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LookupServer: Move parse_dns_name() -> DNSName::parse()

Browse source 
While at it, refactor it slightly.
This commit is contained in:
Sergey Bugaev 2021-02-14 15:10:39 +03:00 • committed by Andreas Kling
parent ae1e82fd2f
commit 42bc5f2cc1
3 changed files with 41 additions and 35 deletions
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33
Userland/Services/LookupServer/DNSName.cpp
View file

@ -1,4 +1,5 @@
/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021, Sergey Bugaev <bugaevc@serenityos.org>
* All rights reserved.
*
@ -36,4 +37,36 @@ DNSName::DNSName(const String& name)
m_name = name;
}
DNSName DNSName::parse(const u8* data, size_t& offset, size_t max_offset, size_t recursion_level)
{
if (recursion_level > 4)
return DNSName({});
StringBuilder builder;
while (true) {
if (offset >= max_offset)
return DNSName({});
u8 b = data[offset++];
if (b == '\0') {
// This terminates the name.
return builder.to_string();
} else if ((b & 0xc0) == 0xc0) {
// The two bytes tell us the offset when to continue from.
if (offset >= max_offset)
return DNSName({});
size_t dummy = (b & 0x3f) << 8 | data[offset++];
auto rest_of_name = parse(data, dummy, max_offset, recursion_level + 1);
builder.append(rest_of_name.as_string());
return builder.to_string();
} else {
// This is the length of a part.
if (offset + b >= max_offset)
return DNSName({});
builder.append((const char*)&data[offset], (size_t)b);
builder.append('.');
offset += b;
}
}
}
}

4
Userland/Services/LookupServer/DNSName.h
View file

@ -1,4 +1,5 @@
/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021, Sergey Bugaev <bugaevc@serenityos.org>
* All rights reserved.
*
@ -33,6 +34,9 @@ namespace LookupServer {
class DNSName {
public:
DNSName(const String&);
static DNSName parse(const u8* data, size_t& offset, size_t max_offset, size_t recursion_level = 0);
const String& as_string() const { return m_name; }
private:

39
Userland/Services/LookupServer/DNSPacket.cpp
View file

@ -26,6 +26,7 @@
*/
#include "DNSPacket.h"
#include "DNSName.h"
#include "DNSPacketHeader.h"
#include <AK/IPv4Address.h>
#include <AK/MemoryStream.h>
@ -108,8 +109,6 @@ ByteBuffer DNSPacket::to_byte_buffer() const
return stream.copy_into_contiguous_buffer();
}
static String parse_dns_name(const u8* data, size_t& offset, size_t max_offset, size_t recursion_level = 0);
class [[gnu::packed]] DNSRecordWithoutName {
public:
DNSRecordWithoutName() { }
@ -159,7 +158,7 @@ Optional<DNSPacket> DNSPacket::from_raw_packet(const u8* raw_data, size_t raw_si
size_t offset = sizeof(DNSPacketHeader);
for (u16 i = 0; i < header.question_count(); i++) {
auto name = parse_dns_name(raw_data, offset, raw_size);
auto name = DNSName::parse(raw_data, offset, raw_size);
struct RawDNSAnswerQuestion {
NetworkOrdered<u16> record_type;
NetworkOrdered<u16> class_code;
@ -174,7 +173,7 @@ Optional<DNSPacket> DNSPacket::from_raw_packet(const u8* raw_data, size_t raw_si
}
for (u16 i = 0; i < header.answer_count(); ++i) {
auto name = parse_dns_name(raw_data, offset, raw_size);
auto name = DNSName::parse(raw_data, offset, raw_size);
auto& record = *(const DNSRecordWithoutName*)(&raw_data[offset]);
@ -184,7 +183,7 @@ Optional<DNSPacket> DNSPacket::from_raw_packet(const u8* raw_data, size_t raw_si
if (record.type() == T_PTR) {
size_t dummy_offset = offset;
data = parse_dns_name(raw_data, dummy_offset, raw_size);
data = DNSName::parse(raw_data, dummy_offset, raw_size).as_string();
} else if (record.type() == T_A) {
data = { record.data(), record.data_length() };
} else {
@ -201,34 +200,4 @@ Optional<DNSPacket> DNSPacket::from_raw_packet(const u8* raw_data, size_t raw_si
return packet;
}
String parse_dns_name(const u8* data, size_t& offset, size_t max_offset, size_t recursion_level)
{
if (recursion_level > 4)
return {};
Vector<char, 128> buf;
while (offset < max_offset) {
u8 ch = data[offset];
if (ch == '\0') {
++offset;
break;
}
if ((ch & 0xc0) == 0xc0) {
if ((offset + 1) >= max_offset)
return {};
size_t dummy = (ch & 0x3f) << 8 | data[offset + 1];
offset += 2;
StringBuilder builder;
builder.append(buf.data(), buf.size());
auto okay = parse_dns_name(data, dummy, max_offset, recursion_level + 1);
builder.append(okay);
return builder.to_string();
}
for (size_t i = 0; i < ch; ++i)
buf.append(data[offset + i + 1]);
buf.append('.');
offset += ch + 1;
}
return String::copy(buf);
}
}