Re: [lwip-users] PolarSSL and mbedTLS

[Dr. Jan Menzel]

mbedtls_ssl_get_bytes_avail() is what you wont to call before selecting.

On 16.03.2017 13:54, Noam Weissman wrote:
> Hi Jan,
> 
> No the error I am seeing is MBEDTLS_ERR_NET_RECV_FAILED
> 
> Actually I found something interesting in my code.
> 
> Normally when you call read (fd, buf, len) the underlying TCP will fetch the 
> amount you need.
> 
> With the mbedtls_ssl_read it is a bit more complicated. As it internally 
> collects a record to its
> own buffer before it returns to the calling part with the requested block of 
> data. If you read less 
> than the internal SSL buffer size you may have more data to read from the 
> internal buffer but NOT 
> from the socket !!. 
> 
> Because in my code, after every mbedtls_ssl_read I called select it would 
> have failed on the last
> fragment even so that the SSL internal buffer still had some data. I added 
> code to check that 
> ssl.in_msglen == 0 before I call select again. This solved one problem but 
> NOT the overall reading 
> problem.
> 
> If I also added large delays in code so now I am able to read 8 x 1K chunks 
> before I get again the 
>     MBEDTLS_ERR_NET_RECV_FAILED
> 
> This is a combined problem... misunderstanding how the SSL works and probably 
> something related
> to the LwIP layer.
> 
> If I print LwIP debug messages I have no problems reading the file. ... 
> delays ???
> 
> I also changed the call to mbedtls_ssl_set_bio to use the 
> mbedtls_net_recv_timeout instead of 
> mbedtls_net_recv function. With this change I am able to read the first SSL 
> record without problems
> 
> Thanks for all the help so far :-)
> 
> 
> BR,
> Noam.
> 
> -----Original Message-----
> From: lwip-users [mailto:address@hidden On Behalf Of Jan Menzel
> Sent: Wednesday, March 15, 2017 10:54 PM
> To: address@hidden
> Subject: Re: [lwip-users] PolarSSL and mbedTLS
> 
> Hi Noam!
>       Did you follow the error code through mbedtls's net.c? In my code its 
> translated into "MBEDTLS_ERR_SSL_WANT_READ" as follows:
> 
> int mbedtls_net_recv( void *ctx, unsigned char *buf, size_t len ) [...]
>     ret = (int) read( fd, buf, len );
> 
>     if( ret < 0 )
>     {
>         if( net_would_block( ctx ) != 0 )
>             return( MBEDTLS_ERR_SSL_WANT_READ ); [...]
> 
> with
> 
> static int net_would_block( const mbedtls_net_context *ctx ) [...]
>     switch( errno )
>     {
> #if defined EAGAIN
>         case EAGAIN:
> #endif
> #if defined EWOULDBLOCK && EWOULDBLOCK != EAGAIN
>         case EWOULDBLOCK:
> #endif
>             return( 1 );
>     }
>     return( 0 );
> }
> 
>       Jan
> 
> On 15.03.2017 20:30, Noam Weissman wrote:
>> Hi Simon,
>>
>> I have triad debugging my code and added :
>> #define LWIP_DEBUG                     LWIP_DBG_ON
>> #define SOCKETS_DEBUG              LWIP_DBG_ON
>>
>> Strange that with this switches on I am able to get a file of about 38K but 
>> it fails at the last part, always?.
>>
>> Without the debug prints it never even starts, it fails on first read. 
>>
>> I have attached my debug printout if that helps.
>>
>> The text is mixed with my own debug prints, sorry:
>>
>> File transfer starts at line 438 with:  From WssHandleReadData: 
>> PayloadLen = 38032, DataLen = 1020
>>
>> The server sends chunks of 4K, my code reads 1K at a time from the ssl layer 
>> hence the 1024 chunks.
>> You can see that PayloadLen reduces by the DataLen chunk ...
>>
>> The last part received is PayloadLen 1172 DataLen 1024 ... on line 
>> 1512
>>
>> It should read one 1024 block and then 148 bytes and finish... This 
>> never happens and it fails on last read This is consistent on every test I 
>> did ?.
>>
>> If I turn off the two debug switches the file transfer never starts, 
>> actually fails on first read and the lwip_recvfrom returns with -1 and 
>> set_errno(EWOULDBLOCK); on line 773 in sockets.c (lwip ver 2.02)
>>
>>
>> Any ideas ?
>>
>>
>> Many thanks,
>> Noam.
>>
>>
>>
>> -----Original Message-----
>> From: lwip-users [mailto:address@hidden 
>> On Behalf Of Simon Goldschmidt
>> Sent: Friday, March 10, 2017 10:36 AM
>> To: address@hidden
>> Subject: Re: [lwip-users] PolarSSL and mbedTLS
>>
>> Noam Weissman wrote:
>>> I get a read error inside lwip_recvfrom function.
>>> [..]
>>> If anyone has any ideas on what more to check or test please respond.
>>
>> 1: Get an idea of the error (if recvfrom returns -1, what's the 
>> corrent errno?)
>> 2: Get a debugger and try to find out why recvfrom returns an error. Without 
>> that information, there's no way of knowing where the error is.
>>
>> Simon
>>
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Dr. Jan Menzel
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