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ladybird/Userland/Libraries/LibC/netdb.cpp
Timothy Flynn 7c6b5ed161 LibIPC+LibC: Add and use a helper to encode/decoder container sizes 
While refactoring the IPC encoders and decoders for fallibility, the
inconsistency in which we transfer container sizes was a frequent thing
to trip over. We currently transfer sizes as any of i32, u32, and u64.
This adds a helper to transfer sizes in one consistent way.

Two special cases here are DeprecatedString and Vector, whose encoding
is depended upon by netdb, so that is also updated here.
2023-01-04 20:13:54 +01:00

858 lines
25 KiB
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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Assertions.h>
#include <AK/ByteBuffer.h>
#include <AK/DeprecatedString.h>
#include <AK/ScopeGuard.h>
#include <Kernel/Net/IPv4.h>
#include <arpa/inet.h>
#include <errno.h>
#include <netdb.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
extern "C" {
#ifdef NO_TLS
int h_errno;
#else
__thread int h_errno;
#endif
static hostent __gethostbyname_buffer;
static in_addr_t __gethostbyname_address;
static in_addr_t* __gethostbyname_address_list_buffer[2];
static char* __gethostbyname_alias_list_buffer[1];
static hostent __gethostbyaddr_buffer;
static in_addr_t* __gethostbyaddr_address_list_buffer[2];
static char* __gethostbyaddr_alias_list_buffer[1];
// IPCCompiler depends on LibC. Because of this, it cannot be compiled
// before LibC is. However, the lookup magic can only be obtained from the
// endpoint itself if IPCCompiler has compiled the IPC file, so this creates
// a chicken-and-egg situation. Because of this, the LookupServer endpoint magic
// is hardcoded here.
// Keep the name synchronized with LookupServer/LookupServer.ipc.
static constexpr u32 lookup_server_endpoint_magic = "LookupServer"sv.hash();
// Get service entry buffers and file information for the getservent() family of functions.
static FILE* services_file = nullptr;
static char const* services_path = "/etc/services";
static bool fill_getserv_buffers(char const* line, ssize_t read);
static servent __getserv_buffer;
static DeprecatedString __getserv_name_buffer;
static DeprecatedString __getserv_protocol_buffer;
static int __getserv_port_buffer;
static Vector<ByteBuffer> __getserv_alias_list_buffer;
static Vector<char*> __getserv_alias_list;
static bool keep_service_file_open = false;
static ssize_t service_file_offset = 0;
// Get protocol entry buffers and file information for the getprotent() family of functions.
static FILE* protocols_file = nullptr;
static char const* protocols_path = "/etc/protocols";
static bool fill_getproto_buffers(char const* line, ssize_t read);
static protoent __getproto_buffer;
static DeprecatedString __getproto_name_buffer;
static Vector<ByteBuffer> __getproto_alias_list_buffer;
static Vector<char*> __getproto_alias_list;
static int __getproto_protocol_buffer;
static bool keep_protocols_file_open = false;
static ssize_t protocol_file_offset = 0;
static int connect_to_lookup_server()
{
int fd = socket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0);
if (fd < 0) {
perror("socket");
return -1;
}
sockaddr_un address {
AF_LOCAL,
"/tmp/portal/lookup"
};
if (connect(fd, (sockaddr const*)&address, sizeof(address)) < 0) {
perror("connect_to_lookup_server");
close(fd);
return -1;
}
return fd;
}
static DeprecatedString gethostbyname_name_buffer;
hostent* gethostbyname(char const* name)
{
h_errno = 0;
auto ipv4_address = IPv4Address::from_string({ name, strlen(name) });
if (ipv4_address.has_value()) {
gethostbyname_name_buffer = ipv4_address.value().to_deprecated_string();
__gethostbyname_buffer.h_name = const_cast<char*>(gethostbyname_name_buffer.characters());
__gethostbyname_alias_list_buffer[0] = nullptr;
__gethostbyname_buffer.h_aliases = __gethostbyname_alias_list_buffer;
__gethostbyname_buffer.h_addrtype = AF_INET;
new (&__gethostbyname_address) IPv4Address(ipv4_address.value());
__gethostbyname_address_list_buffer[0] = &__gethostbyname_address;
__gethostbyname_address_list_buffer[1] = nullptr;
__gethostbyname_buffer.h_addr_list = (char**)__gethostbyname_address_list_buffer;
__gethostbyname_buffer.h_length = 4;
return &__gethostbyname_buffer;
}
int fd = connect_to_lookup_server();
if (fd < 0) {
h_errno = TRY_AGAIN;
return nullptr;
}
auto close_fd_on_exit = ScopeGuard([fd] {
close(fd);
});
auto name_length = strlen(name);
VERIFY(name_length <= NumericLimits<i32>::max());
struct [[gnu::packed]] {
u32 message_size;
u32 endpoint_magic;
i32 message_id;
u32 name_length;
} request_header = {
(u32)(sizeof(request_header) - sizeof(request_header.message_size) + name_length),
lookup_server_endpoint_magic,
1,
static_cast<u32>(name_length),
};
if (auto nsent = write(fd, &request_header, sizeof(request_header)); nsent < 0) {
h_errno = TRY_AGAIN;
return nullptr;
} else if (nsent != sizeof(request_header)) {
h_errno = NO_RECOVERY;
return nullptr;
}
if (auto nsent = write(fd, name, name_length); nsent < 0) {
h_errno = TRY_AGAIN;
return nullptr;
} else if (static_cast<size_t>(nsent) != name_length) {
h_errno = NO_RECOVERY;
return nullptr;
}
struct [[gnu::packed]] {
u32 message_size;
u32 endpoint_magic;
i32 message_id;
i32 code;
u32 addresses_count;
} response_header;
if (auto nreceived = read(fd, &response_header, sizeof(response_header)); nreceived < 0) {
h_errno = TRY_AGAIN;
return nullptr;
} else if (nreceived != sizeof(response_header)) {
h_errno = NO_RECOVERY;
return nullptr;
}
if (response_header.endpoint_magic != lookup_server_endpoint_magic || response_header.message_id != 2) {
h_errno = NO_RECOVERY;
return nullptr;
}
if (response_header.code != 0) {
h_errno = NO_RECOVERY;
return nullptr;
}
if (response_header.addresses_count == 0) {
h_errno = HOST_NOT_FOUND;
return nullptr;
}
i32 response_length;
if (auto nreceived = read(fd, &response_length, sizeof(response_length)); nreceived < 0) {
h_errno = TRY_AGAIN;
return nullptr;
} else if (nreceived != sizeof(response_length)
|| response_length != sizeof(__gethostbyname_address)) {
h_errno = NO_RECOVERY;
return nullptr;
}
if (auto nreceived = read(fd, &__gethostbyname_address, response_length); nreceived < 0) {
h_errno = TRY_AGAIN;
return nullptr;
} else if (nreceived != response_length) {
h_errno = NO_RECOVERY;
return nullptr;
}
gethostbyname_name_buffer = name;
__gethostbyname_buffer.h_name = const_cast<char*>(gethostbyname_name_buffer.characters());
__gethostbyname_alias_list_buffer[0] = nullptr;
__gethostbyname_buffer.h_aliases = __gethostbyname_alias_list_buffer;
__gethostbyname_buffer.h_addrtype = AF_INET;
__gethostbyname_address_list_buffer[0] = &__gethostbyname_address;
__gethostbyname_address_list_buffer[1] = nullptr;
__gethostbyname_buffer.h_addr_list = (char**)__gethostbyname_address_list_buffer;
__gethostbyname_buffer.h_length = 4;
return &__gethostbyname_buffer;
}
static DeprecatedString gethostbyaddr_name_buffer;
hostent* gethostbyaddr(void const* addr, socklen_t addr_size, int type)
{
h_errno = 0;
if (type != AF_INET) {
errno = EAFNOSUPPORT;
return nullptr;
}
if (addr_size < sizeof(in_addr)) {
errno = EINVAL;
return nullptr;
}
int fd = connect_to_lookup_server();
if (fd < 0) {
h_errno = TRY_AGAIN;
return nullptr;
}
auto close_fd_on_exit = ScopeGuard([fd] {
close(fd);
});
in_addr_t const& in_addr = ((const struct in_addr*)addr)->s_addr;
struct [[gnu::packed]] {
u32 message_size;
u32 endpoint_magic;
i32 message_id;
i32 address_length;
} request_header = {
sizeof(request_header) - sizeof(request_header.message_size) + sizeof(in_addr),
lookup_server_endpoint_magic,
3,
sizeof(in_addr),
};
if (auto nsent = write(fd, &request_header, sizeof(request_header)); nsent < 0) {
h_errno = TRY_AGAIN;
return nullptr;
} else if (nsent != sizeof(request_header)) {
h_errno = NO_RECOVERY;
return nullptr;
}
if (auto nsent = write(fd, &in_addr, sizeof(in_addr)); nsent < 0) {
h_errno = TRY_AGAIN;
return nullptr;
} else if (nsent != sizeof(in_addr)) {
h_errno = TRY_AGAIN;
return nullptr;
}
struct [[gnu::packed]] {
u32 message_size;
u32 endpoint_magic;
i32 message_id;
i32 code;
u32 name_length;
} response_header;
if (auto nreceived = read(fd, &response_header, sizeof(response_header)); nreceived < 0) {
h_errno = TRY_AGAIN;
return nullptr;
} else if (nreceived != sizeof(response_header)) {
h_errno = NO_RECOVERY;
return nullptr;
}
if (response_header.endpoint_magic != lookup_server_endpoint_magic
|| response_header.message_id != 4
|| response_header.code != 0) {
h_errno = NO_RECOVERY;
return nullptr;
}
char* buffer;
auto string_impl = StringImpl::create_uninitialized(response_header.name_length, buffer);
if (auto nreceived = read(fd, buffer, response_header.name_length); nreceived < 0) {
h_errno = TRY_AGAIN;
return nullptr;
} else if (static_cast<u32>(nreceived) != response_header.name_length) {
h_errno = NO_RECOVERY;
return nullptr;
}
gethostbyaddr_name_buffer = move(string_impl);
__gethostbyaddr_buffer.h_name = buffer;
__gethostbyaddr_alias_list_buffer[0] = nullptr;
__gethostbyaddr_buffer.h_aliases = __gethostbyaddr_alias_list_buffer;
__gethostbyaddr_buffer.h_addrtype = AF_INET;
// FIXME: Should we populate the hostent's address list here with a sockaddr_in for the provided host?
__gethostbyaddr_address_list_buffer[0] = nullptr;
__gethostbyaddr_buffer.h_addr_list = (char**)__gethostbyaddr_address_list_buffer;
__gethostbyaddr_buffer.h_length = 4;
return &__gethostbyaddr_buffer;
}
struct servent* getservent()
{
// If the services file is not open, attempt to open it and return null if it fails.
if (!services_file) {
services_file = fopen(services_path, "r");
if (!services_file) {
perror("error opening services file");
return nullptr;
}
}
if (fseek(services_file, service_file_offset, SEEK_SET) != 0) {
perror("error seeking file");
fclose(services_file);
return nullptr;
}
char* line = nullptr;
size_t len = 0;
ssize_t read;
auto free_line_on_exit = ScopeGuard([line] {
if (line) {
free(line);
}
});
// Read lines from services file until an actual service name is found.
do {
read = getline(&line, &len, services_file);
service_file_offset += read;
if (read > 0 && (line[0] >= 65 && line[0] <= 122)) {
break;
}
} while (read != -1);
if (read == -1) {
fclose(services_file);
services_file = nullptr;
service_file_offset = 0;
return nullptr;
}
servent* service_entry = nullptr;
if (!fill_getserv_buffers(line, read))
return nullptr;
__getserv_buffer.s_name = const_cast<char*>(__getserv_name_buffer.characters());
__getserv_buffer.s_port = htons(__getserv_port_buffer);
__getserv_buffer.s_proto = const_cast<char*>(__getserv_protocol_buffer.characters());
__getserv_alias_list.clear_with_capacity();
__getserv_alias_list.ensure_capacity(__getserv_alias_list_buffer.size() + 1);
for (auto& alias : __getserv_alias_list_buffer)
__getserv_alias_list.unchecked_append(reinterpret_cast<char*>(alias.data()));
__getserv_alias_list.unchecked_append(nullptr);
__getserv_buffer.s_aliases = __getserv_alias_list.data();
service_entry = &__getserv_buffer;
if (!keep_service_file_open) {
endservent();
}
return service_entry;
}
struct servent* getservbyname(char const* name, char const* protocol)
{
if (name == nullptr)
return nullptr;
bool previous_file_open_setting = keep_service_file_open;
setservent(1);
struct servent* current_service = nullptr;
auto service_file_handler = ScopeGuard([previous_file_open_setting] {
if (!previous_file_open_setting) {
endservent();
}
});
while (true) {
current_service = getservent();
if (current_service == nullptr)
break;
else if (!protocol && strcmp(current_service->s_name, name) == 0)
break;
else if (strcmp(current_service->s_name, name) == 0 && strcmp(current_service->s_proto, protocol) == 0)
break;
}
return current_service;
}
struct servent* getservbyport(int port, char const* protocol)
{
bool previous_file_open_setting = keep_service_file_open;
setservent(1);
struct servent* current_service = nullptr;
auto service_file_handler = ScopeGuard([previous_file_open_setting] {
if (!previous_file_open_setting) {
endservent();
}
});
while (true) {
current_service = getservent();
if (current_service == nullptr)
break;
else if (!protocol && current_service->s_port == port)
break;
else if (current_service->s_port == port && (strcmp(current_service->s_proto, protocol) == 0))
break;
}
return current_service;
}
void setservent(int stay_open)
{
if (!services_file) {
services_file = fopen(services_path, "r");
if (!services_file) {
perror("error opening services file");
return;
}
}
rewind(services_file);
keep_service_file_open = stay_open;
service_file_offset = 0;
}
void endservent()
{
if (!services_file) {
return;
}
fclose(services_file);
services_file = nullptr;
}
// Fill the service entry buffer with the information contained
// in the currently read line, returns true if successful,
// false if failure occurs.
static bool fill_getserv_buffers(char const* line, ssize_t read)
{
// Splitting the line by tab delimiter and filling the servent buffers name, port, and protocol members.
auto split_line = StringView(line, read).replace(" "sv, "\t"sv, ReplaceMode::All).split('\t');
// This indicates an incorrect file format.
// Services file entries should always at least contain
// name and port/protocol, separated by tabs.
if (split_line.size() < 2) {
warnln("getservent(): malformed services file");
return false;
}
__getserv_name_buffer = split_line[0];
auto port_protocol_split = DeprecatedString(split_line[1]).split('/');
if (port_protocol_split.size() < 2) {
warnln("getservent(): malformed services file");
return false;
}
auto number = port_protocol_split[0].to_int();
if (!number.has_value())
return false;
__getserv_port_buffer = number.value();
// Remove any annoying whitespace at the end of the protocol.
__getserv_protocol_buffer = port_protocol_split[1].replace(" "sv, ""sv, ReplaceMode::All).replace("\t"sv, ""sv, ReplaceMode::All).replace("\n"sv, ""sv, ReplaceMode::All);
__getserv_alias_list_buffer.clear();
// If there are aliases for the service, we will fill the alias list buffer.
if (split_line.size() > 2 && !split_line[2].starts_with('#')) {
for (size_t i = 2; i < split_line.size(); i++) {
if (split_line[i].starts_with('#')) {
break;
}
auto alias = split_line[i].to_byte_buffer();
if (alias.try_append("\0", sizeof(char)).is_error())
return false;
__getserv_alias_list_buffer.append(move(alias));
}
}
return true;
}
struct protoent* getprotoent()
{
// If protocols file isn't open, attempt to open and return null on failure.
if (!protocols_file) {
protocols_file = fopen(protocols_path, "r");
if (!protocols_file) {
perror("error opening protocols file");
return nullptr;
}
}
if (fseek(protocols_file, protocol_file_offset, SEEK_SET) != 0) {
perror("error seeking protocols file");
fclose(protocols_file);
return nullptr;
}
char* line = nullptr;
size_t len = 0;
ssize_t read;
auto free_line_on_exit = ScopeGuard([line] {
if (line) {
free(line);
}
});
do {
read = getline(&line, &len, protocols_file);
protocol_file_offset += read;
if (read > 0 && (line[0] >= 65 && line[0] <= 122)) {
break;
}
} while (read != -1);
if (read == -1) {
fclose(protocols_file);
protocols_file = nullptr;
protocol_file_offset = 0;
return nullptr;
}
struct protoent* protocol_entry = nullptr;
if (!fill_getproto_buffers(line, read))
return nullptr;
__getproto_buffer.p_name = const_cast<char*>(__getproto_name_buffer.characters());
__getproto_buffer.p_proto = __getproto_protocol_buffer;
__getproto_alias_list.clear_with_capacity();
__getproto_alias_list.ensure_capacity(__getproto_alias_list_buffer.size() + 1);
for (auto& alias : __getproto_alias_list_buffer)
__getproto_alias_list.unchecked_append(reinterpret_cast<char*>(alias.data()));
__getserv_alias_list.unchecked_append(nullptr);
__getproto_buffer.p_aliases = __getproto_alias_list.data();
protocol_entry = &__getproto_buffer;
if (!keep_protocols_file_open)
endprotoent();
return protocol_entry;
}
struct protoent* getprotobyname(char const* name)
{
bool previous_file_open_setting = keep_protocols_file_open;
setprotoent(1);
struct protoent* current_protocol = nullptr;
auto protocol_file_handler = ScopeGuard([previous_file_open_setting] {
if (!previous_file_open_setting) {
endprotoent();
}
});
while (true) {
current_protocol = getprotoent();
if (current_protocol == nullptr)
break;
else if (strcmp(current_protocol->p_name, name) == 0)
break;
}
return current_protocol;
}
struct protoent* getprotobynumber(int proto)
{
bool previous_file_open_setting = keep_protocols_file_open;
setprotoent(1);
struct protoent* current_protocol = nullptr;
auto protocol_file_handler = ScopeGuard([previous_file_open_setting] {
if (!previous_file_open_setting) {
endprotoent();
}
});
while (true) {
current_protocol = getprotoent();
if (current_protocol == nullptr)
break;
else if (current_protocol->p_proto == proto)
break;
}
return current_protocol;
}
void setprotoent(int stay_open)
{
if (!protocols_file) {
protocols_file = fopen(protocols_path, "r");
if (!protocols_file) {
perror("setprotoent(): error opening protocols file");
return;
}
}
rewind(protocols_file);
keep_protocols_file_open = stay_open;
protocol_file_offset = 0;
}
void endprotoent()
{
if (!protocols_file) {
return;
}
fclose(protocols_file);
protocols_file = nullptr;
}
static bool fill_getproto_buffers(char const* line, ssize_t read)
{
DeprecatedString string_line = DeprecatedString(line, read);
auto split_line = string_line.replace(" "sv, "\t"sv, ReplaceMode::All).split('\t');
// This indicates an incorrect file format. Protocols file entries should
// always have at least a name and a protocol.
if (split_line.size() < 2) {
warnln("getprotoent(): malformed protocols file");
return false;
}
__getproto_name_buffer = split_line[0];
auto number = split_line[1].to_int();
if (!number.has_value())
return false;
__getproto_protocol_buffer = number.value();
__getproto_alias_list_buffer.clear();
// If there are aliases for the protocol, we will fill the alias list buffer.
if (split_line.size() > 2 && !split_line[2].starts_with('#')) {
for (size_t i = 2; i < split_line.size(); i++) {
if (split_line[i].starts_with('#'))
break;
auto alias = split_line[i].to_byte_buffer();
if (alias.try_append("\0", sizeof(char)).is_error())
return false;
__getproto_alias_list_buffer.append(move(alias));
}
}
return true;
}
int getaddrinfo(char const* __restrict node, char const* __restrict service, const struct addrinfo* __restrict hints, struct addrinfo** __restrict res)
{
*res = nullptr;
if (hints && hints->ai_family != AF_INET && hints->ai_family != AF_UNSPEC)
return EAI_FAMILY;
if (!node) {
if (hints && hints->ai_flags & AI_PASSIVE)
node = "0.0.0.0";
else
node = "127.0.0.1";
}
auto host_ent = gethostbyname(node);
if (!host_ent)
return EAI_FAIL;
char const* proto = nullptr;
if (hints && hints->ai_socktype) {
switch (hints->ai_socktype) {
case SOCK_STREAM:
proto = "tcp";
break;
case SOCK_DGRAM:
proto = "udp";
break;
default:
return EAI_SOCKTYPE;
}
}
long port;
int socktype;
servent* svc_ent = nullptr;
if (!hints || (hints->ai_flags & AI_NUMERICSERV) == 0) {
svc_ent = getservbyname(service, proto);
}
if (!svc_ent) {
if (service) {
char* end;
port = htons(strtol(service, &end, 10));
if (*end)
return EAI_FAIL;
} else {
port = htons(0);
}
if (hints && hints->ai_socktype != 0)
socktype = hints->ai_socktype;
else
socktype = SOCK_STREAM;
} else {
port = svc_ent->s_port;
socktype = strcmp(svc_ent->s_proto, "tcp") ? SOCK_STREAM : SOCK_DGRAM;
}
addrinfo* first_info = nullptr;
addrinfo* prev_info = nullptr;
for (int host_index = 0; host_ent->h_addr_list[host_index]; host_index++) {
sockaddr_in* sin = new sockaddr_in;
sin->sin_family = AF_INET;
sin->sin_port = port;
memcpy(&sin->sin_addr.s_addr, host_ent->h_addr_list[host_index], host_ent->h_length);
addrinfo* info = new addrinfo;
info->ai_flags = 0;
info->ai_family = AF_INET;
info->ai_socktype = socktype;
info->ai_protocol = PF_INET;
info->ai_addrlen = sizeof(*sin);
info->ai_addr = reinterpret_cast<sockaddr*>(sin);
if (hints && hints->ai_flags & AI_CANONNAME)
info->ai_canonname = strdup(host_ent->h_name);
else
info->ai_canonname = nullptr;
info->ai_next = nullptr;
if (!first_info)
first_info = info;
if (prev_info)
prev_info->ai_next = info;
prev_info = info;
}
if (first_info) {
*res = first_info;
return 0;
} else
return EAI_NONAME;
}
void freeaddrinfo(struct addrinfo* res)
{
if (res) {
delete reinterpret_cast<sockaddr_in*>(res->ai_addr);
free(res->ai_canonname);
freeaddrinfo(res->ai_next);
delete res;
}
}
char const* gai_strerror(int errcode)
{
switch (errcode) {
case EAI_ADDRFAMILY:
return "no address for this address family available";
case EAI_AGAIN:
return "name server returned temporary failure";
case EAI_BADFLAGS:
return "invalid flags";
case EAI_FAIL:
return "name server returned permanent failure";
case EAI_FAMILY:
return "unsupported address family";
case EAI_MEMORY:
return "out of memory";
case EAI_NODATA:
return "no address available";
case EAI_NONAME:
return "node or service is not known";
case EAI_SERVICE:
return "service not available";
case EAI_SOCKTYPE:
return "unsupported socket type";
case EAI_SYSTEM:
return "system error";
case EAI_OVERFLOW:
return "buffer too small";
default:
return "invalid error code";
}
}
int getnameinfo(const struct sockaddr* __restrict addr, socklen_t addrlen, char* __restrict host, socklen_t hostlen, char* __restrict serv, socklen_t servlen, int flags)
{
if (addr->sa_family != AF_INET || addrlen < sizeof(sockaddr_in))
return EAI_FAMILY;
sockaddr_in const* sin = reinterpret_cast<sockaddr_in const*>(addr);
if (host && hostlen > 0) {
if (flags != 0)
dbgln("getnameinfo flags are not implemented: {:#x}", flags);
if (!inet_ntop(AF_INET, &sin->sin_addr, host, hostlen)) {
if (errno == ENOSPC)
return EAI_OVERFLOW;
else
return EAI_SYSTEM;
}
}
if (serv && servlen > 0) {
if (snprintf(serv, servlen, "%d", (int)ntohs(sin->sin_port)) > (int)servlen)
return EAI_OVERFLOW;
}
return 0;
}
void herror(char const* s)
{
dbgln("herror(): {}: {}", s, hstrerror(h_errno));
warnln("{}: {}", s, hstrerror(h_errno));
}
char const* hstrerror(int err)
{
switch (err) {
case HOST_NOT_FOUND:
return "The specified host is unknown.";
case NO_DATA:
return "The requested name is valid but does not have an IP address.";
case NO_RECOVERY:
return "A nonrecoverable name server error occurred.";
case TRY_AGAIN:
return "A temporary error occurred on an authoritative name server. Try again later.";
default:
return "Unknown error.";
}
}
}
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