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This article is about what the API of TCP and UDP in lwip has. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

01, TCP related API1, tcp_arg ()

This function is used to pass the specific state to the application and can be called after the control block flag is established, that is, after the function tcp_new () is called.

Function

Specify the specific state of the application that should be passed to all callback functions

Prototype

Void tcp_arg (struct tcp_pcb * pcb, void * arg)

Parameters.

Pcb: the control block of the current TCP connection

Arg: the parameter to be passed to the callback function

Return

None

2. Tcp_new ()

This function should be called first after defining a tcp_pcb control block to establish the connection flag of the control block

Function

Create a new connection flag (pcb)

Prototype

Struct tcp_pcb * tcp_new (void)

Parameters.

None

Return

Pcb: the connection flag is established normally, and the established pcb is returned.

NULL: when new pcb memory is not available

3. Tcp_bind ()

The user of this function binds the local IP address and port number. The user can bind it to any local IP address, and it can only be called after the function tcp_new () is called.

Function

Bind local IP address and port number

Prototype

Err_t tcp_bind (struct tcp_pcb * pcb, struct ip_addr * ipaddr, u16dett port)

Parameters.

Pcb: the connection to be bound, similar to Sockets in the BSD standard

Ipaddr: the IP address of the binding. If IP_ADDR_ANY, bind the connection to all local IP addresses

Port: the local port number of the binding. Note: never conflict with other applications

Return

ERR_OK: correctly bound the specified connection

ERR_USE: the specified port number has been bound to a connection, resulting in a conflict

4. Tcp_listen ()

When a requested connection is received, the callback function specified by the tcp_accept () function will be called. Of course, before calling this function, you must first call the function tcp_bind () to bind a local IP address and port number

Function

Causes the specified connection to start listening

Prototype

Struct tcp_pcb * tcp_listen (struct tcp_pcb * pcb)

Parameters.

Pcb: specifies the connection that will enter the listening state

Return

Pcb: returns a new connection flag pcb, which is passed as an argument to the function to be dispatched. The original reason for doing so

Since listening connections generally require less memory, the function tcp_listen () retracts the original connection.

While reallocating a smaller block of memory for a listening connection

NULL: returns NULL when the connected memory block in the listening state is not available. If so, it is passed as an argument to the

The memory occupied by the pcb of the function tcp_listen () will not be allocated.

5. Tcp_listen_with_backlog ()

This function is the same as tcp_listen (), but it limits the number of outstanding connections in the listening queue, which is achieved by the parameter backlog. To use this function, you need to set TCP_LISTEN_BACKLOG=1 in the configuration file lwipopts.h.

Function

Causes the specified connection to start listening, but will limit the number of connections in the listening queue

Prototype

Struct tcp_pcb * tcp_listen_with_backlog (struct tcp_pcb * pcb, u8encrypt backlog)

Parameters.

Pcb: specifies the connection that will enter the listening state

Backlog: limit the number of connections in the listening queue

Return

Pcb: returns a new connection flag pcb, which is passed as an argument to the function to be dispatched. The original reason for doing so

Since listening connections generally require less memory, the function tcp_listen () reclaims the original

The connected memory, while reallocating a smaller block of memory for the connection in the listening state.

NULL: returns NULL when the connected memory block in the listening state is not available. If so, pass it as a parameter

The memory occupied by the pcb for the function tcp_listen () will not be allocated.

6. Tcp_accepted ()

This function is usually called in the callback function of "accept". It allows LwIP to perform housekeeping tasks, such as putting new connections into a listening queue to wait for processing.

Function

Notify LwIP that a new connection has been received

Prototype

Void tcp_accepted (struct tcp_pcb * pcb)

Parameters.

Pcb: connections that have been received

Return

None

7. Tcp_accept ()

When the listening connection is connected to a new connection, the callback function specified by this function will be called. It is usually called after the tcp_listen () function call.

Function

Specifies the callback function to be called after the listening connection is connected

Prototype

Void tcp_accept (struct tcp_pcb * pcb

Err_t (* accept) (void * arg)

Struct tcp_pcb * newpcb

Err_t err))

Parameters.

Pcb: specifies a connection in the listening state

Accept: specifies the callback function to be called after the connection is connected

Return

None

8. Tcp_connect ()

The connection specified by the request parameter pcb connects to the remote host and sends the initial SYN segment that opened the connection. The function tcp_connect () returns as soon as it is called, and it does not wait for the connection to be established correctly. If the connection is established correctly, it will directly call the function specified in the fourth parameter (the connected parameter). On the contrary, if the connection cannot be established correctly, the reason may be that the remote host refuses the connection or the remote host does not answer. No matter what the reason is, the connected function will be called to set the corresponding parameter err.

Function

Request the specified connection to the remote host and send the initial SYN segment that opened the connection

Prototype

Err_t tcp_connect (struct tcp_pcb * pcb

Struct ip_addr * ipaddr

U16_t port

Err_t (* connected) (void * arg)

Struct tcp_pcb * tpcb

Err_t err))

Parameters.

Pcb: specify a connection (pcb)

Ipaddr: specifies the IP address to which the remote host is connected

Port: specifies the port number to connect to the remote host

Connected: specifies the callback function to be called after the connection is established correctly

Return

ERR_MEM: when the memory accessing the SYN segment is not available, the connection is not established successfully

ERR_OK: when the SYN is accessed correctly, the connection is established successfully

9. Tcp_write ()

The function is to send TCP data, but instead of sending data as soon as it is called, it puts the specified data into the send queue, which is decided by the protocol kernel. The size of the available bytes in the send queue can be regained through the function tcp_sndbuf (). A more appropriate way to use this function is to send data with the size of bytes returned by the function tcp_sndbuf (). If the function returns ERR_MEM, the application waits for a while until the data in the current send queue is successfully received by the remote host, and then attempts to send the next data

Function

Send TCP data

Prototype

Err_t tcp_write (struct tcp_pcb * pcb

Void * dataptr

U16_t len

U8pragt copy)

Parameters.

Pcb: specify the connection to be sent (pcb)

Dataptr: is a pointer to the data to be sent

Len: specifies the length of the data to be sent

Copy: this is a logical variable, which is 0 or 1, which specifies whether to allocate new memory space and sets the number to be sent.

According to the copy. If the parameter is 0, no new memory space is allocated for the sent data, so the

Data can only be accessed through the specified pointer

Return

ERR_MEM: if the length of the data exceeds the size of the current send data buffer or the segment queue to be sent

If the length exceeds the upper limit defined in the file lwipopts.h (that is, the maximum value), the function tcp_write () call is lost.

Failed, return ERR_MEM

ERR_OK: the data is correctly put into the send queue and ERR_OK is returned

10. Tcp_sent ()

This function is used to set the callback function that is called after the remote host successfully receives the data, usually after the function tcp_listen ().

Function

Specifies the callback function that the application calls when the remote host successfully receives the data

Prototype

Void tcp_sent (struct tcp_pcb * pcb

Err_t (* sent) (void * arg)

Struct tcp_pcb * tpcb

U16roomt len))

Parameters.

Pcb: specify a connection to the remote host (pcb)

Sent: specifies the callback function to be called after the remote host successfully receives the data. "len" is passed to the callback function as an argument

Give the maximum number of bytes sent that was last confirmed.

Return

None

11. Tcp_recv ()

This function is used to specify the callback function that is called when new data is received, usually in the callback function specified by the function tcp_accept ().

Function

Specifies the callback function that is called when new data is received

Prototype

Void tcp_recv (struct tcp_pcb * pcb

Err_t (* recv) (void * arg)

Struct tcp_pcb * tpcb

Struct pbuf * p

Err_t err))

Parameters.

Pcb: specify a connection to the remote host (pcb)

Recv: specifies the callback function that is called when new data is received. The callback function can be passed by passing a NULL

The pbuf structure is used to indicate that the remote host has closed the connection. If no error occurs, the callback function returns

ERR_OK, and the pbuf structure must be released. Otherwise, if an error occurs in the call to the function, then thousands

Never release this structure so that the LwIP kernel can save it for later processing.

Return

None

12. Tcp_recved ()

When the application receives the data, the function must be called to get the length of the received data, that is, the function should be called in the callback function specified by the function tcp_recv ().

Function

Gets the length of the data received

Prototype

Void tcp_recved (struct tcp_pcb * pcb, u16dett len)

Parameters.

Pcb: specify a connection to the remote host (pcb)

Len: gets the length of the data received

Return

None

13. Tcp_poll ()

This function must be called when using the polling function of LwIP to specify the time interval for polling and the callback function that should be called when polling

Function

Specify the polling interval and the callback function that should be called when polling the application

Prototype

Void tcp_poll (struct tcp_pcb * pcb

Err_t (* poll) (void * arg, struct tcp_pcb * tpcb)

U8pragt interval)

Parameters.

Pcb: specify a connection (pcb)

Poll: specifies the callback function that should be called when polling the application

Interval: specifies the polling interval. The interval should be measured in TCP's fine-grained timer, which is typically set

Twice a second. Setting the parameter "interval" to 10 means that the application will poll every 5 seconds.

Return

None

14. Tcp_close ()

Function

Closes a specified TCP connection, and after calling this function, the TCP code releases (deletes) the pcb structure

Prototype

Err_t tcp_close (struct tcp_pcb * pcb)

Parameters.

Pcb: specify a connection to be closed (pcb)

Return

ERR_MEM: this function returns ERR_MEM when the connection that needs to be closed has no memory available. If this is the case

The application waits and recloses the connection through a pre-established callback function or polling function

ERR_OK: the connection is closed normally.

15. Tcp_abort ()

This function aborts the connection by sending a RST (reset) segment to the remote host. The pcb structure will be released. This function will not fail, it must be able to achieve the purpose of aborting. If the connection is aborted due to an error, the application handles the event sensitively through the callback function. Connection abortions caused by transmission errors are usually caused by a shortage of memory resources. Setting the callback function that handles errors is done through the function tcp_err ().

Function

Abort a specified connection (pcb)

Prototype

Void tcp_abort (struct tcp_pcb * pcb)

Parameters.

Pcb: specify a connection to be closed (pcb)

Return

None

16. Tcp_err ()

This function is used to specify the callback function that handles the error. A reliable and good application generally has to deal with possible errors, such as unavailable memory, so you need to call this function to specify a callback function to get the error information.

Function

Specify the callback function that handles the error

Prototype

Void tcp_err (struct tcp_pcb * pcb

Void (* err) (void * arg, err_t err))

Parameters.

Pcb: specifies the wrong connection (pcb) that needs to be handled

Err: specifies the callback function that is called when an error is sent. Because the pcb structure may have been deleted, errors are being handled

The pcb parameter cannot be passed in the callback function of

Return

None

02, UDP related API1, udp_new ()

This function is used to establish a UDP control block (pcb) for UDP communication, but the pcb is not activated unless the pcb is bound to a local address or connected to a remote host with a fixed address. After defining a udp_pcb control block, this function should be called first to establish the connection flag of the control block.

Function

Establish a UDP control block (pcb) for UDP communication

Prototype

Struct udp_pcb * udp_new (void)

Parameters.

None

Return

Udp_pcb: the control block (pcb) of the established UDP connection

2. Udp_remove ()

This function is used to delete a specified connection, usually after the control block is successfully established, that is, after the function udp_new () is called, when the network connection is no longer needed to communicate, it needs to be deleted to release the resources occupied by the connection (pcb).

Function

Delete and release a udp_pcb

Prototype

Void udp_remove (struct udp_pcb * pcb)

Parameters.

Pcb: specifies the connection to delete (pcb)

Return

None

3. Udp_bind ()

The user of this function binds the local IP address and port number. The user can bind it to any local IP address, and it can only be called after the function udp_new () is called.

Function

Binds the local IP address and port number for the specified connection

Prototype

Err_t udp_bind (struct udp_pcb * pcb

Struct ip_addr * ipaddr

U16dett port)

Parameters.

Pcb: specify a connection (pcb)

Ipaddr: the local IP address bound. If IP_ADDR_ANY, bind the connection to all local IP addresses

Port: the local port number of the binding. Note: never conflict with other applications

Return

ERR_OK: correctly bound the specified connection

ERR_USE: the specified port number has been bound to a connection, resulting in a conflict

4. Udp_connect ()

This function connects a specified connection (pcb) to the remote host. Because UDP communication is connectionless, this does not parameter any network traffic (network data transceiver), it just sets the IP address and port number of a remote connection.

Function

Connect the connection control block specified in the parameter "pcb" to the remote host

Prototype

Err_t udp_connect (struct udp_pcb * pcb

Struct ip_addr * ipaddr

U16dett port)

Parameters.

Pcb: specify a connection (pcb)

Ipaddr: sets the connected remote host IP address

Port: sets the port number of the remote host for the connection

Return

ERR_OK: connect to the remote host correctly

Other values: some error code flags of LwIP, indicating that the connection is not established correctly

5. Udp_disconnect ()

This function closes the connection specified by the parameter "pcb", which is the opposite of the function udp_connect (). Since UDP communication is connectionless, this function also doesn't parameter any network traffic ((network data transceiver), it just deletes the address of the remote connection.

Function

Closes the connection specified by the parameter "pcb", which is the opposite of the function udp_connect ()

Prototype

Void udp_disconnect (struct udp_pcb * pcb)

Parameters.

Pcb: specifies the connection to delete (pcb)

Return

None

6. Udp_send ()

This function uses the UDP protocol to send the data pointed to by pbufp. Called when data needs to be sent, and after sending, the pbuf structure is not released. When this function is called, the packet is sent to the currently specified IP address and port number stored in pcb. If the pcb is not connected to a fixed port number, the function will automatically randomly assign a port number and send the packet out. Usually, the function udp_connect () is called before the call.

Function

Using the UDP protocol to send data pointed to by pbuf p

Prototype

Err_t udp_send (struct udp_pcb * pcb, struct pbuf * p)

Parameters.

Pcb: specifies the connection (pcb) over which the data is sent

P: contains the pbuf chain that needs to send data

Return

ERR_OK: the packet was sent successfully without any errors.

ERR_MEM: memory not available

ERR_RTE: cannot find the route to the remote host

Other values: other error codes indicate that an error was sent

7. Udp_sendto ()

This function works the same as udp_send (), but it specifies the IP address and port number of the destination host to be sent, which is equivalent to the combination of udp_connect () and the function udp_send (). However, if the function udp_connect () has been called before the function is called, the IP address and port number of the sending destination will prevail as specified by this function, and those specified by the function udp_connect () will be refreshed

Function

Send UDP data to a remote host with a specified IP address and port number

Prototype

Err_t udp_sendto (struct udp_pcb * pcb

Struct pbuf * p

Struct ip_addr * dst_ip

U16dett dst_port)

Parameters.

Pcb: specifies the connection (pcb) over which the data is sent

P: contains the pbuf chain that needs to send data

Dst_ip: the IP address of the remote host that sent the data

Dst_port: the port number of the remote host on which the data is sent

Return

Same as the return value of the function udp_send ()

8. Udp_recv ()

This function is used to specify the callback function to be called when new UDP data is received. The parameters to be passed by the callback function will be passed into the IP address, port number and received data of the remote host.

Function

Specify a callback function that is called when a UDP packet is received

Prototype

Void udp_recv (struct udp_pcb * pcb

Void (* recv) (void * arg)

Struct udp_pcb * upcb

Struct pbuf * p

Struct ip_addr * addr

U16dett port)

Void * recv_arg)

Parameters.

Pcb: specify a connection (pcb)

Recv: specifies the callback function when the packet is received

Recv_arg: the parameter passed to the callback function

Return

None

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