#define _GNU_SOURCE
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>

#define READ_BUFFER (64 * 1024)
#define RESPONSE "HTTP/1.1 200 Ok\r\nContent-Length: 11\r\n\r\nHello World"

int find_clrf(const char* buffer, int len) {
    const char* start_buffer = buffer;
    for (; len >= sizeof(int); len--, buffer++)
        if (*((int*)buffer) == *(int*)"\r\n\r\n")
            return buffer - start_buffer;
    return -1;
}

void* connection(void* arg) {
    char buffer[READ_BUFFER];
    int bytes, offset = 0, fd = (int)(size_t)arg;
    while ((bytes = read(fd, buffer + offset, READ_BUFFER - offset)) > 0) {
        int consumed = 0, clrf_offset = 0;
        while ((clrf_offset = find_clrf(buffer + clrf_offset + offset, bytes)) != -1) {
            if (send(fd, RESPONSE, sizeof(RESPONSE) - 1, MSG_NOSIGNAL) == -1) {
                close(fd);
                return NULL;
            }
            consumed += clrf_offset;
        }
        if (consumed) memcpy(buffer, buffer + consumed, consumed);
        offset = consumed;
    }
    close(fd);
}

int main() {
    int opt = 1, server = socket(AF_INET, SOCK_STREAM, 0);
    if (server < 0) perror("socket create");
    if (setsockopt(server, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0) perror("reuse addr");

    struct sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(12345);
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    if (bind(server, (struct sockaddr*)&addr, sizeof(addr)) < 0) perror("bind");
    if (listen(server, SOMAXCONN) < 0) perror("listen");

    int client;
    pthread_t thread;
    while ((client = accept(server, NULL, NULL)) > 0) {
        opt = 1;
        if (setsockopt(client, IPPROTO_TCP, TCP_NODELAY, &opt, sizeof(opt)) < 0) perror("no delay");
        if (pthread_create(&thread, NULL, connection, (void*)(size_t)client) != 0) perror("thread create");
    }
}