ErlangWS

An Erlang implementation of the Websocket Protocol (RFC 6455) for server usage.

This implementation is quite simple and straightforward since it does not depend on external libraries.

##Remarks

• Websockets will only work with TCP Sockets
• ErlangWS does not handle the connection itself which means that:
  • you have to create, bind and open the socket before you call ws_init
• the Socket has to be closed manually, ErlangWS will throw an error when the connection is closed by the client

Data Types

According to the RFC the types of messages as listed in datatype() are supported and messages can also be fragmented or complete.

Besides of the pure data types there are also control frames specified. If needed these can also be received (see below for

datatype() = text
           | binary

msgtype()  = cont
           | close
           | ping
           | pong
           | datatype()

frag()     = complete
           | fragment

rcvmode()  = normal
           | all
           | raw

Messages are represented as tuples. These can either have the simplified form

simple() = {datatype(), Payload}

or the complete form:

message () = {frag(), {msgtype(), Payload}}

Exported Functions

ws_init(Socket)

Types:

• Socket = gen_tcp:socket()

Initializes the websocket connection by performing a websocket handshake. This function will block the caller since it expects to receive a HTTP packet. If the handshake was successful the function will return ok, otherwise error.

---

ws_send(Socket, Type, Content)

Types:

• Socket = gen_tcp:Socket()
• Type = msgtype()
• Content = String

Sends Content with the Type over the Socket.

---

ws_receive(Socket)

Types:

• Socket = gen_tcp:Socket()

Convenience wrapper for ws_receive(Socket, normal).

---

ws_receive(Socket, Mode)

Types:

• Socket = gen_tcp:Socket()
• Mode = rcvmode()

Receives a message on the Socket. If the packet is not a valid websocket message the function will throw error. If it is valid, the return value depends on the mode.

In the normal mode, the function will answer ping frames, handle pong frames and will throw an error if the connection is closed by the client. Furthermore it will buffer incoming fragmented packages until the whole message is complete. In this mode, ws_receive will return the simple message form.

In the all mode, the function will answer ping frames, handle pong frames. All other frames will be returned as they are. Messages will be returned in the complete form.

The raw mode just delivers all valid messages in the complete form including all op frames.