liblinux++

commit f82e20dac4380c99f50519fdddb90b2af2d6733f
parent c0a85970509d1ab9424cb7d8aaa2ac17956af869
Author: Henry Wilson <henry@henryandlizzy.uk>
Date:   Sat, 10 Jan 2026 02:03:35 +0000

tcp-listen: Read port number from cmdline.

Diffstat:
M
cat.cpp
 | 
4
+++-
M
linux.hpp
 | 
4
+++-
M
tcp-listen.cpp
 | 
84
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---

3 files changed, 87 insertions(+), 5 deletions(-)
diff --git a/cat.cpp b/cat.cpp
@@ -20,7 +20,9 @@ static void cat(file fd)
 
 int main(int argc, char* argv[])
 {
-	for (int i = 1; i < argc; ++i)
+	if (argc <= 1)
+		cat(stdin);
+	else for (int i = 1; i < argc; ++i)
 	{
 		auto res = openat(AT_FDCWD, argv[i], 0, O_RDONLY);
 		if (!res)
diff --git a/linux.hpp b/linux.hpp
@@ -163,9 +163,11 @@ struct c_str
 
 		return p - str;
 	}
+	char const* begin() { return str; }
+	char const* end() { return begin() + length(); }
 
 private:
-	[[maybe_unused]] char const* str;
+	char const* str;
 };
 
 [[noreturn]]
diff --git a/tcp-listen.cpp b/tcp-listen.cpp
@@ -1,11 +1,89 @@
 #include "linux.hpp"
 
+struct reader
+{
+	reader(c_str in) : s{in.begin()} {}
+	bool peek(char& out)
+	{
+		if (peeked)
+		{
+			out = buf;
+			return true;
+		}
+		assert(s);
+		if (not *s)
+			return false;
+		out = buf = *s++;
+		peeked = true;
+		return true;
+	}
+	void pop()
+	{
+		assert(peeked);
+		peeked = false;
+	}
+
+private:
+	char const* s;
+	bool peeked = false;
+	char buf;
+};
+
+bool isdigit(char c)
+{
+	return '0' <= c and c <= '9';
+}
+
+bool decimal(reader& r, uint64_t& out)
+{
+	char c;
+	if (not r.peek(c))
+		return false;
+	if (not isdigit(c))
+		return false;
+	r.pop();
+	uint64_t val = c - '0';
+	while (r.peek(c) and isdigit(c))
+	{
+		r.pop();
+		val = val * 10 + c - '0';
+	}
+	out = val;
+	return true;
+}
+
+void test(c_str in, uint64_t expect)
+{
+	reader r{in};
+	uint64_t x;
+	assert(decimal(r, x));
+	assert(x == expect);
+}
+
+#define tst(x) test(#x, x##ull)
+
 int main(int argc, char* argv[], char* envp[])
 {
-	if (argc < 2)
+	tst(0);
+	tst(1);
+	tst(9);
+	tst(10);
+	tst(11);
+	tst(9001);
+	test("130AAXX1", 130);
+	tst(18446744073709551615);
+
+	if (argc <= 2)
 		return 1;
+	reader rdr{argv[1]};
+	uint64_t port;
+	if (not decimal(rdr, port))
+		return 2;
+	if (port > 65535)
+		return 3;
+
 	file sock = *socket(2/*AF_INET*/, 1/*SOCK_STREAM*/, 0/*IPPROTO_IP*/);
-	in_addr addr{1337, 0/*IN_ADDR_ANY*/};
+	in_addr addr{static_cast<uint16_t>(port), 0/*IN_ADDR_ANY*/};
 	*bind(sock, addr);
 	*listen(sock, 1);
 	socklen_t addr_len = sizeof(addr);
@@ -14,5 +92,5 @@ int main(int argc, char* argv[], char* envp[])
 	*dup(conn, stdout);
 	*close(conn);
 	*close(sock);
-	*execve(argv[1], argv+1, envp);
+	*execve(argv[2], argv+2, envp);
 }