Unix sockets demo

socket/Makefile

@@ -0,0 +1,19 @@
+CC ?= gcc
+CFLAGS ?= -Wall -g
+
+all: server.elf client.elf
+
+server.elf: server.c
+client.elf: client.c
+
+%.elf: %.c
+	@echo CC $@
+	@$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+test: all
+	bash test.sh
+
+clean:
+	rm -f *.elf *.o
+
+.PHONY: test clean

socket/client.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#define SOCKET_PATH "/tmp/demosocket"
+
+int main() {
+    int sock_fd;
+    struct sockaddr_un addr;
+    char buffer[100];
+
+    sock_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+    if (sock_fd < 0) {
+        perror("socket");
+        exit(EXIT_FAILURE);
+    }
+
+    memset(&addr, 0, sizeof(struct sockaddr_un));
+    addr.sun_family = AF_UNIX;
+    strncpy(addr.sun_path, SOCKET_PATH, sizeof(addr.sun_path) - 1);
+
+    if (connect(sock_fd, (struct sockaddr *)&addr, sizeof(struct sockaddr_un)) <
+        0) {
+        perror("connect");
+        exit(EXIT_FAILURE);
+    }
+
+    send(sock_fd, "ping\n", 4, 0);
+
+    int bytes = recv(sock_fd, buffer, sizeof(buffer) - 1, 0);
+    if (bytes > 0) {
+        buffer[bytes] = '\0';
+        printf("Client got: %s\n", buffer);
+    }
+
+    close(sock_fd);
+    return 0;
+}

socket/server.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+/* Unix sockets need a path */
+#define SOCK_PATH "/tmp/demosocket"
+#define BUF_SIZE 128
+
+char buf[BUF_SIZE];
+
+int main(void) {
+    struct sockaddr_un addr;
+    int server_fd, client_fd;
+
+    char *msg = "Hello\n";
+    memcpy(buf, msg, strlen(msg));
+
+    // Unlink this in case its still around
+    unlink(SOCK_PATH);
+
+    server_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+    if (server_fd == -1) {
+        perror("Error: Could not open socket...\n");
+        exit(EXIT_FAILURE);
+    }
+
+    // Wipe this for security
+    memset(&addr, 0, sizeof(struct sockaddr_un));
+    addr.sun_family = AF_UNIX;
+    snprintf(addr.sun_path, sizeof(addr.sun_path), "%s", SOCK_PATH);
+
+    if (bind(server_fd, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
+        perror("Could not bind server...\n");
+        close(server_fd);
+        exit(EXIT_FAILURE);
+    }
+
+    if (listen(server_fd, 1) == -1) {
+        perror("Listen");
+        close(server_fd);
+        exit(EXIT_FAILURE);
+    }
+
+    printf("Server listening on %s...\n", SOCK_PATH);
+
+    while (1) {
+        // This will block until a message is recieved
+        client_fd = accept(server_fd, NULL, NULL);
+        if (client_fd == -1) {
+            perror("accept");
+            close(server_fd);
+            exit(EXIT_FAILURE);
+        }
+
+        ssize_t received = recv(client_fd, buf, BUF_SIZE - 1, 0);
+        if (received > 0) {
+            buf[received] = '\0';
+            printf("Server got: %s\n", buf);
+
+            // Send a reply
+            const char *reply = "pong!\n";
+            send(client_fd, reply, strlen(reply), 0);
+        } else {
+            perror("recv");
+        }
+    }
+
+    close(client_fd);
+    close(server_fd);
+    unlink(SOCK_PATH);
+    return 0;
+}

socket/socket.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+#define SOCKET_PATH "/tmp/demosocket"
+#define BUF_SIZE 128
+
+int main(void) {
+    int server_fd, client_fd;
+    struct sockaddr_un addr;
+    char buf[BUF_SIZE];
+
+    // Clean up any leftover socket file
+    unlink(SOCKET_PATH);
+
+    // Create socket
+    server_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+    if (server_fd == -1) {
+        perror("socket");
+        exit(EXIT_FAILURE);
+    }
+
+    // Zero out and set up the address structure
+    memset(&addr, 0, sizeof(addr));
+    addr.sun_family = AF_UNIX;
+    strncpy(addr.sun_path, SOCKET_PATH, sizeof(addr.sun_path) - 1);
+
+    // Bind the socket to the path
+    if (bind(server_fd, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
+        perror("bind");
+        close(server_fd);
+        exit(EXIT_FAILURE);
+    }
+
+    // Listen for a connection
+    if (listen(server_fd, 1) == -1) {
+        perror("listen");
+        close(server_fd);
+        exit(EXIT_FAILURE);
+    }
+
+    printf("Server listening on %s...\n", SOCKET_PATH);
+
+    // Accept a connection
+    client_fd = accept(server_fd, NULL, NULL);
+    if (client_fd == -1) {
+        perror("accept");
+        close(server_fd);
+        exit(EXIT_FAILURE);
+    }
+
+    // Receive a message
+    ssize_t received = recv(client_fd, buf, BUF_SIZE - 1, 0);
+    if (received > 0) {
+        buf[received] = '\0';
+        printf("Received: %s", buf);
+
+        // Send a reply
+        const char *reply = "Got your message!\n";
+        send(client_fd, reply, strlen(reply), 0);
+    } else {
+        perror("recv");
+    }
+
+    // Clean up
+    close(client_fd);
+    close(server_fd);
+    unlink(SOCKET_PATH);
+    return 0;
+}

socket/test.sh

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+#!/bin/bash
+
+SOCKET_PATH="/tmp/demosocket"
+
+# Cleanup function to be run on exit
+cleanup() {
+    echo "Cleaning up..."
+    if [[ -n "$SERVER_PID" ]]; then
+        kill "$SERVER_PID" 2>/dev/null || true
+        wait "$SERVER_PID" 2>/dev/null || true
+    fi
+    rm -f "$SOCKET_PATH"
+}
+
+# Trap EXIT to ensure cleanup runs
+trap cleanup EXIT
+
+echo "Starting server..."
+./server.elf &
+SERVER_PID=$!
+
+# Wait briefly for the server to start
+sleep 0.2
+
+echo "Running client..."
+./client.elf