fix: Fixes QUIC concurrency

Author: ycastorium

.envrc

@@ -0,0 +1 @@
+[ -f .env ] && dotenv

.gitignore

@@ -1,33 +1,119 @@
-# The directory Mix will write compiled artifacts to.
-/_build/
+# Created by https://www.toptal.com/developers/gitignore/api/elixir,erlang,macos,visualstudiocode,vim
+# Edit at https://www.toptal.com/developers/gitignore?templates=elixir,erlang,macos,visualstudiocode,vim
 
-# If you run "mix test --cover", coverage assets end up here.
-/cover/
-
-# The directory Mix downloads your dependencies sources to.
-/deps/
+### Elixir ###
+/_build
+/cover
+/deps
+/doc
+/.fetch
+erl_crash.dump
+*.ez
+*.beam
+/config/*.secret.exs
+.elixir_ls/
 
-# Where third-party dependencies like ExDoc output generated docs.
-/doc/
+### Elixir Patch ###
 
-# Temporary files, for example, from tests.
-/tmp/
+### Erlang ###
+.eunit
+*.o
+*.plt
+.concrete/DEV_MODE
 
-# If the VM crashes, it generates a dump, let's ignore it too.
-erl_crash.dump
+# rebar 2.x
+.rebar
+rel/example_project
+ebin/*.beam
+deps
 
-# Also ignore archive artifacts (built via "mix archive.build").
-*.ez
+# rebar 3
+.rebar3
+_build/
+_checkouts/
 
-# Ignore package tarball (built via "mix hex.build").
-quiver-*.tar
+### Erlang Patch ###
+rebar3.crashdump
 
 ### macOS ###
 # General
 .DS_Store
+.AppleDouble
+.LSOverride
+
+# Icon must end with two \r
+Icon
+
+
+# Thumbnails
+._*
+
+# Files that might appear in the root of a volume
+.DocumentRevisions-V100
+.fseventsd
+.Spotlight-V100
+.TemporaryItems
+.Trashes
+.VolumeIcon.icns
+.com.apple.timemachine.donotpresent
+
+# Directories potentially created on remote AFP share
+.AppleDB
+.AppleDesktop
+Network Trash Folder
+Temporary Items
+.apdisk
+
+### macOS Patch ###
+# iCloud generated files
+*.icloud
+
+### Vim ###
+# Swap
+[._]*.s[a-v][a-z]
+!*.svg  # comment out if you don't need vector files
+[._]*.sw[a-p]
+[._]s[a-rt-v][a-z]
+[._]ss[a-gi-z]
+[._]sw[a-p]
+
+# Session
+Session.vim
+Sessionx.vim
+
+# Temporary
+.netrwhist
+*~
+# Auto-generated tag files
+tags
+# Persistent undo
+[._]*.un~
+
+### VisualStudioCode ###
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+!.vscode/*.code-snippets
+
+# Local History for Visual Studio Code
+.history/
+
+# Built Visual Studio Code Extensions
+*.vsix
+
+### VisualStudioCode Patch ###
+# Ignore all local history of files
+.history
+.ionide
 .env
-.envrc
 
+tmp/*
 /bench/output/
-
 /certs/
+docker/logs
+
+# End of https://www.toptal.com/developers/gitignore/api/elixir,erlang,macos,visualstudiocode,vim
+
+

lib/quiver/conn/http3.ex

@@ -13,7 +13,7 @@ defmodule Quiver.Conn.HTTP3 do
 
   @behaviour Quiver.Conn
 
-  @dialyzer {:nowarn_function, connect: 2, query_peer_max_streams: 2}
+  @dialyzer {:nowarn_function, connect: 2, do_connect: 5, query_peer_max_streams: 2}
 
   alias Quiver.Error.H3StreamError
   alias Quiver.Error.QUICHandshakeFailed
@@ -22,6 +22,11 @@ defmodule Quiver.Conn.HTTP3 do
 
   @forbidden_headers ~w(connection keep-alive transfer-encoding upgrade proxy-connection)
 
+  # Probe budget for a non-final connect candidate, so an unreachable preferred
+  # address fails over to the next family without burning the full connect timeout.
+  # Shared with `Quiver.Pool.HTTP3.Connection` via `connect_probe_timeout/0`.
+  @connect_probe_timeout 1_500
+
   defstruct [
     :h3_conn,
     :host,
@@ -54,11 +59,10 @@ defmodule Quiver.Conn.HTTP3 do
 
     h3_opts =
       opts
-      |> build_h3_opts()
+      |> build_h3_opts(host)
       |> Map.put(:sync, true)
-      |> Map.put(:connect_timeout, timeout)
 
-    case :quic_h3.connect(host, port, h3_opts) do
+    case do_connect(resolve_candidates(host), port, h3_opts, timeout, :nxdomain) do
       {:ok, h3_conn} ->
         {:ok,
          %__MODULE__{
@@ -88,6 +92,21 @@ defmodule Quiver.Conn.HTTP3 do
      )}
   end
 
+  # Dial resolved candidate addresses in turn (IPv6 first), forcing the QUIC direct
+  # path. Non-final candidates get the short probe budget so an unreachable preferred
+  # family fails over quickly; the final candidate gets the full connect timeout.
+  defp do_connect([], _port, _h3_opts, _timeout, last_error), do: {:error, last_error}
+
+  defp do_connect([ip | rest], port, h3_opts, timeout, _last_error) do
+    attempt_timeout = if rest == [], do: timeout, else: min(timeout, @connect_probe_timeout)
+    h3_opts = Map.put(h3_opts, :connect_timeout, attempt_timeout)
+
+    case :quic_h3.connect(ip, port, h3_opts) do
+      {:ok, h3_conn} -> {:ok, h3_conn}
+      {:error, reason} -> do_connect(rest, port, h3_opts, timeout, reason)
+    end
+  end
+
   @impl Quiver.Conn
   def open?(%__MODULE__{h3_conn: pid}) when is_pid(pid), do: Process.alive?(pid)
   def open?(_), do: false
@@ -239,16 +258,56 @@ defmodule Quiver.Conn.HTTP3 do
     end
   end
 
-  defp build_h3_opts(opts) do
+  @doc false
+  @spec connect_probe_timeout() :: pos_integer()
+  def connect_probe_timeout, do: @connect_probe_timeout
+
+  @doc """
+  Resolves a host to at most one address per family, IPv6 first (RFC 8305 §4
+  preference), for the direct-connect path. A literal IP is returned as-is.
+  Shared with `Quiver.Pool.HTTP3.Connection`.
+  """
+  @spec resolve_candidates(String.t()) :: [:inet.ip_address()]
+  def resolve_candidates(host) do
+    hostc = to_charlist(host)
+
+    case :inet.parse_address(hostc) do
+      {:ok, ip} -> [ip]
+      {:error, _} -> first_addr(hostc, :inet6) ++ first_addr(hostc, :inet)
+    end
+  end
+
+  defp first_addr(hostc, family) do
+    case :inet.getaddrs(hostc, family) do
+      {:ok, [ip | _]} -> [ip]
+      _ -> []
+    end
+  end
+
+  defp build_h3_opts(opts, host) do
     base = %{verify: Keyword.get(opts, :verify, :verify_peer)}
 
     base
     |> maybe_put(:cacerts, Keyword.get(opts, :cacerts))
     |> maybe_put(:settings, Keyword.get(opts, :h3_settings))
-    |> maybe_put(:quic_opts, Keyword.get(opts, :quic_opts))
+    |> Map.put(:quic_opts, build_quic_opts(Keyword.get(opts, :quic_opts), host))
     |> maybe_put_datagram(Keyword.get(opts, :h3_datagram_enabled, true))
   end
 
+  # Disable Happy-Eyeballs and dial the resolved literal address: the QUIC race
+  # coordinator transfers connection ownership only after the handshake completes,
+  # dropping the server's SETTINGS streams. `server_name` carries the hostname for
+  # SNI / `verify_peer` since the dialed host is an IP. See `do_connect/5`.
+  defp build_quic_opts(quic_opts, host) do
+    quic_opts
+    |> normalize_quic_opts()
+    |> Map.put(:happy_eyeballs, false)
+    |> Map.put(:server_name, to_string(host))
+  end
+
+  defp normalize_quic_opts(opts) when is_map(opts), do: opts
+  defp normalize_quic_opts(_), do: %{}
+
   defp maybe_put(map, _k, nil), do: map
   defp maybe_put(map, _k, :default), do: map
   defp maybe_put(map, _k, v) when is_map(v) and map_size(v) == 0, do: map