv6 localhost
    if (mapMultiArgs.count("-rpcallowip")) {
        const std::vector<std::string>& vAllow = mapMultiArgs["-rpcallowip"];
        BOOST_FOREACH (std::string strAllow, vAllow) {
            CSubNet subnet(strAllow);
            if (!subnet.IsValid()) {
                uiInterface.ThreadSafeMessageBox(
                    strprintf("Invalid -rpcallowip subnet specification: %s. Valid are a single IP (e.g. 1.2.3.4), a network/netmask (e.g. 1.2.3.4/255.255.255.0) or a network/CIDR (e.g. 1.2.3.4/24).", strAllow),
                    "", CClientUIInterface::MSG_ERROR);
                return false;
            }
            rpc_allow_subnets.push_back(subnet);
        }
    }
    std::string strAllowed;
    BOOST_FOREACH (const CSubNet& subnet, rpc_allow_subnets)
        strAllowed += subnet.ToString() + " ";
    logCritical(Log::HTTP) << "Allowing HTTP connections from:" << strAllowed;
    return true;
}

/** HTTP request method as string - use for logging only */
static std::string RequestMethodString(HTTPRequest::RequestMethod m)
{
    switch (m) {
    case HTTPRequest::GET:
        return "GET";
        break;
    case HTTPRequest::POST:
        return "POST";
        break;
    case HTTPRequest::HEAD:
        return "HEAD";
        break;
    case HTTPRequest::PUT:
        return "PUT";
        break;
    default:
        return "unknown";
    }
}

/** HTTP request callback */
static void http_request_cb(struct evhttp_request* req, void* arg)
{
    std::unique_ptr<HTTPRequest> hreq(new HTTPRequest(req));

    logInfo(Log::HTTP) << "Received a" << RequestMethodString(hreq->GetRequestMethod()) << "request for"
                       << hreq->GetURI() << "from" << hreq->GetPeer().ToString();

    // Early address-based allow check
    if (!ClientAllowed(hreq->GetPeer())) {
        hreq->WriteReply(HTTP_FORBIDDEN);
        return;
    }

    // Early reject unknown HTTP methods
    if (hreq->GetRequestMethod() == HTTPRequest::UNKNOWN) {
        hreq->WriteReply(HTTP_BADMETHOD);
        return;
    }

    // Find registered handler for prefix
    std::string strURI = hreq->GetURI();
    std::string path;
    std::vector<HTTPPathHandler>::const_iterator i = pathHandlers.begin();
    std::vector<HTTPPathHandler>::const_iterator iend = pathHandlers.end();
    for (; i != iend; ++i) {
        bool match = false;
        if (i->exactMatch)
            match = (strURI == i->prefix);
        else
            match = (strURI.substr(0, i->prefix.size()) == i->prefix);
        if (match) {
            path = strURI.substr(i->prefix.size());
            break;
        }
    }

    // Dispatch to worker thread
    if (i != iend) {
        std::unique_ptr<HTTPWorkItem> item(new HTTPWorkItem(hreq.release(), path, i->handler));
        assert(workQueue);
        if (workQueue->Enqueue(item.get()))
            item.release(); /* if true, queue took ownership */
        else
            item->req->WriteReply(HTTP_INTERNAL, "Work queue depth exceeded");
    } else {
        hreq->WriteReply(HTTP_NOTFOUND);
    }
}

/** Callback to reject HTTP requests after shutdown. */
static void http_reject_request_cb(struct evhttp_request* req, void*)
{
    logDebug(Log::HTTP) << "Rejecting request while shutting down";
    evhttp_send_error(req, HTTP_SERVUNAVAIL, NULL);
}

/** Event dispatcher thread */
static void ThreadHTTP(struct event_base* base, struct evhttp* http)
{
    RenameThread("bitcoin-http");
    logDebug(Log::HTTP) << "Entering http event loop";
    event_base_dispatch(base);
    // Event loop will be interrupted by InterruptHTTPServer()
    logDebug(Log::HTTP) << "Exited http event loop";
}

/** Bind HTTP server to specified addresses */
static bool HTTPBindAddresses(struct evhttp* http)
{
    int defaultPort = GetArg("-rpcport", BaseParams().RPCPort());
    std::vector<std::pair<std::string, uint16_t> > endpoints;

    // Determine what addresses to bind to
    if (!mapArgs.count("-rpcallowip")) { // Default to loopback if not allowing external IPs
        endpoints.push_back(std::make_pair("::1", defaultPort));
        endpoints.push_back(std::make_pair("127.0.0.1", defaultPort));
        if (mapArgs.count("-rpcbind")) {
            logCritical(Log::HTTP) << "WARNING: option -rpcbind was ignored because -rpcallowip was not specified, refusing to allow everyone to connect";
        }
    } else if (mapArgs.count("-rpcbind")) { // Specific bind address
        const std::vector<std::string>& vbind = mapMultiArgs["-rpcbind"];
        for (std::vector<std::string>::const_iterator i = vbind.begin(); i != vbind.end(); ++i) {
            uint16_t port = defaultPort;
            std::string host;
            SplitHostPort(*i, port, host);
            endpoints.push_back(std::make_pair(host, port));
        }
    } else { // No specific bind address specified, bind to any
        endpoints.push_back(std::make_pair("::", defaultPort));
        endpoints.push_back(std::make_pair("0.0.0.0", defaultPort));
    }

    // Bind addresses
    for (std::vector<std::pair<std::string, uint16_t> >::iterator i = endpoints.begin(); i != endpoints.end(); ++i) {
        logInfo(Log::HTTP) << "Binding RPC on address" << i->first << "port" << i->second;
        evhttp_bound_socket *bind_handle = evhttp_bind_socket_with_handle(http, i->first.empty() ? NULL : i->first.c_str(), i->second);
        if (bind_handle) {
            boundSockets.push_back(bind_handle);
        } else {
            logFatal(Log::HTTP) <<"Binding RPC on address" << i->first << "port" << i->second << "failed";
        }
    }
    return !boundSockets.empty();
}

/** Simple wrapper to set thread name and run work queue */
static void HTTPWorkQueueRun(WorkQueue<HTTPClosure>* queue)
{
    RenameThread("httpworker");
    queue->Run();
}

/** libevent event log callback */
static void libevent_log_cb(int severity, const char *msg)
{
#ifndef EVENT_LOG_WARN
// EVENT_LOG_WARN was added in 2.0.19; but before then _EVENT_LOG_WARN existed.
# define EVENT_LOG_WARN _EVENT_LOG_WARN
#endif
    // unfortunately some methods on libEvent (notably evhttp_add_header)
    // adds a linefeed to the message.
    // We copy the message on stack and strip off a linefeed if there is one.
    char buf[170];
    const int stringLen = strnlen(msg, sizeof(buf));
    memcpy(buf, msg, stringLen);
    buf[sizeof(buf) - 1] = 0; // ensure terminating zero
    if ('\n' == buf[stringLen - 1])
        buf[stringLen - 1] = 0; // remove trailing linefeed.
    switch (severity) {
    case EVENT_LOG_DEBUG: logDebug(Log::LibEvent) << buf; break;
    case EVENT_LOG_MSG: logInfo(Log::LibEvent) << buf; break;
    case EVENT_LOG_WARN: logWarning(Log::LibEvent) << buf; break;
    case EVENT_LOG_ERR: logCritical(Log::LibEvent) << buf; break;
    }
}

bool InitHTTPServer()
{
    struct evhttp* http = 0;
    struct event_base* base = 0;

    if (!InitHTTPAllowList())
        return false;

    // Redirect libevent's logging to our own log
    event_set_log_callback(&libevent_log_cb);
#if LIBEVENT_VERSION_NUMBER >= 0x02010100
    if (Log::Manager::instance()->isEnabled(Log::LibEvent, Log::DebugLevel))
        event_enable_debug_logging(EVENT_DBG_ALL);
    else
        event_enable_debug_logging(EVENT_DBG_NONE);
#endif
#ifdef WIN32
    evthread_use_windows_threads();
#else
    evthread_use_pthreads();
#endif

    base = event_base_new(); // XXX RAII
    if (!base) {
        logCritical(Log::LibEvent) << "Couldn't create an event_base: exiting";
        return false;
    }

    /* Create a new evhttp object to handle requests. */
    http = evhttp_new(base); // XXX RAII
    if (!http) {
        logCritical(Log::LibEvent) << "couldn't create evhttp. Exiting.";
        event_base_free(base);
        return false;
    }

    evhttp_set_timeout(http, GetArg("-rpcservertimeout", Settings::DefaultHttpServerTimeout));
    evhttp_set_max_headers_size(http, MAX_HEADERS_SIZE);
    evhttp_set_max_body_size(http, MIN_SUPPORTED_BODY_SIZE + 2 * Policy::blockSizeAcceptLimit());

    evhttp_set_gencb(http, http_request_cb, NULL);

    if (!HTTPBindAddresses(http)) {
        logCritical(Log::LibEvent) << "Unable to bind any endpoint for RPC server";
        evhttp_free(http);
        event_base_free(base);
        return false;
    }

    logCritical(Log::HTTP) << "Initialized HTTP server";
    int workQueueDepth = std::max((long)GetArg("-rpcworkqueue", Settings::DefaultHttpWorkQueue), 1L);
    logInfo(Log::HTTP) << "creating work queue of depth" << workQueueDepth;

    workQueue = new WorkQueue<HTTPClosure>(workQueueDepth);
    eventBase = base;
    eventHTTP = http;
    return true;
}

boost::thread threadHTTP;

void StartHTTPServer()
{
    logInfo(Log::HTTP) << "Starting HTTP server";
    int rpcThreads = std::max((long)GetArg("-rpcthreads", Settings::DefaultHttpThreads), 1L);
    logInfo(Log::HTTP) << "starting" << rpcThreads << "worker threads";
    threadHTTP = boost::thread(std::bind(&ThreadHTTP, eventBase, eventHTTP));

    for (int i = 0; i < rpcThreads; i++)
        boost::thread(std::bind(&HTTPWorkQueueRun, workQueue));
}

void InterruptHTTPServer()
{
    if (eventHTTP) {
        logCritical(Log::HTTP) << "Interrupting HTTP server";
        // Unlisten sockets
        BOOST_FOREACH (evhttp_bound_socket *socket, boundSockets) {
            evhttp_del_accept_socket(eventHTTP, socket);
        }
        // Reject requests on current connections
        evhttp_set_gencb(eventHTTP, http_reject_request_cb, NULL);
    }
    if (workQueue)
        workQueue->Interrupt();
}

void StopHTTPServer()
{
    bool stopped = false;
    if (workQueue) {
        stopped = true;
        logCritical(Log::HTTP) << "Stopping HTTP server";
        logInfo(Log::HTTP) << "Waiting for HTTP worker threads to exit";
        workQueue->WaitExit();
        delete workQueue;
    }
    if (eventBase) {
        stopped = true;
        logInfo(Log::HTTP) << "Waiting for HTTP event thread to exit";
        // Give event loop a few seconds to exit (to send back last RPC responses), then break it
        // Before this was solved with event_base_loopexit, but that didn't work as expected in
        // at least libevent 2.0.21 and always introduced a delay. In libevent
        // master that appears to be solved, so in the future that solution
        // could be used again (if desirable).
        // (see discussion in https://github.com/bitcoin/bitcoin/pull/6990)
#if BOOST_VERSION >= 105000
        if (!threadHTTP.try_join_for(boost::chrono::milliseconds(2000))) {
#else
        if (!threadHTTP.timed_join(boost::posix_time::milliseconds(2000))) {
#endif
            logCritical(Log::HTTP) << "HTTP event loop did not exit within allotted time, sending loopbreak";
            event_base_loopbreak(eventBase);
            threadHTTP.join();
        }
    }
    if (eventHTTP) {
        stopped = true;
        evhttp_free(eventHTTP);
        eventHTTP = 0;
    }
    if (eventBase) {
        stopped = true;
        event_base_free(eventBase);
        eventBase = 0;
    }
    if (stopped)
        logCritical(Log::HTTP) << "Stopped HTTP server";
}

struct event_base* EventBase()
{
    return eventBase;
}

static void httpevent_callback_fn(evutil_socket_t, short, void* data)
{
    // Static handler: simply call inner handler
    HTTPEvent *self = ((HTTPEvent*)data);
    self->handler();
    if (self->deleteWhenTriggered)
        delete self;
}

HTTPEvent::HTTPEvent(struct event_base* base, bool deleteWhenTriggered, const boost::function<void(void)>& handler):
    deleteWhenTriggered(deleteWhenTriggered), handler(handler)
{
    ev = event_new(base, -1, 0, httpevent_callback_fn, this);
    assert(ev);
}
HTTPEvent::~HTTPEvent()
{
    event_free(ev);
}
void HTTPEvent::trigger(struct timeval* tv)
{
    if (tv == NULL)
        event_active(ev, 0, 0); // immediately trigger event in main thread
    else
        evtimer_add(ev, tv); // trigger after timeval passed
}
HTTPRequest::HTTPRequest(struct evhttp_request* req) : req(req),
                                                       replySent(false)
{
}
HTTPRequest::~HTTPRequest()
{
    if (!replySent) {
        // Keep track of whether reply was sent to avoid request leaks
        logDebug(Log::HTTP) << "Unhandled request";
        WriteReply(HTTP_INTERNAL, "Unhandled request");
    }
    // evhttpd cleans up the request, as long as a reply was sent.
}

std::pair<bool, std::string> HTTPRequest::GetHeader(const std::string& hdr)
{
    const struct evkeyvalq* headers = evhttp_request_get_input_headers(req);
    assert(headers);
    const char* val = evhttp_find_header(headers, hdr.c_str());
    if (val)
        return std::make_pair(true, val);
    else
        return std::make_pair(false, "");
}

std::string HTTPRequest::ReadBody()
{
    struct evbuffer* buf = evhttp_request_get_input_buffer(req);
    if (!buf)
        return "";
    size_t size = evbuffer_get_length(buf);
    /** Trivial implementation: if this is ever a performance bottleneck,
     * internal copying can be avoided in multi-segment buffers by using
     * evbuffer_peek and an awkward loop. Though in that case, it'd be even
     * better to not copy into an intermediate string but use a stream
     * abstraction to consume the evbuffer on the fly in the parsing algorithm.
     */
    const char* data = (const char*)evbuffer_pullup(buf, size);
    if (!data) // returns NULL in case of empty buffer
        return "";
    std::string rv(data, size);
    evbuffer_drain(buf, size);
    return rv;
}

void HTTPRequest::WriteHeader(const std::string& hdr, const std::string& value)
{
    struct evkeyvalq* headers = evhttp_request_get_output_headers(req);
    assert(headers);
    evhttp_add_header(headers, hdr.c_str(), value.c_str());
}

/** Closure sent to main thread to request a reply to be sent to
 * a HTTP request.
 * Replies must be sent in the main loop in the main http thread,
 * this cannot be done from worker threads.
 */
void HTTPRequest::WriteReply(int nStatus, const std::string& strReply)
{
    assert(!replySent && req);
    // Send event to main http thread to send reply message
    struct evbuffer* evb = evhttp_request_get_output_buffer(req);
    assert(evb);
    evbuffer_add(evb, strReply.data(), strReply.size());
    HTTPEvent* ev = new HTTPEvent(eventBase, true,
        std::bind(evhttp_send_reply, req, nStatus, (const char*)NULL, (struct evbuffer *)NULL));
    ev->trigger(0);
    replySent = true;
    req = 0; // transferred back to main thread
}

CService HTTPRequest::GetPeer()
{
    evhttp_connection* con = evhttp_request_get_connection(req);
    CService peer;
    if (con) {
        // evhttp retains ownership over returned address string
        const char* address = "";
        uint16_t port = 0;
        evhttp_connection_get_peer(con, (char**)&address, &port);
        peer = CService(address, port);
    }
    return peer;
}

std::string HTTPRequest::GetURI()
{
    return evhttp_request_get_uri(req);
}

HTTPRequest::RequestMethod HTTPRequest::GetRequestMethod()
{
    switch (evhttp_request_get_command(req)) {
    case EVHTTP_REQ_GET:
        return GET;
        break;
    case EVHTTP_REQ_POST:
        return POST;
        break;
    case EVHTTP_REQ_HEAD:
        return HEAD;
        break;
    case EVHTTP_REQ_PUT:
        return PUT;
        break;
    default:
        return UNKNOWN;
        break;
    }
}

void RegisterHTTPHandler(const std::string &prefix, bool exactMatch, const HTTPRequestHandler &handler)
{
    logInfo(Log::HTTP) << "Registering HTTP handler for" << prefix << "exactmatch:" << exactMatch;
    pathHandlers.push_back(HTTPPathHandler(prefix, exactMatch, handler));
}

void UnregisterHTTPHandler(const std::string &prefix, bool exactMatch)
{
    std::vector<HTTPPathHandler>::iterator i = pathHandlers.begin();
    std::vector<HTTPPathHandler>::iterator iend = pathHandlers.end();
    for (; i != iend; ++i)
        if (i->prefix == prefix && i->exactMatch == exactMatch)
            break;
    if (i != iend) {
        logInfo(Log::HTTP) << "Unregistering HTTP handler for" << prefix << "exactmatch:" << exactMatch;
        pathHandlers.erase(i);
    }
}