First commit

.gitignore

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+test/runner

LICENSE

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+Copyright (C) 2023 by 0x1eef <0x1eef@protonmail.com>
+
+Permission to use, copy, modify, and/or distribute this
+software for any purpose with or without fee is hereby
+granted.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS
+ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
+EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
+RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
+OF THIS SOFTWARE.

Makefile

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+SRCDIR = src
+INCDIR = include
+TESTDIR = test
+TESTBIN = $(TESTDIR)/runner
+
+CC = cc
+CFLAGS = -I$(INCDIR) -Wall -Wextra -pedantic
+
+test:
+	$(CC) $(CFLAGS) $(SRCDIR)/isinetaddr.c $(TESTDIR)/isinetaddr_test.c -o $(TESTBIN)
+	$(TESTBIN)
+
+.PHONY: test

README.md

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+## About
+
+isinetaddr is a simple C library that provides an interface that can
+be used to validate one or more IPv4 addresses.
+
+## Examples
+
+### IPv4
+
+The following example demonstrates the `isinetaddr` function with
+both valid and invalid inputs. The `isinetaddr` function returns 1
+when the input given is valid, and otherwise returns 0.
+
+```C
+#include <isinetaddr.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+const char *strings[] = {
+  "127.0.0.1", "1.1.1.1", "0.0.0.0",
+  "foobar", "0.0.0.0.0"
+};
+
+int
+main(void)
+{
+    const char *str;
+    const int i = sizeof(strings) / sizeof(strings[0]);
+    for (int j = 0; j < i; j++) {
+        str = strings[j];
+        if(isinetaddr(str)) {
+            printf("%s is a valid IPv4 address\n", str);
+        } else {
+            printf("%s is an invalid IPv4 address\n", str);
+        }
+    }
+    return EXIT_SUCCESS;
+}
+```
+
+When the above source code is compiled and run the output is
+expected to be as follows:
+
+```
+$ cc -Iinclude src/isinetaddr.c share/isinetaddr/examples/IPv4.c -o example
+$ ./example
+127.0.0.1 is a valid IPv4 address
+1.1.1.1 is a valid IPv4 address
+0.0.0.0 is a valid IPv4 address
+foobar is an invalid IPv4 address
+0.0.0.0.0 is an invalid IPv4 address
+```
+
+## Sources
+
+* [Source code (GitHub)](https://github.com/0x1eef/isinetaddr#readme)
+* [Source code (GitLab)](https://gitlab.com/0x1eef/isinetaddr#about)
+
+## <a id="license"> License </a>
+
+[BSD Zero Clause](https://choosealicense.com/licenses/0bsd/).
+<br>
+See [LICENSE](./LICENSE).

include/isinetaddr.h

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+#pragma once
+int isinetaddr(const char *str);

share/isinetaddr/examples/IPv4.c

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+#include <isinetaddr.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+const char *strings[] = {
+  "127.0.0.1", "1.1.1.1", "0.0.0.0",
+  "foobar", "0.0.0.0.0"
+};
+
+int
+main(void)
+{
+    const char *str;
+    const int i = sizeof(strings) / sizeof(strings[0]);
+    for (int j = 0; j < i; j++) {
+        str = strings[j];
+        if(isinetaddr(str)) {
+            printf("%s is a valid IPv4 address\n", str);
+        } else {
+            printf("%s is an invalid IPv4 address\n", str);
+        }
+    }
+    return EXIT_SUCCESS;
+}

src/isinetaddr.c

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+#include <ctype.h>
+#include <string.h>
+#include <stdlib.h>
+#include <isinetaddr.h>
+
+int
+isinetaddr(const char *str)
+{
+  char buf[4];
+  const char *err;
+  int i = 0, j = 0, k = 0;
+
+  for(int l = 0; l < (int)strnlen(str, 16); l++) {
+    if (str[l] == '.') {
+      strtonum(buf, 0, 255, &err);
+      if (err != NULL) {
+        return 0;
+      } else {
+        k = 0;
+        j++;
+        bzero(buf, 3);
+        buf[3] = '\0';
+      }
+    } else if (isdigit(str[l])) {
+      buf[k++] = str[l];
+      buf[k] = '\0';
+      i++;
+    } else {
+      return 0;
+    }
+  }
+  return j == 3 && i <= 12 ? 1 : 0;
+}

test/isinetaddr_test.c

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+#include <isinetaddr.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+int
+main(void) {
+  /* Assertions */
+  assert(isinetaddr("192.168.1.1") == 1);
+  assert(isinetaddr("0.0.0.0") == 1);
+  assert(isinetaddr("255.255.255.255") == 1);
+  assert(isinetaddr("123.45.67.89") == 1);
+  assert(isinetaddr("192.168.500.1") == 0);
+  assert(isinetaddr(".192.168.1.1") == 0);
+  assert(isinetaddr("192..168.1.1") == 0);
+  assert(isinetaddr("192.168.1.1.") == 0);
+  assert(isinetaddr("192.168.1.1..") == 0);
+  assert(isinetaddr("192.168.1.1a") == 0);
+  assert(isinetaddr("") == 0);
+  /* Record success */
+  printf("OK\n");
+  return EXIT_SUCCESS;
+}