Read exactly the entire 16bytes smpp header

[komuw]

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Now,

What(What have you changed?)

• make sire that naz reads exacly the first 16bytes of the smpp header
  this builds on the earlier work; make sure the command length header data be 4 bytes #153 but now naz takes it a step further and will unbind & close connection if it is unable to read the entire SMPP header

Why(Why did you change it?)

• this is done to prevent inconsistency and also to try and be faithful to the smpp spec.
• updates; Investigate: what if naz reads 4bytes and they are not part of the header? #135
• Other[1] smpp clients also do something similar

References:

1. https://github.com/fiorix/go-smpp/blob/6dbf72b9bcea72cea4a035e3a2fc434c4dabaae7/smpp/pdu/header.go#L67-L73

[codecov-io]

Codecov Report

Merging #155 into master will increase coverage by 0.19%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #155      +/-   ##
==========================================
+ Coverage   86.23%   86.43%   +0.19%     
==========================================
  Files          14       14              
  Lines        1308     1312       +4     
==========================================
+ Hits         1128     1134       +6     
+ Misses        180      178       -2

Impacted Files	Coverage Δ
naz/__version__.py	100% <ø> (ø)	⬆️
naz/client.py	80.59% <100%> (+0.41%)	⬆️

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[komuw]

Golang smpp client using io.ReadFull

https://github.com/fiorix/go-smpp/blob/6dbf72b9bcea72cea4a035e3a2fc434c4dabaae7/smpp/pdu/header.go#L67-L73