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std.Io.net.HostName: implement DNS name expansion

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This commit is contained in:
Andrew Kelley 2025-10-02 20:45:16 -07:00
parent b08f1d0e2a
commit 88693a56fc
1 changed files with 44 additions and 52 deletions
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96
lib/std/Io/net/HostName.zig
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@ -51,6 +51,7 @@ pub const LookupError = error{
ResolvConfParseFailed,
InvalidDnsARecord,
InvalidDnsAAAARecord,
InvalidDnsCnameRecord,
NameServerFailure,
} || Io.Timestamp.Error || IpAddress.BindError || Io.File.OpenError || Io.File.Reader.Error || Io.Cancelable;
@ -381,16 +382,8 @@ fn lookupDns(io: Io, lookup_canon_name: []const u8, rc: *const ResolvConf, optio
addresses_len += 1;
},
std.posix.RR.CNAME => {
_ = &canonical_name;
@panic("TODO");
//var tmp: [256]u8 = undefined;
//// Returns len of compressed name. strlen to get canon name.
//_ = try posix.dn_expand(packet, record.data, &tmp);
//const canon_name = mem.sliceTo(&tmp, 0);
//if (isValidHostName(canon_name)) {
// ctx.canon.items.len = 0;
// try ctx.canon.appendSlice(gpa, canon_name);
//}
_, canonical_name = expand(record.packet, record.data_off, options.canonical_name_buffer) catch
return error.InvalidDnsCnameRecord;
},
else => continue,
};
@ -525,51 +518,50 @@ fn writeResolutionQuery(q: *[280]u8, op: u4, dname: []const u8, class: u8, ty: u
return n;
}
pub const ExpandDomainNameError = error{InvalidDnsPacket};
pub const ExpandError = error{InvalidDnsPacket} || InitError;
pub fn expandDomainName(
msg: []const u8,
comp_dn: []const u8,
exp_dn: []u8,
) ExpandDomainNameError!usize {
// This implementation is ported from musl libc.
// A more idiomatic "ziggy" implementation would be welcome.
var p = comp_dn.ptr;
var len: usize = std.math.maxInt(usize);
const end = msg.ptr + msg.len;
if (p == end or exp_dn.len == 0) return error.InvalidDnsPacket;
var dest = exp_dn.ptr;
const dend = dest + @min(exp_dn.len, 254);
// detect reference loop using an iteration counter
var i: usize = 0;
while (i < msg.len) : (i += 2) {
// loop invariants: p<end, dest<dend
if ((p[0] & 0xc0) != 0) {
if (p + 1 == end) return error.InvalidDnsPacket;
const j = @as(usize, p[0] & 0x3f) << 8 | p[1];
if (len == std.math.maxInt(usize)) len = @intFromPtr(p) + 2 - @intFromPtr(comp_dn.ptr);
if (j >= msg.len) return error.InvalidDnsPacket;
p = msg.ptr + j;
} else if (p[0] != 0) {
if (dest != exp_dn.ptr) {
dest[0] = '.';
dest += 1;
}
var j = p[0];
p += 1;
if (j >= @intFromPtr(end) - @intFromPtr(p) or j >= @intFromPtr(dend) - @intFromPtr(dest)) {
return error.InvalidDnsPacket;
}
while (j != 0) {
j -= 1;
dest[0] = p[0];
dest += 1;
p += 1;
/// Decompresses a DNS name.
///
/// Returns number of bytes consumed from `packet` starting at `i`,
/// along with the expanded `HostName`.
///
/// Asserts `buffer` is has length at least `max_len`.
pub fn expand(noalias packet: []const u8, start_i: usize, noalias dest_buffer: []u8) ExpandError!struct { usize, HostName } {
const dest = dest_buffer[0..max_len];
var i = start_i;
var dest_i: usize = 0;
var len: ?usize = null;
// Detect reference loop using an iteration counter.
for (0..packet.len / 2) |_| {
if (i >= packet.len) return error.InvalidDnsPacket;
const c = packet[i];
if ((c & 0xc0) != 0) {
if (i + 1 >= packet.len) return error.InvalidDnsPacket;
const j: usize = (@as(usize, c & 0x3F) << 8) | packet[i + 1];
if (j >= packet.len) return error.InvalidDnsPacket;
if (len == null) len = (i + 2) - start_i;
i = j;
} else if (c != 0) {
if (dest_i != 0) {
dest[dest_i] = '.';
dest_i += 1;
}
const label_len: usize = c;
if (i + 1 + label_len > packet.len) return error.InvalidDnsPacket;
if (dest_i + label_len + 1 > dest.len) return error.InvalidDnsPacket;
@memcpy(dest[dest_i..][0..label_len], packet[i + 1 ..][0..label_len]);
dest_i += label_len;
i += 1 + label_len;
} else {
dest[0] = 0;
if (len == std.math.maxInt(usize)) len = @intFromPtr(p) + 1 - @intFromPtr(comp_dn.ptr);
return len;
dest[dest_i] = 0;
dest_i += 1;
return .{
len orelse i - start_i + 1,
try .init(dest[0..dest_i]),
};
}
}
return error.InvalidDnsPacket;