Network

Macros
#define	BJ_ADDR_STRLEN   46
#define	BJ_NET_BACKLOG_DEFAULT   0
#define	BJ_NET_BACKLOG_MAX   (-1)

Enumerations
enum	bj_net_hints {   BJ_NET_NOHINT = 0x0 , BJ_RESOLVE_IPV4 = 0x01 , BJ_RESOLVE_IPV6 = 0x02 , BJ_EXCLUSIVE_BIND = 0x04 ,   BJ_TCP_DELAY_ACK = 0x08 , BJ_NONBLOCKING = 0x10 , BJ_BROADCAST = 0x20 }
enum	bj_net_shutdown { BJ_SHUTDOWN_RECEIVE = 0x01 , BJ_SHUTDOWN_SEND = 0x02 , BJ_SHUTDOWN_BOTH = 0x03 }

Functions
struct bj_tcp_listener *	bj_listen_tcp (const char *host, uint16_t port, uint16_t hint, int backlog, struct bj_error **error)
struct bj_tcp_stream *	bj_connect_tcp (const char *host, uint16_t port, uint16_t hint, uint32_t ms_timeout, struct bj_error **error)
struct bj_tcp_stream *	bj_connect_tcp_to (struct bj_address *addr, uint16_t hints, uint32_t ms_timeout, struct bj_error **error)
struct bj_tcp_stream *	bj_accept_tcp (struct bj_tcp_listener *listener, uint32_t ms_timeout, struct bj_error **error)
int	bj_tcp_recv (struct bj_tcp_stream *stream, void *buf, size_t len)
int	bj_tcp_peek (struct bj_tcp_stream *stream, void *buf, size_t len)
int	bj_tcp_send (struct bj_tcp_stream *stream, const void *buf, size_t len)
void	bj_tcp_shutdown (struct bj_tcp_stream *stream, int mode)
bj_bool	bj_set_tcp_keepalive (struct bj_tcp_stream *stream, bj_bool enable)
bj_bool	bj_get_tcp_keepalive (struct bj_tcp_stream *stream)
bj_bool	bj_tcp_wait (struct bj_tcp_stream *stream, uint32_t ms_timeout)
bj_bool	bj_set_tcp_recv_timeout (struct bj_tcp_stream *stream, uint32_t ms_timeout)
uint32_t	bj_get_tcp_recv_timeout (struct bj_tcp_stream *stream)
bj_bool	bj_set_tcp_send_timeout (struct bj_tcp_stream *stream, uint32_t ms_timeout)
uint32_t	bj_get_tcp_send_timeout (struct bj_tcp_stream *stream)
void	bj_close_tcp_stream (struct bj_tcp_stream *stream)
void	bj_close_tcp_listener (struct bj_tcp_listener *listener)
size_t	bj_tcp_peer_address (const struct bj_tcp_stream *stream, char *buf, size_t size)
size_t	bj_tcp_local_address (const struct bj_tcp_stream *stream, char *buf, size_t size)
uint16_t	bj_tcp_listener_port (const struct bj_tcp_listener *listener)
int	bj_tcp_available (struct bj_tcp_stream *stream)

Address Resolution Functions
struct bj_address *	bj_resolve_address (const char *host, uint16_t port, uint16_t hints, struct bj_error **error)
size_t	bj_address_string (const struct bj_address *addr, char *buf, size_t size)
uint16_t	bj_address_port (const struct bj_address *addr)
bj_bool	bj_address_equals (const struct bj_address *a, const struct bj_address *b)
size_t	bj_address_count (const struct bj_address *addr)
bj_bool	bj_address_next (struct bj_address *addr)
void	bj_address_reset (struct bj_address *addr)
void	bj_free_address (struct bj_address *addr)

UDP Functions
struct bj_udp *	bj_open_udp (const char *host, uint16_t port, uint16_t hints, struct bj_error **error)
void	bj_close_udp (struct bj_udp *udp)
int	bj_udp_send (struct bj_udp *udp, const char *host, uint16_t port, const void *data, size_t len, struct bj_error **error)
int	bj_udp_send_to (struct bj_udp *udp, const struct bj_address *addr, const void *data, size_t len, struct bj_error **error)
struct bj_datagram *	bj_udp_recv (struct bj_udp *udp, struct bj_error **error)
bj_bool	bj_udp_available (struct bj_udp *udp)
bj_bool	bj_udp_wait (struct bj_udp *udp, uint32_t ms_timeout)
uint16_t	bj_udp_local_port (const struct bj_udp *udp)
size_t	bj_udp_local_address (const struct bj_udp *udp, char *buf, size_t size)

Datagram Accessors
size_t	bj_datagram_addr (const struct bj_datagram *dgram, char *buf, size_t size)
uint16_t	bj_datagram_port (const struct bj_datagram *dgram)
const void *	bj_datagram_data (const struct bj_datagram *dgram)
size_t	bj_datagram_len (const struct bj_datagram *dgram)
void	bj_close_datagram (struct bj_datagram *dgram)

Network Simulation
void	bj_tcp_simulate_loss (struct bj_tcp_stream *stream, int percent)
void	bj_udp_simulate_loss (struct bj_udp *udp, int percent)

Detailed Description

Basic network API.

The net API provides a thin wrapping mechanism around POSIX sockets and Winsocks for TCP network communication.

Basic Usage

// Server
struct bj_tcp_listener* listener = bj_listen_tcp(NULL, 8080, 0, 0, &error);
struct bj_tcp_stream* client = bj_accept_tcp(listener, UINT32_MAX, &error);
 
// Client
struct bj_tcp_stream* stream = bj_connect_tcp("localhost", 8080, 0, 5000, &error);

Address Family Hints

Use BJ_RESOLVE_IPV4 and BJ_RESOLVE_IPV6 to control address resolution:

• 0 or both flags: Accept any address family
• BJ_RESOLVE_IPV4: IPv4 only
• BJ_RESOLVE_IPV6: IPv6 only

Macro Definition Documentation

BJ_ADDR_STRLEN

#define BJ_ADDR_STRLEN   46

Maximum length of an address string (including null terminator).

Sufficient for both IPv4 (e.g., "255.255.255.255") and IPv6 (e.g., "ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255") addresses.

BJ_NET_BACKLOG_DEFAULT

#define BJ_NET_BACKLOG_DEFAULT   0

Default backlog value for bj_listen_tcp.

Uses a reasonable implementation-defined default.

BJ_NET_BACKLOG_MAX

#define BJ_NET_BACKLOG_MAX   (-1)

Maximum backlog value for bj_listen_tcp.

Uses the system's maximum allowed backlog (SOMAXCONN).

Enumeration Type Documentation

bj_net_hints

enum bj_net_hints

Hint flags for network operations.

These flags can be combined with bitwise OR to configure socket behavior.

Enumerator
BJ_NET_NOHINT	No hint provided.
BJ_RESOLVE_IPV4	Restrict address resolution to IPv4.
BJ_RESOLVE_IPV6	Restrict address resolution to IPv6.
BJ_EXCLUSIVE_BIND	Disable address reuse.
BJ_TCP_DELAY_ACK	Enable Nagle's algorithm.
BJ_NONBLOCKING	Non-blocking mode.
BJ_BROADCAST	Enable UDP broadcast (SO_BROADCAST).

bj_net_shutdown

enum bj_net_shutdown

Shutdown mode for bj_tcp_shutdown.

Enumerator
BJ_SHUTDOWN_RECEIVE	Shutdown receive operations.
BJ_SHUTDOWN_SEND	Shutdown send operations.
BJ_SHUTDOWN_BOTH	Shutdown both send and receive.

Function Documentation

bj_accept_tcp()

struct bj_tcp_stream * bj_accept_tcp	(	struct bj_tcp_listener *	listener,
		uint32_t	ms_timeout,
		struct bj_error **	error )

Accepts an incoming connection on a TCP listener with timeout.

Waits for a client connection up to the specified timeout.

Parameters

listener	The listener to accept connections on.
ms_timeout	Timeout in milliseconds. 0 = non-blocking, UINT32_MAX = infinite.
error	Optional error output. Set to BJ_ERROR_NETWORK_TIMEOUT on timeout.

Returns

A new TCP stream for the accepted connection, or NULL on timeout/failure.

See also

bj_listen_tcp To create a listener.

bj_close_tcp_stream To close the accepted connection.

bj_address_count()

size_t bj_address_count

(

const struct bj_address *

addr

)

Returns number of resolved addresses.

DNS resolution may return multiple IPs for a single hostname.

Parameters

addr	The address to query.

Returns

Number of resolved addresses.

bj_address_equals()

bj_bool bj_address_equals	(	const struct bj_address *	a,
		const struct bj_address *	b )

Compares two addresses for equality.

Parameters

a	First address.
b	Second address.

Returns

BJ_TRUE if addresses are equal.

bj_address_next()

bj_bool bj_address_next

(

struct bj_address *

addr

)

Advances to the next resolved address.

Use this to manually iterate through multiple resolved IPs for fallback on connection failure.

Parameters

addr	The address to advance.

Returns

BJ_TRUE if advanced to next, BJ_FALSE if no more addresses.

bj_address_port()

uint16_t bj_address_port

(

const struct bj_address *

addr

)

Gets the port from a resolved address.

Parameters

addr	The address to query.

Returns

Port number in host byte order.

bj_address_reset()

void bj_address_reset

(

struct bj_address *

addr

)

Resets address iteration to the first resolved address.

Parameters

addr	The address to reset.

bj_address_string()

size_t bj_address_string	(	const struct bj_address *	addr,
		char *	buf,
		size_t	size )

Gets the IP address string from a resolved address.

Parameters

addr	The address to query.
buf	Buffer to store the string. May be NULL to query length.
size	Buffer size.

Returns

Length of address string, or 0 on error.

bj_close_datagram()

void bj_close_datagram

(

struct bj_datagram *

dgram

)

Closes a datagram and frees resources.

NULL-safe.

Parameters

dgram

The datagram to close. May be NULL.

bj_close_tcp_listener()

void bj_close_tcp_listener

(

struct bj_tcp_listener *

listener

)

Closes a TCP listener and releases associated resources.

Safe to call with NULL.

Parameters

listener

The TCP listener to close. May be NULL.

bj_close_tcp_stream()

void bj_close_tcp_stream

(

struct bj_tcp_stream *

stream

)

Closes a TCP stream and releases associated resources.

Safe to call with NULL.

Parameters

stream

The TCP stream to close. May be NULL.

bj_close_udp()

void bj_close_udp

(

struct bj_udp *

udp

)

Closes a UDP socket.

NULL-safe.

Parameters

udp	The UDP socket to close. May be NULL.

bj_connect_tcp()

struct bj_tcp_stream * bj_connect_tcp	(	const char *	host,
		uint16_t	port,
		uint16_t	hint,
		uint32_t	ms_timeout,
		struct bj_error **	error )

Connects to a TCP server at the specified host and port.

Resolves the hostname and attempts to connect. If multiple addresses are returned by DNS, each is tried until one succeeds.

Parameters

host	Hostname or IP address to connect to.
port	Port number to connect to.
hint	Address family hint. Use 0 for any, BJ_RESOLVE_IPV4 for IPv4 only, or BJ_RESOLVE_IPV6 for IPv6 only.
ms_timeout	Attempt timeout in milliseconds (0 = infinite)
error	Optional error output. May be NULL.

Returns

A new TCP stream, or NULL on failure.

See also

bj_tcp_send To send data.

bj_tcp_recv To receive data.

bj_close_tcp_stream To close the connection.

bj_connect_tcp_to()

struct bj_tcp_stream * bj_connect_tcp_to	(	struct bj_address *	addr,
		uint16_t	hints,
		uint32_t	ms_timeout,
		struct bj_error **	error )

Connects to a pre-resolved address, trying all resolved IPs.

Automatically iterates through all addresses returned by DNS resolution until one succeeds.

Parameters

addr	Destination address (from bj_resolve_address).
hints	Socket hints (BJ_TCP_DELAY_ACK, etc.).
ms_timeout	Connection timeout per address in milliseconds.
error	Optional error output.

Returns

TCP stream, or NULL on failure.

See also

bj_resolve_address To create the address.

bj_connect_tcp For hostname-based connection.

bj_datagram_addr()

size_t bj_datagram_addr	(	const struct bj_datagram *	dgram,
		char *	buf,
		size_t	size )

Gets the sender's address from a datagram.

Parameters

dgram	Datagram.
buf	Output buffer (may be NULL to query length).
size	Buffer size.

Returns

Address string length, or 0 on error.

bj_datagram_data()

const void * bj_datagram_data

(

const struct bj_datagram *

dgram

)

Gets the data pointer from a datagram.

Parameters

dgram

Datagram.

Returns

Pointer to data, or NULL on error.

bj_datagram_len()

size_t bj_datagram_len

(

const struct bj_datagram *

dgram

)

Gets the data length from a datagram.

Parameters

dgram

Datagram.

Returns

Data length, or 0 on error.

bj_datagram_port()

uint16_t bj_datagram_port

(

const struct bj_datagram *

dgram

)

Gets the sender's port from a datagram.

Parameters

dgram

Datagram.

Returns

Sender port, or 0 on error.

bj_free_address()

void bj_free_address

(

struct bj_address *

addr

)

Frees a resolved address.

NULL-safe.

Parameters

addr	The address to free. May be NULL.

bj_get_tcp_keepalive()

bj_bool bj_get_tcp_keepalive

(

struct bj_tcp_stream *

stream

)

Gets the current TCP keep-alive setting.

Parameters

stream

TCP stream.

Returns

BJ_TRUE if keep-alive is enabled, BJ_FALSE otherwise.

bj_get_tcp_recv_timeout()

uint32_t bj_get_tcp_recv_timeout

(

struct bj_tcp_stream *

stream

)

Gets the current receive timeout.

Parameters

stream

TCP stream.

Returns

Timeout in milliseconds, or 0 if no timeout set.

bj_get_tcp_send_timeout()

uint32_t bj_get_tcp_send_timeout

(

struct bj_tcp_stream *

stream

)

Gets the current send timeout.

Parameters

stream

TCP stream.

Returns

Timeout in milliseconds, or 0 if no timeout set.

bj_listen_tcp()

struct bj_tcp_listener * bj_listen_tcp	(	const char *	host,
		uint16_t	port,
		uint16_t	hint,
		int	backlog,
		struct bj_error **	error )

Creates a TCP listener bound to the specified host and port.

The listener accepts incoming TCP connections via bj_accept_tcp.

Parameters

host	Hostname or IP address to bind to. Pass NULL to bind to all interfaces.
port	Port number to listen on.
hint	Address family hint. Use 0 for any, BJ_RESOLVE_IPV4 for IPv4 only, or BJ_RESOLVE_IPV6 for IPv6 only.
backlog	Maximum pending connections queue size. Use BJ_NET_BACKLOG_DEFAULT for a reasonable default, or BJ_NET_BACKLOG_MAX for the system maximum.
error	Optional error output. May be NULL.

Returns

A new TCP listener, or NULL on failure.

See also

bj_accept_tcp To accept incoming connections.

bj_close_tcp_listener To close the listener.

bj_open_udp()

struct bj_udp * bj_open_udp	(	const char *	host,
		uint16_t	port,
		uint16_t	hints,
		struct bj_error **	error )

Opens a UDP socket bound to the specified port.

Parameters

host	Hostname/IP to bind to. NULL for any interface.
port	Port to bind. 0 for ephemeral (system-assigned).
hints	Flags: BJ_RESOLVE_IPV4, BJ_RESOLVE_IPV6, BJ_NONBLOCKING, BJ_BROADCAST
error	Optional error output.

Returns

New UDP socket, or NULL on failure.

bj_resolve_address()

struct bj_address * bj_resolve_address	(	const char *	host,
		uint16_t	port,
		uint16_t	hints,
		struct bj_error **	error )

Resolves a hostname to a network address.

The returned address can be used with bj_connect_tcp_to and bj_udp_send_to to avoid repeated DNS lookups.

Parameters

host	Hostname or IP string to resolve.
port	Port number.
hints	BJ_RESOLVE_IPV4, BJ_RESOLVE_IPV6, or 0 for any.
error	Optional error output.

Returns

Resolved address, or NULL on failure.

See also

bj_free_address To free the address.

bj_address_next To iterate through multiple resolved IPs.

bj_set_tcp_keepalive()

bj_bool bj_set_tcp_keepalive	(	struct bj_tcp_stream *	stream,
		bj_bool	enable )

Enables or disables TCP keep-alive probes.

When enabled, the OS sends periodic probes on idle connections to detect dead peers. If no response is received, the connection is terminated.

Parameters

stream	TCP stream.
enable	BJ_TRUE to enable, BJ_FALSE to disable.

Returns

BJ_TRUE on success.

Note

Keep-alive timing is controlled by the implementation.

bj_set_tcp_recv_timeout()

bj_bool bj_set_tcp_recv_timeout	(	struct bj_tcp_stream *	stream,
		uint32_t	ms_timeout )

Sets the receive timeout for a TCP stream.

When set, recv operations will timeout after the specified duration.

Parameters

stream	TCP stream.
ms_timeout	Timeout in milliseconds. 0 = no timeout (blocking).

Returns

BJ_TRUE on success.

bj_set_tcp_send_timeout()

bj_bool bj_set_tcp_send_timeout	(	struct bj_tcp_stream *	stream,
		uint32_t	ms_timeout )

Sets the send timeout for a TCP stream.

When set, send operations will timeout after the specified duration.

Parameters

stream	TCP stream.
ms_timeout	Timeout in milliseconds. 0 = no timeout (blocking).

Returns

BJ_TRUE on success.

bj_tcp_available()

int bj_tcp_available

(

struct bj_tcp_stream *

stream

)

Checks bytes available to read without blocking.

Parameters

stream

TCP stream.

Returns

Bytes available (>=0), or -1 on error/closed connection.

bj_tcp_listener_port()

uint16_t bj_tcp_listener_port

(

const struct bj_tcp_listener *

listener

)

Get the listening port of the given server.

Parameters

listener

The listener to get the local port from.

Returns

Listener port number

Will return 0 if listener is 0 or closed.

bj_tcp_local_address()

size_t bj_tcp_local_address	(	const struct bj_tcp_stream *	stream,
		char *	buf,
		size_t	size )

Gets the local address of a TCP stream.

Writes the local IP address as a string into buf. Works like snprintf: returns the length of the address string regardless of buffer size.

Parameters

stream	The TCP stream to query.
buf	Buffer to store the address string. May be NULL to query length only.
size	Size of the buffer in bytes.

Returns

Length of the address string (excluding null terminator), or 0 on error. If the return value is >= size, the output was truncated.

See also

BJ_ADDR_STRLEN For the recommended buffer size.

bj_tcp_peer_address To get the remote address.

bj_tcp_peek()

int bj_tcp_peek	(	struct bj_tcp_stream *	stream,
		void *	buf,
		size_t	len )

Peek at incoming data without consuming it.

Like bj_tcp_recv but data remains in the buffer for subsequent reads. Useful for protocol parsing where you need to inspect headers.

Parameters

stream	The TCP stream to peek from.
buf	Buffer to store peeked data.
len	Maximum number of bytes to peek.

Returns

Number of bytes peeked, 0 if connection closed, or -1 on error.

See also

bj_tcp_recv

bj_tcp_peer_address()

size_t bj_tcp_peer_address	(	const struct bj_tcp_stream *	stream,
		char *	buf,
		size_t	size )

Gets the remote address of a TCP stream.

Writes the peer's IP address as a string into buf. Works like snprintf: returns the length of the address string regardless of buffer size.

Parameters

stream	The TCP stream to query.
buf	Buffer to store the address string. May be NULL to query length only.
size	Size of the buffer in bytes.

Returns

Length of the address string (excluding null terminator), or 0 on error. If the return value is >= size, the output was truncated.

See also

BJ_ADDR_STRLEN For the recommended buffer size.

bj_tcp_local_address To get the local address.

bj_tcp_recv()

int bj_tcp_recv	(	struct bj_tcp_stream *	stream,
		void *	buf,
		size_t	len )

Receives data from a TCP stream.

Reads up to len bytes from the stream into buf. Blocks until data is available or the connection is closed.

Parameters

stream	The TCP stream to receive from.
buf	Buffer to store received data.
len	Maximum number of bytes to receive.

Returns

Number of bytes received, 0 if connection closed, or -1 on error.

See also

bj_tcp_peek

bj_tcp_send()

int bj_tcp_send	(	struct bj_tcp_stream *	stream,
		const void *	buf,
		size_t	len )

Sends data over a TCP stream.

Sends up to len bytes from buf over the stream.

Parameters

stream	The TCP stream to send on.
buf	Buffer containing data to send.
len	Number of bytes to send.

Returns

Number of bytes sent, or -1 on error.

bj_tcp_shutdown()

void bj_tcp_shutdown	(	struct bj_tcp_stream *	stream,
		int	mode )

Shuts down part or all of a TCP connection.

Gracefully shuts down the send and/or receive side of the connection without closing the socket.

Parameters

stream	The TCP stream to shutdown.
mode	Shutdown mode: BJ_SHUTDOWN_RECEIVE, BJ_SHUTDOWN_SEND, or BJ_SHUTDOWN_BOTH.

See also

bj_close_tcp_stream To fully close the connection.

bj_tcp_simulate_loss()

void bj_tcp_simulate_loss	(	struct bj_tcp_stream *	stream,
		int	percent )

Simulates packet loss on a TCP stream.

Parameters

stream	TCP stream.
percent	Loss percentage (0-100). 0 disables simulation.

bj_tcp_wait()

bj_bool bj_tcp_wait	(	struct bj_tcp_stream *	stream,
		uint32_t	ms_timeout )

Waits for data to become available on a TCP stream.

Uses select() internally to wait for readability with a timeout.

Parameters

stream	TCP stream to wait on.
ms_timeout	Timeout in milliseconds. 0 = non-blocking poll.

Returns

BJ_TRUE if data available, BJ_FALSE on timeout.

bj_udp_available()

bj_bool bj_udp_available

(

struct bj_udp *

udp

)

Checks if a datagram is available without blocking.

Parameters

udp	UDP socket.

Returns

BJ_TRUE if data available, BJ_FALSE otherwise.

bj_udp_local_address()

size_t bj_udp_local_address	(	const struct bj_udp *	udp,
		char *	buf,
		size_t	size )

Gets the local address of a UDP socket (snprintf-style).

Parameters

udp	UDP socket.
buf	Output buffer (may be NULL to query length).
size	Buffer size.

Returns

Address string length, or 0 on error.

bj_udp_local_port()

uint16_t bj_udp_local_port

(

const struct bj_udp *

udp

)

Gets the local port of a UDP socket.

Parameters

udp	UDP socket.

Returns

Local port, or 0 on error.

bj_udp_recv()

struct bj_datagram * bj_udp_recv	(	struct bj_udp *	udp,
		struct bj_error **	error )

Receives a datagram from the UDP socket.

If BJ_NONBLOCKING was set and no data available, returns NULL without error. If blocking, waits until a datagram arrives.

Parameters

udp	UDP socket.
error	Optional error output.

Returns

Received datagram (caller must close), or NULL if no data/error. Check error to distinguish: NULL + no error = no data available.

bj_udp_send()

int bj_udp_send	(	struct bj_udp *	udp,
		const char *	host,
		uint16_t	port,
		const void *	data,
		size_t	len,
		struct bj_error **	error )

Sends a datagram to the specified destination.

Resolves hostname internally on each call.

Parameters

udp	UDP socket.
host	Destination hostname or IP.
port	Destination port.
data	Data to send.
len	Data length.
error	Optional error output.

Returns

Bytes sent, or -1 on error.

bj_udp_send_to()

int bj_udp_send_to	(	struct bj_udp *	udp,
		const struct bj_address *	addr,
		const void *	data,
		size_t	len,
		struct bj_error **	error )

Sends a datagram to a pre-resolved address (no DNS lookup).

More efficient than bj_udp_send when sending many packets to the same destination, as it avoids repeated DNS lookups.

Parameters

udp	UDP socket.
addr	Destination address (from bj_resolve_address).
data	Data to send.
len	Data length.
error	Optional error output.

Returns

Bytes sent, or -1 on error.

See also

bj_resolve_address To create the address.

bj_udp_send For hostname-based sending.

bj_udp_simulate_loss()

void bj_udp_simulate_loss	(	struct bj_udp *	udp,
		int	percent )

Simulates packet loss on a UDP socket.

Parameters

udp	UDP socket.
percent	Loss percentage (0-100). 0 disables simulation.

bj_udp_wait()

bj_bool bj_udp_wait	(	struct bj_udp *	udp,
		uint32_t	ms_timeout )

Waits for data to become available on a UDP socket.

Uses select() internally to wait for readability with a timeout.

Parameters

udp	UDP socket.
ms_timeout	Timeout in milliseconds. 0 = non-blocking poll.

Returns

BJ_TRUE if data available, BJ_FALSE on timeout.