Impl mutual exchange of UDP messages

2 files changed, 148 insertions, 31 deletions

diff --git a/client.c b/client.c
index 007bf2d..8f4d5ff 100644
--- a/client.c
+++ b/client.c
@@ -3,17 +3,21 @@
 #include <netinet/in.h>
 #include <stdbool.h>
 #include <stdint.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
 #include <unistd.h>
 
+static unsigned char udp_buffer[UINT16_MAX];
+
 static inline bool IsDigit(char c) { return c >= '0' && c <= '9'; }
 
-static unsigned ParseAddress(char const *str, FILE *log_stream)
+static uint32_t ParseAddress(char const *str, FILE *log_stream)
 {
-    unsigned addr = 0, byte_counter = 0, byte = 0, digits_counter = 0;
+    uint32_t addr = 0;
+    unsigned byte_counter = 0, byte = 0, digits_counter = 0;
     for (size_t i = 0;; i++) {
         char const c = str[i];
         if (c == '\0') {
@@ -74,7 +78,7 @@ int main(int const argc, char *const argv[])
     }
     int const port = atoi(argv[2]);
     if (port <= 0 || port > UINT16_MAX) {
-        fprintf(stderr, "Invalid port specifed\n");
+        fprintf(stderr, "Invalid port specified\n");
         return 1;
     }
     int const fd = socket(AF_INET, SOCK_DGRAM, 0);
@@ -87,14 +91,29 @@ int main(int const argc, char *const argv[])
         .sin_port = htons(port),
         .sin_addr.s_addr = htonl(addr),
     };
-    for (int i = 0; i < 4; i++) {
-        ssize_t const ret = sendto(
-                fd, "hello", 5, 0, (struct sockaddr const *)&serveraddr, sizeof(serveraddr));
-        if (ret < 0) {
-            perror("sendto failed");
-            break;
-        }
-        printf("message sent\n");
+    ssize_t const ret = sendto(
+            fd, "\x2a", 1, 0, (struct sockaddr const *)&serveraddr, sizeof(serveraddr));
+    if (ret < 0) {
+        perror("sendto failed");
+        return 1;
     }
+    printf("message sent\n");
+    struct sockaddr_in source_address;
+    socklen_t source_address_len = sizeof(source_address);
+    int const length = recvfrom(
+            fd,
+            udp_buffer,
+            sizeof(udp_buffer) - 1,
+            0,
+            (struct sockaddr*)&source_address,
+            &source_address_len);
+    (void) length;
+    uint32_t const addr2 = ntohl(source_address.sin_addr.s_addr);
+    uint8_t const a0 = addr2 >> 24;
+    uint8_t const a1 = addr2 >> 16;
+    uint8_t const a2 = addr2 >> 8;
+    uint8_t const a3 = addr2;
+    uint16_t const port2 = ntohs(source_address.sin_port);
+    printf("Received: %u from %u.%u.%u.%u:%u\n", udp_buffer[0], a0, a1, a2, a3, port2);
     close(fd);
 }
diff --git a/server.c b/server.c
index 7288eca..ffb7c42 100644
--- a/server.c
+++ b/server.c
@@ -1,11 +1,90 @@
 // Initially based on https://stackoverflow.com/a/35570418
 
+#include <errno.h>
+#include <fcntl.h>
 #include <netinet/in.h>
+#include <poll.h>
+#include <stdbool.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/socket.h>
 #include <unistd.h>
 
+enum frame_type {
+    FT_NONE = 0,
+    FT_HELLO = 42,
+};
+
+struct frame {
+    uint32_t addr;
+    uint16_t port;
+    enum frame_type type;
+};
+
+static unsigned char udp_buffer[UINT16_MAX];
+
+static int ReceiveFrame(int const fd, struct frame *const frame)
+{
+    frame->type = FT_NONE;
+    struct sockaddr_in source_address;
+    socklen_t source_address_len = sizeof(source_address);
+    int const length = recvfrom(
+            fd,
+            udp_buffer,
+            sizeof(udp_buffer) - 1,
+            0,
+            (struct sockaddr*)&source_address,
+            &source_address_len);
+    if (length == 0) {
+        return -EWOULDBLOCK;
+    }
+    if (length < 0) {
+        int const err = errno;
+        if (err != EWOULDBLOCK) {
+            perror("recvfrom failed");
+        }
+        return -err;
+    }
+    uint32_t const addr = ntohl(source_address.sin_addr.s_addr);
+    uint32_t const port = ntohs(source_address.sin_port);
+    if (length) {
+        unsigned char frame_type = udp_buffer[0];
+        if (frame_type == FT_HELLO) {
+            *frame = (struct frame){
+                .addr = addr,
+                .port = port,
+                .type = frame_type,
+            };
+        }
+    }
+    uint8_t const a0 = addr >> 24;
+    uint8_t const a1 = addr >> 16;
+    uint8_t const a2 = addr >> 8;
+    uint8_t const a3 = addr;
+    printf("Received %u from %u.%u.%u.%u:%u\n", udp_buffer[0], a0, a1, a2, a3, port);
+    return 0;
+}
+
+static int SendFrame(int const fd, struct frame const *const frame)
+{
+    udp_buffer[0] = frame->type;
+    struct sockaddr_in const addr = {
+        .sin_family = AF_INET,
+        .sin_port = htons(frame->port),
+        .sin_addr.s_addr = htonl(frame->addr),
+    };
+    ssize_t const ret = sendto(
+            fd, udp_buffer, 1, 0, (struct sockaddr const *)&addr, sizeof(addr));
+    if (ret < 0) {
+        int const err = errno;
+        perror("sendto failed");
+        return -err;
+    }
+    printf("message sent\n");
+    return 0;
+}
+
 int main(void)
 {
     int const fd = socket(AF_INET, SOCK_DGRAM, 0);
@@ -13,6 +92,7 @@ int main(void)
         perror("socket failed");
         return 1;
     }
+    fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_NONBLOCK);
     struct sockaddr_in const serveraddr = {
         .sin_family = AF_INET,
         .sin_port = htons(50037u),
@@ -22,28 +102,46 @@ int main(void)
         perror("bind failed");
         return 1;
     }
+    struct pollfd fds[1] = { { .fd = fd, .events = POLLIN, }, };
     for (;;) {
-        struct sockaddr_in source_address;
-        char buffer[200];
-        socklen_t source_address_len = sizeof(source_address);
-        int const length = recvfrom(
-                fd,
-                buffer,
-                sizeof(buffer) - 1,
-                0,
-                (struct sockaddr*)&source_address,
-                &source_address_len);
-        if (length < 0) {
-            perror("recvfrom failed");
-            break;
+        int const timeout_msecs = 500;
+        int const pollret = poll(fds, sizeof(fds)/sizeof(*fds), timeout_msecs);
+        if (pollret > 0) {
+            if (fds[0].revents & POLLIN) {
+                while (1) {
+                    struct frame frame = { .type = FT_NONE, };
+                    int const ret = ReceiveFrame(fd, &frame);
+                    if (ret) {
+                        break;
+                    }
+                    if (frame.type == FT_HELLO) {
+                        SendFrame(fd, &frame);
+                    }
+                }
+            }
+            if (fds[0].revents & POLLRDNORM) {
+                printf("POLLRDNORM, ignoring...\n");
+            }
+            if (fds[0].revents & POLLRDBAND) {
+                printf("POLLRDBAND, ignoring...\n");
+            }
+            if (fds[0].revents & POLLPRI) {
+                printf("POLLPRI, ignoring...\n");
+            }
+            if (fds[0].revents & POLLPRI) {
+                printf("POLLPRI, ignoring...\n");
+            }
+            if (fds[0].revents & POLLHUP) {
+                printf("POLLHUP, ignoring...\n");
+            }
+            if (fds[0].revents & POLLERR) {
+                printf("POLLERR, ignoring...\n");
+            }
+            if (fds[0].revents & POLLNVAL) {
+                printf("POLLNVAL, exiting...\n");
+                return 1;
+            }
         }
-        uint32_t const addr = ntohl(source_address.sin_addr.s_addr);
-        uint8_t const a0 = addr >> 24;
-        uint8_t const a1 = addr >> 16;
-        uint8_t const a2 = addr >> 8;
-        uint8_t const a3 = addr;
-        printf("%d bytes: '%.*s' from %u.%u.%u.%u:%u\n",
-                length, (int)length, buffer, a0, a1, a2, a3, source_address.sin_port);
     }
     close(fd);
 }