The "test-xfer" command:

This command is used for debugging the server.  There is a single
argument which is the uncompressed content of an "xfer" message
from client to server.  This command interprets that message as
if had been received by the server.

On the client side, run:

     fossil push http://bogus/ --httptrace

Or a similar command to provide the output.  The content of the
message will appear on standard output.  Capture this message
into a file named (for example) out.txt.  Then run the
server in gdb:

    gdb fossil
    r test-xfer out.txt