Client Class

Methods documented for Client in Arduino

  1. WiFiClient()
  2. connected()
  3. connect()
  4. write()
  5. print()
  6. println()
  7. available()
  8. read()
  9. flush()
  10. stop()

Methods and properties described further down are specific to ESP8266. They are not covered in Arduino WiFi library documentation. Before they are fully documented please refer to information below.

flush and stop

flush(timeoutMs) and stop(timeoutMs) both have now an optional argument: timeout in millisecond, and both return a boolean.

Default input value 0 means that effective value is left at the discretion of the implementer.

flush() returning true indicates that output data have effectively been sent, and false that a timeout has occurred.

stop() returns false in case of an issue when closing the client (for instance a timed-out flush). Depending on implementation, its parameter can be passed to flush().



With nodelay set to true, this function will to disable Nagle algorithm.

This algorithm is intended to reduce TCP/IP traffic of small packets sent over the network by combining a number of small outgoing messages, and sending them all at once. The downside of such approach is effectively delaying individual messages until a big enough packet is assembled.




Returns whether NoDelay is enabled or not for the current connection.


This is an experimental API that will set the client in synchronized mode. In this mode, every write() is flushed. It means that after a call to write(), data are ensured to be received where they went sent to (that is flush semantic).

When set to true in WiFiClient implementation,

  • It slows down transfers, and implicitely disable the Nagle algorithm.
  • It also allows to avoid a temporary copy of data that otherwise consumes at most TCP_SND_BUF = (2 * MSS) bytes per connection,


Returns whether Sync is enabled or not for the current connection.

setDefaultNoDelay and setDefaultSync

These set the default value for both setSync and setNoDelay for every future instance of WiFiClient (including those coming from WiFiServer.available() by default).

Default values are false for both NoDelay and Sync.

This means that Nagle is enabled by default for all new connections.

getDefaultNoDelay and getDefaultSync

Return the values to be used as default for NoDelay and Sync for all future connections.

Other Function Calls

uint8_t  status ()
virtual size_t  write (const uint8_t *buf, size_t size)
size_t  write_P (PGM_P buf, size_t size)
size_t  write (Stream &stream)
size_t  write (Stream &stream, size_t unitSize) __attribute__((deprecated))
virtual int  read (uint8_t *buf, size_t size)
virtual int  peek ()
virtual size_t  peekBytes (uint8_t *buffer, size_t length)
size_t  peekBytes (char *buffer, size_t length)
virtual  operator bool ()
IPAddress  remoteIP ()
uint16_t  remotePort ()
IPAddress  localIP ()
uint16_t  localPort ()

Documentation for the above functions is not yet prepared.

For code samples please refer to separate section with examples :arrow_right: dedicated specifically to the Client Class.