read input & save in shared memory in Socket in C - c

Question

I work on the server side Socket (use Telnet client) in Linux. Client input a line with command(GET/PUT/DEL, key and an associated value (spaces to seperate in between). This key-value pair is then passed accordingly on to the function(GET/PUT/DEL), which saves the data in the shared memory (keyValueStore).
Expected client side: (> is the output from Server)
GET key1
> GET:key1:key_nonexistent
PUT key1 value1
> PUT:key1:value1
PUT key2 value2
> PUT:key2:value2
DEL key2
> DEL:key2:key_deleted
Questions:
1/ i tried to use strtok() and keyValueStore to seperate & save the tokens in a normal c file, but how should I do (or transform) it into the data transfer communication between server and client?
2/ when or where should I call the command functions (e.g. int put(char* key, char* value) )? in server.c after reading the input but before giving output?
Any advices is appreicated. Thanks for your kindness!
server.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define BUFSIZE 1024 // Buffer Size
#define TRUE 1
#define PORT 5678
int main() {
int rfd; // Create-Descriptor
int cfd; // Connection-Descriptor (accept)
struct sockaddr_in client;
socklen_t client_len;
char in[BUFSIZE];
int bytes_read;
// 1. socket()
rfd = socket(AF_INET, SOCK_STREAM, 0);
if (rfd < 0 ){
fprintf(stderr, "Error\n");
exit(-1);
}
//Initialize the server address by the port and IP
struct sockaddr_in server;
memset(&server, '\0', sizeof(server));
server.sin_family = AF_INET; // Internet address family: v4 address
server.sin_addr.s_addr = INADDR_ANY; // Server IP address
server.sin_port = htons(PORT); // Server port
// 2. bind()
int brt = bind(rfd, (struct sockaddr *) &server, sizeof(server));
if (brt < 0 ){
fprintf(stderr, "Error\n");
exit(-1);
}
// 3. listen() = listen for connections
int lrt = listen(rfd, 5);
if (lrt < 0 ){
fprintf(stderr, "Error\n");
exit(-1);
}
while (1) {
// 4. accept()
cfd = accept(rfd, (struct sockaddr *) &client, &client_len);
// read() = read from a socket (Client's data)
bytes_read = read(cfd, in, BUFSIZE);
while (bytes_read > 0) {
printf("sending back the %d bytes I received...\n", bytes_read);
// write() = write data on a socket (Client's data)
write(cfd, in, bytes_read);
bytes_read = read(cfd, in, BUFSIZE);
}
close(cfd);
}
close(rfd);
}
Input.c
#include <stdio.h>
#include <string.h>
#include <stdio.h>
#define MAX_ARRAY 100
int main() {
typedef struct Value_ {
char key[MAX_ARRAY];
char value[MAX_ARRAY];
} KeyStorage;
KeyStorage storageKey[MAX_ARRAY];
char client_input[MAX_ARRAY];
char *argv[3];
char *token;
int count = 0;
while (1) {
printf("Input: ");
gets(client_input);
//get the first token
token = strtok(client_input, " ");
int i = 0;
//walk through other tokens
while (token != NULL) {
argv[i] = token;
i++;
token = strtok(NULL, " ");
}
argv[i] = NULL; //argv ends with NULL
// arg[0] = command z.B. GET, PUT
printf("Commend: %s\n", argv[0]);
strcpy(storageKey[count].key, argv[1]);
printf("Key: %s\n", storageKey[count].key);
strcpy(storageKey[count].value, argv[2]);
printf("Value: %s\n", storageKey[count].value);
count++;
if (strcmp(argv[0], "QUIT") == 0) {
break;
}
}
return 0;
}

Answer 1

There are a number of errors in your code. I have fixed all to build a working example. Of course, this is not your complete application and there is even a lot of room for enhancements.
I developed and tested my code with MSVC2019 under Windows but I used a #define to isolate Windows specific code so it should compile and run correctly under Linux as well (I have not tested that).
The main problem your code had is a misunderstanding of TCP connection. It is a stream oriented connection and you must assemble "command lines" yourself, receiving one character at a time.
It is only when a line is complete that you can parse it to detect the command sent by the client. I made simple: only one command "exit" does something (close the connection). Everything else is simply ignored.
I made line assembling the easy way. That means that there is no edit possible. Backspace, delete, cursor keys and more and input as any other characters and doesn't work a a user would expect. You should take care of that.
Finally, I kept the code close to what you used. This code is single user. It accept a connection, accept commands from it and only accept a new connection once the first is closed. This is not normally the way to create a server program. To make it multiuser, you should use non-blocking socket and select() or use multi-threading.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#ifdef WIN32
#include <WinSock2.h>
#include <io.h>
typedef int socklen_t;
#pragma warning(disable : 4996) // No warning for deprecated function names such as read() and write()
#else
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define closesocket close
#endif
#define BUFSIZE 1024 // Buffer Size
#define TRUE 1
#define PORT 5678
int main(int argc, char *argv[])
{
#ifdef WIN32
int iResult;
WSADATA wsaData;
// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != 0) {
printf("WSAStartup failed: %d\n", iResult);
return 1;
}
#endif
int rfd; // Create-Descriptor
int cfd; // Connection-Descriptor (accept)
struct sockaddr_in client;
socklen_t client_len;
char in[BUFSIZE];
int bytes_read;
// 1. socket()
rfd = socket(AF_INET, SOCK_STREAM, 0);
if (rfd < 0) {
fprintf(stderr, "Error\n");
exit(-1);
}
// Initialize the server address by the port and IP
struct sockaddr_in server;
memset(&server, '\0', sizeof(server));
server.sin_family = AF_INET; // Internet address family: v4 address
server.sin_addr.s_addr = INADDR_ANY; // Server IP address
server.sin_port = htons(PORT); // Server port
// 2. bind()
int brt = bind(rfd, (struct sockaddr*)&server, sizeof(server));
if (brt < 0) {
fprintf(stderr, "Error\n");
exit(-1);
}
// 3. listen() = listen for connections
int lrt = listen(rfd, 5);
if (lrt < 0) {
fprintf(stderr, "Error\n");
exit(-1);
}
while (1) {
client_len = sizeof(client);
cfd = accept(rfd, (struct sockaddr*)&client, &client_len);
if (cfd < 0) {
fprintf(stderr, "accept failed with error %d\n", WSAGetLastError());
exit(-1);
}
printf("Client connected\n");
while (1) {
/*
// Send prompt to client
char* prompt = "> ";
if (send(cfd, prompt, strlen(prompt), 0) <= 0) {
fprintf(stderr, "send() failed with error %d\n", WSAGetLastError());
exit(1);
}
*/
// read a line from a socket (Client's data)
int bytes_idx = -1;
while (1) {
if (bytes_idx >= (int)sizeof(in)) {
fprintf(stderr, "input buffer overflow\n");
break;
}
// Receive on byte (character) at a time
bytes_read = recv(cfd, &in[++bytes_idx], 1, 0);
if (bytes_read <= 0) // Check error or no data read
break;
/*
printf("sending back the %d bytes I received...\n", bytes_read);
if (send(cfd, &in[bytes_idx], 1, 0) <= 0) {
fprintf(stderr, "send() failed with error %d\n", WSAGetLastError());
exit(1);
}
*/
if (in[bytes_idx] == '\n') {
// Received a complete line, including CRLF
// Remove ending CR
bytes_idx--;
if ((bytes_idx >= 0) && (in[bytes_idx] == '\r'))
in[bytes_idx] = 0;
break;
}
}
if (bytes_idx > 0) { // Check for empty line
printf("Received \"%s\"\n", in);
// Check for client command
if (stricmp(in, "exit") == 0)
break;
else {
printf("Client sent unknown command\n");
}
}
}
closesocket(cfd);
printf("Client disconnected\n");
}
closesocket(rfd);
#ifdef WIN32
WSACleanup();
#endif
}