add forking versions and subscribe feature

.gitignore

@@ -1 +1,2 @@
 .idea/
+build/

src/c90/metric_client.c

@@ -1,4 +1,4 @@
-/* metric_client.c - C89/C90 custom binary metric client */
+/* metric_client.c - STRICT C89/C90 custom binary metric client */
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -10,7 +10,7 @@
 #define PORT     9999
 #define BUF_SIZE 1024
 
-/* same constants */
+/* Protocol constants (must match server) */
 #define MSG_PING        0x01
 #define MSG_PONG        0x02
 #define MSG_METRIC_REQ  0x03
@@ -19,89 +19,119 @@
 
 #define HEADER_SIZE 3
 
-static void send_message(int sock, unsigned char type, const void *payload, unsigned short len) {
+static void send_message(int sock, unsigned char type,
+                         const void *payload, unsigned short len)
+{
     unsigned char header[HEADER_SIZE];
     header[0] = type;
-    header[1] = (len >> 8) & 0xFF;
+    header[1] = (len >> 8) & 0xFF;   /* big-endian */
     header[2] = len & 0xFF;
     write(sock, header, HEADER_SIZE);
-    if (len > 0) write(sock, payload, len);
+    if (len > 0)
+        write(sock, payload, len);
 }
 
-static int recv_exact(int sock, void *buf, int n) {
+static int recv_exact(int sock, void *buf, int n)
+{
     int total = 0;
     while (total < n) {
-        int r = read(sock, (char*)buf + total, n - total);
+        int r = read(sock, (char *)buf + total, n - total);
         if (r <= 0) return -1;
         total += r;
     }
     return total;
 }
 
-static void print_wire_comparison(void) {
+static void print_wire_comparison(void)
+{
     printf("\n--- Wire overhead comparison ---\n");
     printf("Our protocol (METRIC_REQ 'cpu'):  %d bytes\n", HEADER_SIZE + 3);
     printf("Equivalent HTTP GET:              77 bytes\n");
     printf("HTTP is ~13x larger\n\n");
 }
 
-int main(void) {
+int main(void)
+{
     int sock;
     struct sockaddr_in addr;
     unsigned char header[HEADER_SIZE];
     unsigned char payload[BUF_SIZE];
     double val;
     char line[256];
+    unsigned char type;
+    unsigned short len;
+    const char *metric;
 
     sock = socket(AF_INET, SOCK_STREAM, 0);
+    if (sock < 0) {
+        perror("socket");
+        exit(1);
+    }
+
     addr.sin_family = AF_INET;
     addr.sin_port   = htons(PORT);
     inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr);
 
-    if (connect(sock, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
+    if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
         perror("connect");
+        close(sock);
         exit(1);
     }
 
-    printf("Connected to 127.0.0.1:%d\n", PORT);
+    printf("Connected to 127.0.0.1:%d (STRICT C89 client)\n", PORT);
     print_wire_comparison();
 
-    printf("Commands: ping | get <metric> | quit\nMetrics: cpu, memory, disk, loadavg, uptime\n\n");
+    printf("Commands: ping | get <metric> | quit\n");
+    printf("Metrics:  cpu, memory, disk, loadavg, uptime\n\n");
 
     while (1) {
         printf("> ");
-        if (fgets(line, sizeof(line), stdin) == NULL) break;
+        if (fgets(line, sizeof(line), stdin) == NULL)
+            break;
+
         line[strcspn(line, "\n")] = '\0';
 
-        if (strcmp(line, "quit") == 0) break;
+        if (strcmp(line, "quit") == 0) {
-        if (strcmp(line, "ping") == 0) {
+            break;
+        }
+        else if (strcmp(line, "ping") == 0) {
             send_message(sock, MSG_PING, NULL, 0);
-        } else if (strncmp(line, "get ", 4) == 0) {
+        }
-            const char *metric = line + 4;
+        else if (strncmp(line, "get ", 4) == 0) {
+            metric = line + 4;
             send_message(sock, MSG_METRIC_REQ, metric, strlen(metric));
-        } else {
+        }
+        else {
             printf("  Unknown command.\n");
             continue;
         }
 
         /* blocking receive */
-        if (recv_exact(sock, header, HEADER_SIZE) != HEADER_SIZE) break;
+        if (recv_exact(sock, header, HEADER_SIZE) != HEADER_SIZE)
-        unsigned char type = header[0];
+            break;
-        unsigned short len = (header[1] << 8) | header[2];
+
+        type = header[0];
+        len  = (header[1] << 8) | header[2];
 
         if (len > 0) {
-            if (recv_exact(sock, payload, len) != len) break;
+            if (recv_exact(sock, payload, len) != len)
+                break;
         }
 
         if (type == MSG_PONG) {
             printf("  [PONG] server alive\n");
-        } else if (type == MSG_METRIC_RESP) {
+        }
+        else if (type == MSG_METRIC_RESP) {
             memcpy(&val, payload, sizeof(double));
             printf("  [METRIC] %.2f\n", val);
-        } else if (type == MSG_ERROR) {
+        }
+        else if (type == MSG_ERROR) {
             payload[len] = '\0';
             printf("  [ERROR] %s\n", payload);
         }
+        else {
+            printf("  [???] Unknown message type 0x%02X\n", type);
+        }
     }
 
     close(sock);

src/c90/metric_client_sub.c

@@ -0,0 +1,173 @@
+/* metric_client.c - STRICT C89/C90 client with live SUBSCRIBE/PUSH using select() */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <sys/select.h>
+#include <errno.h>
+
+#define PORT     9999
+#define BUF_SIZE 1024
+
+#define MSG_PING        0x01
+#define MSG_PONG        0x02
+#define MSG_METRIC_REQ  0x03
+#define MSG_METRIC_RESP 0x04
+#define MSG_SUBSCRIBE   0x05
+#define MSG_PUSH        0x06
+#define MSG_ERROR       0xFF
+
+#define HEADER_SIZE 3
+
+static void send_message(int sock, unsigned char type,
+                         const void *payload, unsigned short len)
+{
+    unsigned char header[HEADER_SIZE];
+    header[0] = type;
+    header[1] = (len >> 8) & 0xFF;
+    header[2] = len & 0xFF;
+    write(sock, header, HEADER_SIZE);
+    if (len > 0)
+        write(sock, payload, len);
+}
+
+static int recv_exact(int sock, void *buf, int n)
+{
+    int total = 0;
+    while (total < n) {
+        int r = read(sock, (char *)buf + total, n - total);
+        if (r <= 0) return -1;
+        total += r;
+    }
+    return total;
+}
+
+static void print_wire_comparison(void)
+{
+    printf("\n--- Wire overhead comparison ---\n");
+    printf("Our protocol (METRIC_REQ 'cpu'):  %d bytes\n", HEADER_SIZE + 3);
+    printf("Equivalent HTTP GET:              77 bytes\n");
+    printf("HTTP is ~13x larger\n\n");
+}
+
+int main(void)
+{
+    int sock, maxfd;
+    struct sockaddr_in addr;
+    unsigned char header[HEADER_SIZE];
+    unsigned char payload[BUF_SIZE];
+    double val;
+    char line[256];
+    unsigned char type;
+    unsigned short len;
+    const char *metric;
+    unsigned int interval_ms;
+    unsigned char name_len;
+    fd_set readfds;
+
+    sock = socket(AF_INET, SOCK_STREAM, 0);
+    if (sock < 0) { perror("socket"); exit(1); }
+
+    addr.sin_family = AF_INET;
+    addr.sin_port   = htons(PORT);
+    inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr);
+
+    if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
+        perror("connect"); close(sock); exit(1);
+    }
+
+    printf("Connected to 127.0.0.1:%d (STRICT C89 live client)\n", PORT);
+    print_wire_comparison();
+
+    printf("Commands: ping | get <metric> | sub <metric> <ms> | quit\n");
+    printf("Metrics:  cpu, memory, disk, loadavg, uptime\n\n");
+
+    maxfd = sock > 0 ? sock : 0;
+
+    while (1) {
+        FD_ZERO(&readfds);
+        FD_SET(0, &readfds);      /* stdin */
+        FD_SET(sock, &readfds);   /* socket */
+
+        if (select(maxfd + 1, &readfds, NULL, NULL, NULL) < 0) {
+            if (errno == EINTR) continue;
+            perror("select");
+            break;
+        }
+
+        /* 1. Data ready on the socket → handle PUSH / response immediately */
+        if (FD_ISSET(sock, &readfds)) {
+            if (recv_exact(sock, header, HEADER_SIZE) != HEADER_SIZE) break;
+
+            type = header[0];
+            len  = (header[1] << 8) | header[2];
+
+            if (len > 0) {
+                if (recv_exact(sock, payload, len) != len) break;
+            }
+
+            if (type == MSG_PONG) {
+                printf("\n  [PONG] server alive\n");
+            }
+            else if (type == MSG_METRIC_RESP) {
+                memcpy(&val, payload, sizeof(double));
+                printf("\n  [METRIC] %.2f\n", val);
+            }
+            else if (type == MSG_PUSH) {
+                name_len = payload[0];
+                payload[1 + name_len] = '\0';
+                memcpy(&val, payload + 1 + name_len, sizeof(double));
+                printf("\n  [PUSH] %s: %.2f\n", (char *)payload + 1, val);
+            }
+            else if (type == MSG_ERROR) {
+                payload[len] = '\0';
+                printf("\n  [ERROR] %s\n", payload);
+            }
+            else {
+                printf("\n  [???] Unknown type 0x%02X\n", type);
+            }
+            printf("> "); fflush(stdout);   /* re-print prompt after async message */
+        }
+
+        /* 2. User typed something on stdin */
+        if (FD_ISSET(0, &readfds)) {
+            if (fgets(line, sizeof(line), stdin) == NULL) break;
+            line[strcspn(line, "\n")] = '\0';
+
+            if (strcmp(line, "quit") == 0) break;
+            else if (strcmp(line, "ping") == 0) {
+                send_message(sock, MSG_PING, NULL, 0);
+            }
+            else if (strncmp(line, "get ", 4) == 0) {
+                metric = line + 4;
+                send_message(sock, MSG_METRIC_REQ, metric, strlen(metric));
+            }
+            else if (strncmp(line, "sub ", 4) == 0) {
+                metric = strtok(line + 4, " ");
+                if (metric) {
+                    interval_ms = atoi(strtok(NULL, " "));
+                    name_len = strlen(metric);
+                    payload[0] = name_len;
+                    memcpy(payload + 1, metric, name_len);
+                    payload[1 + name_len]     = (interval_ms >> 24) & 0xFF;
+                    payload[1 + name_len + 1] = (interval_ms >> 16) & 0xFF;
+                    payload[1 + name_len + 2] = (interval_ms >>  8) & 0xFF;
+                    payload[1 + name_len + 3] =  interval_ms        & 0xFF;
+                    send_message(sock, MSG_SUBSCRIBE, payload, 1 + name_len + 4);
+                    printf("  Subscribed to '%s' every %u ms\n", metric, interval_ms);
+                }
+            }
+            else {
+                printf("  Unknown command.\n");
+            }
+            printf("> "); fflush(stdout);
+        }
+    }
+
+    close(sock);
+    printf("\nDisconnected.\n");
+    return 0;
+}

src/c90/metric_server_fork.c

@@ -1,4 +1,4 @@
-/* metric_server_fork.c - C89/C90 multi-client metric server using fork() */
+/* metric_server_fork.c - STRICT C89/C90 multi-client metric server using fork() */
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -58,9 +58,12 @@ static int recv_exact(int sock, void *buf, int n)
 
 static void handle_client(int client_sock, struct sockaddr_in *addr)
 {
-    unsigned char header[HEADER_SIZE];
+    unsigned char header[HEADER_SIZE];      /* all declarations first */
     unsigned char payload[BUF_SIZE];
     char client_ip[INET_ADDRSTRLEN];
+    unsigned char type;
+    unsigned short len;
+    double val;
 
     inet_ntop(AF_INET, &addr->sin_addr, client_ip, sizeof(client_ip));
     printf("[+] Connected from %s:%d\n", client_ip, ntohs(addr->sin_port));
@@ -69,8 +72,8 @@ static void handle_client(int client_sock, struct sockaddr_in *addr)
         if (recv_exact(client_sock, header, HEADER_SIZE) != HEADER_SIZE)
             break;
 
-        unsigned char type = header[0];
+        type = header[0];
-        unsigned short len = (header[1] << 8) | header[2];
+        len  = (header[1] << 8) | header[2];
 
         if (len > 0) {
             if (recv_exact(client_sock, payload, len) != len)
@@ -83,7 +86,7 @@ static void handle_client(int client_sock, struct sockaddr_in *addr)
         }
         else if (type == MSG_METRIC_REQ) {
             payload[len] = '\0';
-            double val = get_metric((char *)payload);
+            val = get_metric((char *)payload);
             printf("  <- METRIC_REQ '%s' from %s\n", (char *)payload, client_ip);
             if (val < 0.0) {
                 const char *err = "Unknown metric";
@@ -111,7 +114,6 @@ int main(void)
 
     srand(time(NULL));
 
-    /* Classic Unix trick to reap children automatically (no zombies) */
     signal(SIGCHLD, SIG_IGN);
 
     srv_sock = socket(AF_INET, SOCK_STREAM, 0);
@@ -147,17 +149,17 @@ int main(void)
         }
 
         pid = fork();
-        if (pid < 0) {               /* fork failed */
+        if (pid < 0) {
             perror("fork");
             close(client_sock);
         }
-        else if (pid == 0) {         /* CHILD process */
+        else if (pid == 0) {         /* CHILD */
-            close(srv_sock);         /* child does not need the listening socket */
+            close(srv_sock);
             handle_client(client_sock, &client_addr);
             exit(0);
         }
-        else {                       /* PARENT process */
+        else {                       /* PARENT */
-            close(client_sock);      /* parent does not need the client socket */
+            close(client_sock);
         }
     }
 

src/c90/metric_server_fork_sub.c

@@ -0,0 +1,191 @@
+/* metric_server_fork_sub.c - STRICT C89/C90 multi-client metric server with SUBSCRIBE/PUSH */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <time.h>
+#include <signal.h>
+#include <errno.h>
+
+#define PORT     9999
+#define BACKLOG  10
+#define BUF_SIZE 1024
+
+#define MSG_PING        0x01
+#define MSG_PONG        0x02
+#define MSG_METRIC_REQ  0x03
+#define MSG_METRIC_RESP 0x04
+#define MSG_SUBSCRIBE   0x05
+#define MSG_PUSH        0x06
+#define MSG_ERROR       0xFF
+
+#define HEADER_SIZE 3
+
+static double get_metric(const char *name)
+{
+    if (strcmp(name, "cpu")     == 0) return  5.0 + (rand() % 9000)/100.0;
+    if (strcmp(name, "memory")  == 0) return 30.0 + (rand() % 5000)/100.0;
+    if (strcmp(name, "disk")    == 0) return 40.0 + (rand() % 5000)/100.0;
+    if (strcmp(name, "loadavg") == 0) return  0.5 + (rand() % 350)/100.0;
+    if (strcmp(name, "uptime")  == 0) return (double)(time(NULL) % 100000);
+    return -1.0;
+}
+
+static void send_message(int sock, unsigned char type,
+                         const void *payload, unsigned short len)
+{
+    unsigned char header[HEADER_SIZE];
+    header[0] = type;
+    header[1] = (len >> 8) & 0xFF;
+    header[2] = len & 0xFF;
+    write(sock, header, HEADER_SIZE);
+    if (len > 0)
+        write(sock, payload, len);
+}
+
+static int recv_exact(int sock, void *buf, int n)
+{
+    int total = 0;
+    while (total < n) {
+        int r = read(sock, (char *)buf + total, n - total);
+        if (r <= 0) return -1;
+        total += r;
+    }
+    return total;
+}
+
+static void handle_client(int client_sock, struct sockaddr_in *addr)
+{
+    unsigned char header[HEADER_SIZE];
+    unsigned char payload[BUF_SIZE];
+    char client_ip[INET_ADDRSTRLEN];
+    unsigned char type;
+    unsigned short len;
+    double val;
+    char *metric_name;
+    unsigned int interval_ms;
+    unsigned char name_len;
+
+    inet_ntop(AF_INET, &addr->sin_addr, client_ip, sizeof(client_ip));
+    printf("[+] Connected from %s:%d\n", client_ip, ntohs(addr->sin_port));
+
+    while (1) {
+        if (recv_exact(client_sock, header, HEADER_SIZE) != HEADER_SIZE)
+            break;
+
+        type = header[0];
+        len  = (header[1] << 8) | header[2];
+
+        if (len > 0) {
+            if (recv_exact(client_sock, payload, len) != len)
+                break;
+        }
+
+        if (type == MSG_PING) {
+            printf("  <- PING from %s\n", client_ip);
+            send_message(client_sock, MSG_PONG, NULL, 0);
+        }
+        else if (type == MSG_METRIC_REQ) {
+            payload[len] = '\0';
+            val = get_metric((char *)payload);
+            printf("  <- METRIC_REQ '%s' from %s\n", (char *)payload, client_ip);
+            if (val < 0.0) {
+                const char *err = "Unknown metric";
+                send_message(client_sock, MSG_ERROR, err, strlen(err));
+            } else {
+                send_message(client_sock, MSG_METRIC_RESP, &val, sizeof(double));
+            }
+        }
+        else if (type == MSG_SUBSCRIBE) {
+            name_len = payload[0];
+            payload[name_len + 1] = '\0';
+            metric_name = (char *)payload + 1;
+            interval_ms = (payload[name_len + 1] << 24) |
+                          (payload[name_len + 2] << 16) |
+                          (payload[name_len + 3] <<  8) |
+                           payload[name_len + 4];
+            printf("  -> SUBSCRIBE '%s' every %u ms from %s\n", metric_name, interval_ms, client_ip);
+
+            /* Simple push loop inside this child process */
+            while (1) {
+                val = get_metric(metric_name);
+                if (val < 0.0) break;
+
+                name_len = strlen(metric_name);
+                payload[0] = name_len;
+                memcpy(payload + 1, metric_name, name_len);
+                memcpy(payload + 1 + name_len, &val, sizeof(double));
+
+                send_message(client_sock, MSG_PUSH,
+                             payload, 1 + name_len + sizeof(double));
+
+                usleep(interval_ms * 1000);
+            }
+        }
+        else {
+            const char *err = "Unknown message type";
+            send_message(client_sock, MSG_ERROR, err, strlen(err));
+        }
+    }
+
+    close(client_sock);
+    printf("[-] Disconnected from %s\n", client_ip);
+}
+
+int main(void)
+{
+    int srv_sock, client_sock;
+    struct sockaddr_in server_addr, client_addr;
+    socklen_t client_len = sizeof(client_addr);
+    pid_t pid;
+
+    srand(time(NULL));
+    signal(SIGCHLD, SIG_IGN);
+
+    srv_sock = socket(AF_INET, SOCK_STREAM, 0);
+    if (srv_sock < 0) { perror("socket"); exit(1); }
+
+    server_addr.sin_family      = AF_INET;
+    server_addr.sin_addr.s_addr = INADDR_ANY;
+    server_addr.sin_port        = htons(PORT);
+
+    if (bind(srv_sock, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
+        perror("bind"); exit(1);
+    }
+    if (listen(srv_sock, BACKLOG) < 0) {
+        perror("listen"); exit(1);
+    }
+
+    printf("Metric server (fork() + SUBSCRIBE/PUSH) listening on port %d\n", PORT);
+    printf("Available metrics: cpu, memory, disk, loadavg, uptime\n");
+    printf("Commands: ping, get <metric>, sub <metric> <ms>\n\n");
+
+    while (1) {
+        client_sock = accept(srv_sock, (struct sockaddr *)&client_addr, &client_len);
+        if (client_sock < 0) {
+            if (errno == EINTR) continue;
+            perror("accept");
+            continue;
+        }
+
+        pid = fork();
+        if (pid < 0) {
+            perror("fork");
+            close(client_sock);
+        }
+        else if (pid == 0) {
+            close(srv_sock);
+            handle_client(client_sock, &client_addr);
+            exit(0);
+        }
+        else {
+            close(client_sock);
+        }
+    }
+
+    close(srv_sock);
+    return 0;
+}