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std.net.HostName.connect: rework to avoid waiting for DNS

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The previous implementation would eagerly attempt TCP connection upon
receiving a DNS reply, but it would still wait for all the DNS results
before returning from the function.

This implementation returns immediately upon first successful TCP
connection, canceling not only in-flight TCP connection attempts but
also unfinished DNS queries.
This commit is contained in:
Andrew Kelley 2025-10-15 10:20:04 -07:00
parent d3c4158a10
commit adaef433d2
1 changed files with 58 additions and 26 deletions
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84
lib/std/Io/net/HostName.zig
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@ -206,34 +206,16 @@ pub fn connect(
port: u16,
options: IpAddress.ConnectOptions,
) ConnectError!Stream {
var canonical_name_buffer: [max_len]u8 = undefined;
var results_buffer: [32]HostName.LookupResult = undefined;
var results: Io.Queue(LookupResult) = .init(&results_buffer);
var connect_many_buffer: [32]ConnectManyResult = undefined;
var connect_many_queue: Io.Queue(ConnectManyResult) = .init(&connect_many_buffer);
var lookup_task = io.async(HostName.lookup, .{ host_name, io, &results, .{
.port = port,
.canonical_name_buffer = &canonical_name_buffer,
} });
defer lookup_task.cancel(io);
const Result = union(enum) { connect_result: IpAddress.ConnectError!Stream };
var finished_task_buffer: [results_buffer.len]Result = undefined;
var select: Io.Select(Result) = .init(io, &finished_task_buffer);
defer select.cancel();
while (results.getOne(io)) |result| switch (result) {
.address => |address| select.async(.connect_result, IpAddress.connect, .{ address, io, options }),
.canonical_name => continue,
.end => |lookup_result| {
try lookup_result;
break;
},
} else |err| return err;
var connect_many = io.async(connectMany, .{ host_name, io, port, &connect_many_queue, options });
defer connect_many.cancel(io);
var aggregate_error: ConnectError = error.UnknownHostName;
while (select.outstanding != 0) switch (try select.wait()) {
.connect_result => |connect_result| if (connect_result) |stream| return stream else |err| switch (err) {
while (connect_many_queue.getOne(io)) |result| switch (result) {
.connection => |connection| if (connection) |stream| return stream else |err| switch (err) {
error.SystemResources => |e| return e,
error.OptionUnsupported => |e| return e,
error.ProcessFdQuotaExceeded => |e| return e,
@ -242,9 +224,59 @@ pub fn connect(
error.WouldBlock => return error.Unexpected,
else => |e| aggregate_error = e,
},
};
.end => |end| {
try end;
return aggregate_error;
},
} else |err| return err;
}
pub const ConnectManyResult = union(enum) {
connection: IpAddress.ConnectError!Stream,
end: ConnectError!void,
};
/// Asynchronously establishes a connection to all IP addresses associated with
/// a host name, adding them to a results queue upon completion.
pub fn connectMany(
host_name: HostName,
io: Io,
port: u16,
results: *Io.Queue(ConnectManyResult),
options: IpAddress.ConnectOptions,
) void {
var canonical_name_buffer: [max_len]u8 = undefined;
var lookup_buffer: [32]HostName.LookupResult = undefined;
var lookup_queue: Io.Queue(LookupResult) = .init(&lookup_buffer);
host_name.lookup(io, &lookup_queue, .{
.port = port,
.canonical_name_buffer = &canonical_name_buffer,
});
var group: Io.Group = .init;
defer group.cancel(io);
while (lookup_queue.getOne(io)) |dns_result| switch (dns_result) {
.address => |address| group.async(io, enqueueConnection, .{ address, io, results, options }),
.canonical_name => continue,
.end => |lookup_result| {
group.wait(io);
results.putOneUncancelable(io, .{ .end = lookup_result });
return;
},
} else |err| switch (err) {
error.Canceled => |e| results.putOneUncancelable(io, .{ .end = e }),
}
}
fn enqueueConnection(
address: IpAddress,
io: Io,
queue: *Io.Queue(ConnectManyResult),
options: IpAddress.ConnectOptions,
) void {
queue.putOneUncancelable(io, .{ .connection = address.connect(io, options) });
}
pub const ResolvConf = struct {