diff --git a/.gitignore b/.gitignore
index cd531cf..d119bc8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -52,3 +52,6 @@ Module.symvers
 Mkfile.old
 dkms.conf
 
+#Bin
+bin/*
+
diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000..728bda3
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,3 @@
+{
+    "C_Cpp.default.defines": ["_GNU_SOURCE"]
+}
\ No newline at end of file
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..5405da0
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,17 @@
+CC = gcc
+CFLAGS = -lm -Wall -O2
+
+all:
+	make client
+	make server
+
+socket_wrapper.o: socket_wrapper.c socket_wrapper.h
+	$(CC) -c  socket_wrapper.c -o socket_wrapper.o $(CFLAGS)
+
+client: socket_wrapper.o client.c
+	$(CC) -o client client.c socket_wrapper.o $(CFLAGS)
+server:
+	$(CC) -o server server.c socket_wrapper.o $(CFLAGS)
+
+clean:
+	rm *.o server client
diff --git a/client.c b/client.c
new file mode 100644
index 0000000..1581068
--- /dev/null
+++ b/client.c
@@ -0,0 +1,196 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <unistd.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <errno.h>
+#include <sys/stat.h>
+#include <signal.h>
+#include <assert.h>
+#include <fcntl.h>
+#include "socket_wrapper.h"
+
+/*========
+ *Operation
+ *========*/
+/*send user error message
+80 character limit
+*/
+int send_fail(int sock,const char * msg){
+    struct TransferResult res;
+    res.res = RES_USR_ERR;
+    res.file_size = 0;
+    res.err_number = 0;
+    res.error_msg_size = strlen(msg);
+    //os will be combining if tcp_autocorking emabled.
+    if(send(sock,&res,sizeof(res),0) < 0){
+        perror("error msg send");
+        return -1;
+    }
+    if (send(sock,msg,res.error_msg_size,0) < 0){
+        perror("error msg send");
+        return -1;
+    }
+    return 0;
+}
+
+int send_errno(int sock){
+    struct TransferResult r;
+    r.res = RES_ERR;
+    r.err_number = errno;
+    r.file_size = 0;
+    r.error_msg_size = 0;
+    if(send(sock,&r,sizeof(r),0)){
+        perror("errno send");
+        return -1;
+    }
+    return 0;
+}
+/* return fd, if success.
+otherwise, return -1.
+*/
+int read_request(int sock,uint8_t * buf,size_t bufsize){
+    struct ReadOp p;
+    int fd;
+    ssize_t n = recv_until_byte(sock,&p,sizeof(p),TIMEOUT);
+    if (n < 0){
+        if (n == -2) fprintf(stderr,"timeout!");
+        else perror("receive fail"); 
+        return -1;
+    }
+    if(bufsize <= p.file_url_size + sizeof(p) + 1){
+        send_fail(sock,"buffer overflow");
+        return -1;
+    }
+    else if(p.file_url_size + 1 > MAX_PATH_SIZE){
+        send_fail(sock,"max path fail");
+        return -1;
+    }
+    else if(p.file_url_size == 0){
+        send_fail(sock,"filename zero fail");
+        return -1;
+    }
+    n = recv_until_byte(sock,buf,p.file_url_size,TIMEOUT);
+    buf[p.file_url_size] = '\0';
+    printf("str size: %d, request %s\n",p.file_url_size,buf);
+    if(strchr((char *)buf,'/') != NULL){
+        send_fail(sock,"Illegal character /");
+        return -1;
+    }
+    fd = open((char *)buf,O_RDONLY);
+    if(fd < 0){
+        send_errno(sock);
+        close(fd);
+        return -1;
+    }
+    return fd;
+}
+
+int send_response(int sock,int fd, uint8_t * buf, size_t bufsize){
+    struct TransferResult r;
+    struct stat st;
+    off_t offset = 0;
+    ssize_t readed = 0;
+    r.res = RES_OK;
+    r.err_number = 0;
+    r.error_msg_size = 0;
+    if(fstat(fd,&st) < 0){
+        return send_errno(sock);
+    }
+    if(S_ISDIR(st.st_mode)){
+        return send_fail(sock,"is a directory");
+    }
+    r.file_size = st.st_size;
+    if(send(sock,&r,sizeof(r),0)<0){
+        perror("send fail");
+        return -1;
+    }
+#ifdef USE_SENDFILE
+    while (r.file_size != offset)
+    {
+        size_t count = SEND_FILE_CHUNK_SIZE < (r.file_size - offset) ? SEND_FILE_CHUNK_SIZE : (r.file_size - offset);
+        if((readed = sendfile(sock,fd,&offset,count)) < 0){
+            perror("send file fail");
+            return -1;
+        }
+    }
+#else
+    while (offset < r.file_size)
+    {
+        readed = bufsize < (r.file_size - offset) ? bufsize : r.file_size - offset;
+        if(read(fd,buf,readed)<0){
+            perror("send response read fail");
+            return -1;
+        }
+        if(send(sock,buf,readed,0)<0){
+            perror("send response send fail");
+            return -1;
+        }
+        offset += readed;
+    }
+    
+#endif
+    return 0;
+}
+static int sock;
+void safe_exit(){
+    close(sock);
+}
+int main(int argc, const char *argv[]){
+    uint8_t * buf;
+    struct sockaddr_in addr;
+    struct sockaddr_in client_addr;
+    socklen_t client_addr_len = sizeof(client_addr);
+    int csock;
+    int bufsize;
+    register_alarm();
+    sock = socket(AF_INET,SOCK_STREAM,0);
+    atexit(safe_exit);
+    if(sock < 0){
+        perror("sock create fail");
+        return 1;
+    }
+    bufsize = getBufferSizeFrom(sock);
+    buf = malloc(bufsize * sizeof(*buf));
+    if (buf == NULL){
+        fprintf(stderr,"lack of memory");
+        return 1;
+    }
+    
+    addr.sin_addr.s_addr = htonl(INADDR_ANY); /*0.0.0.0 모든 네트워크 인터페이스에 묶임.*/
+    addr.sin_family = AF_INET;
+    addr.sin_port = htons(SERVER_PORT);
+
+    if(bind(sock, (struct sockaddr *)&addr,sizeof(addr)) < 0){
+        perror("bind failed");
+        return 1;
+    }
+    fprintf(stderr,"server bind on %s:%d\n",inet_ntoa(addr.sin_addr),SERVER_PORT);
+
+    if(listen(sock,1) < 0){
+        perror("listen failed");
+        return 1;
+    }
+
+    while ((csock = accept(sock, (struct sockaddr *)&client_addr,&client_addr_len)) >= 0)
+    {
+        int fd;
+        /*inet_ntoa is not reentrant function. do not use it in signal handler.*/
+        printf("Connect : %s\n",(inet_ntoa(client_addr.sin_addr)));
+        if((fd = read_request(csock,buf,bufsize)) > 0){
+            send_response(csock,fd,buf,bufsize);
+            close(fd);
+        }
+
+        if(close(csock) < 0)
+            perror("csock close error");
+
+    }
+    free(buf);
+    perror("accept error");
+    return 1;
+}
\ No newline at end of file
diff --git a/hw12.c b/hw12.c
new file mode 100644
index 0000000..53c5fdf
--- /dev/null
+++ b/hw12.c
@@ -0,0 +1 @@
+#include <stdio.h>
diff --git a/server.c b/server.c
new file mode 100644
index 0000000..e8e90ee
--- /dev/null
+++ b/server.c
@@ -0,0 +1,159 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <unistd.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <errno.h>
+#include <sys/stat.h>
+
+#include <assert.h>
+#include <fcntl.h>
+#include "socket_wrapper.h"
+
+#ifdef USE_SENDFILE
+#include <sys/sendfile.h>
+const size_t SEND_FILE_CHUNK_SIZE = 0x100000; /*1MB*/
+#endif
+
+/*========
+ *Operation
+ *========*/
+
+int sendReadOp(int sock,const char * filename){
+    struct ReadOp op;
+    op.file_url_size = strlen(filename);
+    op.padding0 = 0;
+    if(send(sock,&op,sizeof(op),0)<0){
+        perror("readop send fail");
+        return -1;
+    }
+    if(send(sock,filename,op.file_url_size,0)<0){
+        perror("readop filename send fail");
+        return -1;
+    }
+    return 0;
+}
+
+int recvFile(int sock, const char * filename,size_t file_size){
+    int fd;
+    size_t count = 0;
+    int i;
+    int cur_progress = 1;
+    int return_value = 0;
+    int buf_sz = getBufferSizeFrom(sock);
+    uint8_t * buf = malloc(buf_sz*sizeof(*buf));
+    if (buf == NULL){
+        return -1;
+    }
+    fd = open(filename,O_WRONLY|O_CREAT|O_TRUNC,S_IRWXU|S_IRWXG|S_IROTH);
+    if (fd < 0)
+    {
+        perror("file open fail");
+        return -1;
+    }
+    
+    while (file_size - count > 0)
+    {
+        int readed = buf_sz < file_size - count ? buf_sz : file_size - count;
+        if((i = recv_until_byte(sock,buf,readed,TIMEOUT)) < 0){
+            if(i == -2) 
+                fprintf(stderr,"recv file failed : timeout connetion lost\n");
+            else perror("recv file failed");
+            return_value = -1;
+            goto END;
+        }
+        if(write(fd,buf,readed)<0){
+            perror("file write failed");
+            return_value = -1;
+            goto END;
+        }
+        if( ((double)count / (double)file_size) * 100.0 > ((double)cur_progress) ){
+            printf("\rprogress : %d%% current bytes: %ld bytes",cur_progress,count);
+            cur_progress = (int)((((double)count / (double)file_size)) * 100.0 + 1.0);
+            fflush(stdout);
+        }
+        count += readed;
+    }
+    printf("\rprogress : 100.00%% current bytes: %ld bytes\n",count);
+END:
+    free(buf);
+    return return_value;
+}
+
+int recvData(int sock,const char * filename){
+    struct TransferResult res;
+    int i=0;
+    if((i=recv_until_byte(sock,&res,sizeof(res),TIMEOUT)) < 0){
+        if (i == -2) fprintf(stderr,"timeout");
+        else perror("recv fail");
+        return -1;
+    }
+    static char error_meesage_buf[80] = "";
+    switch(res.res){
+        case RES_ERR:
+            fprintf(stderr,"Server Fail: %s", strerror(res.err_number));
+            return -1;
+        case RES_USR_ERR:
+            assert(res.error_msg_size < 80);/*todo : fix*/
+            if((i=recv_until_byte(sock,error_meesage_buf,res.error_msg_size,TIMEOUT)) < 0){
+                if (i == -2) fprintf(stderr,"timeout");
+                else perror("recv fail");
+                return -1;
+            }
+            fprintf(stderr,"Error Message From Server: %s",error_meesage_buf);
+            return -1;
+        case RES_OK:
+            return recvFile(sock,filename,res.file_size);
+            break;
+        default:
+            fprintf(stderr,"unknown value!");
+            return -1;
+    }
+
+    return 0;
+}
+
+int main(int argc, const char *argv[]){
+    struct sockaddr_in addr;
+    const char * filename;
+    const char * server_name;
+    in_port_t server_port = SERVER_PORT;
+    int sock;
+    register_alarm();
+    if (argc != 4){
+        fprintf(stderr,"invaild arguments number.");
+        return 1;
+    }
+    server_name = argv[1];
+    server_port = atoi(argv[2]);
+    filename = argv[3];
+    if (server_port == 0)
+    {
+        fprintf(stderr,"port invalid");
+        return 1;
+    }
+    
+    sock = socket(AF_INET,SOCK_STREAM,0);
+    if(sock < 0){
+        perror("sock create fail");
+        return 1;
+    }
+    addr.sin_addr.s_addr = inet_addr(server_name);
+    addr.sin_family = AF_INET;
+    addr.sin_port = htons(server_port);
+    if(connect(sock,(struct sockaddr *)&addr,sizeof(addr)) < 0){
+        perror("connect failed");
+        return 1;
+    }
+    if(sendReadOp(sock,filename) == 0){
+        int ret = recvData(sock,filename);
+        close(sock);
+        return ret;
+    }
+    close(sock);
+    return 0;
+}
\ No newline at end of file
diff --git a/socket_wrapper.c b/socket_wrapper.c
new file mode 100644
index 0000000..f6dc431
--- /dev/null
+++ b/socket_wrapper.c
@@ -0,0 +1,71 @@
+#include <signal.h>
+#include <assert.h>
+#include <stdio.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include "socket_wrapper.h"
+
+int getBufferSizeFrom(int sock){
+    int buffer_sz;
+    socklen_t len = sizeof(buffer_sz);
+    if(getsockopt(sock,SOL_SOCKET,SO_SNDBUF,&buffer_sz,&len) < 0){
+        perror("failed to get sock buffer size: getsockopt");
+        buffer_sz = DEFAULT_BUF_SIZE;/*set to default*/
+    }
+    if(buffer_sz < MINIMUM_BUF_SIZE)
+        buffer_sz = MINIMUM_BUF_SIZE;
+    return buffer_sz;
+}
+
+static uint64_t timer_ticks = 0;
+static void alarm_handler(int signum){
+    timer_ticks++;
+}
+
+void register_alarm(){
+    struct sigaction sigact;
+    sigact.sa_flags = SA_INTERRUPT;
+    sigemptyset(&sigact.sa_mask);
+    sigaddset(&sigact.sa_mask,SIGALRM);
+    sigact.sa_handler = alarm_handler;
+    sigaction(SIGALRM, &sigact ,NULL);
+}
+
+ssize_t timeout_recv(int fd,void * buf,size_t n,int timeout)
+{
+    ssize_t ret;
+    uint64_t cur = timer_ticks;
+    int die_count = 0;
+    for(;;){
+        alarm(timeout);
+        ret = recv(fd,buf,n,0);
+        if (ret < 0 && errno == EINTR && cur != timer_ticks)
+            return -2;
+        alarm(0);
+        if (ret == 0){
+            usleep(100000);
+            die_count++;
+            if(die_count > timeout*10){
+                return -2;
+            }
+        }
+        else break;
+    }
+    return ret;
+}
+
+ssize_t recv_until_byte(int fd,void * buf, size_t n,int timeout){
+    ssize_t cur = 0;
+    uint8_t * b = buf;
+    while (cur < n)
+    {
+        ssize_t r = timeout_recv(fd,&b[cur],n-cur,timeout);
+        if (r < 0){
+            return r;
+        }
+        cur += r;
+    }
+    assert(cur == n);
+    return cur;
+}
\ No newline at end of file
diff --git a/socket_wrapper.h b/socket_wrapper.h
new file mode 100644
index 0000000..6bb7fd7
--- /dev/null
+++ b/socket_wrapper.h
@@ -0,0 +1,60 @@
+#ifndef _SOCKET_WRAPPER_H_
+#define _SOCKET_WRAPPER_H_
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#ifdef USE_SENDFILE
+#include <sys/sendfile.h>
+const size_t SEND_FILE_CHUNK_SIZE = 0x100000; /*1MB*/
+#endif
+
+static const in_port_t SERVER_PORT = 9091;
+static const size_t DEFAULT_BUF_SIZE = 4096;
+static const size_t MINIMUM_BUF_SIZE = 1024;
+/*0 < x < MAX_PATH_SIZE*/
+static const uint16_t MAX_PATH_SIZE = 256;
+static const int TIMEOUT = 5;
+
+enum{
+    RES_OK = 0,
+    RES_ERR = 1,
+    RES_USR_ERR = 2
+};
+
+#pragma pack(push,1)
+struct ReadOp{
+    uint16_t file_url_size;/* strlen(data) */
+    uint16_t padding0;
+};
+struct TransferResult{
+    int16_t res;
+    int16_t error_msg_size;
+    int64_t file_size; /**/
+    int32_t err_number; /*errno*/
+};
+#pragma pack(pop)
+
+#ifdef USE_GETADDRINFO
+
+#endif
+
+int getBufferSizeFrom(int sock);
+
+/*register alarm for timeout_recv()*/
+void register_alarm();
+/*
+return -2 if timeout occur.
+otherwise, implement equal to 'recv'.
+you must call register_alarm() before you use this.
+Since alarm() is called by internal implementation, don't use it if other alarms already exist.
+*/
+ssize_t timeout_recv(int fd,void * buf,size_t n,int timeout);
+/*
+recieve data to buf until all bytes.
+*/
+ssize_t recv_until_byte(int fd,void * buf, size_t n,int timeout);
+
+#endif
\ No newline at end of file