echo_op example

[octobanana]

Set the reuse_address socket option to match the style of the other examples.

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Add the ability to set the listening address and port through command line arguments. Print out usage and return error exit status on invalid or missing arguments.

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Currently, the echo-op example uses the carriage return \r delimiter for async_read_until. Running the server and sending a message to it with curl or netcat:

printf 'Hello, World!\r\n' | nc 127.0.0.1 8080

leads to some potentially confusing behaviour. The async_read_until function reads up to and including the first \r. When the message is received by the client and printed to stdout, the trailing \r ends up moving the cursor back to the start of the line, resulting in the prompt overwriting the message. It appears as if nothing has happened.

If async_read_until uses the newline \n as the delimiter, the echoed output will not be overwritten, regardless of whether the line ends in \n or \r\n.

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Had a go at adding a synchronous echo op function #1275.

[codecov]

Codecov Report

Merging #1347 into develop will increase coverage by <.01%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #1347      +/-   ##
===========================================
+ Coverage    92.06%   92.07%   +<.01%     
===========================================
  Files          124      124              
  Lines        11526    11526              
===========================================
+ Hits         10611    10612       +1     
+ Misses         915      914       -1

Impacted Files	Coverage Δ
include/boost/beast/core/impl/buffers_prefix.ipp	92.22% <0%> (+1.11%)	⬆️

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[vinniefalco]

The sync echo-op needs exposition and documentation...

[octobanana]

It does, I'll add some documentation to it.