Simple Hello Server/Client program

Server-Client Program/Client/Client.cbp

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+<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
+<CodeBlocks_project_file>
+	<FileVersion major="1" minor="6" />
+	<Project>
+		<Option title="Client" />
+		<Option pch_mode="2" />
+		<Option compiler="gcc" />
+		<Build>
+			<Target title="Debug">
+				<Option output="bin/Debug/Client" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Debug/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-g" />
+				</Compiler>
+			</Target>
+			<Target title="Release">
+				<Option output="bin/Release/Client" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Release/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-O2" />
+				</Compiler>
+				<Linker>
+					<Add option="-s" />
+				</Linker>
+			</Target>
+		</Build>
+		<Compiler>
+			<Add option="-Wall" />
+			<Add option="-fexceptions" />
+		</Compiler>
+		<Unit filename="main.cpp" />
+		<Extensions />
+	</Project>
+</CodeBlocks_project_file>

Server-Client Program/Client/Client.cpp

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+//Client side program in C/C++
+
+#include <stdint.h>
+#include <netinet/ip.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <unistd.h>
+#include <errno.h>
+#include <arpa/inet.h>
+
+
+using namespace std;
+static void msg( const char* msg){
+    fprintf(stderr, "%s\n", msg);
+}
+
+static void die(const char* msg){
+    int err = errno;
+    fprintf(stderr, "[%d] %s\n", err,msg);
+    abort();
+}
+
+int main(){
+
+    int fd = socket(AF_INET, SOCK_STREAM, 0);
+    if( fd < 0 ){
+        die("socket()");
+    }
+
+    struct sockaddr_in addr = {};
+    addr.sin_family = AF_INET;
+    addr.sin_port = ntohs(1234);
+    addr.sin_addr.s_addr = ntohl(INADDR_LOOPBACK);// 127.0.0.1
+    int rv = connect(fd, (const struct sockaddr*)&addr, sizeof(addr));
+    if( rv ){
+        die("connect");
+    }
+
+    char msg[] = "hello";
+    write(fd, msg, strlen(msg));
+
+    char rbuf[64] = {};
+    ssize_t n = read(fd, rbuf , sizeof(rbuf) - 1);
+    if( n < 0 ){
+        die("read");
+    }
+    printf("server says: %s\n", rbuf);
+    close(fd);
+    return 0;
+}

Server-Client Program/Client/Client.depend

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+# depslib dependency file v1.0
+1699986008 source:/home/hizenberg/Desktop/My Own Redis/Server-Client Program/Client/Client.cpp
+	<stdint.h>
+	<netinet/ip.h>
+	<stdio.h>
+	<stdlib.h>
+	<string.h>
+	<sys/socket.h>
+	<unistd.h>
+	<errno.h>
+	<arpa/inet.h>
+

Server-Client Program/Server/Server.cbp

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+<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
+<CodeBlocks_project_file>
+	<FileVersion major="1" minor="6" />
+	<Project>
+		<Option title="Server" />
+		<Option pch_mode="2" />
+		<Option compiler="gcc" />
+		<Build>
+			<Target title="Debug">
+				<Option output="bin/Debug/Server" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Debug/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-g" />
+				</Compiler>
+			</Target>
+			<Target title="Release">
+				<Option output="bin/Release/Server" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Release/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-O2" />
+				</Compiler>
+				<Linker>
+					<Add option="-s" />
+				</Linker>
+			</Target>
+		</Build>
+		<Compiler>
+			<Add option="-Wall" />
+			<Add option="-fexceptions" />
+		</Compiler>
+		<Unit filename="main.cpp" />
+		<Extensions />
+	</Project>
+</CodeBlocks_project_file>

Server-Client Program/Server/Server.cpp

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+//Server side Program in C/C++
+
+#include <stdint.h>
+#include <netinet/ip.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <unistd.h>
+#include <errno.h>
+#include <arpa/inet.h>
+
+
+static void msg( const char* msg){
+    fprintf(stderr, "%s\n", msg);
+}
+
+static void die(const char* msg){
+    int err = errno;
+    fprintf(stderr, "[%d] %s\n", err,msg);
+    abort();
+}
+
+static void do_something(int connfd){
+    char rbuf[64] = {};
+
+    ssize_t n = read(connfd, rbuf, sizeof(rbuf) - 1);
+
+    if( n < 0 ){
+        msg("read() error");
+        return;
+    }
+
+    printf("Client says: %s\n",rbuf);
+
+    char wbuf[] = "world";
+    write(connfd , wbuf, strlen(wbuf));
+}
+
+
+int main(){
+    //syscall to return integer for socket communication from kernel
+    int fd = socket(AF_INET, SOCK_STREAM , 0);
+    if( fd < 0 ){
+        die("socket()");
+    }
+
+    //Set the option in various layer which will establish communication.
+    int val = 1;
+    setsockopt(fd, SOL_SOCKET , SO_REUSEADDR, &val , sizeof(val));
+
+    //bind, dealing wih IPv4 addresses
+    struct sockaddr_in addr = {};
+    addr.sin_family = AF_INET;
+    addr.sin_port = ntohs(1234);
+    addr.sin_addr.s_addr = ntohl(0);// wildcard address 0.0.0.0
+    int rv = bind(fd, (const sockaddr*)&addr, sizeof(addr));
+
+    if(rv){
+        die("bind()");
+    }
+
+    //listen
+    rv = listen(fd , SOMAXCONN);
+
+    if( rv ){
+        die("listen()");
+    }
+
+    //Looping to connect to each connection.
+    while(true){
+        //accept
+        struct sockaddr_in client_addr = {};
+        socklen_t socklen = sizeof( client_addr );
+        int connfd = accept(fd , (struct sockaddr*)& client_addr, &socklen);
+        if( connfd < 0 ){
+            //error
+            printf("Error encountered while connecting with client.");
+        }
+
+        do_something(connfd);
+        close(connfd);
+    }
+
+    return 0;
+}

Server-Client Program/Tut-Sheet-1.txt

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+socket() -> this is a syscall which returns an fd.
+
+        fd - It is like a integer which is like an ID used by kernel. It is basically related
+            to kernel functionality.
+
+bind() -> It is used to bind the address to the fd.
+       -> The address is which we want to connect with.
+
+listen() -> listen helps to establish connection with that address.
+
+accept() -> when connection is made my client, it returns an fd which represents the established connection.
+
+WORKFLOW OF SERVER (PSEUDO CODE):
+
+    fd = socket();
+    bind(fd,address)
+    listen(fd)
+    while(true)
+        conn_fd = accept(fd)
+        /**************/
+            do something with conn_fd
+            doing something in this connection
+        /**************/
+        close(conn_fd)
+
+
+connect() -> take the fd from client side and make the connection from the address that
+          -> the address is of the server side.
+WORKFLOW OF CLIENT (PSEUDO CODE)
+
+    fd = socket()
+    connect(fd,address)
+    /*********/
+        doing something in the connection/
+    /*********/
+    close(fd)

Server-Client Program/Tut-Sheet-2.txt

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+Starting of client and server.
+
+1. First we need fd using socket()
+
+    int fd = socket(AF_INET,SOCK_STREAM,0);
+
+    ->AF_INET = It is used to provide IPv4
+        NOTE: AF_INET6 = It is used to provide IPv6 or dual-stack socket.
+    ->SOCK_STREAM = It is used to set the TCP protocol.
+
+
+2. NEW SYSTEM CALL
+
+    setsocketopt()
+    -> There are various layer of network communication and each layer have various option, from which we pick one to
+        configure the network communication.
+    -> This syscall is to set those option
+
+    IMPORTANT: SO_REUSEADDR-> It is an option to reuse the same address when the process(communication) is restarted.
+        -> Risk of using it.
+         # If the previous connection using the same address didn't took all the packets and the process got closed
+           before taking it, the same address might be used by the same program with new instance of process or by another
+           program with new instance of process. This rouge packets is intented to send it to the address which is in reuse.
+           This cause problem. This problem also make it hackable.
+
+
+    NEW TERM: WILDCARD ADDRESS -> when we use sockets, the communication is design to between two process only.
+    Not allowing multicast or multiple communication. To establish this multiple communication we use wildcard address.
+    This is used on server-side program.
+
+
+3. read() and write()
+    It returns number of read and written bytes.

Server-Client Program/default.workspace

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+<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
+<CodeBlocks_workspace_file>
+	<Workspace title="Workspace">
+		<Project filename="Server/Server.cbp" />
+		<Project filename="Client/Client.cbp" />
+	</Workspace>
+</CodeBlocks_workspace_file>

Server-Client Program/default.workspace.layout

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+<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
+<CodeBlocks_workspace_layout_file>
+	<FileVersion major="1" minor="0" />
+	<ActiveProject path="Server/Server.cbp" />
+	<PreferredTarget name="Debug" />
+</CodeBlocks_workspace_layout_file>