proxy_server_cache.c

#include "parse_server.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <fcntl.h>
#include <time.h>
#include <errno.h>
#include <pthread.h>
#include <semaphore.h>

#define MAX_BYTES 4096                  // Maximum allowed size of request/response
#define MAX_CLIENTS 400                 // Maximum number of client requests served at a time
#define MAX_SIZE 200*(1<<20)            // Size of the cache
#define MAX_ELEMENT_SIZE 10*(1<<20)     // Maximum size of an element in cache

typedef struct cache_element cache_element;

struct cache_element
{
    char *data;             // stores the response
    int len;                // length of data
    char *url;              // stores the request
    time_t lru_time_track;  // stores the latest time that element is accessing
    cache_element *next;    // pointer to next element
};

cache_element* find(char *url);
int add_cache_element(char *data, int size, char *url);
void remove_cache_element();

int port_num = 8080;        // Default port
int proxy_socketId;         // Socket descriptor of proxy server
pthread_t tId[MAX_CLIENTS]; // Array to store thread Ids of clients
sem_t semaphore;            // Puts waiting threads to sleep if client requests exceed MAX_CLIENTS
pthread_mutex_t lock;       // locks the cache
cache_element *head;        // pointer to cache
int cache_size;             // current size of cache


int sendErrorMsg(int socket, int status_code){
    char str[1024];
    char currentTime[50];
    time_t now = time(0);

    struct tm data = *gmtime(&now);
    strftime(currentTime, sizeof(currentTime), "%a, %d %b %Y %H:%M:%S %Z", &data);

    switch(status_code){
        case 400: snprintf(str, sizeof(str), "HTTP/1.1 400 Bad Request\r\nContent-Length: 95\r\nConnection: keep-alive\r\nContent-Type: text/html\r\nDate: %s\r\nServer: HarshvardhanS/21064\r\n\r\n<HTML><HEAD><TITLE>400 Bad Request</TITLE></HEAD>\n<BODY><H1>400 Bad Request</H1>\n</BODY></HTML>", currentTime);
                    printf("400 Bad Request\n");
                    send(socket, str, strlen(str), 0);
                    break;

        case 403: snprintf(str, sizeof(str), "HTTP/1.1 403 Forbidden\r\nContent-Length: 112\r\nConnection: keep-alive\r\nContent-Type: text/html\r\nDate: %s\r\nServer: HarshvardhanS/21064\r\n\r\n<HTML><HEAD><TITLE>403 Forbidden</TITLE></HEAD>\n<BODY><H1>403 Forbidden</H1><br>Permission Denied\n</BODY></HTML>", currentTime);
                    printf("403 Forbidded\n");
                    send(socket, str, strlen(str), 0);
                    break;

        case 404: snprintf(str, sizeof(str), "HTTP/1.1 404 Not Found\r\nContent-Length: 91\r\nConnection: keep-alive\r\nContent-Type: text/html\r\nDate: %s\r\nServer: HarshvardhanS/21064\r\n\r\n<HTML><HEAD><TITLE>404 Not Found</TITLE></HEAD>\n<BODY><H1>404 Not Found</H1>\n</BODY></HTML>", currentTime);
                    printf("404 Not Found\n");
                    send(socket, str, strlen(str), 0);
                    break;

        case 500: snprintf(str, sizeof(str), "HTTP/1.1 500 Internal Server Error\r\nContent-Length: 115\r\nConnection: keep-alive\r\nContent-Type: text/html\r\nDate: %s\r\nServer: HarshvardhanS/21064\r\n\r\n<HTML><HEAD><TITLE>500 Internal Server Error</TITLE></HEAD>\n<BODY><H1>500 Internal Server Error</H1>\n</BODY></HTML>", currentTime);
                    printf("500 Internal Server Error\n");
                    send(socket, str, strlen(str), 0);
                    break;

        case 501: snprintf(str, sizeof(str), "HTTP/1.1 501 Not Implemented\r\nContent-Length: 103\r\nConnection: keep-alive\r\nContent-Type: text/html\r\nDate: %s\r\nServer: HarshvardhanS/21064\r\n\r\n<HTML><HEAD><TITLE>501 Not Implemented</TITLE></HEAD>\n<BODY><H1>501 Not Implemented</H1>\n</BODY></HTML>", currentTime);
                    printf("501 Not Implemented\n");
                    send(socket, str, strlen(str), 0);
                    break;

        case 505: snprintf(str, sizeof(str), "HTTP/1.1 505 HTTP Version Not Supported\r\nContent-Length: 125\r\nConnection: keep-alive\r\nContent-Type: text/html\r\nDate: %s\r\nServer: HarshvardhanS/21064\r\n\r\n<HTML><HEAD><TITLE>505 HTTP Version Not Supported</TITLE></HEAD>\n<BODY><H1>505 HTTP Version Not Supported</H1>\n</BODY></HTML>", currentTime);
                    printf("505 HTTP Version Not Supported\n");
                    send(socket, str, strlen(str), 0);
                    break;

        default: return -1;
    }

    return 1;
}

int connectRemoteServer(char *host_address, int port_num){
    // Create socker for remote server
    int remoteSocket = socket(AF_INET, SOCK_STREAM, 0);

    if(remoteSocket < 0){
        printf("Error in creating socket.\n");
        return -1;
    }

    // Get host by name or IP address provided
    struct hostent *host = gethostbyname(host_address);

    if(host == NULL){
        fprintf(stderr, "No such host found.\n");
        return -1;
    }

    // Inserts IP address and port number of host in struct `server_address`
    struct sockaddr_in server_address;

    bzero((char*)&server_address, sizeof(server_address));
    server_address.sin_family = AF_INET;
    server_address.sin_port = htons(port_num);

    bcopy((char*)host->h_addr_list[0], (char*)&server_address.sin_addr.s_addr, host->h_length);

    // Connect to remote server
    if(connect(remoteSocket, (struct sockaddr*)&server_address, (socklen_t)sizeof(server_address)) < 0){
        fprintf(stderr, "Error in connecting!\n");
        return -1;
    }

    // free(host_address);
    return remoteSocket;
}

int handle_request(int clientSocket, struct ParsedRequest *request, char *tempReq){
    char *buf = (char*)malloc(sizeof(char)*MAX_BYTES);
    strcpy(buf, "GET ");
    strcat(buf, request->path);
    strcat(buf, " ");
    strcat(buf, request->version);
    strcat(buf, "\r\n");

    size_t len = strlen(buf);

    if(set_ParsedHeader(request, "Connection", "close") < 0){
        printf("Set header key not working\n");
    }

    if(get_ParsedHeader(request, "Host") == NULL){
        if(set_ParsedHeader(request, "Host", request->host) < 0){
            printf("Set \"Host\" header key not working\n");
        }
    }

    if(unparse_headers_ParsedRequest(request, buf + len, (size_t)MAX_BYTES - len) < 0){
        printf("unparse failed\n");     // Still try to send request without header
    }

    int server_port = 80;       // Default remote server port

    if(request->port != NULL){
        server_port = atoi(request->port);
    }

    int remoteSocketId = connectRemoteServer(request->host, server_port);

    if(remoteSocketId < 0)
        return -1;

    int bytes_send = send(remoteSocketId, buf, strlen(buf), 0);

    bzero(buf, MAX_BYTES);

    bytes_send = recv(remoteSocketId, buf, MAX_BYTES-1, 0);
    char *temp_buf = (char*)malloc(sizeof(char)*MAX_BYTES);
    int temp_buf_size = MAX_BYTES;
    int temp_buf_ind = 0;

    while(bytes_send > 0){
        bytes_send = send(clientSocket, buf, bytes_send, 0);

        for(int i=0;i<bytes_send/sizeof(char);i++){
            temp_buf[temp_buf_ind] = buf[i];
            temp_buf_ind++;
        }

        temp_buf_size += MAX_BYTES;
        temp_buf = (char*)realloc(temp_buf, temp_buf_size);

        if(bytes_send < 0){
            perror("Error in sending data to client socket.\n");
            break;
        }

        bzero(buf, MAX_BYTES);

        bytes_send = recv(remoteSocketId, buf, MAX_BYTES-1, 0);
    }

    temp_buf[temp_buf_ind] = '\0';
    free(buf);
    add_cache_element(temp_buf, strlen(temp_buf), tempReq);
    printf("Done\n");
    free(temp_buf);

    close(remoteSocketId);
    return 0;
}

int checkHTTPVersion(char *msg){
    int version = -1;

    if(strncmp(msg, "HTTP/1.1", 8) == 0){
        version = 1;
    }
    else if(strncmp(msg, "HTTP/1.0", 8) == 0){
        version = 1;
    }

    return version;
}

void* thread_func(void* socketNew){
    sem_wait(&semaphore);
    int p;
    sem_getvalue(&semaphore, &p);
    printf("Semaphore value: %d\n", p);

    int* t = (int*)(socketNew);
    int socket = *t;                // Socket is the socket descriptor of the connected client
    int client_bytes_send, len;     // Bytes transferred

    char *buf = (char*)calloc(MAX_BYTES, sizeof(char));     // Create buffer of 4Kb for client

    bzero(buf, MAX_BYTES);                                  // Make buffer zero
    client_bytes_send = recv(socket, buf, MAX_BYTES, 0);    //Receiving request of client by proxy server

    while(client_bytes_send > 0){
        len = strlen(buf);

        if(strstr(buf, "\r\n\r\n") == NULL){
            client_bytes_send = recv(socket, buf + len, MAX_BYTES - len, 0);
        }
        
        else{
            break;
        }
    }

    char *tempReq = (char*)malloc(strlen(buf)*sizeof(char)+1);

    // tempReq and buf both store the request sent by the client
    for(int i=0;i<strlen(buf);i++){
        tempReq[i] = buf[i];
    }

    struct cache_element* temp = find(tempReq);

    if(temp != NULL){
        // If request found in cache then send response to client from proxy cache
        int size = temp->len/sizeof(char);
        int pos = 0;
        char response[MAX_BYTES];

        while(pos < size){
            bzero(response, MAX_BYTES);

            for(int i=0;i<MAX_BYTES;i++){
                response[i] = temp->data[pos];
                pos++;
            }

            send(socket, response, MAX_BYTES, 0);
        }

        printf("Data received from the cache\n\n");
        printf("%s\n\n", response);
        // close(socket);
        // free(buf);
        // sem_post(&semaphore);
        // return NULL;
    }

    else if(client_bytes_send > 0){
        len = strlen(buf);

        struct ParsedRequest* request = create_ParsedRequest();        // Parsing request

        // parse_ParsedRequest returns 0 on success and -1 pn failure
        if(parse_ParsedRequest(request, buf, len) < 0){
            printf("Parsing failed\n");
        }
        
        else{
            bzero(buf, MAX_BYTES);
            
            if(!strcmp(request->method, "GET")){
                if(request->host && request->path && (checkHTTPVersion(request->version) == 1)){
                    client_bytes_send = handle_request(socket, request, tempReq);       // Handle GET request

                    if(client_bytes_send == -1){
                        sendErrorMsg(socket, 500);
                    }
                }

                else{
                    sendErrorMsg(socket, 500);      // Internal server error
                }
            }

            else{
                printf("This code doesn't support any method other than GET\n");
            }
        }
        // Free up the request pointer
        destroy_ParsedRequest(request);
    }

    else if(client_bytes_send < 0){
        perror("Error in receiving from client\n");
    }

    else if(client_bytes_send == 0){
        printf("Client disconnected\n");
    }

    shutdown(socket, SHUT_RDWR);
    close(socket);
    free(buf);
    sem_post(&semaphore);

    sem_getvalue(&semaphore, &p);
    printf("Semaphore post value: %d\n", p);
    free(tempReq);
    return NULL;
}

int main(int argc, char* argv[]){
    int client_socketId, client_len;
    struct sockaddr_in server_addr, client_addr;        // Address of server and client

    sem_init(&semaphore, 0, MAX_CLIENTS);       // Initialize semaphore and lock
    pthread_mutex_init(&lock, NULL);            // Initialize lock for cache

    // Checl whether two arguments are recived or not
    if(argc == 2){
        port_num = atoi(argv[1]);
    }
    
    else{
        printf("Too few arguments\n");
        exit(1);
    }

    printf("Setting Proxy Server Port: %d\n", port_num);

    // Create proxy socket
    proxy_socketId = socket(AF_INET, SOCK_STREAM, 0);

    if(proxy_socketId < 0){
        perror("Failed to create socket\n");
        exit(1);
    }

    int reuse = 1;

    if(setsockopt(proxy_socketId, SOL_SOCKET, SO_REUSEADDR, (const char*)&reuse, sizeof(reuse)) < 0){
        perror("setsockopt(SO_REUSEADDR) failed\n");
    }

    bzero((char*)&server_addr, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(port_num);     // Assign port to proxy
    server_addr.sin_addr.s_addr = INADDR_ANY;   // Assign any available address

    // Bind the socket
    if(bind(proxy_socketId, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0){
        perror("Port is not free\n");
        exit(1);
    }

    printf("Binding on port: %d\n", port_num);

    // Proxy socket listening to request
    int listen_status = listen(proxy_socketId, MAX_CLIENTS);

    if(listen_status < 0){
        perror("Error while listening\n");
        exit(1);
    }

    int i = 0;                              // Iterator for thread_id (tid)
    int connected_socketId[MAX_CLIENTS];    // Stores socket descriptors of connected clients

    // Infinite loop for accepting connections
    while(1){
        bzero((char*)&client_addr, sizeof(client_addr));
        client_len = sizeof(client_addr);

        // Accept connections
        client_socketId = accept(proxy_socketId, (struct sockaddr*)&client_addr, (socklen_t*)&client_len);

        if(client_socketId < 0){
            fprintf(stderr, "Error accepting connection");
            exit(1);
        }

        else{
            connected_socketId[i] = client_socketId;    // Store accepted client
        }

        // Get IP address and port number of client
        struct sockaddr_in* client_port = (struct sockaddr_in*)&client_addr;
        struct in_addr ip_addr = client_port->sin_addr;
        char str[INET_ADDRSTRLEN];                              // Default IP Address size
        inet_ntop(AF_INET, &ip_addr, str, INET_ADDRSTRLEN);

        printf("Client is connected with port number: %d and IP Address: %s \n", ntohs(client_addr.sin_port), str);

        pthread_create(&tId[i], NULL, thread_func, (void*)&connected_socketId[i]);      // Create a thread for each accepted client
        i++;
    }

    close(proxy_socketId);
    return 0;
}

cache_element* find(char* url){
    // Check for url in the cache, if found return pointer to the respective cache element, else return NULL
    cache_element* site = NULL;

    int temp_lock_val = pthread_mutex_lock(&lock);
    printf("Remove Cache lock acquired %d\n", temp_lock_val);

    if(head != NULL){
        site = head;

        while(site != NULL){
            if(!strcmp(site->url, url)){
                printf("LRU time track before: %ld", site->lru_time_track);
                printf("\nurl found\n");

                // Update time_track
                site->lru_time_track = time(NULL);
                printf("LRU time track after: %ld", site->lru_time_track);

                break;
            }

            site = site->next;
        }
    }

    else{
        printf("\nurl not found\n");
    }

    temp_lock_val = pthread_mutex_unlock(&lock);
    printf("Remove Cache lock unlocked %d\n", temp_lock_val);

    return site;
}

void remove_cache_element(){
    // If cache is not empty then search for node which has least lru_time_track and delete it

    // Deletion of node from singly linked list
    cache_element* p;       // Prev Pointer
    cache_element* q;       // Next Pointer
    cache_element* temp;    // Cache element to remove

    int temp_lock_val = pthread_mutex_lock(&lock);
    printf("Remove Cache lock acquired %d\n", temp_lock_val);

    if(head != NULL){
        // Iterate through entire cache and search for oldest time track
        for(q=head, p=head, temp=head;q->next != NULL;q=q->next){
            if(((q->next)->lru_time_track) < (temp->lru_time_track)){
                temp = q->next;
                p = q;
            }
        }

        if(temp == head){
            head = head->next;
        }

        else{
            p->next = temp->next;
        }

        cache_size = cache_size - (temp->len) - sizeof(cache_element) - strlen(temp->url) - 1;      // Update cache size
        free(temp->data);
        free(temp->url);
        free(temp);
    }

    temp_lock_val = pthread_mutex_unlock(&lock);
    printf("Remove Cache lock unlocked %d\n", temp_lock_val);
}

int add_cache_element(char* data, int size, char* url){
    // Adds new element to the cache
    int temp_lock_val = pthread_mutex_lock(&lock);
    printf("Add Cache lock acquired %d\n", temp_lock_val);

    int element_size = size + 1 + strlen(url) + sizeof(cache_element);      // Size of new element added to cache

    if(element_size > MAX_ELEMENT_SIZE){
        temp_lock_val = pthread_mutex_unlock(&lock);
        printf("Add Cache lock unlocked %d\n", temp_lock_val);

        return 0;
    }

    else{
        while(cache_size + element_size > MAX_SIZE){
            // Keep removing elements from cache until there is enough space to add new element
            remove_cache_element();
        }

        // Add new element at head in singly linked list
        cache_element* element = (cache_element*)malloc(sizeof(cache_element));     // Allocate memory for new cache element
        element->data = (char*)malloc(size+1);          // Allocate memory for response to be stored in cache element
        strcpy(element->data, data);
        element->url = (char*)malloc(1+(strlen(url)*sizeof(char)));         // Allocate memory for request to be stored in cache element
        strcpy(element->url, url);
        element->lru_time_track = time(NULL);
        element->next = head;
        element->len = size;
        head = element;
        cache_size += element_size;

        temp_lock_val = pthread_mutex_unlock(&lock);
        printf("Add Cache lock unlocked %d\n", temp_lock_val);

        return 1;
    }

    return 0;
}