net/LocalSocketAddress: new class wrapping struct sockaddr_un

src/net/LocalSocketAddress.cxx

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: BSD-2-Clause
+// author: Max Kellermann <max.kellermann@gmail.com>
+
+#include "LocalSocketAddress.hxx"
+
+const char *
+LocalSocketAddress::GetLocalPath() const noexcept
+{
+	const auto raw = GetLocalRaw();
+	return !raw.empty() &&
+		/* must be an absolute path */
+		raw.front() == '/' &&
+		/* must be null-terminated and there must not be any
+		   other null byte */
+		raw.find('\0') == raw.size() - 1
+		? raw.data()
+		: nullptr;
+}

src/net/LocalSocketAddress.hxx

@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: BSD-2-Clause
+// author: Max Kellermann <max.kellermann@gmail.com>
+
+#pragma once
+
+#include "SocketAddress.hxx" // IWYU pragma: export
+
+#include <algorithm> // for std::copy()
+#include <stdexcept> // for std::length_error
+#include <string_view>
+
+#include <sys/un.h>
+
+/**
+ * An OO wrapper for struct sockaddr_un.
+ */
+class LocalSocketAddress {
+	friend class SocketDescriptor;
+
+public:
+	typedef SocketAddress::size_type size_type;
+
+private:
+	size_type size;
+	struct sockaddr_un address;
+
+public:
+	constexpr LocalSocketAddress() noexcept = default;
+
+	constexpr explicit LocalSocketAddress(std::string_view path) noexcept
+		:address{} {
+		SetLocal(path);
+	}
+
+	constexpr operator SocketAddress() const noexcept {
+		return SocketAddress{*this, size};
+	}
+
+	constexpr operator struct sockaddr *() noexcept {
+		return (struct sockaddr *)(void *)&address;
+	}
+
+	constexpr operator const struct sockaddr *() const noexcept {
+		return (const struct sockaddr *)(const void *)&address;
+	}
+
+	constexpr size_type GetCapacity() const noexcept {
+		return sizeof(address);
+	}
+
+	constexpr size_type GetSize() const noexcept {
+		return size;
+	}
+
+	constexpr int GetFamily() const noexcept {
+		return address.sun_family;
+	}
+
+	constexpr bool IsDefined() const noexcept {
+		return GetFamily() != AF_UNSPEC;
+	}
+
+	constexpr void Clear() noexcept {
+		address.sun_family = AF_UNSPEC;
+	}
+
+	/**
+	 * @see SocketAddress::GetLocalRaw()
+	 */
+	constexpr std::string_view GetLocalRaw() const noexcept {
+		if (GetFamily() != AF_LOCAL)
+			return {};
+
+		const auto start = (const char *)&address;
+		const auto path = address.sun_path;
+		const size_t header_size = path - start;
+		if (size < size_type(header_size))
+			/* malformed address */
+			return {};
+
+		return {path, size - header_size};
+	}
+
+	/**
+	 * @see SocketAddress::GetLocalPath()
+	 */
+	[[nodiscard]] [[gnu::pure]]
+	const char *GetLocalPath() const noexcept;
+
+	/**
+	 * Make this a "local" address (UNIX domain socket).  If the path
+	 * begins with a '@', then the rest specifies an "abstract" local
+	 * address.
+	 */
+	constexpr LocalSocketAddress &SetLocal(std::string_view path) {
+		const bool is_abstract = path.starts_with('@');
+
+		/* sun_path must be null-terminated unless it's an abstract
+		   socket */
+		const size_t path_length = path.size() + !is_abstract;
+
+		if (path_length > sizeof(address.sun_path))
+			throw std::length_error{"Path is too long"};
+
+		size = sizeof(address) - sizeof(address.sun_path) + path_length;
+
+		address.sun_family = AF_LOCAL;
+		auto out = std::copy(path.begin(), path.end(), address.sun_path);
+		if (is_abstract)
+			address.sun_path[0] = 0;
+		else
+			*out = 0;
+
+		return *this;
+	}
+
+	[[nodiscard]] [[gnu::pure]]
+	std::span<const std::byte> GetSteadyPart() const noexcept;
+
+	[[nodiscard]] [[gnu::pure]]
+	bool operator==(SocketAddress other) const noexcept {
+		return static_cast<const SocketAddress>(*this) == other;
+	}
+
+	[[nodiscard]] [[gnu::pure]]
+	bool operator!=(SocketAddress other) const noexcept {
+		return !(*this == other);
+	}
+};

src/net/meson.build

@@ -27,6 +27,7 @@ conf.set('HAVE_UN', have_local_socket)
 if have_local_socket
   conf.set('HAVE_STRUCT_UCRED', compiler.has_header_symbol('sys/socket.h', 'struct ucred') and compiler.has_header_symbol('sys/socket.h', 'SO_PEERCRED'))
   conf.set('HAVE_GETPEEREID', compiler.has_function('getpeereid'))
+  net_sources += 'LocalSocketAddress.cxx'
 endif
 
 if not have_tcp and not have_local_socket

test/net/TestLocalSocketAddress.cxx

@@ -2,12 +2,44 @@
 // author: Max Kellermann <max.kellermann@gmail.com>
 
 #include "net/AllocatedSocketAddress.hxx"
+#include "net/LocalSocketAddress.hxx"
 #include "net/ToString.hxx"
 
 #include <gtest/gtest.h>
 
 #include <sys/un.h>
 
+TEST(LocalSocketAddress, Path1)
+{
+	const char *path = "/run/foo/bar.socket";
+	LocalSocketAddress a;
+	a.SetLocal(path);
+	EXPECT_TRUE(a.IsDefined());
+	EXPECT_EQ(a.GetFamily(), AF_LOCAL);
+	EXPECT_EQ(ToString(a), path);
+	EXPECT_STREQ(a.GetLocalPath(), path);
+
+	const struct sockaddr *const sa = a;
+	const auto &sun = *(const struct sockaddr_un *)sa;
+	EXPECT_STREQ(sun.sun_path, path);
+	EXPECT_EQ(sun.sun_path + strlen(path) + 1, (const char *)sa + a.GetSize());
+}
+
+TEST(LocalSocketAddress, Path2)
+{
+	static constexpr const char *path = "/run/foo/bar.socket";
+	static constexpr LocalSocketAddress a{path};
+	EXPECT_TRUE(a.IsDefined());
+	EXPECT_EQ(a.GetFamily(), AF_LOCAL);
+	EXPECT_EQ(ToString(a), path);
+	EXPECT_STREQ(a.GetLocalPath(), path);
+
+	const struct sockaddr *const sa = a;
+	const auto &sun = *(const struct sockaddr_un *)sa;
+	EXPECT_STREQ(sun.sun_path, path);
+	EXPECT_EQ(sun.sun_path + strlen(path) + 1, (const char *)sa + a.GetSize());
+}
+
 TEST(LocalSocketAddress, Path)
 {
 	const char *path = "/run/foo/bar.socket";
@@ -17,6 +49,7 @@ TEST(LocalSocketAddress, Path)
 	EXPECT_TRUE(a.IsDefined());
 	EXPECT_EQ(a.GetFamily(), AF_LOCAL);
 	EXPECT_EQ(ToString(a), path);
+	EXPECT_STREQ(a.GetLocalPath(), path);
 
 	const auto &sun = *(const struct sockaddr_un *)a.GetAddress();
 	EXPECT_STREQ(sun.sun_path, path);
@@ -25,6 +58,27 @@ TEST(LocalSocketAddress, Path)
 
 #ifdef __linux__
 
+TEST(LocalSocketAddress, Abstract1)
+{
+	const char *path = "@foo.bar";
+	LocalSocketAddress a;
+	a.SetLocal(path);
+	EXPECT_TRUE(a.IsDefined());
+	EXPECT_EQ(a.GetFamily(), AF_LOCAL);
+	EXPECT_EQ(ToString(a), path);
+	EXPECT_EQ(a.GetLocalPath(), nullptr);
+
+	const struct sockaddr *const sa = a;
+	const auto &sun = *(const struct sockaddr_un *)sa;
+
+	/* Linux's abstract sockets start with a null byte, ... */
+	EXPECT_EQ(sun.sun_path[0], 0);
+
+	/* ... but are not null-terminated */
+	EXPECT_EQ(memcmp(sun.sun_path + 1, path + 1, strlen(path) - 1), 0);
+	EXPECT_EQ(sun.sun_path + strlen(path), (const char *)sa + a.GetSize());
+}
+
 TEST(LocalSocketAddress, Abstract)
 {
 	const char *path = "@foo.bar";
@@ -34,6 +88,7 @@ TEST(LocalSocketAddress, Abstract)
 	EXPECT_TRUE(a.IsDefined());
 	EXPECT_EQ(a.GetFamily(), AF_LOCAL);
 	EXPECT_EQ(ToString(a), path);
+	EXPECT_EQ(a.GetLocalPath(), nullptr);
 
 	const auto &sun = *(const struct sockaddr_un *)a.GetAddress();