webserver.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <pthread.h>
#include <time.h>

#define PORT 8080
#define BUFFER_SIZE 4096
#define MAX_THREADS 100

int user_id_counter = 0;

// Handler functions that bpftrace can hook into
void handle_users_endpoint(int user_id) {
    printf("[handle_users_endpoint] user_id=%d\n", user_id);
    sleep(0);  // Simulate work
}

void handle_data_endpoint(int user_id, int data_size) {
    printf("[handle_data_endpoint] user_id=%d, data_size=%d\n", user_id, data_size);
    usleep(10000);  // Simulate work
}

void handle_health_endpoint(void) {
    printf("[handle_health_endpoint] called\n");
}

// Parse query param from URL (e.g., "user_id=123" from "/api/users?user_id=123")
int extract_user_id(const char *request) {
    const char *query = strchr(request, '?');
    if (!query) return 1;  // Default user ID
    
    const char *user_param = strstr(query, "user_id=");
    if (!user_param) return 1;
    
    int user_id = atoi(user_param + 8);  // Skip "user_id="
    return user_id > 0 ? user_id : 1;
}

void send_response(int client_socket, const char *status, const char *body) {
    char response[BUFFER_SIZE];
    snprintf(response, sizeof(response),
             "HTTP/1.1 %s\r\n"
             "Content-Type: text/plain\r\n"
             "Content-Length: %lu\r\n"
             "Connection: close\r\n"
             "\r\n"
             "%s",
             status, strlen(body), body);
    send(client_socket, response, strlen(response), 0);
}

void* handle_client(void *arg) {
    int client_socket = *(int *)arg;
    free(arg);
    
    char request[BUFFER_SIZE] = {0};
    if (recv(client_socket, request, sizeof(request) - 1, 0) < 0) {
        perror("recv");
        close(client_socket);
        return NULL;
    }
    
    // Parse request line
    char method[16], path[256];
    sscanf(request, "%s %s", method, path);
    
    // Route handling
    if (strncmp(path, "/api/users", 10) == 0) {
        int user_id = extract_user_id(request);
        handle_users_endpoint(user_id);
        send_response(client_socket, "200 OK", "User data retrieved");
    }
    else if (strncmp(path, "/api/data", 9) == 0) {
        int user_id = extract_user_id(request);
        int data_size = rand() % 1000 + 100;
        handle_data_endpoint(user_id, data_size);
        send_response(client_socket, "200 OK", "Data retrieved");
    }
    else if (strncmp(path, "/health", 7) == 0) {
        handle_health_endpoint();
        send_response(client_socket, "200 OK", "OK");
    }
    else {
        send_response(client_socket, "404 Not Found", "Endpoint not found");
    }
    
    close(client_socket);
    return NULL;
}

int main() {
    int server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket < 0) {
        perror("socket");
        exit(1);
    }
    
    int opt = 1;
    if (setsockopt(server_socket, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0) {
        perror("setsockopt");
        exit(1);
    }
    
    struct sockaddr_in server_addr;
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(PORT);
    
    if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("bind");
        exit(1);
    }
    
    if (listen(server_socket, 5) < 0) {
        perror("listen");
        exit(1);
    }
    
    printf("Server listening on port %d\n", PORT);
    
    while (1) {
        struct sockaddr_in client_addr;
        socklen_t client_addr_len = sizeof(client_addr);
        
        int *client_socket = malloc(sizeof(int));
        *client_socket = accept(server_socket, (struct sockaddr *)&client_addr, &client_addr_len);
        
        if (*client_socket < 0) {
            perror("accept");
            free(client_socket);
            continue;
        }
        
        pthread_t thread;
        if (pthread_create(&thread, NULL, handle_client, client_socket) != 0) {
            perror("pthread_create");
            free(client_socket);
        } else {
            pthread_detach(thread);
        }
    }
    
    close(server_socket);
    return 0;
}