Python wrapper for the C implementation of the Generic Sensor Format library.
- Free software: MIT license
- Notes on licensing: The bundled
libgsf/libgsf03_08.sois covered by the LGPL v2.1 license. A copy of this license is included in the project atlibgsf/libgsf_LICENSE.md. This does not affect the top-level MIT licensing of the project. However, as required by the libgsf license, the libgsf shared object library used by gsfpy at runtime may be replaced with a different version by setting theGSFPY_LIBGSF_PATHenvironment variable to the absolute file path of the new library.
-
gsfpy.bindings provides wrappers for all GSFlib functions, including I/O, utility and info functions. Minor exceptions are noted in the sections below.
-
For added convenience the gsfpy top level package provides the following higher level abstractions:
open_gsf()GsfFile(class)GsfFile.read()GsfFile.get_number_records()GsfFile.seek()GsfFile.write()GsfFile.close()
pip install gsfpypip install git+ssh://git@github.com/UKHO/gsfpy.git@masterpip install git+https://github.com/UKHO/gsfpy.git@masterfrom ctypes import string_at
from gsfpy import open_gsf
from gsfpy.enums import RecordType
with open_gsf("path/to/file.gsf") as gsf_file:
# Note - file is closed automatically upon exiting 'with' block
_, record = gsf_file.read(RecordType.GSF_RECORD_COMMENT)
# Note use of ctypes.string_at() to access POINTER(c_char) contents of
# c_gsfComment.comment field.
print(string_at(record.comment.comment))from ctypes import c_int, create_string_buffer
from gsfpy import open_gsf
from gsfpy.enums import FileMode, RecordType
from gsfpy.gsfRecords import c_gsfRecords
comment = "My comment"
# Initialize the contents of the record that will be written.
# Note use of ctypes.create_string_buffer() to set POINTER(c_char) contents.
record = c_gsfRecords()
record.comment.comment_time.tvsec = c_int(1000)
record.comment.comment_length = c_int(len(comment))
record.comment.comment = create_string_buffer(comment)
with open_gsf("path/to/file.gsf", mode=FileMode.GSF_CREATE) as gsf_file:
gsf_file.write(record, RecordType.GSF_RECORD_COMMENT)from ctypes import byref, c_int, pointer
import gsfpy
from gsfpy.enums import FileMode, RecordType
from gsfpy.gsfDataID import c_gsfDataID
from gsfpy.gsfRecords import c_gsfRecords
# This example uses gsfpy.bindings to illustrate use of the lower level functions
file_handle = c_int(0)
data_id = c_gsfDataID()
source_records = c_gsfRecords()
target_records = c_gsfRecords()
ret_val_open = gsfpy.bindings.gsfOpen(
"path/to/file.gsf", FileMode.GSF_READONLY, byref(file_handle)
)
# Note use of ctypes.byref() as a shorthand way of passing POINTER parameters to
# the underlying foreign function call. ctypes.pointer() may also be used.
bytes_read = gsfpy.bindings.gsfRead(
file_handle,
RecordType.GSF_RECORD_COMMENT,
byref(data_id),
byref(source_records),
)
# Note use of pointer() rather than byref() when passing parameters to
# gsfCopyRecords(). Implementation of this function is in Python as calling
# the native underlying function causes memory ownership clashes. byref()
# is only suitable for passing parameters to foreign function calls (see
# ctypes docs).
ret_val_cpy = gsfpy.bindings.gsfCopyRecords(
pointer(target_records), pointer(source_records)
)
ret_val_close = gsfpy.bindings.gsfClose(file_handle)import gsfpy
# The gsfIntError() and gsfStringError() functions are useful for
# diagnostics. They return an error code and corresponding error
# message, respectively.
retValIntError = gsfpy.bindings.gsfIntError()
retValStringError = gsfpy.bindings.gsfStringError()
print(retValStringError)The gsfPrintError() method of GSFlib is not implemented as there is no
FILE* equivalent in Python. Use gsfStringError() instead - this will
give the same error message, which can then be written to file as
required.
gsfFree() the sibling method to gsfCopyRecord() in GSFlib, used to
deallocate memory assigned by the library but managed by the calling
application, is not required by gsfpy as memory allocation and
deallocation is handled by ctypes. gsfFree() is therefore omitted from
the package.
Implementation of the GSFlib function
gsf_register_progress_callback() is not applicable for gsfpy as the
DISPLAY_SPINNER macro was not defined during compilation. It is
therefore omitted from the package.
Generic Sensor Format specification: see e.g. https://github.com/schwehr/generic-sensor-format/blob/master/doc/GSF_lib_03-06.pdf
Generic Sensor Format C library v3.06 specification: see e.g. https://github.com/schwehr/generic-sensor-format/blob/master/doc/GSF_spec_03-06.pdf
More recent versions of these documents can be downloaded from the Leidos website.
Ensure Poetry is installed before proceeding
By default Poetry will create it's own virtual environment using your system's Python. This feature can be disabled.
git clone git@github.com:UKHO/gsfpy.git
cd gsfpy
poetry installA good choice if you want to run a version of Python different than available through your system's package manager
git clone git@github.com:UKHO/gsfpy.git
cd gsfpy
pyenv install 3.8.3
pyenv virtualenv 3.8.3 gsfpy
pyenv local gsfpy
poetry installmake testmake lintSome known concerns relating to the underlying GSFlib C library are documented at dwcaress/MB-System#368 and https://github.com/schwehr/generic-sensor-format/issues. Note that gsfpy simply wraps GSFlib and does not purport to stop or mitigate these potential vulnerabilities. It is left to the authors of applications calling gsfpy to assess these risks and mitigate where deemed necessary.
GSF data processed using gsfpy should be sourced from reliable providers and checked for integrity where possible.
Please also refer to the LICENSE file for the terms of use of gsfpy.
libgsf03-08.so was built from the
Leidos C code using the
Makefile in UKHO/libgsf
This package was created with Cookiecutter and the UKHO/cookiecutter-pypackage project template.
Also see schwehr/generic-sensor-format