Refactor: simpler read #11221

pull gnuser wants to merge 1 commits into bitcoin:master from gnuser:refactor-streams changing 1 files +5 −7

gnuser commented at 5:46 AM on September 3, 2017: contributor

No description provided.
Refactor: make the read function simpler 9db9d6215f
in src/streams.h:351 in 9db9d6215f
```
 344 | @@ -345,18 +345,16 @@ class CDataStream
 345 |  
 346 |          // Read from the beginning of the buffer
 347 |          unsigned int nReadPosNext = nReadPos + nSize;
 348 | -        if (nReadPosNext >= vch.size())
 349 | +        if (nReadPosNext > vch.size()) {
 350 | +            throw std::ios_base::failure("CDataStream::read(): end of data");
 351 | +        }
 352 | +        memcpy(pch, &vch[nReadPos], nSize);        
```
sipa commented at 6:44 AM on September 3, 2017:

This is not correct. When vch is empty, and nReadPos and nSize are 0, this will invoke operator[] on vch, which is not valid.

meshcollider commented at 7:34 AM on September 3, 2017:

Note that that's a bug with the original code though, not with the refactor

laanwj commented at 5:42 PM on September 6, 2017:

probably better to use vch.data() + nNreadPos? (but yes, this is not a bug introduced in this PR)

promag commented at 4:22 PM on October 8, 2017:

@sipa above there is an early return if nSize == 0 so that doesn't happen. Out of bounds access is prevented with the std::ios_base::failure exception.

sipa commented at 11:27 PM on October 12, 2017:

Agree, there is no bug here. It would still be clearer using vch.data() + nReadPos though.
dcousens approved
laanwj added the label Refactoring on Sep 5, 2017
promag commented at 4:24 PM on October 8, 2017: member

utACK 9db9d62.

Nit, commit message could mention CDataStream::read instead read only.

in src/streams.h:352 in 9db9d6215f

 344 | @@ -345,18 +345,16 @@ class CDataStream
 345 |  
 346 |          // Read from the beginning of the buffer
 347 |          unsigned int nReadPosNext = nReadPos + nSize;
 348 | -        if (nReadPosNext >= vch.size())
 349 | +        if (nReadPosNext > vch.size()) {
 350 | +            throw std::ios_base::failure("CDataStream::read(): end of data");
 351 | +        }
 352 | +        memcpy(pch, &vch[nReadPos], nSize);        
 353 | +        if (nReadPosNext == vch.size())

promag commented at 4:24 PM on October 8, 2017:

Nit, { on this line.

laanwj merged this on Nov 9, 2017
laanwj closed this on Nov 9, 2017
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#11697 [trivial] remove trailing whitespace in streams.h