Martin Slachta
58 lines
1.9 KiB
C++
58 lines
1.9 KiB
C++
#pragma once
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#include "ResolutionError.hpp"
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#include "tl/expected.hpp"
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#include <cstring>
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#include <netdb.h>
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#include <string>
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#include <sys/socket.h>
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namespace tw::net {
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/**
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* Turns a host name or an address literal into a socket address.
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*
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* `family` is the family of the socket the result will be given to. AF_INET6
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* asks for IPv4-only names as ::ffff: mapped addresses, so that one dual-stack
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* socket reaches both; AF_UNSPEC takes the name as it comes and suits addresses
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* that are only being validated, displayed or stored.
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*
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* Blocks for the length of a DNS round trip when the name is not already known,
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* so it belongs at connect time rather than anywhere periodic.
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*/
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inline tl::expected<sockaddr_storage, ResolutionError>
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resolve_host(const std::string& host, int port, sa_family_t family = AF_UNSPEC) {
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addrinfo hints {};
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hints.ai_family = family;
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hints.ai_socktype = SOCK_DGRAM;
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// AI_ADDRCONFIG is deliberately absent. Together with AF_INET6 it discards
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// every result on a host that carries no global IPv6 address, which is the
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// default state of a container on a bridge network.
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if(family == AF_INET6) {
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hints.ai_flags = AI_V4MAPPED | AI_ALL;
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}
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// Passing the port as the service spares us setting sin_port or sin6_port
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// by hand once the family of the answer is known.
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const std::string service = std::to_string(port);
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addrinfo* results = nullptr;
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const int rc = ::getaddrinfo(host.c_str(), service.c_str(), &hints, &results);
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if(rc != 0) {
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return tl::make_unexpected(ResolutionError::from_gai(rc));
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}
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// The list arrives ordered by RFC 6724, so the head is the address the
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// system would have picked for itself.
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sockaddr_storage storage {};
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std::memcpy(&storage, results->ai_addr, results->ai_addrlen);
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::freeaddrinfo(results);
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return storage;
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}
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}
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