On 1/26/2012 7:25 AM, Prabu RM wrote:
Hi,
We have been used to CRC via MD5 hash algorithm for a file to be
transferred in socket we kepp below steps.
_*At Client side:*_
1.Md5 Init()
2.MD5 Update
MD5 Update
MD5 Update
MD5 Update
.
.
.
3.MD5 Final
4.Get Checksum *C1*
_*At Server side:*_
1.Md5 Init()
2.MD5 Update
MD5 Update
MD5 Update
MD5 Update
.
.
.
3.MD5 Final
4.Get Checksum *C2*
*if(C1 == C2)
{
crc is sucess!
}
*
What my case is if i transfer a file with large size about 1GB and if
the socket closed at the time of file reaching 500MB and i re-transfer
the file in next schedule. In this how can i work with MD5,SHA hash
algorithms where i wish "Where it left off"?
Could you please help me? Simply how can i handle CRC of incomplete
file in next schedule? Is there any other way rather than transferring
entire file?
Regards,
Prabu RM.
Simple:
At Server side first pass the bytes from the previously
received 500MB to MD5 Update, then the bytes of the
sent 500MB, so MD5 Update gets the same bytes as for a
full transfer but with only the missing bytes
transferred.
At Client side first pass the 500MB that will not be
sent to MD5 Update, then the 500MB that are sent.
If you use HTTP with the "Range" and "MD5-something"
headers for this job, be sure your client handles the
possibility of the server choosing to send a larger
fraction of the file than requested (it is allowed to
do that, by specifying a different range or the entire
file in its response HTTP headers). For the excess
bytes you can decide to use either the newly received
of the previously received values of those bytes, just
make sure you give MD5 Update the bytes that you will
actually put/keep in the final file.
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