Hi Mark,

 

If you did need a libcurl library for windows there is one that uses the EPICS build system at https://github.com/ISISComputingGroup/EPICS-curl by default it will expect the OpenSSL built from https://github.com/ISISComputingGroup/EPICS-OpenSSL but can probably use one downloaded from elsewhere too

 

Regards,

 

Freddie

 

 

 

Folks,

 

I am working on the driver for the Newport XPS motor controllers.  These controllers can execute Position-Velocity-Time (PVT) trajectory scans which are complex multi-axis coordinated motion along a user-defined path in 8-space.  The trajectory is defined in a text file, which the EPICS driver creates and then uploads to the controller.  The older XPS-C8 and XPS-Q8 controllers support FTP for the upload.  I have a small C implementation of FTP which the driver uses.  This C code is standalone, it only needs to call the standard socket functions.

 

The new XPS-D8 controller does not support FTP, it only supports SFTP/SCP.  I need a solution to be able to do SFTP transfers from within my C++ EPICS driver.  I want the solution to work on both Linux and Windows, and ideally on vxWorks as well.

 

I have tried 3 solutions, and measured the time that each solution required to upload a 5KB file. The results surprised me, and I am curious if anyone can explain them.

 

The code for the 3 solutions is in the attached xpsSFTPUpload.cpp and the test program is testSFTPUpload.cpp.

 

Solution 1.  Use libssh2.  This is selected if CONFIG_SITE defines HAVE_LIBSSH2=YES.

Execution time = 326 ms

 

Solution 2.  Use libcurl with the curl_easy API.  This is selected if CONFIG_SITE defines HAVE_LIBCURL=YES.

Execution time = 323 ms

 

Solution 3. Run the “curl” program with the C system() call.  The driver builds the text of the curl command and runs it with the system() call. This is selected if CONFIG_SITE does not define HAVE_LIBSSH2=YES or HAVE_LIBCURL=YES.

Execution time (Linux) = 126 ms

Execution time (Windows) = 270 ms

 

So on Linux running the “curl” command via a call to system() is actually almost 3 times faster than calling either of the libraries directly.  This surprises me.

 

Note that I actually prefer to use Solution 3 because it is easy to implement on Windows.  There are several sites that provide downloads of a pre-built “curl” executable.  However, I have not been able to find any site that provides the libssh2 or libcurl libraries in a form that can be called from Visual Studio.  They are built with mingw and give errors when I try to link with Visual Studio.  Note that because of the performance measurements above I am not motivated to pursue the library solution either, since it seems to be significantly slower.

 

Ideally I would like this driver to work on vxWorks as well, but I don’t see any solution for doing sftp from within a C program on vxWorks?

 

Thanks,

Mark