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# Example Python plugin.
#
# This example can be freely used for any purpose.
# Run it from the build directory like this:
#
# ./nbdkit -f -v python ./plugins/python/examples/file.py file=test.img
#
# Or run it after installing nbdkit like this:
#
# nbdkit -f -v python ./plugins/python/examples/file.py file=test.img
#
# The -f -v arguments are optional. They cause the server to stay in
# the foreground and print debugging, which is useful when testing.
import os
import nbdkit
# There are several variants of the API. nbdkit will use this
# constant to determine which one you want to use. This is the latest
# version at the time this example was written.
API_VERSION = 2
# The file we want to serve.
filename = None
# Parse the file parameter which contains the name of the file that we
# want to serve.
def config(key, value):
global filename
if key == "file":
filename = os.path.abspath(value)
else:
raise RuntimeError("unknown parameter: " + key)
def config_complete():
if filename is None:
raise RuntimeError("file parameter is required")
# Although Python code cannot be run in parallel, if your
# plugin callbacks sleep then you can improve parallelism
# by relaxing the thread model.
def thread_model():
return nbdkit.THREAD_MODEL_PARALLEL
# This is called when a client connects.
def open(readonly):
if readonly:
flags = os.O_RDONLY
else:
flags = os.O_RDWR
fd = os.open(filename, flags)
return {'fd': fd}
def get_size(h):
sb = os.stat(h['fd'])
return sb.st_size
def pread(h, buf, offset, flags):
n = os.preadv(h['fd'], [buf], offset)
if n != len(buf):
raise RuntimeError("unexpected short read from file")
def pwrite(h, buf, offset, flags):
n = os.pwritev(h['fd'], [buf], offset)
if n != len(buf):
raise RuntimeError("short write")
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