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LookupServer+LibC: Add support for reverse DNS lookups via gethostbyaddr().

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LookupServer can now take two types of requests:

* L: Lookup
* R: Reverse lookup

The /bin/host program now does a reverse lookup if the input string is a
valid IPv4 address. :^)
This commit is contained in:
Andreas Kling 2019-06-06 05:35:03 +02:00
parent d03505bc29
commit 01f1333856
4 changed files with 156 additions and 46 deletions
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52
Servers/LookupServer/main.cpp
View file

@ -24,7 +24,7 @@
#define C_IN 1
static Vector<IPv4Address> lookup(const String& hostname, bool& did_timeout, const String& DNS_IP);
static Vector<String> lookup(const String& hostname, bool& did_timeout, const String& DNS_IP, unsigned short record_type);
static String parse_dns_name(const byte*, int& offset, int max_offset);
int main(int argc, char**argv)
@ -98,19 +98,28 @@ int main(int argc, char**argv)
client_buffer[nrecv] = '\0';
auto hostname = String(client_buffer, nrecv, Chomp);
char lookup_type = client_buffer[0];
if (lookup_type != 'L' && lookup_type != 'R') {
dbgprintf("LookupServer: Invalid lookup_type '%c'\n", lookup_type);
close(client_fd);
continue;
}
auto hostname = String(client_buffer + 1, nrecv - 1, Chomp);
dbgprintf("LookupServer: Got request for '%s' (using IP %s)\n",
hostname.characters(),
DNS_IP.characters());
Vector<IPv4Address> addresses;
Vector<String> responses;
if (!hostname.is_empty()) {
bool did_timeout;
int retries = 3;
do {
did_timeout = false;
addresses = lookup(hostname, did_timeout, DNS_IP);
if (lookup_type == 'L')
responses = lookup(hostname, did_timeout, DNS_IP, T_A);
else if (lookup_type == 'R')
responses = lookup(hostname, did_timeout, DNS_IP, T_PTR);
if (!did_timeout)
break;
} while (--retries);
@ -121,15 +130,15 @@ int main(int argc, char**argv)
}
}
if (addresses.is_empty()) {
if (responses.is_empty()) {
int nsent = write(client_fd, "Not found.\n", sizeof("Not found.\n"));
if (nsent < 0)
perror("write");
close(client_fd);
continue;
}
for (auto& address : addresses) {
auto line = String::format("%s\n", address.to_string().characters());
for (auto& response : responses) {
auto line = String::format("%s\n", response.characters());
int nsent = write(client_fd, line.characters(), line.length());
if (nsent < 0) {
perror("write");
@ -147,10 +156,8 @@ static word get_next_id()
return ++s_next_id;
}
Vector<IPv4Address> lookup(const String& hostname, bool& did_timeout, const String& DNS_IP)
Vector<String> lookup(const String& hostname, bool& did_timeout, const String& DNS_IP, unsigned short record_type)
{
// FIXME: First check if it's an IP address in a string!
DNSPacket request_header;
request_header.set_id(get_next_id());
request_header.set_is_query();
@ -170,7 +177,7 @@ Vector<IPv4Address> lookup(const String& hostname, bool& did_timeout, const Stri
stream << part;
}
stream << '\0';
stream << htons(T_A);
stream << htons(record_type);
stream << htons(C_IN);
stream.snip();
}
@ -249,22 +256,31 @@ Vector<IPv4Address> lookup(const String& hostname, bool& did_timeout, const Stri
auto question = parse_dns_name((const byte*)response_header.payload(), offset, nrecv);
offset += 4;
Vector<IPv4Address> addresses;
Vector<String> addresses;
for (word i = 0; i < response_header.answer_count(); ++i) {
auto& record = *(const DNSRecord*)(&((const byte*)response_header.payload())[offset]);
auto ipv4_address = IPv4Address((const byte*)record.data());
dbgprintf("LookupServer: Answer #%u: (question: %s), type=%u, ttl=%u, length=%u, data=%s\n",
dbgprintf("LookupServer: Answer #%u: (question: %s), type=%u, ttl=%u, length=%u, data=",
i,
question.characters(),
record.type(),
record.ttl(),
record.data_length(),
ipv4_address.to_string().characters());
record.data_length());
offset += sizeof(DNSRecord) + record.data_length();
if (record.type() == T_A)
addresses.append(ipv4_address);
if (record.type() == T_PTR) {
int dummy = 0;
auto name = parse_dns_name((const byte*)record.data(), dummy, record.data_length());
dbgprintf("%s\n", name.characters());
addresses.append(name);
} else if (record.type() == T_A) {
auto ipv4_address = IPv4Address((const byte*)record.data());
dbgprintf("%s\n", ipv4_address.to_string().characters());
addresses.append(ipv4_address.to_string());
} else {
dbgprintf("(unimplemented)\n");
dbgprintf("LookupServer: FIXME: Handle record type %u\n", record.type());
}
// FIXME: Parse some other record types perhaps?
}