From 574ef210268681aab4c6729cb7556793d89f4b5a Mon Sep 17 00:00:00 2001
From: Oxore <oxore@protonmail.com>
Date: Wed, 13 Dec 2023 00:20:34 +0300
Subject: Impl ip addr parser

---
 client.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 72 insertions(+), 3 deletions(-)

diff --git a/client.c b/client.c
index c5491f6..007bf2d 100644
--- a/client.c
+++ b/client.c
@@ -1,13 +1,82 @@
 // Initially based on https://stackoverflow.com/a/35570418
 
 #include <netinet/in.h>
+#include <stdbool.h>
+#include <stdint.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
 #include <unistd.h>
 
-int main(void)
+static inline bool IsDigit(char c) { return c >= '0' && c <= '9'; }
+
+static unsigned ParseAddress(char const *str, FILE *log_stream)
+{
+    unsigned addr = 0, byte_counter = 0, byte = 0, digits_counter = 0;
+    for (size_t i = 0;; i++) {
+        char const c = str[i];
+        if (c == '\0') {
+            if (byte_counter != 3) {
+                fprintf(log_stream, "Invalid address specified: %u bytes of 4 expected are specified\n", byte_counter + 1);
+                return INADDR_NONE;
+            }
+            if (digits_counter == 0) {
+                fprintf(log_stream, "Invalid address specified: no digits on byte %u\n", byte_counter + 1);
+                return INADDR_NONE;
+            }
+            addr |= byte << (8 * (3 - byte_counter));
+            break;
+        } else if (IsDigit(c)) {
+            digits_counter++;
+            if (digits_counter > 3) {
+                fprintf(log_stream, "Invalid address specified: too many digits for byte %u\n", byte_counter + 1);
+                return INADDR_NONE;
+            }
+            byte = byte * 10 + (c - '0');
+            if (byte > UINT8_MAX) {
+                fprintf(log_stream, "Invalid address specified: too big number for byte %u\n", byte_counter + 1);
+                return INADDR_NONE;
+            }
+        } else if (c == '.') {
+            if (digits_counter == 0) {
+                fprintf(log_stream, "Invalid address specified: no digits on byte %u\n", byte_counter + 1);
+                return INADDR_NONE;
+            }
+            digits_counter = 0;
+            addr |= byte << (8 * (3 - byte_counter));
+            byte = 0;
+            byte_counter++;
+            if (byte_counter > 3) {
+                fprintf(log_stream, "Invalid address specified: unexpected dot after 4th byte\n");
+                return INADDR_NONE;
+            }
+        } else {
+            fprintf(log_stream, "Invalid address specified: char '%c' (0x%02x) is not allowed\n", c, c);
+            return INADDR_NONE;
+        }
+    }
+    if (addr == INADDR_NONE) {
+        fprintf(log_stream, "Invalid address specified\n");
+    }
+    return addr;
+}
+
+int main(int const argc, char *const argv[])
 {
+    if (argc < 3) {
+        fprintf(stderr, "Usage: %s <address> <port>\n", argv[0]);
+        return 1;
+    }
+    unsigned const addr = ParseAddress(argv[1], stderr);
+    if (addr == INADDR_NONE) {
+        return 1;
+    }
+    int const port = atoi(argv[2]);
+    if (port <= 0 || port > UINT16_MAX) {
+        fprintf(stderr, "Invalid port specifed\n");
+        return 1;
+    }
     int const fd = socket(AF_INET, SOCK_DGRAM, 0);
     if (fd < 0) {
         perror("socket failed");
@@ -15,8 +84,8 @@ int main(void)
     }
     struct sockaddr_in const serveraddr = {
         .sin_family = AF_INET,
-        .sin_port = htons(50037u),
-        .sin_addr.s_addr = htonl(INADDR_LOOPBACK),
+        .sin_port = htons(port),
+        .sin_addr.s_addr = htonl(addr),
     };
     for (int i = 0; i < 4; i++) {
         ssize_t const ret = sendto(
-- 
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