Re: read image from socket

On Tue, 20 Oct 2009, long wang wrote:

> I have a question about the graphicsmagick api. How should I read a 
> image from a socket?

Assuming that the code works as intended, if you pass an open stdio 
file handle via the ImageInfo file member, then it should be used for 
reading or writing.  Under Unix, you would use fdopen() to create a 
FILE* from a socket file descriptor.

> I'm writing a program which reads image from client via socket and 
> resizes the image then sends the new image back. But I found I 
> cannot read the image from socket. Did i miss something?

You could use the ImageInfo->file member as I mention above, but 
unless the image data is very large, I recommend buffering the data in 
memory (and using BlobToImage() and ImageToBlob()), or if it is very 
large, buffering it to disk.  The reason for this is that network 
sockets may expire (or get stuck) at any time so it is useful to 
simplify the data transfer and error handling to the maximum extent 
possible.  Otherwise if the network becomes extremely slow then the 
GraphicsMagick API would appear to be hung and without a very nice way 
to terminate it (you would have to close the socket file descriptor 
while GraphicsMagick is using it and hope for the best).

Bob
--
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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