http_server_websocket_server_openssl_epoll.cpp

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <openssl/sha.h>
#include <openssl/bio.h>
#include <openssl/evp.h>
#include <openssl/buffer.h>

#define PORT 8081
#define BUFFER_SIZE 1024
#define MAGIC_STRING "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
#define MAX_EVENTS 10
#define MAX_CLIENTS 100

// Client state
typedef struct {
    int fd;           // Client socket FD
    char buffer[BUFFER_SIZE]; // Incoming data buffer
    int buf_len;      // Bytes in buffer
    int is_websocket; // 0 = HTTP, 1 = WebSocket
} Client;

// Compute Sec-WebSocket-Accept
char* compute_accept_key(const char* client_key) {
    char combined[100];
    snprintf(combined, sizeof(combined), "%s%s", client_key, MAGIC_STRING);
    unsigned char sha1[SHA_DIGEST_LENGTH];
    SHA1((unsigned char*)combined, strlen(combined), sha1);

    BIO* b64 = BIO_new(BIO_f_base64());
    BIO* mem = BIO_new(BIO_s_mem());
    b64 = BIO_push(b64, mem);
    BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL);
    BIO_write(b64, sha1, SHA_DIGEST_LENGTH);
    BIO_flush(b64);

    BUF_MEM* buffer;
    BIO_get_mem_ptr(b64, &buffer);
    char* accept_key = (char *)malloc(buffer->length + 1);
    memcpy(accept_key, buffer->data, buffer->length);
    accept_key[buffer->length] = '\0';

    BIO_free_all(b64);
    return accept_key;
}

// Send WebSocket handshake response
void send_websocket_handshake(int client_fd, const char* client_key) {
    char* accept_key = compute_accept_key(client_key);
    char response[BUFFER_SIZE];
    snprintf(response, sizeof(response),
             "HTTP/1.1 101 Switching Protocols\r\n"
             "Upgrade: websocket\r\n"
             "Connection: Upgrade\r\n"
             "Sec-WebSocket-Accept: %s\r\n\r\n",
             accept_key);
    write(client_fd, response, strlen(response));
    free(accept_key);
}

// Send HTTP Hello World response
void send_http_response(int client_fd) {
    const char* response = 
        "HTTP/1.1 200 OK\r\n"
        "Content-Type: text/plain\r\n"
        "Content-Length: 11\r\n"
        "Connection: close\r\n\r\n"
        "Hello World";
    write(client_fd, response, strlen(response));
}

// Extract Sec-WebSocket-Key
char* extract_key(const char* request) {
    const char* key_start = strstr(request, "Sec-WebSocket-Key: ");
    if (!key_start) return NULL;
    key_start += 19;
    char* key_end = (char *)strstr(key_start, "\r\n");
    if (!key_end) return NULL;
    int key_len = key_end - key_start;
    char* key = (char *)malloc(key_len + 1);
    strncpy(key, key_start, key_len);
    key[key_len] = '\0';
    return key;
}

// Check if request is a WebSocket upgrade
int is_websocket_request(const char* request) {
    return strstr(request, "Upgrade: websocket") != NULL && 
           strstr(request, "Sec-WebSocket-Key: ") != NULL;
}

// Decode masked payload
void decode_payload(char* payload, unsigned char* mask_key, int payload_len) {
    for (int i = 0; i < payload_len; i++) {
        payload[i] ^= mask_key[i % 4];
    }
}

// Set socket to non-blocking
void set_nonblocking(int fd) {
    int flags = fcntl(fd, F_GETFL, 0);
    fcntl(fd, F_SETFL, flags | O_NONBLOCK);
}

int main() {
    int server_fd, epoll_fd;
    struct sockaddr_in address;
    int addrlen = sizeof(address);
    Client clients[MAX_CLIENTS] = {0};

    // Create server socket
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("Socket failed");
        exit(EXIT_FAILURE);
    }
    set_nonblocking(server_fd);

    // Set up address
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    // Bind and listen
    if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
        perror("Bind failed");
        exit(EXIT_FAILURE);
    }
    if (listen(server_fd, SOMAXCONN) < 0) {
        perror("Listen failed");
        exit(EXIT_FAILURE);
    }
    printf("Server listening on port %d\n", PORT);

    // Create epoll instance
    epoll_fd = epoll_create1(0);
    if (epoll_fd == -1) {
        perror("Epoll create failed");
        exit(EXIT_FAILURE);
    }

    // Add server socket to epoll
    struct epoll_event ev, events[MAX_EVENTS];
    ev.events = EPOLLIN;
    ev.data.fd = server_fd;
    if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server_fd, &ev) == -1) {
        perror("Epoll add server failed");
        exit(EXIT_FAILURE);
    }

    // Main event loop
    while (1) {
        int nfds = epoll_wait(epoll_fd, events, MAX_EVENTS, -1);
        if (nfds == -1) {
            perror("Epoll wait failed");
            continue;
        }

        for (int i = 0; i < nfds; i++) {
            int fd = events[i].data.fd;

            if (fd == server_fd) {
                // Accept new connection
                int client_fd = accept(server_fd, (struct sockaddr*)&address, (socklen_t*)&addrlen);
                if (client_fd == -1) {
                    perror("Accept failed");
                    continue;
                }
                set_nonblocking(client_fd);

                // Add client to epoll
                ev.events = EPOLLIN | EPOLLET;
                ev.data.fd = client_fd;
                if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_fd, &ev) == -1) {
                    perror("Epoll add client failed");
                    close(client_fd);
                    continue;
                }

                // Store client
                for (int j = 0; j < MAX_CLIENTS; j++) {
                    if (clients[j].fd == 0) {
                        clients[j].fd = client_fd;
                        clients[j].is_websocket = 0;
                        clients[j].buf_len = 0;
                        break;
                    }
                }
                printf("New client connected: %d\n", client_fd);
            } else {
                // Find client
                Client* client = NULL;
                for (int j = 0; j < MAX_CLIENTS; j++) {
                    if (clients[j].fd == fd) {
                        client = &clients[j];
                        break;
                    }
                }
                if (!client) continue;

                // Read data
                int bytes_read = read(fd, client->buffer + client->buf_len, BUFFER_SIZE - client->buf_len);
                if (bytes_read <= 0) {
                    epoll_ctl(epoll_fd, EPOLL_CTL_DEL, fd, NULL);
                    close(fd);
                    memset(client, 0, sizeof(Client));
                    printf("Client disconnected: %d\n", fd);
                    continue;
                }
                client->buf_len += bytes_read;
                client->buffer[client->buf_len] = '\0'; // Null-terminate for string ops

                if (!client->is_websocket) {
                    // Initial request: HTTP or WebSocket?
                    if (is_websocket_request(client->buffer)) {
                        char* client_key = extract_key(client->buffer);
                        if (client_key) {
                            send_websocket_handshake(fd, client_key);
                            client->is_websocket = 1;
                            client->buf_len = 0;
                            free(client_key);
                            printf("Client %d upgraded to WebSocket\n", fd);
                        }
                    } else {
                        // Assume HTTP, send Hello World and close
                        send_http_response(fd);
                        epoll_ctl(epoll_fd, EPOLL_CTL_DEL, fd, NULL);
                        close(fd);
                        memset(client, 0, sizeof(Client));
                        printf("Served HTTP request to %d\n", fd);
                    }
                } else {
                    // WebSocket frame handling
                    if (client->buf_len >= 2) {
                        unsigned char* buf = (unsigned char*)client->buffer;
                        int opcode = buf[0] & 0x0F;
                        int mask = (buf[1] & 0x80) >> 7;
                        int payload_len = buf[1] & 0x7F;

                        if (opcode == 0x1 && client->buf_len >= (2 + (mask ? 4 : 0) + payload_len)) {
                            char* payload = mask ? client->buffer + 6 : client->buffer + 2;
                            if (mask) {
                                unsigned char* mask_key = (unsigned char*)client->buffer + 2;
                                decode_payload(payload, mask_key, payload_len);
                            }
                            printf("Received from %d: %.*s\n", fd, payload_len, payload);

                            // Echo back
                            char frame[BUFFER_SIZE] = {(char)0x81, (char)payload_len};
                            memcpy(frame + 2, payload, payload_len);
                            write(fd, frame, 2 + payload_len);

                            // Shift remaining data
                            int frame_len = 2 + (mask ? 4 : 0) + payload_len;
                            memmove(client->buffer, client->buffer + frame_len, client->buf_len - frame_len);
                            client->buf_len -= frame_len;
                        }
                    }
                }
            }
        }
    }

    close(server_fd);
    close(epoll_fd);
    return 0;
}