Browser-like WebSocket client API for Elixir.

Events are delivered as messages to the owner process:

{HTTP.WebSocket, socket, %HTTP.WebSocket.Event.Open{}}
{HTTP.WebSocket, socket, %HTTP.WebSocket.Event.Message{}}
{HTTP.WebSocket, socket, %HTTP.WebSocket.Event.Error{}}
{HTTP.WebSocket, socket, %HTTP.WebSocket.Event.Close{}}

HTTP/1 is the default. Select http_version: :http2, :h2c, or :auto explicitly; http_version/1 reports the negotiated HTTP version, while protocol/1 continues to report the selected WebSocket subprotocol.

With delivery: :ack, message events include a delivery reference:

{HTTP.WebSocket, socket, %HTTP.WebSocket.Event.Message{}, ref}

Call acknowledge/2 after consuming each message. Open, Error, and Close retain their three-element event envelopes. Receive queues, pending sends, and fragmented messages have finite configurable limits. Established sessions default to idle_timeout: :infinity; opening and close deadlines are separate.

Telemetry URLs omit query, userinfo, authority, and fragment by default. Pass telemetry_url: nil to omit all URL-derived telemetry metadata, or a URI/string containing only caller-approved fields to replace the telemetry URL (for example, telemetry_url: "ws://127.0.0.1:8080" omits a private path). Invalid replacements reject construction; replacement credentials are always stripped. This option applies to every lifecycle/message event and never changes the transport URL or handshake.

HTTP/1 WebSocket proxy boundary

For frame forwarding, select mode: :proxy, http_version: :http1, delivery: :ack and automatic_pong: false. Proxy mode delivers %HTTP.WebSocket.Event.Frame{opcode: opcode, data: binary} for text, binary, ping and pong, with the same delivery reference/acknowledge/2 contract. binary_type does not alter proxy frame data. Close retains its lifecycle event and automatic reply. send_frame/2 and send_frame_ack/2 accept {opcode, binary} for those four opcodes. Automatic pong defaults to true; disabling it requires proxy mode. Proxy close/3 accepts nil with an empty reason, 1000-1014 except 1004/1005/1006, and 3000-4999. Reserved/non-wire codes, invalid UTF-8 and reasons over 123 bytes remain rejected.

Proxy HTTP/2, h2c and auto selection return {:error, :proxy_requires_http1}. Wait for successful completion of every send_frame_ack/2 reference before initiating Close: local close discards queued application frames in both HTTP versions. This provides ordered local write completion over HTTP/1; proxy mode supplies no HTTP/2 drain contract. Control sends share the bounded application send FIFO, including zero-length payloads. Control delivery uses the receive limits too; ACK capacity must accommodate at least 132 bytes.

Use this public client for the upstream half of a WebSocket proxy. Select http_version: :http1 and delivery: :ack; acknowledge each Message only after downstream consumption. Set finite opening_timeout, idle_timeout, write_timeout and close_timeout, and size/count limits for messages, receive queues and pending sends. send_ack/2 reports local transport completion for each admitted frame. send/2 reports admission only.

The client validates status 101, Upgrade/Connection tokens, exactly one matching Sec-WebSocket-Accept and the selected subprotocol. Bytes coalesced after the response head enter the frame parser. Redirects and uncertain operations are never replayed. Ping is answered with Pong automatically; Close is exchanged with the peer. This interface proxies WebSocket messages, not raw TCP bytes or exact frame fragmentation. Forward binary messages with array_buffer/1 and configure the upstream protocols explicitly.

WSS retains the selected TLS backend's CA, hostname and SNI verification; supply trusted ssl: [cacertfile: ...] for private CAs. Owner death closes the connection. close/1 signals cancellation; monitor the socket's public pid for :DOWN to confirm cleanup, including a cancelled opening. A Close event describes the handshake result; it does not prove peer application receipt of earlier writes. Terminal cancellation discards pending transport bytes, so a failed write may have reached the peer partly.

Plain Elixir binaries are sent as text frames. Use array_buffer/1 or HTTP.Blob for binary frames.

For wss connections, pass tls_backend: :ssl | :ex_ssl (or the equivalent string in a map). When omitted, the shared :http_core TLS backend setting is captured when the socket is created.