Initial support for IPv6 (#8225)

- Merge rabit socket into XGBoost.
- Dask interface support.
- Add test to the socket.

src/collective/socket.cc

@@ -0,0 +1,94 @@
+/*!
+ * Copyright (c) 2022 by XGBoost Contributors
+ */
+#include "xgboost/collective/socket.h"
+
+#include <cstddef>       // std::size_t
+#include <cstdint>       // std::int32_t
+#include <cstring>       // std::memcpy, std::memset
+#include <system_error>  // std::error_code, std::system_category
+
+#if defined(__unix__) || defined(__APPLE__)
+#include <netdb.h>  // getaddrinfo, freeaddrinfo
+#endif              // defined(__unix__) || defined(__APPLE__)
+
+namespace xgboost {
+namespace collective {
+SockAddress MakeSockAddress(StringView host, in_port_t port) {
+  struct addrinfo hints;
+  std::memset(&hints, 0, sizeof(hints));
+  hints.ai_protocol = SOCK_STREAM;
+  struct addrinfo *res = nullptr;
+  int sig = getaddrinfo(host.c_str(), nullptr, &hints, &res);
+  if (sig != 0) {
+    return {};
+  }
+  if (res->ai_family == static_cast<std::int32_t>(SockDomain::kV4)) {
+    sockaddr_in addr;
+    std::memcpy(&addr, res->ai_addr, res->ai_addrlen);
+    addr.sin_port = htons(port);
+    auto v = SockAddrV4{addr};
+    freeaddrinfo(res);
+    return SockAddress{v};
+  } else if (res->ai_family == static_cast<std::int32_t>(SockDomain::kV6)) {
+    sockaddr_in6 addr;
+    std::memcpy(&addr, res->ai_addr, res->ai_addrlen);
+
+    addr.sin6_port = htons(port);
+    auto v = SockAddrV6{addr};
+    freeaddrinfo(res);
+    return SockAddress{v};
+  } else {
+    LOG(FATAL) << "Failed to get addr info for: " << host;
+  }
+
+  return SockAddress{};
+}
+
+SockAddrV4 SockAddrV4::Loopback() { return MakeSockAddress("127.0.0.1", 0).V4(); }
+SockAddrV4 SockAddrV4::InaddrAny() { return MakeSockAddress("0.0.0.0", 0).V4(); }
+
+SockAddrV6 SockAddrV6::Loopback() { return MakeSockAddress("::1", 0).V6(); }
+SockAddrV6 SockAddrV6::InaddrAny() { return MakeSockAddress("::", 0).V6(); }
+
+std::size_t TCPSocket::Send(StringView str) {
+  CHECK(!this->IsClosed());
+  CHECK_LT(str.size(), std::numeric_limits<std::int32_t>::max());
+  std::int32_t len = static_cast<std::int32_t>(str.size());
+  CHECK_EQ(this->SendAll(&len, sizeof(len)), sizeof(len)) << "Failed to send string length.";
+  auto bytes = this->SendAll(str.c_str(), str.size());
+  CHECK_EQ(bytes, str.size()) << "Failed to send string.";
+  return bytes;
+}
+
+std::size_t TCPSocket::Recv(std::string *p_str) {
+  CHECK(!this->IsClosed());
+  std::int32_t len;
+  CHECK_EQ(this->RecvAll(&len, sizeof(len)), sizeof(len)) << "Failed to recv string length.";
+  p_str->resize(len);
+  auto bytes = this->RecvAll(&(*p_str)[0], len);
+  CHECK_EQ(bytes, len) << "Failed to recv string.";
+  return bytes;
+}
+
+std::error_code Connect(SockAddress const &addr, TCPSocket *out) {
+  sockaddr const *addr_handle{nullptr};
+  socklen_t addr_len{0};
+  if (addr.IsV4()) {
+    addr_handle = reinterpret_cast<const sockaddr *>(&addr.V4().Handle());
+    addr_len = sizeof(addr.V4().Handle());
+  } else {
+    addr_handle = reinterpret_cast<const sockaddr *>(&addr.V6().Handle());
+    addr_len = sizeof(addr.V6().Handle());
+  }
+  auto socket = TCPSocket::Create(addr.Domain());
+  CHECK_EQ(static_cast<std::int32_t>(socket.Domain()), static_cast<std::int32_t>(addr.Domain()));
+  auto rc = connect(socket.Handle(), addr_handle, addr_len);
+  if (rc != 0) {
+    return std::error_code{errno, std::system_category()};
+  }
+  *out = std::move(socket);
+  return std::make_error_code(std::errc{});
+}
+}  // namespace collective
+}  // namespace xgboost