path: root/src/plugins/youtube/YoutubeMediaProxy.cpp

#include "../../../plugins/youtube/YoutubeMediaProxy.hpp"
#include "../../../include/NetUtils.hpp"

#include <vector>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <assert.h>

#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>

// TODO: What if the client sends a new header without reconnecting? is that even allowed by http standard?
// TODO: Detect when download has finished (and close connection).

namespace QuickMedia {
    static const int MAX_BUFFER_SIZE = 65536;
    static const int64_t RANGE = 524287;
    static const int64_t THROTTLED_DOWNLOAD_LIMIT_KB = 80; // TODO: What about people with really slow internet? What if the video player cache is not working and download is stuck, leading to false download speed calculation?
    static const int64_t THROTTLED_DURATION_SECS = 3;
    static const char download_error_response_msg[] = 
        "HTTP/1.1 500 Internal Server Error\r\n"
        "Content-Length: 0\r\n\r\n";

    static bool set_non_blocking(int fd) {
        const int flags = fcntl(fd, F_GETFL, 0);
        if(fd == -1 || fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1)
            return false;
        return true;
    }

    // TODO: Restrict range end to remote file size (content-length which we have saved).
    // TODO: Check if custom youtube redirect code is needed
    bool YoutubeMediaProxy::start_download(const std::string &media_url, ReadProgram &read_program, int64_t range_start, bool include_header, bool is_livestream, int livestream_sequence) {
        std::string r = std::to_string(range_start) + "-" + std::to_string(range_start + RANGE);

        std::string url = media_url + "&rn=" + std::to_string(rn) + "&rbuf=" + std::to_string(rbuf);
        std::vector<const char*> args = { "curl",
            //"-H", "Accept-Language: en-US,en;q=0.5", "-H", "Connection: keep-alive",
            "--no-buffer",
            "-H", "user-agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36",
            "-g", "-s", "-L", "-f" };

        if(is_livestream) {
            if(livestream_sequence != -1)
                url += "&sq=" + std::to_string(livestream_sequence);
        } else {
            args.insert(args.end(), { "-r", r.c_str() });
        }

        if(include_header)
            args.push_back("-i");

        //fprintf(stderr, "url: %s\n", url.c_str());

        args.insert(args.end(), { "--", url.c_str(), nullptr });

        if(exec_program_pipe(args.data(), &read_program) != 0)
            return false;

        if(!set_non_blocking(read_program.read_fd)) {
            perror("start_download: failed to set curl pipe non blocking mode");
            close(read_program.read_fd);
            kill(read_program.pid, SIGTERM);
            read_program.read_fd = -1;
            read_program.pid = -1;
            return false;
        }

        ++rn;
        rbuf += 3000;
        if(rbuf > 75000) rbuf = 75000;
        return true;
    }

    YoutubeStaticMediaProxy::YoutubeStaticMediaProxy(ThrottleHandler throttle_handler) : throttle_handler(std::move(throttle_handler)) {

    }

    YoutubeStaticMediaProxy::~YoutubeStaticMediaProxy() {
        stop();
    }

    bool YoutubeStaticMediaProxy::start(const std::string &youtube_media_url, int64_t content_length) {
        if(socket_fd != -1)
            return false;

        socket_fd = socket(AF_INET, SOCK_STREAM, 0);
        if(socket_fd == -1) {
            perror("YoutubeStaticMediaProxy::start: socket failed");
            return false;
        }

        socklen_t response_sock_addr_len;
        struct sockaddr_in server_addr;
        memset(&server_addr, 0, sizeof(server_addr));
        server_addr.sin_family = AF_INET;
        server_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
        server_addr.sin_port = htons(0);

        if(bind(socket_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
            perror("YoutubeStaticMediaProxy::start: bind failed");
            goto err;
        }

        if(listen(socket_fd, 2) == -1) {
            perror("YoutubeStaticMediaProxy::start: listen failed");
            goto err;
        }

        if(!set_non_blocking(socket_fd)) {
            perror("YoutubeStaticMediaProxy::start: failed to set socket non blocking mode");
            goto err;
        }

        struct sockaddr_in response_sock_addr;
        response_sock_addr_len = sizeof(response_sock_addr);
        if(getsockname(socket_fd, (struct sockaddr*)&response_sock_addr, &response_sock_addr_len) == -1) {
            perror("YoutubeStaticMediaProxy::start: getsockname failed");
            goto err;
        }

        port = ntohs(response_sock_addr.sin_port);
        this->youtube_media_url = youtube_media_url;
        this->content_length = content_length;
        return true;

        err:
        if(downloader_read_program.read_fd != -1)
            close(downloader_read_program.read_fd);
        if(downloader_read_program.pid != -1)
            kill(downloader_read_program.pid, SIGTERM);
        close(socket_fd);
        socket_fd = -1;
        return false;
    }

    void YoutubeStaticMediaProxy::stop() {
        if(downloader_read_program.read_fd != -1) {
            close(downloader_read_program.read_fd);
            downloader_read_program.read_fd = -1;
        }

        if(downloader_read_program.pid != -1) {
            kill(downloader_read_program.pid, SIGTERM);
            wait_program(downloader_read_program.pid);
            downloader_read_program.pid = -1;
        }

        if(client_fd != -1) {
            close(client_fd);
            client_fd = -1;
        }

        if(socket_fd != -1) {
            close(socket_fd);
            socket_fd = -1;
        }

        clear_download_state();
        client_request_buffer.clear();
        client_request_finished = false;
    }

    YoutubeStaticMediaProxy::Error YoutubeStaticMediaProxy::update() {
        if(socket_fd == -1)
            return Error::OK;

        if(client_fd == -1) {
            client_fd = accept_client();
            if(client_fd == -1)
                return Error::OK;
        } else {
            const int new_client_fd = accept_client();
            if(new_client_fd != -1) {
                on_client_disconnect();
                client_fd = new_client_fd;
            }
        }

        Error err = read_client_data();
        if(err != Error::OK || !client_request_finished)
            return err;
        if(downloader_read_program.pid == -1)
            return Error::ERROR;
        return handle_download();
    }

    bool YoutubeStaticMediaProxy::get_address(std::string &address) {
        if(socket_fd == -1)
            return false;

        address = "http://127.0.0.1:" + std::to_string(port);
        return true;
    }

    void YoutubeStaticMediaProxy::on_client_disconnect() {
        client_request_buffer.clear();
        client_request_finished = false;
        download_started = false;
        throttle_started = false;

        if(client_fd != -1) {
            close(client_fd);
            client_fd = -1;
        }

        if(downloader_read_program.pid != -1)
            kill(downloader_read_program.pid, SIGTERM);

        update_download_program_status(true);
    }

    // Returns 0 if start range is not found
    static int64_t header_extract_start_range(const std::string &header) {
        std::string range = header_extract_value(header, "range");
        if(range.empty())
            return 0;

        int64_t start_range = 0;
        if(sscanf(range.c_str(), " bytes=%lld", &start_range) != 1)
            return 0;

        return start_range;
    }

    // TODO: What about hls (live streams)? need to test with that. There may not be a need to use YoutubeMediaProxy for that case (in that case document it).
    YoutubeStaticMediaProxy::Error YoutubeStaticMediaProxy::read_client_data() {
        if(client_request_finished)
            return Error::OK;

        char read_buffer[4096];
        const ssize_t num_bytes_read = read(client_fd, read_buffer, sizeof(read_buffer));
        if(num_bytes_read == -1) {
            const int err = errno;
            if(err == EAGAIN || err == EWOULDBLOCK) {
                return Error::OK;
            } else if(err == EPIPE || err == ECONNRESET) {
                //fprintf(stderr, "YoutubeStaticMediaProxy::read_client_data: client disconnected\n");
                on_client_disconnect();
                return Error::ERROR;
            } else {
                perror("YoutubeStaticMediaProxy::read_client_data: read failed");
                return Error::ERROR;
            }
        } else if(num_bytes_read == 0) {
            //fprintf(stderr, "YoutubeStaticMediaProxy::read_client_data: client disconnected\n");
            on_client_disconnect();
            return Error::ERROR;
        }

        client_request_buffer.append(read_buffer, num_bytes_read);
        const size_t header_end = client_request_buffer.find("\r\n\r\n");
        if(header_end != std::string::npos) {
            client_request_buffer.erase(header_end + 4);
            client_request_finished = true;
            download_started = false;
            throttle_started = false;
            download_read_buffer_offset = 0;

            const int64_t new_start_range = header_extract_start_range(client_request_buffer);
            if(downloader_read_program.pid != -1) {
                kill(downloader_read_program.pid, SIGTERM);
                wait_program(downloader_read_program.pid);
                downloader_read_program.pid = -1;
            }
            clear_download_state();
            return update_download_program_status(false, new_start_range, true);
        } else {
            if(client_request_buffer.size() > MAX_BUFFER_SIZE) {
                client_request_finished = true;
                fprintf(stderr, "YoutubeStaticMediaProxy::read_client_data: buffer is full (malicious client?)\n");
                return Error::ERROR;
            }
        }
        return Error::OK;
    }

    void YoutubeStaticMediaProxy::clear_download_state() {
        download_header.clear();
        download_header_finished = false;
        download_header_sent = false;
        download_header_remaining_sent = false;
        download_header_written_offset = 0;
        download_read_buffer_offset = 0;
    }

    YoutubeStaticMediaProxy::Error YoutubeStaticMediaProxy::update_download_program_status(bool client_disconnected, int64_t new_range_start, bool restart_download) {
        int program_status = 0;
        if(downloader_read_program.pid != -1) {
            if(client_disconnected) {
                wait_program(downloader_read_program.pid);
            } else {
                if(wait_program_non_blocking(downloader_read_program.pid, &program_status) == 0 && program_status == 0)
                    return Error::OK;
            }
            downloader_read_program.pid = -1;
        }
        
        if(downloader_read_program.read_fd != -1) {
            close(downloader_read_program.read_fd);
            downloader_read_program.read_fd = -1;
        }

        // TODO: Why is this not 0 when download finishes?
        if(program_status != 0) {
            //fprintf(stderr, "YoutubeStaticMediaProxy::update_download_program_status: download failed, exit status: %d\n", program_status);
            if(client_fd != -1) {
                write(client_fd, download_error_response_msg, sizeof(download_error_response_msg) - 1);
                close(client_fd);
                client_fd = -1;
                client_request_buffer.clear();
                client_request_finished = false;
            }
            return Error::ERROR;
        }

        if(client_disconnected) {
            current_download_range = 0;
        } else {
            current_download_range += RANGE + 1;
        }

        if(new_range_start != -1) {
            download_range_start = new_range_start;
            current_download_range = download_range_start;
        }

        if(new_range_start == -1) {
            download_header_finished = true;
            download_header_sent = true;
            download_header_remaining_sent = true;
        } else {
            clear_download_state();
        }

        if(client_disconnected) {
            clear_download_state();
            return Error::ERROR;
        }

        if(!restart_download)
            return Error::OK;

        if(new_range_start == -1) {
            download_header_finished = true;
            download_header_sent = true;
            download_header_remaining_sent = true;
        }

        const bool start_download_success = start_download(youtube_media_url, downloader_read_program, current_download_range, new_range_start != -1);
        if(!start_download_success) {
            fprintf(stderr, "YoutubeStaticMediaProxy::update_download_program_status: failed to start download\n");
            if(client_fd != -1) {
                write(client_fd, download_error_response_msg, sizeof(download_error_response_msg) - 1);
                close(client_fd);
                client_fd = -1;
                client_request_buffer.clear();
                client_request_finished = false;
            }

            clear_download_state();
            return Error::ERROR;
        }

        return Error::OK;
    }

    static void header_replace_content_length(std::string &header, size_t header_size, int64_t new_content_length) {
        if(new_content_length < 0)
            new_content_length = 0;

        const char *content_length_p = strcasestr(header.c_str(), "content-length:");
        if(!content_length_p)
            return;

        const size_t content_length_start = (content_length_p + 15) - header.c_str();
        if(content_length_start >= header_size)
            return;
        const size_t line_end = header.find("\r\n", content_length_start);
        header.replace(content_length_start, line_end - content_length_start, std::to_string(new_content_length));
    }

    YoutubeStaticMediaProxy::Error YoutubeStaticMediaProxy::continue_send(const char *buffer_start, size_t total_bytes_to_write, int &buffer_offset) {
        int num_bytes_to_write = total_bytes_to_write - buffer_offset;
        //assert(num_bytes_to_write >= 0);
        if(num_bytes_to_write < 0) num_bytes_to_write = 0;
        if(num_bytes_to_write == 0) {
            buffer_offset = 0;
            return Error::OK;
        }

        const ssize_t num_bytes_written = write(client_fd, buffer_start + buffer_offset, num_bytes_to_write);
        if(num_bytes_written == -1) {
            const int err = errno;
            if(err == EAGAIN || err == EWOULDBLOCK) {
                return Error::OK;
            } else if(err == EPIPE || err == ECONNRESET) {
                //fprintf(stderr, "YoutubeStaticMediaProxy::continue_send: client disconnected\n");
                on_client_disconnect();
                return Error::ERROR;
            } else {
                perror("YoutubeStaticMediaProxy::continue_send: write failed");
                return Error::ERROR;
            }
        } else if(num_bytes_written == 0) {
            //fprintf(stderr, "YoutubeStaticMediaProxy::continue_send: client disconnected\n");
            on_client_disconnect();
            return Error::ERROR;
        } else if(num_bytes_written != num_bytes_to_write) {
            buffer_offset += num_bytes_written;
        } else {
            buffer_offset = 0;
        }
        return Error::OK;
    }

    static bool http_is_redirect(const char *header, size_t size) {
        const void *end_of_first_line_p = memmem(header, size, "\r\n", 2);
        if(!end_of_first_line_p)
            return false;
        return memmem(header, (const char*)end_of_first_line_p - header, " 30", 3) != nullptr;
    }

    static size_t find_start_of_first_non_redirect_header(const char *headers, size_t size, size_t &header_end) {
        const char *start = headers;
        while(size > 0) {
            const void *end_of_header = memmem(headers, size, "\r\n\r\n", 4);
            if(!end_of_header)
                return std::string::npos;

            const size_t offset_to_end_of_headers = ((const char*)end_of_header + 4) - headers;
            if(!http_is_redirect(headers, offset_to_end_of_headers)) {
                header_end = (headers - start) + offset_to_end_of_headers;
                return headers - start;
            }

            headers += offset_to_end_of_headers;
            size -= offset_to_end_of_headers;
        }
        return std::string::npos;
    }

    YoutubeStaticMediaProxy::Error YoutubeStaticMediaProxy::handle_download() {
        // TODO: Maybe read even if write is being slow and failing?
        if(download_read_buffer_offset == 0) {
            downloader_num_read_bytes = read(downloader_read_program.read_fd, download_read_buffer, sizeof(download_read_buffer));
            if(downloader_num_read_bytes == -1) {
                const int err = errno;
                if(err == EAGAIN || err == EWOULDBLOCK) {
                    return Error::OK;
                } else {
                    perror("YoutubeStaticMediaProxy::handle_download: curl read failed");
                    return Error::ERROR;
                }
            } else if(downloader_num_read_bytes == 0) {
                Error err = update_download_program_status(false, -1, true);
                if(err != Error::OK)
                    return err;
            } else {
                if(!download_started) {
                    total_downloaded_bytes = 0;
                    download_started = true;
                    throttle_started = false;

                    struct timespec tp;
                    clock_gettime(CLOCK_MONOTONIC, &tp);
                    download_start_time = tp.tv_sec;
                }
                total_downloaded_bytes += downloader_num_read_bytes;
            }
        }

#if 0
        if(download_started) {
            struct timespec tp;
            clock_gettime(CLOCK_MONOTONIC, &tp);

            int64_t time_elapsed = tp.tv_sec - download_start_time;
            int64_t download_speed_kb_sec = 0;
            if(time_elapsed > 0)
                download_speed_kb_sec = (total_downloaded_bytes / time_elapsed) / 1024;

            if(download_speed_kb_sec < THROTTLED_DOWNLOAD_LIMIT_KB) {
                if(throttle_started) {
                    if(tp.tv_sec - throttle_start_time >= THROTTLED_DURATION_SECS && !throttle_callback_called) {
                        total_downloaded_bytes = 0;
                        download_started = false;
                        throttle_started = false;
                        throttle_callback_called = true;
                        if(throttle_handler)
                            throttle_handler();
                    }
                } else {
                    throttle_started = true;
                    throttle_start_time = tp.tv_sec;
                }
            } else {
                throttle_started = false;
            }
        }
#endif

        // TODO: Remove this code and instead create the header ourselves and send it to the client. Then pipe the curl output directly to the client input.
        if(!download_header_finished) {
            download_header.append(download_read_buffer, downloader_num_read_bytes);
            size_t header_end = std::string::npos;
            const size_t offset_to_start_of_header = find_start_of_first_non_redirect_header(download_header.c_str(), download_header.size(), header_end);
            if(header_end != std::string::npos) {
                download_header.erase(0, offset_to_start_of_header);
                header_end -= offset_to_start_of_header;

                download_header_finished = true;
                download_header_sent = false;
                download_header_remaining_sent = false;
                download_header_written_offset = 0;
                download_header_offset_to_end_of_header = header_end;
                download_read_buffer_offset = -1;

                header_replace_content_length(download_header, header_end, content_length - download_range_start);
            } else {
                if(download_header.size() > MAX_BUFFER_SIZE) {
                    fprintf(stderr, "YoutubeStaticMediaProxy::handle_download: buffer is full (malicious server?)\n");
                    if(downloader_read_program.pid != -1) {
                        kill(downloader_read_program.pid, SIGTERM);
                        wait_program(downloader_read_program.pid);
                        downloader_read_program.pid = -1;
                    }
                    clear_download_state();
                    update_download_program_status(false, 0, false);
                    return Error::ERROR;
                }
            }
        }

        if(download_header_finished && !download_header_sent) {
            Error err = continue_send(download_header.data(), download_header_offset_to_end_of_header, download_header_written_offset);
            if(err != Error::OK)
                return err;

            if(download_header_written_offset == 0) {
                download_header_sent = true;
                download_header_written_offset = download_header_offset_to_end_of_header;
            }
        }

        if(download_header_finished && !download_header_remaining_sent) {
            Error err = continue_send(download_header.data(), download_header.size(), download_header_written_offset);
            if(err != Error::OK)
                return err;

            if(download_header_written_offset == 0) {
                download_header_remaining_sent = true;
                download_read_buffer_offset = 0;
                return Error::OK;
            }
        }

        if(download_header_remaining_sent)
            return continue_send(download_read_buffer, downloader_num_read_bytes, download_read_buffer_offset);

        return Error::OK;
    }

    int YoutubeStaticMediaProxy::accept_client() {
        struct sockaddr_in client_addr;
        socklen_t client_addr_len = sizeof(client_addr);
        int new_client_fd = accept(socket_fd, (struct sockaddr*)&client_addr, &client_addr_len);
        if(new_client_fd == -1) {
            const int err = errno;
            if(err == EAGAIN || err == EWOULDBLOCK) {
                return -1;
            } else {
                perror("YoutubeStaticMediaProxy::accept_client accept failed");
                return -1;
            }
        }

        if(!set_non_blocking(new_client_fd)) {
            perror("YoutubeStaticMediaProxy::accept_client: failed to set client socket non blocking mode");
            close(new_client_fd);
            return -1;
        }

        //fprintf(stderr, "YoutubeStaticMediaProxy::accept_client: client connected!\n");
        return new_client_fd;
    }

    YoutubeLiveStreamMediaProxy::~YoutubeLiveStreamMediaProxy() {
        stop();
    }

    bool YoutubeLiveStreamMediaProxy::start(const std::string &youtube_media_url, int64_t) {
        fd[0] = -1;
        fd[1] = -1;
        if(pipe(fd) == -1) {
            perror("YoutubeLiveStreamMediaProxy::start: failed to open pipe");
            return false;
        }

       //if(socketpair(AF_UNIX, SOCK_STREAM, 0, fd) == -1) {
       //    perror("YoutubeLiveStreamMediaProxy::start: failed to open pipe");
       //    return false;
       //}

        for(int i = 0; i < 2; ++i) {
            if(!set_non_blocking(fd[i])) {
                stop();
                return false;
            }
        }

        if(!start_download(youtube_media_url, downloader_read_program, 0, true, true)) {
            stop();
            return false;
        }

        this->youtube_media_url = youtube_media_url;
        return true;
    }

    void YoutubeLiveStreamMediaProxy::stop() {
        for(int i = 0; i < 2; ++i) {
            if(fd[i] != -1) {
                close(fd[i]);
                fd[i] = -1;
            }
        }

        if(downloader_read_program.read_fd != -1) {
            close(downloader_read_program.read_fd);
            downloader_read_program.read_fd = -1;
        }

        if(downloader_read_program.pid != -1) {
            kill(downloader_read_program.pid, SIGTERM);
            wait_program(downloader_read_program.pid);
            downloader_read_program.pid = -1;
        }
    }

    YoutubeMediaProxy::Error YoutubeLiveStreamMediaProxy::update_download_program_status() {
        int program_status = 0;
        if(wait_program_non_blocking(downloader_read_program.pid, &program_status) == 0 && program_status == 0)
            return Error::OK;

        downloader_read_program.pid = -1;
        if(downloader_read_program.read_fd != -1) {
            close(downloader_read_program.read_fd);
            downloader_read_program.read_fd = -1;
        }

        // TODO: Why is this not 0 when download finishes?
        if(program_status != 0) {
            //fprintf(stderr, "YoutubeLiveStreamMediaProxy::update_download_program_status: download failed, exit status: %d\n", program_status);
            stop();
            return Error::ERROR;
        }

        ++livestream_sequence_num;
        const bool start_download_success = start_download(youtube_media_url, downloader_read_program, 0, false, true, livestream_sequence_num);
        if(!start_download_success) {
            fprintf(stderr, "YoutubeLiveStreamMediaProxy::update_download_program_status: failed to start download\n");
            stop();
            return Error::ERROR;
        }

        return Error::OK;
    }

    YoutubeMediaProxy::Error YoutubeLiveStreamMediaProxy::continue_send(const char *buffer_start, size_t total_bytes_to_write, int &buffer_offset) {
        int num_bytes_to_write = total_bytes_to_write - buffer_offset;
        //assert(num_bytes_to_write >= 0);
        if(num_bytes_to_write < 0) num_bytes_to_write = 0;
        if(num_bytes_to_write == 0) {
            buffer_offset = 0;
            return Error::OK;
        }

        const ssize_t num_bytes_written = write(fd[1], buffer_start + buffer_offset, num_bytes_to_write);
        if(num_bytes_written == -1) {
            const int err = errno;
            if(err == EAGAIN || err == EWOULDBLOCK) {
                return Error::OK;
            } else if(err == EPIPE || err == ECONNRESET) {
                //fprintf(stderr, "YoutubeLiveStreamMediaProxy::continue_send: client disconnected\n");
                stop();
                return Error::ERROR;
            } else {
                perror("YoutubeLiveStreamMediaProxy::continue_send: write failed");
                return Error::ERROR;
            }
        } else if(num_bytes_written == 0) {
            //fprintf(stderr, "YoutubeLiveStreamMediaProxy::continue_send: client disconnected\n");
            stop();
            return Error::ERROR;
        } else if(num_bytes_written != num_bytes_to_write) {
            buffer_offset += num_bytes_written;
        } else {
            buffer_offset = 0;
        }
        return Error::OK;
    }

    YoutubeMediaProxy::Error YoutubeLiveStreamMediaProxy::update() {
        if(fd[1] == -1 || downloader_read_program.read_fd == -1)
            return Error::OK;

        if(download_read_buffer_offset == 0) {
            downloader_num_read_bytes = read(downloader_read_program.read_fd, download_read_buffer, sizeof(download_read_buffer));
            if(downloader_num_read_bytes == -1) {
                const int err = errno;
                if(err == EAGAIN || err == EWOULDBLOCK) {
                    return Error::OK;
                } else {
                    perror("YoutubeLiveStreamMediaProxy::update: curl read failed");
                    return Error::ERROR;
                }
            } else if(downloader_num_read_bytes == 0) {
                Error err = update_download_program_status();
                if(err != Error::OK)
                    return err;
            }
        }

        if(!download_header_finished) {
            download_header.append(download_read_buffer, downloader_num_read_bytes);
            size_t header_end = std::string::npos;
            const size_t offset_to_start_of_header = find_start_of_first_non_redirect_header(download_header.c_str(), download_header.size(), header_end);
            if(header_end != std::string::npos) {
                download_header.erase(0, offset_to_start_of_header);
                header_end -= offset_to_start_of_header;

                download_header_finished = true;
                download_header_remaining_sent = false;
                download_header_written_offset = header_end;
                download_read_buffer_offset = -1;
                fprintf(stderr, "header: |%.*s|\n", download_header_written_offset, download_header.c_str());

                if(livestream_sequence_num == -1) {
                    // TODO: What about |header_end|?
                    std::string sequence_num = header_extract_value(download_header, "x-sequence-num");
                    fprintf(stderr, "server sequence num: |%s|\n", sequence_num.c_str());
                    if(sequence_num.empty())
                        fprintf(stderr, "YoutubeLiveStreamMediaProxy::update: missing sequence num from server\n");
                    else
                        livestream_sequence_num = strtoll(sequence_num.c_str(), nullptr, 10);
                }
            } else {
                if(download_header.size() > MAX_BUFFER_SIZE) {
                    fprintf(stderr, "YoutubeLiveStreamMediaProxy::update: buffer is full (malicious server?)\n");
                    if(downloader_read_program.pid != -1) {
                        kill(downloader_read_program.pid, SIGTERM);
                        wait_program(downloader_read_program.pid);
                        downloader_read_program.pid = -1;
                    }
                    download_header_finished = true;
                    return Error::ERROR;
                }
            }
        }

        if(download_header_finished && !download_header_remaining_sent) {
            Error err = continue_send(download_header.data(), download_header.size(), download_header_written_offset);
            if(err != Error::OK)
                return err;

            if(download_header_written_offset == 0) {
                download_header_remaining_sent = true;
                download_read_buffer_offset = 0;
                return Error::OK;
            }
        }

        if(download_header_remaining_sent)
            return continue_send(download_read_buffer, downloader_num_read_bytes, download_read_buffer_offset);

        return Error::OK;
    }

    bool YoutubeLiveStreamMediaProxy::get_address(std::string &address) {
        if(fd[0] == -1)
            return false;

        address = "fd://" + std::to_string(fd[0]);
        return true;
    }
}