From 6f6cbeba8069f8570a8838ca711a9809c76450fb Mon Sep 17 00:00:00 2001
From: Max Kellermann <mk@cm4all.com>
Date: Fri, 12 Jan 2024 12:09:41 +0100
Subject: [PATCH] net/SocketDescriptor: add Send()/Receive() overloads with
 iovec

---
 src/net/MsgHdr.hxx                 | 62 ++++++++++++++++++++++++++++++
 src/net/SocketDescriptor.cxx       | 14 +++++++
 src/net/SocketDescriptor.hxx       | 21 ++++++++--
 src/net/UniqueSocketDescriptor.hxx |  5 +--
 4 files changed, 94 insertions(+), 8 deletions(-)
 create mode 100644 src/net/MsgHdr.hxx

diff --git a/src/net/MsgHdr.hxx b/src/net/MsgHdr.hxx
new file mode 100644
index 000000000..a013fb78b
--- /dev/null
+++ b/src/net/MsgHdr.hxx
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: BSD-2-Clause
+// Copyright CM4all GmbH
+// author: Max Kellermann <mk@cm4all.com>
+
+#pragma once
+
+#include "SocketAddress.hxx"
+#include "StaticSocketAddress.hxx"
+
+#include <span>
+
+#include <sys/socket.h>
+
+inline constexpr struct msghdr
+MakeMsgHdr(std::span<const struct iovec> iov) noexcept
+{
+	struct msghdr mh{};
+	mh.msg_iov = const_cast<struct iovec *>(iov.data());
+	mh.msg_iovlen = iov.size();
+	return mh;
+}
+
+/**
+ * Construct a struct msghdr.  The parameters are `const` because that
+ * is needed for sending; but for receiving, these buffers must
+ * actually be writable.
+ */
+inline constexpr struct msghdr
+MakeMsgHdr(SocketAddress name, std::span<const struct iovec> iov,
+	   std::span<const std::byte> control) noexcept
+{
+	auto mh = MakeMsgHdr(iov);
+	mh.msg_name = const_cast<struct sockaddr *>(name.GetAddress());
+	mh.msg_namelen = name.GetSize();
+	mh.msg_control = const_cast<std::byte *>(control.data());
+	mh.msg_controllen = control.size();
+	return mh;
+}
+
+inline constexpr struct msghdr
+MakeMsgHdr(StaticSocketAddress &name, std::span<const struct iovec> iov,
+	   std::span<const std::byte> control) noexcept
+{
+	auto mh = MakeMsgHdr(iov);
+	mh.msg_name = name;
+	mh.msg_namelen = name.GetCapacity();
+	mh.msg_control = const_cast<std::byte *>(control.data());
+	mh.msg_controllen = control.size();
+	return mh;
+}
+
+inline constexpr struct msghdr
+MakeMsgHdr(struct sockaddr_storage &name, std::span<const struct iovec> iov,
+	   std::span<const std::byte> control) noexcept
+{
+	auto mh = MakeMsgHdr(iov);
+	mh.msg_name = static_cast<struct sockaddr *>(static_cast<void *>(&name));
+	mh.msg_namelen = sizeof(name);
+	mh.msg_control = const_cast<std::byte *>(control.data());
+	mh.msg_controllen = control.size();
+	return mh;
+}
diff --git a/src/net/SocketDescriptor.cxx b/src/net/SocketDescriptor.cxx
index b86a07dfa..f255bd885 100644
--- a/src/net/SocketDescriptor.cxx
+++ b/src/net/SocketDescriptor.cxx
@@ -6,6 +6,7 @@
 #include "StaticSocketAddress.hxx"
 #include "IPv4Address.hxx"
 #include "IPv6Address.hxx"
+#include "MsgHdr.hxx"
 
 #ifdef _WIN32
 #include <ws2tcpip.h>
@@ -423,6 +424,13 @@ SocketDescriptor::Receive(struct msghdr &msg, int flags) const noexcept
 	return ::recvmsg(Get(), &msg, flags);
 }
 
+ssize_t
+SocketDescriptor::Receive(std::span<const struct iovec> v, int flags) const noexcept
+{
+	auto msg = MakeMsgHdr(v);
+	return Receive(msg, flags);
+}
+
 ssize_t
 SocketDescriptor::Send(std::span<const std::byte> src, int flags) const noexcept
 {
@@ -443,6 +451,12 @@ SocketDescriptor::Send(const struct msghdr &msg, int flags) const noexcept
 	return ::sendmsg(Get(), &msg, flags);
 }
 
+ssize_t
+SocketDescriptor::Send(std::span<const struct iovec> v, int flags) const noexcept
+{
+	return Send(MakeMsgHdr(v), flags);
+}
+
 ssize_t
 SocketDescriptor::ReadNoWait(std::span<std::byte> dest) const noexcept
 {
diff --git a/src/net/SocketDescriptor.hxx b/src/net/SocketDescriptor.hxx
index 029c4ed83..0aeb50fe7 100644
--- a/src/net/SocketDescriptor.hxx
+++ b/src/net/SocketDescriptor.hxx
@@ -1,8 +1,7 @@
 // SPDX-License-Identifier: BSD-2-Clause
 // author: Max Kellermann <max.kellermann@gmail.com>
 
-#ifndef SOCKET_DESCRIPTOR_HXX
-#define SOCKET_DESCRIPTOR_HXX
+#pragma once
 
 #include "Features.hxx"
 
@@ -19,6 +18,8 @@
 #include <winsock2.h> // for SOCKET, INVALID_SOCKET
 #endif
 
+struct msghdr;
+struct iovec;
 class SocketAddress;
 class StaticSocketAddress;
 class IPv4Address;
@@ -309,6 +310,12 @@ public:
 	[[nodiscard]]
 	ssize_t Receive(struct msghdr &msg, int flags=0) const noexcept;
 
+	/**
+	 * Wrapper for recvmsg().
+	 */
+	[[nodiscard]]
+	ssize_t Receive(std::span<const struct iovec> v, int flags=0) const noexcept;
+
 	/**
 	 * Wrapper for send().
 	 *
@@ -325,6 +332,14 @@ public:
 	[[nodiscard]]
 	ssize_t Send(const struct msghdr &msg, int flags=0) const noexcept;
 
+	/**
+	 * Wrapper for sendmsg().
+	 *
+	 * MSG_NOSIGNAL is implicitly added (if available).
+	 */
+	[[nodiscard]]
+	ssize_t Send(std::span<const struct iovec> v, int flags=0) const noexcept;
+
 	[[nodiscard]]
 	ssize_t Read(std::span<std::byte> dest) const noexcept {
 		return Receive(dest);
@@ -383,5 +398,3 @@ public:
 };
 
 static_assert(std::is_trivial<SocketDescriptor>::value, "type is not trivial");
-
-#endif
diff --git a/src/net/UniqueSocketDescriptor.hxx b/src/net/UniqueSocketDescriptor.hxx
index a6809aef5..159f80222 100644
--- a/src/net/UniqueSocketDescriptor.hxx
+++ b/src/net/UniqueSocketDescriptor.hxx
@@ -1,8 +1,7 @@
 // SPDX-License-Identifier: BSD-2-Clause
 // author: Max Kellermann <max.kellermann@gmail.com>
 
-#ifndef UNIQUE_SOCKET_DESCRIPTOR_SOCKET_HXX
-#define UNIQUE_SOCKET_DESCRIPTOR_SOCKET_HXX
+#pragma once
 
 #include "SocketDescriptor.hxx"
 
@@ -90,5 +89,3 @@ public:
 	}
 #endif
 };
-
-#endif