What protocol does swoole use?

#TCP is a streaming protocol. After the client sends a piece of data to the server, it may not be completely received by the server at once. The client sends multiple pieces of data to the server, and the server may receive them all at once.                                                                                                                                                                                     (Recommended learning: swoole video tutorial )

In practical applications, we hope that the server can receive a complete piece of data at a time, no more and no less.

In traditional TCP servers, programmers often need to maintain a cache area, first write the read data into the cache area, and then distinguish the beginning of a complete piece of data through the preset protocol content. , end and length, and hand over a complete piece of data to the logical part for processing. This is the function of the custom protocol.

In Swoole, a data cache area has been implemented at the bottom layer, and several commonly used protocol types have been built in. The data has been split directly at the bottom layer to ensure that in the onReceive callback function, certain Able to receive one or several complete data segments.

The size of the data buffer can be controlled by configuring pakcage_max_length.

$configs = [];
$configs["package_max_length"] = 8192;
$server->set($configs);

swoole currently supports two communication protocols: EOF terminator protocol and fixed header plus body protocol

package_max_length

package_max_length is used to set the maximum packet size , when protocol parsing such as open_length_check or open_eof_check or open_http_protocol is turned on, the bottom layer of Swoole will process data packet splicing. At this time, when the data packet is not completely received, all data will be saved in the memory.

So you need to set package_max_length to the maximum allowed memory size of a data packet.

If there are 10,000 TCP connections sending data at the same time, each data packet is 2MB, which will occupy 20GB of memory space in the most extreme case. Therefore, this parameter should not be set too large, otherwise it will occupy a lot of memory.

Related configuration options

open_length_check

When it is found that the length of the data packet exceeds package_max_length, the data will be discarded directly and the connection will be closed, so it will not occupy any memory and is suitable for websocket, mqtt, http2 protocols.

open_eof_check

Since the length of the data packet cannot be known in advance, the received data will still be stored in the memory and continue to grow. When it is found that the memory usage has exceeded package_max_length, the data packet will be dropped directly and the connection will be closed.

open_http_protocol

The HTTP GET request allows a maximum of 8KB data and this configuration cannot be modified. The POST request will detect the Content-Type. If it is found that the package_max_length is exceeded, the data will be discarded directly, an HTTP 400 error will be sent and the connection will be closed.

EOF protocol

Uses a fixed set of strings /r/n that will not appear in normal data as the mark of the split protocol, called EOF protocol.

What is the EOF protocol?

EOF stands for End of File, and uses \r\n as the end tag.

When reading the data in the data stream one by one, if the EOF mark is found, it means that the end of the data has been read.

In the TCP data flow, the characteristics of the data flow using the EOF protocol are |data|EOF|data|EOF|.

The principle of EOF protocol processing is that at the end of each string of normal data, a predetermined string that will never appear in the data will be added as an end mark, so that the received data can be marked according to the EOF to split the data.

Typical memcached, ftp, and stmp all use /r/n as the terminator. When sending data just add /r/n at the end of the data packet.

When using EOF protocol processing, you must ensure that EOF does not occur in the middle of the data packet, otherwise it will cause subpackaging errors.

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