Peculiar Error in Network Transmission

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Guest

Hi,
I am trying to transfer data from a Unix machine to Windows machine
using C Network functions.

In unix i send image data to windows using send() function in a loop
running till the end of image data (length is known beforehand). sending 1022
bytes at a time

when i send binary image data, i use recv command in windows to get data
1022 bytes at a time.it works fine.
But when i try to send JPEG image data. Only the first 4 bytes of JPEG
header (FF D8 FF E0) are received. the rest of the 1018 bytes are not
received, in the next send(), transmission starts from 1023 bytes after the
start of image data, from this point on data is transmitted and received
correctly.
I have observed that if Image data has consecutive zeros - 00 i.e 0x30
0x30. Data is either not read by recv() or transmitted by send() [i actually
dont know which command is at fault since both return 1022 bytes data
read/written].

Any help will be greatly appreciated.

thanks and regards
 
Actually i figured out the problem, I am using a String Array to write data
from Image file and am using this String Array to transmit data using Send().
The 00 is a NULL character in C and when encountered in the array C thinks
the Array has ended.
But the JPEG image data i want to transfer contains a lot of NULL characters
(viewed using Hex editor), and i want to transfer the data through the
network. How can I use a BYTE Array in C? Any suggestions?
 
Are you using Winsock? Or some higher level wrapper library?

If you are using Winsock, the 3rd parameter to send() is the length in bytes
of the byte array (2nd parameter).

--
Regards,
Nish [VC++ MVP]
http://www.voidnish.com
http://blog.voidnish.com


Pravin Prabhu said:
Actually i figured out the problem, I am using a String Array to write
data
from Image file and am using this String Array to transmit data using
Send().
The 00 is a NULL character in C and when encountered in the array C thinks
the Array has ended.
But the JPEG image data i want to transfer contains a lot of NULL
characters
(viewed using Hex editor), and i want to transfer the data through the
network. How can I use a BYTE Array in C? Any suggestions?

Pravin Prabhu said:
Hi,
I am trying to transfer data from a Unix machine to Windows machine
using C Network functions.

In unix i send image data to windows using send() function in a loop
running till the end of image data (length is known beforehand). sending
1022
bytes at a time

when i send binary image data, i use recv command in windows to get
data
1022 bytes at a time.it works fine.
But when i try to send JPEG image data. Only the first 4 bytes of
JPEG
header (FF D8 FF E0) are received. the rest of the 1018 bytes are not
received, in the next send(), transmission starts from 1023 bytes after
the
start of image data, from this point on data is transmitted and received
correctly.
I have observed that if Image data has consecutive zeros - 00 i.e
0x30
0x30. Data is either not read by recv() or transmitted by send() [i
actually
dont know which command is at fault since both return 1022 bytes data
read/written].

Any help will be greatly appreciated.

thanks and regards
Click to expand...
Click to expand...
 
Hi Nishanth,
I am using Winsock on the windows side for recv().
Actually the send() command is in the unix side. I do give
the Length of the array (1022 bytes). but the problem is that there is a null
character at the 5th position of the array. There are a lot of null
characters in the image data stored in the array. Since NULL is the end of
string in C, i am facing problems sending the whole image data.

Nishant Sivakumar said:
Are you using Winsock? Or some higher level wrapper library?

If you are using Winsock, the 3rd parameter to send() is the length in bytes
of the byte array (2nd parameter).

--
Regards,
Nish [VC++ MVP]
http://www.voidnish.com
http://blog.voidnish.com


Pravin Prabhu said:
Actually i figured out the problem, I am using a String Array to write
data
from Image file and am using this String Array to transmit data using
Send().
The 00 is a NULL character in C and when encountered in the array C thinks
the Array has ended.
But the JPEG image data i want to transfer contains a lot of NULL
characters
(viewed using Hex editor), and i want to transfer the data through the
network. How can I use a BYTE Array in C? Any suggestions?

Pravin Prabhu said:
Hi,
I am trying to transfer data from a Unix machine to Windows machine
using C Network functions.

In unix i send image data to windows using send() function in a loop
running till the end of image data (length is known beforehand). sending
1022
bytes at a time

when i send binary image data, i use recv command in windows to get
data
1022 bytes at a time.it works fine.
But when i try to send JPEG image data. Only the first 4 bytes of
JPEG
header (FF D8 FF E0) are received. the rest of the 1018 bytes are not
received, in the next send(), transmission starts from 1023 bytes after
the
start of image data, from this point on data is transmitted and received
correctly.
I have observed that if Image data has consecutive zeros - 00 i.e
0x30
0x30. Data is either not read by recv() or transmitted by send() [i
actually
dont know which command is at fault since both return 1022 bytes data
read/written].

Any help will be greatly appreciated.

thanks and regards
Click to expand...
Click to expand...
Click to expand...
 
You are trying to use null-terminated strings to store binary data. That's
your basic problem.

Instead use a char array [but do not use any string manipulation functions
on it] or use a void* instead. And then use the Buffer-Manipulation Routines
like memcpy, memcmp etc.

--
Regards,
Nish [VC++ MVP]
http://www.voidnish.com
http://blog.voidnish.com


Pravin Prabhu said:
Hi Nishanth,
I am using Winsock on the windows side for recv().
Actually the send() command is in the unix side. I do give
the Length of the array (1022 bytes). but the problem is that there is a
null
character at the 5th position of the array. There are a lot of null
characters in the image data stored in the array. Since NULL is the end of
string in C, i am facing problems sending the whole image data.

Nishant Sivakumar said:
Are you using Winsock? Or some higher level wrapper library?

If you are using Winsock, the 3rd parameter to send() is the length in
bytes
of the byte array (2nd parameter).

--
Regards,
Nish [VC++ MVP]
http://www.voidnish.com
http://blog.voidnish.com


Pravin Prabhu said:
Actually i figured out the problem, I am using a String Array to write
data
from Image file and am using this String Array to transmit data using
Send().
The 00 is a NULL character in C and when encountered in the array C
thinks
the Array has ended.
But the JPEG image data i want to transfer contains a lot of NULL
characters
(viewed using Hex editor), and i want to transfer the data through the
network. How can I use a BYTE Array in C? Any suggestions?

:

Hi,
I am trying to transfer data from a Unix machine to Windows
machine
using C Network functions.

In unix i send image data to windows using send() function in a
loop
running till the end of image data (length is known beforehand).
sending
1022
bytes at a time

when i send binary image data, i use recv command in windows to
get
data
1022 bytes at a time.it works fine.
But when i try to send JPEG image data. Only the first 4 bytes of
JPEG
header (FF D8 FF E0) are received. the rest of the 1018 bytes are not
received, in the next send(), transmission starts from 1023 bytes
after
the
start of image data, from this point on data is transmitted and
received
correctly.
I have observed that if Image data has consecutive zeros - 00 i.e
0x30
0x30. Data is either not read by recv() or transmitted by send() [i
actually
dont know which command is at fault since both return 1022 bytes data
read/written].

Any help will be greatly appreciated.

thanks and regards
Click to expand...
Click to expand...
Click to expand...
 
Hi Nishant,
Actually I am storing (binary) Image data which i obtain from
an imaging device in a Char Array. The Image data already has lots of null
characters as part of image data, so when i copy into a char array it
automatically becomes a null terminated string. and when i try to transmit
the Char array i face problems.

Nishant Sivakumar said:
You are trying to use null-terminated strings to store binary data. That's
your basic problem.

Instead use a char array [but do not use any string manipulation functions
on it] or use a void* instead. And then use the Buffer-Manipulation Routines
like memcpy, memcmp etc.

--
Regards,
Nish [VC++ MVP]
http://www.voidnish.com
http://blog.voidnish.com


Pravin Prabhu said:
Hi Nishanth,
I am using Winsock on the windows side for recv().
Actually the send() command is in the unix side. I do give
the Length of the array (1022 bytes). but the problem is that there is a
null
character at the 5th position of the array. There are a lot of null
characters in the image data stored in the array. Since NULL is the end of
string in C, i am facing problems sending the whole image data.

Nishant Sivakumar said:
Are you using Winsock? Or some higher level wrapper library?

If you are using Winsock, the 3rd parameter to send() is the length in
bytes
of the byte array (2nd parameter).

--
Regards,
Nish [VC++ MVP]
http://www.voidnish.com
http://blog.voidnish.com


Actually i figured out the problem, I am using a String Array to write
data
from Image file and am using this String Array to transmit data using
Send().
The 00 is a NULL character in C and when encountered in the array C
thinks
the Array has ended.
But the JPEG image data i want to transfer contains a lot of NULL
characters
(viewed using Hex editor), and i want to transfer the data through the
network. How can I use a BYTE Array in C? Any suggestions?

:

Hi,
I am trying to transfer data from a Unix machine to Windows
machine
using C Network functions.

In unix i send image data to windows using send() function in a
loop
running till the end of image data (length is known beforehand).
sending
1022
bytes at a time

when i send binary image data, i use recv command in windows to
get
data
1022 bytes at a time.it works fine.
But when i try to send JPEG image data. Only the first 4 bytes of
JPEG
header (FF D8 FF E0) are received. the rest of the 1018 bytes are not
received, in the next send(), transmission starts from 1023 bytes
after
the
start of image data, from this point on data is transmitted and
received
correctly.
I have observed that if Image data has consecutive zeros - 00 i.e
0x30
0x30. Data is either not read by recv() or transmitted by send() [i
actually
dont know which command is at fault since both return 1022 bytes data
read/written].

Any help will be greatly appreciated.

thanks and regards
Click to expand...
Click to expand...
Click to expand...
 
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