Make improvements

- Clean up sigaction() code
- Add a port scanner example
- Introduce a ParseCidr() API
- Clean up our futex abstraction code
- Fix a harmless integer overflow in ParseIp()
- Use kernel semaphores on NetBSD to make threads much faster

net/http/parsecidr.c

@@ -0,0 +1,67 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ 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.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/str/str.h"
+#include "net/http/ip.h"
+
+/**
+ * Parse IPv4 network address.
+ *
+ * For example, a router address might be `10.10.10.1/24` in which case
+ * the IP address word `0x0a0a0a01` would be returned, whose CIDR would
+ * be 24. That means your IP address is on a network with 24 bits which
+ * converts to a netmask `0xffffff00` by using `1u << (32 - res.cidr)`.
+ * You may specify the IP address portion as an integer. As an example,
+ * the value `168430081/1` would be the same as `10.10.10.1/1`
+ *
+ * @param n if -1 implies strlen
+ * @return ip is uint32 IPv4 address, or -1 on failure
+ * @return cidr is number of bits in network, on interval [1,32]; it
+ *     defaults to 32; if the return ip is -1 then cidr is undefined
+ */
+struct Cidr ParseCidr(const char *s, size_t n) {
+  size_t i;
+  const char *p;
+  struct Cidr c;
+  if (n == -1) n = s ? strlen(s) : 0;
+  if ((p = strchr(s, '/'))) {
+    if ((c.addr = ParseIp(s, (i = p - s))) != -1) {
+      c.cidr = 0;
+      for (++i; i < n; ++i) {
+        if (isdigit(s[i])) {
+          c.cidr *= 10;
+          c.cidr += s[i] - '0';
+          if (c.cidr > 32) {
+            c.cidr = -1;
+            break;
+          }
+        } else {
+          c.cidr = -1;
+          break;
+        }
+      }
+      if (c.cidr <= 0) {
+        c.addr = -1;
+      }
+    }
+  } else {
+    c.addr = ParseIp(s, n);
+    c.cidr = 32;
+  }
+  return c;
+}