Start P4

7 files changed, 747 insertions, 0 deletions

diff --git a/P4/4061_Project4.pdf b/P4/4061_Project4.pdf
new file mode 100644
index 0000000..dd5effe
--- /dev/null
+++ b/P4/4061_Project4.pdf
diff --git a/P4/Makefile b/P4/Makefile
new file mode 100644
index 0000000..6f8b473
--- /dev/null
+++ b/P4/Makefile
@@ -0,0 +1,9 @@
+CC = gcc
+CFLAGS = -D_REENTRANT
+LDFLAGS = -lpthread -pthread
+
+web_server: server.c util.c
+	${CC} -Wall -o web_server server.c util.c ${LDFLAGS}
+
+clean:
+	rm web_server
diff --git a/P4/server.c b/P4/server.c
new file mode 100644
index 0000000..b306def
--- /dev/null
+++ b/P4/server.c
@@ -0,0 +1,554 @@
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <pthread.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <fcntl.h>
+#include <sys/time.h>
+#include <time.h>
+#include "util.h"
+#include <stdbool.h>
+#include <unistd.h>
+#include <signal.h>
+
+#define MAX_THREADS 100
+#define MAX_queue_len 100
+#define MAX_CE 100
+#define INVALID -1
+#define BUFF_SIZE 1024
+
+// structs:
+typedef struct request_queue {
+  int fd;
+  char *request;
+} request_t;
+
+typedef struct cache_entry {
+  int len;
+  char *request;
+  char *content;
+} cache_entry_t;
+
+
+// globals:
+FILE *logfile;
+
+// Dispatcher Threads
+pthread_t dispatch_threads[MAX_THREADS];
+// Worker Threads
+pthread_t worker_threads[MAX_THREADS];
+// Thread ID array
+int wid_arr[MAX_THREADS];
+int did_arr[MAX_THREADS];
+
+
+pthread_mutex_t cache_mutex = PTHREAD_MUTEX_INITIALIZER;
+pthread_mutex_t log_mutex = PTHREAD_MUTEX_INITIALIZER;
+pthread_mutex_t req_queue_mutex = PTHREAD_MUTEX_INITIALIZER;
+pthread_cond_t req_queue_notfull = PTHREAD_COND_INITIALIZER; // wait until queue isn't full (dispatch)
+pthread_cond_t req_queue_notempty = PTHREAD_COND_INITIALIZER; // wait until queue isn't empty (worker)
+request_t requests[MAX_queue_len];
+
+int req_remove_index = 0;
+int req_insert_index = 0;
+int curr_queue_len = 0;
+int queue_len;
+int cache_size = INVALID;
+int cache_evict_index = 0;
+int num_worker = INVALID;
+
+// Cache
+cache_entry_t *cache;
+
+void *dispatch(void *arg);
+
+void *worker(void *arg);
+
+// For grace termination
+static volatile sig_atomic_t doneflag = 0;
+static void setdoneflag(int signo) {
+  doneflag = 1;
+}
+
+/* ************************ Dynamic Pool Code ***********************************/
+bool alive_pool[MAX_THREADS];
+
+// Extra Credit: This function implements the policy to change the worker thread pool dynamically
+// depending on the number of requests
+void *dynamic_pool_size_update(void *arg) {
+  while (1) {
+    usleep(500000);
+    // Lock the mutex to dynamically change thread pool
+    if (pthread_mutex_lock(&req_queue_mutex) < 0) {
+      printf("Failed to lock queue! %s\n", strerror(errno));
+      continue;
+    }
+
+    int i;
+    // Cancel some threads
+    // printf("curr_queue_len: %d --- num_worker: %d\n", curr_queue_len, num_worker);
+    if (curr_queue_len < num_worker) {
+      if (num_worker > 1) {
+        printf("Deleted %d worker threads because server load decreased\n", num_worker - curr_queue_len - 1);
+      }
+      for (i = 0; (i < MAX_THREADS) && (curr_queue_len < num_worker) && (num_worker > 1); i++) {
+        if (alive_pool[i] == true) {
+          alive_pool[i] = false;
+          num_worker--;
+        }
+      }
+      pthread_cond_broadcast(&req_queue_notempty);
+    }
+
+    // Create new threads
+    else if (curr_queue_len > num_worker) {
+      pthread_attr_t attr;
+      int s;
+      s = pthread_attr_init(&attr);
+      if (s != 0) {
+        fprintf(stderr, "error - attribute init failed.\n");
+        exit(EXIT_FAILURE);
+      }
+      s = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+      if (s != 0) {
+        fprintf(stderr, "error - setting detached state failed.\n");
+        exit(EXIT_FAILURE);
+      }
+      printf("Created %d worker threads because server load increased\n", curr_queue_len - num_worker);
+      for (i = 0; i < MAX_THREADS && curr_queue_len > num_worker; i++) {
+        if (alive_pool[i] == false) {
+          alive_pool[i] = true;
+          s = pthread_create(worker_threads + i, &attr, worker, (void *) &wid_arr[i]);
+          if (s != 0) {
+            fprintf(stderr, "error - pthread_create for worker threads dynamically.\n");
+          }
+          num_worker++;
+        }
+      }
+    }
+
+    if (pthread_mutex_unlock(&req_queue_mutex) < 0) {
+      printf("Failed to unlock queue! %s\n", strerror(errno));
+    }
+  }
+}
+/**********************************************************************************/
+
+/* ************************************ Cache Code ********************************/
+
+// Function to check whether the given request is present in cache
+int getCacheIndex(char *request) {
+  //printf("Checking cache\n");
+  int i;
+  for (i = 0; i < cache_size; i++) {
+    if (cache[i].request != NULL && strcmp(cache[i].request, request) == 0) {
+      //printf("Found in cache %d\n",i);
+      return i;
+    }
+  }
+  //printf("Not in cache\n");
+  return INVALID;
+}
+
+// Function to add the request and its file content into the cache
+// It should add the request at an index according to the cache replacement policy you are using
+void addIntoCache(char *mybuf, char *memory, int memory_size) {
+  //printf("Adding to cache\n");
+  if (cache[cache_evict_index].request != NULL) {
+    free(cache[cache_evict_index].request);
+  }
+  if (cache[cache_evict_index].content != NULL) {
+    free(cache[cache_evict_index].content);
+  }
+
+  //printf("Allocating cache entry\n");
+  cache[cache_evict_index].request = (char *) malloc(BUFF_SIZE * sizeof(char));
+  cache[cache_evict_index].content = (char *) malloc(memory_size);
+
+  //printf("Filling cache entry\n");
+  strcpy(cache[cache_evict_index].request, mybuf);
+  memcpy(cache[cache_evict_index].content, memory, memory_size);
+  cache[cache_evict_index].len = memory_size;
+
+  cache_evict_index = (cache_evict_index + 1) % cache_size;
+  //printf("Cache add done\n");
+}
+
+// clear the memory allocated to the cache
+void deleteCache() {
+  int i;
+  for (i = 0; i < cache_size; i++) {
+    free(cache[i].request);
+    free(cache[i].content);
+  }
+  free(cache);
+}
+
+// Function to initialize the cache
+void initCache() {
+  cache = malloc(sizeof(cache_entry_t) * cache_size);
+  int i;
+  for (i = 0; i < cache_size; i++) {
+    cache[i].len = 0;
+    cache[i].request = NULL;
+    cache[i].content = NULL;
+  }
+}
+
+
+/**********************************************************************************/
+
+// Function to get the content type from the request
+char *getContentType(char *mybuf) {
+  int requeue_len = strlen(mybuf);
+  char *contenttype;
+  if (strcmp(&mybuf[requeue_len - 5], ".html") == 0) {
+    contenttype = "text/html";
+  } else if (strcmp(&mybuf[requeue_len - 4], ".jpg") == 0) {
+    contenttype = "image/jpeg";
+  } else if (strcmp(&mybuf[requeue_len - 4], ".gif") == 0) {
+    contenttype = "image/gif";
+  } else {
+    contenttype = "text/plain";
+  }
+  return contenttype;
+}
+
+
+// Function to open and read the file from the disk into the memory
+// You can return the file size if it is useful
+int readFromDisk(int fd, char *mybuf, void **memory, int id, int myreqnum) {
+  int filefd;
+  if ((filefd = open(mybuf + 1, O_RDONLY)) == -1) {
+    // it is mybuf + 1 because get request will return the path with a '/' in the front
+    return_error(fd, "Requested file not found.");
+    // Stop recording the time
+    pthread_mutex_lock(&log_mutex);
+    printf("[%d][%d][%d][%s][%s][%s]\n", id, myreqnum, fd, mybuf, "Requested file not found.", "MISS");
+    fprintf(logfile, "[%d][%d][%d][%s][%s][%s]\n", id, myreqnum, fd, mybuf, "Requested file not found.", "MISS");
+    fflush(logfile);
+    pthread_mutex_unlock(&log_mutex);
+    return -1;
+  }
+  struct stat st;
+  fstat(filefd, &st);
+  int filesize = st.st_size;
+  *memory = malloc(filesize);
+  read(filefd, *memory, filesize);
+  close(filefd);
+  return filesize;
+}
+
+
+/**********************************************************************************/
+// Function to receive the request from the client and put into the queue
+void *dispatch(void *arg) {
+  int fd;
+  char mybuf[BUFF_SIZE];
+  char *reqptr;
+
+  while (1) {
+    fd = accept_connection();
+    if (fd < 0) { return NULL; }
+    if (get_request(fd, mybuf) != 0) { continue; /*back to top of loop!*/ }
+
+    reqptr = (char *) malloc(strlen(mybuf) + 1);
+    if (reqptr == NULL) {
+      printf("Failed to allocate memory: %s", strerror(errno));
+    }
+    strcpy(reqptr, mybuf);
+
+    // put request in queue
+    if (pthread_mutex_lock(&req_queue_mutex) < 0) {
+      printf("Failed to lock queue! %s\n", strerror(errno));
+    }
+    while (curr_queue_len == queue_len) { // the queue is full!
+      pthread_cond_wait(&req_queue_notfull, &req_queue_mutex);
+    }
+
+    requests[req_insert_index].fd = fd;
+    requests[req_insert_index].request = reqptr;
+
+    curr_queue_len++;
+    req_insert_index = (req_insert_index + 1) % queue_len; // ring buffer
+
+    pthread_cond_signal(&req_queue_notempty);
+    if (pthread_mutex_unlock(&req_queue_mutex) < 0) {
+      printf("Failed to unlock queue! %s\n", strerror(errno));
+    }
+  }
+  return NULL;
+}
+
+/**********************************************************************************/
+
+// Function to take the request from the queue, process it and then return a result to the client
+void *worker(void *arg) {
+  int id = *(int *) arg;
+  int fd, filesize, myreqnum;
+  void *memory;
+  char mybuf[BUFF_SIZE];
+  myreqnum = 0;
+
+  while (1) {
+    // get request from queue
+    if (pthread_mutex_lock(&req_queue_mutex) < 0) {
+      printf("Failed to lock! %s\n", strerror(errno));
+      continue;
+    }
+
+    while (curr_queue_len == 0) { // the queue is empty!
+      if (pthread_cond_wait(&req_queue_notempty, &req_queue_mutex) < 0) {
+        printf("Failed to wait! %s\n", strerror(errno));
+      }
+      if (alive_pool[id] == false) {
+        if (pthread_mutex_unlock(&req_queue_mutex) < 0) {
+          printf("Failed to unlock queue! %s\n", strerror(errno));
+        }
+        return NULL;
+      }
+    }
+
+    if (alive_pool[id] == false) {
+      if (pthread_mutex_unlock(&req_queue_mutex) < 0) {
+        printf("Failed to unlock queue! %s\n", strerror(errno));
+      }
+      return NULL;
+    }
+
+    // Code to get the request from the queue
+    fd = requests[req_remove_index].fd;
+    strcpy(mybuf, requests[req_remove_index].request);
+    free(requests[req_remove_index].request);
+
+    curr_queue_len--;
+    req_remove_index = (req_remove_index + 1) % queue_len; // ring buffer
+
+    if (pthread_cond_signal(&req_queue_notfull) < 0) {
+      printf("Failed to signal! %s\n", strerror(errno));
+    }
+
+    if (pthread_mutex_unlock(&req_queue_mutex) < 0) {
+      printf("Failed to unlock! %s\n", strerror(errno));
+    }
+
+    myreqnum++;
+
+    if (strcmp(mybuf, "/") == 0) {
+      strcpy(mybuf, "/index.html");
+    }
+
+    // Code to get the data from cache or from the disk
+    bool hit = false;
+    if (pthread_mutex_lock(&cache_mutex) < 0) {
+      printf("Failed to lock cache mutex! %s\n", strerror(errno));
+    }
+
+    int index = getCacheIndex(mybuf);
+    if (index != INVALID) {
+      filesize = cache[index].len;
+      memory = malloc(filesize);
+      memcpy(memory, cache[index].content, filesize);
+      hit = true;
+    } else {
+      filesize = readFromDisk(fd, mybuf, &memory, id, myreqnum);
+      if (filesize == -1) {
+        if (pthread_mutex_unlock(&cache_mutex) < 0) {
+          printf("Failed to unlock cache mutex! %s\n", strerror(errno));
+        }
+        continue;
+      }
+      addIntoCache(mybuf, memory, filesize);
+    }
+
+    if (pthread_mutex_unlock(&cache_mutex) < 0) {
+      printf("Failed to unlock cache mutex! %s\n", strerror(errno));
+    }
+
+    // Code to log the request into the file and terminal
+    if (pthread_mutex_lock(&log_mutex) < 0) {
+      printf("Failed to lock log mutex! %s\n", strerror(errno));
+    }
+
+    printf("[%d][%d][%d][%s][%d][%s]\n", id, myreqnum, fd, mybuf, filesize, (hit == true) ? "HIT" : "MISS");
+    if (fprintf(logfile, "[%d][%d][%d][%s][%d][%s]\n", id, myreqnum, fd, mybuf, filesize,
+          (hit == true) ? "HIT" : "MISS") < 0) {
+      printf("Failed to print to log file! %s\n", strerror(errno));
+    }
+
+    fflush(logfile);
+
+    if (pthread_mutex_unlock(&log_mutex) < 0) {
+      printf("Failed to unlock log mutex! %s\n", strerror(errno));
+    }
+
+    char *contenttype = getContentType(mybuf);
+    if (return_result(fd, contenttype, memory, filesize) != 0) {
+      printf("Couldn't return result, thread id=%d\n", id);
+    }
+
+    free(memory);
+  }
+  return NULL;
+}
+
+/**********************************************************************************/
+
+int main(int argc, char **argv) {
+
+  // Error check on number of arguments
+  // Decided to check if caching is enabled [argc == 8 -> Caching enabled]
+  if (argc != 8) {
+    printf("usage: %s port path num_dispatcher num_workers dynamic_flag queue_length cache_size\n", argv[0]);
+    return -1;
+  }
+
+  // Init variables
+  int port = atoi(argv[1]);
+  int num_dispatch = atoi(argv[3]);
+  num_worker = atoi(argv[4]);
+  int dynamic_flag = atoi(argv[5]);
+  queue_len = atoi(argv[6]);
+  if (atoi(argv[7]) > 0) {
+    cache_size = atoi(argv[7]);
+  }
+
+  // Sanity error checks
+  if (num_dispatch > MAX_THREADS || num_dispatch < 1) {
+    fprintf(stderr, "Invalid number of dispatch threads.\n");
+    return -2;
+  }
+  if (num_worker > MAX_THREADS || num_worker < 1) {
+    fprintf(stderr, "Invalid number of worker threads.\n");
+    return -2;
+  }
+  if (queue_len > MAX_queue_len || queue_len < 1) {
+    fprintf(stderr, "Invalid queue_len size.\n");
+    return -2;
+  }
+  if (cache_size > MAX_CE || cache_size < 1) {
+    fprintf(stderr, "Invalid cache_size.\n");
+    return -2;
+  }
+
+  // Change SIGINT action for grace termination
+  struct sigaction act;
+  act.sa_handler = setdoneflag;
+  act.sa_flags = 0;
+  if ((sigemptyset(&act.sa_mask) == -1) || (sigaction(SIGINT, &act, NULL) == -1)) {
+    perror("Failed to set SIGINT handler");
+    return 1;
+  }
+
+  // Open log file
+  logfile = fopen("webserver_log", "w");
+
+  // Change the current working directory to server root directory
+  if (chdir(argv[2]) != 0) {
+    perror("Couldn't change directory to server root.");
+    return -1;
+  }
+
+  // Init cache if required
+  initCache();
+
+  // Start the server
+  init(port);
+  printf("Starting server on port %d: %d disp, %d work\n", port, num_dispatch, num_worker);
+
+  // Create dispatcher and worker threads
+  int i;
+  for (i = 0; i < MAX_THREADS; i++) {
+    alive_pool[i] = false;
+  }
+  for (i = 0; i < num_worker; i++) {
+    wid_arr[i] = i;
+  }
+  for (i = 0; i < num_dispatch; i++) {
+    did_arr[i] = i;
+  }
+
+  pthread_attr_t attr;
+  int s;
+
+  s = pthread_attr_init(&attr);
+  if (s != 0) {
+    fprintf(stderr, "error - attribute init failed.\n");
+    exit(EXIT_FAILURE);
+  }
+  s = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+  if (s != 0) {
+    fprintf(stderr, "error - setting detached state failed.\n");
+    exit(EXIT_FAILURE);
+  }
+
+  for (i = 0; i < num_worker; i++) {
+    alive_pool[i] = true;
+    s = pthread_create(worker_threads + i, &attr, worker, (void *) &wid_arr[i]);
+    /* Alternative */
+    //        s = pthread_create(worker_threads + i, NULL, worker, (void *) &wid_arr[i]);
+    //        s = pthread_detach(*(worker_threads + i));
+    if (s != 0) {
+      fprintf(stderr, "error - pthread_create for worker threads.\n");
+      exit(EXIT_FAILURE);
+    }
+  }
+  for (i = 0; i < num_dispatch; i++) {
+    s = pthread_create(dispatch_threads + i, &attr, dispatch, (void *) &did_arr[i]);
+    if (s != 0) {
+      fprintf(stderr, "error - pthread_create for dispatcher threads.\n");
+      exit(EXIT_FAILURE);
+    }
+  }
+
+  pthread_t dynamic_pool_deamon;
+  if (dynamic_flag == 1) {
+    int dynamic_pool_deamon_id = MAX_THREADS + 1;
+    s = pthread_create(&dynamic_pool_deamon, &attr, dynamic_pool_size_update, (void *) &dynamic_pool_deamon_id);
+    if (s != 0) {
+      fprintf(stderr, "error - pthread_create for dynamic pool management.\n");
+      exit(EXIT_FAILURE);
+    }
+  }
+
+  // Terminate server gracefully
+  while (!doneflag) {
+    sleep(1);
+  }
+
+  printf("Server terminating ...\n");
+
+  // Print the number of pending requests in the request queue
+  printf("The number of pending requests in the request queue: %d\n", curr_queue_len);
+
+
+  if (pthread_mutex_lock(&log_mutex) < 0) {
+    printf("Failed to lock log mutex! %s\n", strerror(errno));
+  }
+
+  // close log file
+  fclose(logfile);
+
+  if (pthread_mutex_unlock(&log_mutex) < 0) {
+    printf("Failed to unlock log mutex! %s\n", strerror(errno));
+  }
+
+
+
+  if (pthread_mutex_lock(&cache_mutex) < 0) {
+    printf("Failed to lock cache mutex! %s\n", strerror(errno));
+  }
+
+  // Remove cache
+  deleteCache();
+
+  if (pthread_mutex_unlock(&cache_mutex) < 0) {
+    printf("Failed to unlock cache mutex! %s\n", strerror(errno));
+  }
+
+  printf("Main thread exiting.\n");
+  return 0;
+}
diff --git a/P4/testing.zip b/P4/testing.zip
new file mode 100644
index 0000000..a170fbc
--- /dev/null
+++ b/P4/testing.zip
diff --git a/P4/util.c b/P4/util.c
new file mode 100644
index 0000000..2e2be63
--- /dev/null
+++ b/P4/util.c
@@ -0,0 +1,108 @@
+#ifndef _REENTRANT
+#define _REENTRANT
+#endif
+
+#include <stdio.h>
+#include <pthread.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "util.h"
+
+//Global socket for all things
+int socket;
+
+/**********************************************
+ * init
+   - port is the number of the port you want the server to be
+     started on
+   - initializes the connection acception/handling system
+   - YOU MUST CALL THIS EXACTLY ONCE (not once per thread,
+     but exactly one time, in the main thread of your program)
+     BEFORE USING ANY OF THE FUNCTIONS BELOW
+   - if init encounters any errors, it will call exit().
+************************************************/
+void init(int port) {
+  struct sockaddr_in addr;
+  addr.sin_family = AF_INET;
+  addr.sin_addr.s_addr = htonl(INADDR_ANY);
+  addr.sin_port = htons(port);
+  //Allow port to be released
+  int enable = 1;
+  if (setsockopt(socket, SOL_SOCKET, SO_REUSEADDR, (char *)&enable, sizeof(int)) == -1) {
+    perror("Cannot set socket option");
+    exit(EXIT_FAILURE);
+  }
+  if (bind(socket, (struct sockaddr*) &addr, sizeof(addr)) == -1) {
+    perror("Cannot bind socket");
+    exit(EXIT_FAILURE);
+  }
+}
+
+/**********************************************
+ * accept_connection - takes no parameters
+   - returns a file descriptor for further request processing.
+     DO NOT use the file descriptor on your own -- use
+     get_request() instead.
+   - if the return value is negative, the request should be ignored.
+***********************************************/
+int accept_connection(void) {
+}
+
+/**********************************************
+ * get_request
+   - parameters:
+      - fd is the file descriptor obtained by accept_connection()
+        from where you wish to get a request
+      - filename is the location of a character buffer in which
+        this function should store the requested filename. (Buffer
+        should be of size 1024 bytes.)
+   - returns 0 on success, nonzero on failure. You must account
+     for failures because some connections might send faulty
+     requests. This is a recoverable error - you must not exit
+     inside the thread that called get_request. After an error, you
+     must NOT use a return_request or return_error function for that
+     specific 'connection'.
+************************************************/
+int get_request(int fd, char *filename) {
+}
+
+/**********************************************
+ * return_result
+   - returns the contents of a file to the requesting client
+   - parameters:
+      - fd is the file descriptor obtained by accept_connection()
+        to where you wish to return the result of a request
+      - content_type is a pointer to a string that indicates the
+        type of content being returned. possible types include
+        "text/html", "text/plain", "image/gif", "image/jpeg" cor-
+        responding to .html, .txt, .gif, .jpg files.
+      - buf is a pointer to a memory location where the requested
+        file has been read into memory (the heap). return_result
+        will use this memory location to return the result to the
+        user. (remember to use -D_REENTRANT for CFLAGS.) you may
+        safely deallocate the memory after the call to
+        return_result (if it will not be cached).
+      - numbytes is the number of bytes the file takes up in buf
+   - returns 0 on success, nonzero on failure.
+************************************************/
+int return_result(int fd, char *content_type, char *buf, int numbytes) {
+}
+
+/**********************************************
+ * return_error
+   - returns an error message in response to a bad request
+   - parameters:
+      - fd is the file descriptor obtained by accept_connection()
+        to where you wish to return the error
+      - buf is a pointer to the location of the error text
+   - returns 0 on success, nonzero on failure.
+************************************************/
+int return_error(int fd, char *buf) {
+}
diff --git a/P4/util.h b/P4/util.h
new file mode 100644
index 0000000..d197763
--- /dev/null
+++ b/P4/util.h
@@ -0,0 +1,76 @@
+#ifndef _UTIL_H
+#define _UTIL_H
+
+/**********************************************
+ * init
+   - port is the number of the port you want the server to be
+     started on
+   - initializes the connection acception/handling system
+   - YOU MUST CALL THIS EXACTLY ONCE (not once per thread,
+     but exactly one time, in the main thread of your program)
+     BEFORE USING ANY OF THE FUNCTIONS BELOW
+   - if init encounters any errors, it will call exit().
+************************************************/
+void init(int port);
+
+/**********************************************
+ * accept_connection - takes no parameters
+   - returns a file descriptor for further request processing.
+     DO NOT use the file descriptor on your own -- use
+     get_request() instead.
+   - if the return value is negative, the request should be ignored.
+***********************************************/
+int accept_connection(void);
+
+/**********************************************
+ * get_request
+   - parameters:
+      - fd is the file descriptor obtained by accept_connection()
+        from where you wish to get a request
+      - filename is the location of a character buffer in which
+        this function should store the requested filename. (Buffer
+        should be of size 1024 bytes.)
+   - returns 0 on success, nonzero on failure. You must account
+     for failures because some connections might send faulty
+     requests. This is a recoverable error - you must not exit
+     inside the thread that called get_request. After an error, you
+     must NOT use a return_request or return_error function for that
+     specific 'connection'.
+************************************************/
+int get_request(int fd, char *filename);
+
+/**********************************************
+ * return_result
+   - returns the contents of a file to the requesting client and cleans
+     up the connection to the client
+   - parameters:
+      - fd is the file descriptor obtained by accept_connection()
+        to where you wish to return the result of a request
+      - content_type is a pointer to a string that indicates the
+        type of content being returned. possible types include
+        "text/html", "text/plain", "image/gif", "image/jpeg" cor-
+        responding to .html, .txt, .gif, .jpg files.
+      - buf is a pointer to a memory location where the requested
+        file has been read into memory (the heap). return_result
+        will use this memory location to return the result to the
+        user. (remember to use -D_REENTRANT for CFLAGS.) you may
+        safely deallocate the memory after the call to
+        return_result (if it will not be cached).
+      - numbytes is the number of bytes the file takes up in buf
+   - returns 0 on success, nonzero on failure.
+************************************************/
+int return_result(int fd, char *content_type, char *buf, int numbytes);
+
+/**********************************************
+ * return_error
+   - returns an error message in response to a bad request and cleans
+     up the connection to the client
+   - parameters:
+      - fd is the file descriptor obtained by accept_connection()
+        to where you wish to return the error
+      - buf is a pointer to the location of the error text
+   - returns 0 on success, nonzero on failure.
+************************************************/
+int return_error(int fd, char *buf);
+
+#endif /* _UTIL_H */
diff --git a/P4/web_server_sol b/P4/web_server_sol
new file mode 100644
index 0000000..042753b
--- /dev/null
+++ b/P4/web_server_sol