mirror of
https://github.com/qpdf/qpdf.git
synced 2024-11-09 23:00:57 +00:00
263 lines
8.8 KiB
ReStructuredText
263 lines
8.8 KiB
ReStructuredText
|
||
.. _qpdf-job:
|
||
|
||
QPDFJob: a Job-Based Interface
|
||
==============================
|
||
|
||
All of the functionality from the :command:`qpdf` command-line
|
||
executable is available from inside the C++ library using the
|
||
``QPDFJob`` class. There are several ways to access this functionality:
|
||
|
||
- Command-line options
|
||
|
||
- Run the :command:`qpdf` command line
|
||
|
||
- Use from the C++ API with ``QPDFJob::initializeFromArgv``
|
||
|
||
- Use from the C API with ``qpdfjob_run_from_argv`` from
|
||
:file:`qpdfjob-c.h`. If you are calling from a Windows-style main
|
||
and have an argv array of ``wchar_t``, you can use
|
||
``qpdfjob_run_from_wide_argv``.
|
||
|
||
- The job JSON file format
|
||
|
||
- Use from the CLI with the :qpdf:ref:`--job-json-file` parameter
|
||
|
||
- Use from the C++ API with ``QPDFJob::initializeFromJson``
|
||
|
||
- Use from the C API with ``qpdfjob_run_from_json`` from :file:`qpdfjob-c.h`
|
||
|
||
- Note: this is unrelated to :qpdf:ref:`--json` but can be combined
|
||
with it. For more information on qpdf JSON (vs. QPDFJob JSON), see
|
||
:ref:`json`.
|
||
|
||
- The ``QPDFJob`` C++ API
|
||
|
||
If you can understand how to use the :command:`qpdf` CLI, you can
|
||
understand the ``QPDFJob`` class and the JSON file. qpdf guarantees
|
||
that all of the above methods are in sync. Here's how it works:
|
||
|
||
.. list-table:: QPDFJob Interfaces
|
||
:widths: 30 30 30
|
||
:header-rows: 1
|
||
|
||
- - CLI
|
||
- JSON
|
||
- C++
|
||
|
||
- - ``--some-option``
|
||
- ``"someOption": ""``
|
||
- ``config()->someOption()``
|
||
|
||
- - ``--some-option=value``
|
||
- ``"someOption": "value"``
|
||
- ``config()->someOption("value")``
|
||
|
||
- - positional argument
|
||
- ``"otherOption": "value"``
|
||
- ``config()->otherOption("value")``
|
||
|
||
In the JSON file, the JSON structure is an object (dictionary) whose
|
||
keys are command-line flags converted to camelCase. Positional
|
||
arguments have some corresponding key, which you can find by running
|
||
``qpdf`` with the :qpdf:ref:`--job-json-help` flag. For example, input
|
||
and output files are named by positional arguments on the CLI. In the
|
||
JSON, they appear in the ``"inputFile"`` and ``"outputFile"`` keys.
|
||
The following are equivalent:
|
||
|
||
.. It would be nice to have an automated test that these are all the
|
||
same, but we have so few live examples that it's not worth it for
|
||
now.
|
||
|
||
CLI:
|
||
::
|
||
|
||
qpdf infile.pdf outfile.pdf \
|
||
--pages . other.pdf --password=x 1-5 -- \
|
||
--encrypt user owner 256 --print=low -- \
|
||
--object-streams=generate
|
||
|
||
Job JSON:
|
||
.. code-block:: json
|
||
|
||
{
|
||
"inputFile": "infile.pdf",
|
||
"outputFile": "outfile.pdf",
|
||
"pages": [
|
||
{
|
||
"file": "."
|
||
},
|
||
{
|
||
"file": "other.pdf",
|
||
"password": "x",
|
||
"range": "1-5"
|
||
}
|
||
],
|
||
"encrypt": {
|
||
"userPassword": "user",
|
||
"ownerPassword": "owner",
|
||
"256bit": {
|
||
"print": "low"
|
||
}
|
||
},
|
||
"objectStreams": "generate"
|
||
}
|
||
|
||
C++ code:
|
||
.. code-block:: c++
|
||
|
||
#include <qpdf/QPDFJob.hh>
|
||
#include <qpdf/QPDFUsage.hh>
|
||
#include <iostream>
|
||
|
||
int main(int argc, char* argv[])
|
||
{
|
||
try
|
||
{
|
||
QPDFJob j;
|
||
j.config()
|
||
->inputFile("infile.pdf")
|
||
->outputFile("outfile.pdf")
|
||
->pages()
|
||
->pageSpec(".", "1-z")
|
||
->pageSpec("other.pdf", "1-5", "x")
|
||
->endPages()
|
||
->encrypt(256, "user", "owner")
|
||
->print("low")
|
||
->endEncrypt()
|
||
->objectStreams("generate")
|
||
->checkConfiguration();
|
||
j.run();
|
||
}
|
||
catch (QPDFUsage& e)
|
||
{
|
||
std::cerr << "configuration error: " << e.what() << std::endl;
|
||
return 2;
|
||
}
|
||
catch (std::exception& e)
|
||
{
|
||
std::cerr << "other error: " << e.what() << std::endl;
|
||
return 2;
|
||
}
|
||
return 0;
|
||
}
|
||
|
||
Note the ``QPDFUsage`` exception above. This is thrown whenever a
|
||
configuration error occurs. These exactly correspond to usage messages
|
||
issued by the :command:`qpdf` CLI for things like omitting an output
|
||
file, specifying `--pages` multiple times, or other invalid
|
||
combinations of options. ``QPDFUsage`` is thrown by the argv and JSON
|
||
interfaces as well as the native ``QPDFJob`` interface.
|
||
|
||
It is also possible to mix and match command-line options and JSON
|
||
from the CLI. For example, you could create a file called
|
||
:file:`my-options.json` containing the following:
|
||
|
||
.. code-block:: json
|
||
|
||
{
|
||
"encrypt": {
|
||
"userPassword": "",
|
||
"ownerPassword": "owner",
|
||
"256bit": {
|
||
}
|
||
},
|
||
"objectStreams": "generate"
|
||
}
|
||
|
||
and use it with other options to create 256-bit encrypted (but
|
||
unrestricted) files with object streams while specifying other
|
||
parameters on the command line, such as
|
||
|
||
::
|
||
|
||
qpdf infile.pdf outfile.pdf --job-json-file=my-options.json
|
||
|
||
.. _qpdfjob-design:
|
||
|
||
See also :file:`examples/qpdf-job.cc` in the source distribution as
|
||
well as comments in ``QPDFJob.hh``.
|
||
|
||
|
||
QPDFJob Design
|
||
--------------
|
||
|
||
This section describes some of the design rationale and history behind
|
||
``QPDFJob``.
|
||
|
||
Documentation of ``QPDFJob`` is divided among three places:
|
||
|
||
- "HOW TO ADD A COMMAND-LINE ARGUMENT" in :file:`README-maintainer`
|
||
provides a quick reminder of how to add a command-line argument.
|
||
|
||
- The source file :file:`generate_auto_job` has a detailed explanation
|
||
about how ``QPDFJob`` and ``generate_auto_job`` work together.
|
||
|
||
- This chapter of the manual has other details.
|
||
|
||
Prior to qpdf version 10.6.0, the qpdf CLI executable had a lot of
|
||
functionality built into it that was not callable from the library as
|
||
such. This created a number of problems:
|
||
|
||
- Some of the logic in :file:`qpdf.cc` was pretty complex, such as
|
||
image optimization, generating JSON output, and many of the page
|
||
manipulations. While those things could all be coded using the C++
|
||
API, there would be a lot of duplicated code.
|
||
|
||
- Page splitting and merging will get more complicated over time as
|
||
qpdf supports a wider range of document-level options. It would be
|
||
nice to be able to expose this to library users instead of baking it
|
||
all into the CLI.
|
||
|
||
- Users of other languages who just wanted an interface to do things
|
||
that the CLI could do didn't have a good way to do it, such as just
|
||
handing a library call a set of command-line options or an
|
||
equivalent JSON object that could be passed in as a string.
|
||
|
||
- The qpdf CLI itself was almost 8,000 lines of code. It needed to be
|
||
refactored, cleaned up, and split.
|
||
|
||
- Exposing a new feature via the command-line required making lots of
|
||
small edits to lots of small bits of code, and it was easy to forget
|
||
something. Adding a code generator, while complex in some ways,
|
||
greatly reduces the chances of error when extending qpdf.
|
||
|
||
Here are a few notes on some design decisions about QPDFJob and its
|
||
various interfaces.
|
||
|
||
- Bare command-line options (flags with no parameter) map to config
|
||
functions that take no options and to JSON keys whose values are
|
||
required to be the empty string. The rationale is that we can later
|
||
change these bare options to options that take an optional parameter
|
||
without breaking backward compatibility in the CLI or the JSON.
|
||
Options that take optional parameters generate two config functions:
|
||
one has no arguments, and one that has a ``char const*`` argument.
|
||
This means that adding an optional parameter to a previously bare
|
||
option also doesn't break binary compatibility.
|
||
|
||
- Adding a new argument to :file:`job.yml` automatically triggers
|
||
almost everything by declaring and referencing things that you have
|
||
to implement. This way, once you get the code to compile and link,
|
||
you know you haven't forgotten anything. There are two tricky cases:
|
||
|
||
- If an argument handler has to do something special, like call a
|
||
nested config method or select an option table, you have to
|
||
implement it manually. This is discussed in
|
||
:file:`generate_auto_job`.
|
||
|
||
- When you add an option that has optional parameters or choices,
|
||
both of the handlers described above are declared, but only the
|
||
one that takes an argument is referenced. You have to remember to
|
||
implement the one that doesn't take an argument or else people
|
||
will get a linker error if they try to call it. The assumption is
|
||
that things with optional parameters started out as bare, so the
|
||
argument-less version is already there.
|
||
|
||
- If you have to add a new option that requires its own option table,
|
||
you will have to do some extra work including adding a new nested
|
||
Config class, adding a config member variable to ``ArgParser`` in
|
||
:file:`QPDFJob_argv.cc` and ``Handlers`` in :file:`QPDFJob_json.cc`,
|
||
and make sure that manually implemented handlers are consistent with
|
||
each other. It is best to add explicit test cases for all the
|
||
various ways to get to the option.
|