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image_tagger.c

+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <arpa/inet.h>
+#include <fcntl.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <strings.h>
+#include <sys/select.h>
+#include <sys/sendfile.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+// constants
+static char const * const HTTP_200_FORMAT = "HTTP/1.1 200 OK\r\n\
+Content-Type: text/html\r\n\
+Content-Length: %ld\r\n\r\n";
+static char const * const HTTP_400 = "HTTP/1.1 400 Bad Request\r\nContent-Length: 0\r\n\r\n";
+static int const HTTP_400_LENGTH = 47;
+static char const * const HTTP_404 = "HTTP/1.1 404 Not Found\r\nContent-Length: 0\r\n\r\n";
+static int const HTTP_404_LENGTH = 45;
+
+// represents the types of method
+typedef enum
+{
+    GET,
+    POST,
+    UNKNOWN
+} METHOD;
+
+static bool handle_http_request(int sockfd)
+{
+    // try to read the request
+    char buff[2049];
+    int n = read(sockfd, buff, 2049);
+    if (n <= 0)
+    {
+        if (n < 0)
+            perror("read");
+        else
+            printf("socket %d close the connection\n", sockfd);
+        return false;
+    }
+
+    // terminate the string
+    buff[n] = 0;
+
+    char * curr = buff;
+
+    // parse the method
+    METHOD method = UNKNOWN;
+    if (strncmp(curr, "GET ", 4) == 0)
+    {
+        curr += 4;
+        method = GET;
+    }
+    else if (strncmp(curr, "POST ", 5) == 0)
+    {
+        curr += 5;
+        method = POST;
+    }
+    else if (write(sockfd, HTTP_400, HTTP_400_LENGTH) < 0)
+    {
+        perror("write");
+        return false;
+    }
+
+    // sanitise the URI
+    while (*curr == '.' || *curr == '/')
+        ++curr;
+    // assume the only valid request URI is "/" but it can be modified to accept more files
+    if (*curr == ' ')
+        if (method == GET)
+        {
+            // get the size of the file
+            struct stat st;
+            stat("1_intro.html", &st);
+            n = sprintf(buff, HTTP_200_FORMAT, st.st_size);
+            // send the header first
+            if (write(sockfd, buff, n) < 0)
+            {
+                perror("write");
+                return false;
+            }
+            // send the file
+            int filefd = open("1_intro.html", O_RDONLY);
+            do
+            {
+                n = sendfile(sockfd, filefd, NULL, 2048);
+            }
+            while (n > 0);
+            if (n < 0)
+            {
+                perror("sendfile");
+                close(filefd);
+                return false;
+            }
+            close(filefd);
+        }
+        else if (method == POST)
+        {
+            // locate the username, it is safe to do so in this sample code, but usually the result is expected to be
+            // copied to another buffer using strcpy or strncpy to ensure that it will not be overwritten.
+            char * username = strstr(buff, "user=") + 5;
+            int username_length = strlen(username);
+            // the length needs to include the "Hi, " before the username
+            long added_length = username_length + 4;
+
+            // get the size of the file
+            struct stat st;
+            stat("2_start.html", &st);
+            // increase file size to accommodate the username
+            long size = st.st_size + added_length;
+            n = sprintf(buff, HTTP_200_FORMAT, size);
+            // send the header first
+            if (write(sockfd, buff, n) < 0)
+            {
+                perror("write");
+                return false;
+            }
+            // read the content of the HTML file
+            int filefd = open("2_start.html", O_RDONLY);
+            n = read(filefd, buff, 2048);
+            if (n < 0)
+            {
+                perror("read");
+                close(filefd);
+                return false;
+            }
+            close(filefd);
+            //move the trailing part backward
+            int p2;
+            /*for (p1 = size - 1, p2 = p1 - added_length; p1 >= size - 25; --p1, --p2)
+                buff[p1] = buff[p2];
+            ++p2;*/
+            // put the separator
+            buff[p2++] = 'H';
+            buff[p2++] ='i';
+            buff[p2++] = ',';
+            buff[p2++] = ' ';
+            // copy the username
+            strncpy(buff + p2, username, username_length);
+            if (write(sockfd, buff, size) < 0)
+            {
+                perror("write");
+                return false;
+            }
+        }
+        else
+            // never used, just for completeness
+            fprintf(stderr, "no other methods supported");
+    // send 404
+    else if (write(sockfd, HTTP_404, HTTP_404_LENGTH) < 0)
+    {
+        perror("write");
+        return false;
+    }
+
+    return true;
+}
+
+int main(int argc, char * argv[])
+{
+    if (argc < 3)
+    {
+        fprintf(stderr, "usage: %s ip port\n", argv[0]);
+        return 0;
+    }
+
+    // create TCP socket which only accept IPv4
+    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
+    if (sockfd < 0)
+    {
+        perror("socket");
+        exit(EXIT_FAILURE);
+    }
+
+    // reuse the socket if possible
+    int const reuse = 1;
+    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(int)) < 0)
+    {
+        perror("setsockopt");
+        exit(EXIT_FAILURE);
+    }
+
+    // create and initialise address we will listen on
+    struct sockaddr_in serv_addr;
+    bzero(&serv_addr, sizeof(serv_addr));
+    serv_addr.sin_family = AF_INET;
+    // if ip parameter is not specified
+    serv_addr.sin_addr.s_addr = inet_addr(argv[1]);
+    serv_addr.sin_port = htons(atoi(argv[2]));
+
+    // bind address to socket
+    if (bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
+    {
+        perror("bind");
+        exit(EXIT_FAILURE);
+    }
+
+    // listen on the socket
+    listen(sockfd, 5);
+
+    // initialise an active file descriptors set
+    fd_set masterfds;
+    FD_ZERO(&masterfds);
+    FD_SET(sockfd, &masterfds);
+    // record the maximum socket number
+    int maxfd = sockfd;
+
+    while (1)
+    {
+        // monitor file descriptors
+        fd_set readfds = masterfds;
+        if (select(FD_SETSIZE, &readfds, NULL, NULL, NULL) < 0)
+        {
+            perror("select");
+            exit(EXIT_FAILURE);
+        }
+
+        // loop all possible descriptor
+        for (int i = 0; i <= maxfd; ++i)
+            // determine if the current file descriptor is active
+            if (FD_ISSET(i, &readfds))
+            {
+                // create new socket if there is new incoming connection request
+                if (i == sockfd)
+                {
+                    struct sockaddr_in cliaddr;
+                    socklen_t clilen = sizeof(cliaddr);
+                    int newsockfd = accept(sockfd, (struct sockaddr *)&cliaddr, &clilen);
+                    if (newsockfd < 0)
+                        perror("accept");
+                    else
+                    {
+                        // add the socket to the set
+                        FD_SET(newsockfd, &masterfds);
+                        // update the maximum tracker
+                        if (newsockfd > maxfd)
+                            maxfd = newsockfd;
+                        // print out the IP and the socket number
+                        char ip[INET_ADDRSTRLEN];
+                        printf(
+                            "new connection from %s on socket %d\n",
+                            // convert to human readable string
+                            inet_ntop(cliaddr.sin_family, &cliaddr.sin_addr, ip, INET_ADDRSTRLEN),
+                            newsockfd
+                        );
+                    }
+                }
+                // a request is sent from the client
+                else if (!handle_http_request(i))
+                {
+                    close(i);
+                    FD_CLR(i, &masterfds);
+                }
+            }
+    }
+
+    return 0;
+}