# Building and Installing QPDF

This chapter describes how to build and install qpdf.

## Dependencies

qpdf has few external dependencies. This section describes what you need to build qpdf in various circumstances.

### Basic Dependencies

- A C++ compiler that supports C++-17

- CMake version 3.16 or later

- zlib or a compatible zlib implementation

- A libjpeg-compatible library such as jpeg or libjpeg-turbo

- Recommended but not required: gnutls to be able to use the gnutls crypto provider and/or openssl to be able to use the openssl crypto provider

The qpdf source tree includes a few automatically generated files. The code generator uses Python 3. Automatic code generation is off by default. For a discussion, refer to Build Options.

### Test Dependencies

qpdf’s test suite is run by `ctest`, which is part of CMake, but the tests themselves are implemented using an embedded copy of qtest, which is implemented in perl. On Windows, MSYS2’s perl is known to work.

qtest requires GNU diffutils or any other diff that supports diff -u. The default `diff` command works on GNU/Linux and MacOS.

Part of qpdf’s test suite does comparisons of the contents PDF files by converting them to images and comparing the images. The image comparison tests are disabled by default. Those tests are not required for determining correctness of a qpdf build since the test suite also contains expected output files that are compared literally. The image comparison tests provide an extra check to make sure that any content transformations don’t break the rendering of pages. Transformations that affect the content streams themselves are off by default and are only provided to help developers look into the contents of PDF files. If you are making deep changes to the library that cause changes in the contents of the files that qpdf generates, then you should enable the image comparison tests. Enable them by setting the `QPDF_TEST_COMPARE_IMAGES` environment variable to `1` before running tests. Image comparison tests add these additional requirements:

- libtiff command-line utilities

- GhostScript version 8.60 or newer

Note: prior to qpdf 11, image comparison tests were enabled within `qpdf.test`, and you had to disable them by setting `QPDF_SKIP_TEST_COMPARE_IMAGES` to `1`. This was done automatically by `./configure`. Now you have to enable image comparison tests by setting an environment variable. This change was made because developers have to set the environment variable themselves now rather than setting it through the build. Either way, they are off by default.

### Additional Requirements on Windows

- To build qpdf with Visual Studio, there are no additional requirements when the default cmake options are used. You can build qpdf from a Visual C++ command-line shell.

- To build with mingw, MSYS2 is recommended with the mingw32 and/or mingw64 tool chains. You can also build with MSVC from an MSYS2 environment.

- qpdf’s test suite can run within the MSYS2 environment for both mingw and MSVC-based builds.

For additional notes, see `README-windows.md` in the source distribution.

### Requirements for Building Documentation

The qpdf manual is written in reStructured Text and built with Sphinx using the Read the Docs Sphinx Theme. Versions of sphinx prior to version 4.3.2 probably won’t work. Sphinx requires Python 3. In order to build the HTML documentation from source, you need to install sphinx and the theme, which you can typically do with `pip install sphinx sphinx_rtd_theme`. To build the PDF version of the documentation, you need `pdflatex`, `latexmk`, and a fairly complete LaTeX installation. Detailed requirements can be found in the Sphinx documentation. To see how the documentation is built for the qpdf distribution, refer to the `build-scripts/build-doc` file in the qpdf source distribution.

## Build Instructions

Starting with qpdf 11, qpdf is built with CMake.

### Basic Build Invocation

qpdf uses cmake in an ordinary way, so refer to the CMake documentation for details about how to run `cmake`. Here is a brief summary.

You can usually just run

    cmake -S . -B build
    cmake --build build

If you are using a multi-configuration generator such as MSVC, you should pass `--config <Config>` (where `<Config>` is `Release`, `Debug`, `RelWithDebInfo`, or `MinSizeRel` as discussed in the CMake documentation) to the build command. If you are running a single configuration generator such as the default Makefile generators in Linux or MSYS, you may want to pass `-DCMAKE_BUILD_TYPE=<Config>` to the original `cmake` command.

Run `ctest` to run the test suite. Since the real tests are implemented with qtest, you will want to pass `--verbose` to `cmake` so you can see the individual test outputs. Otherwise, you will see a small number of `ctest` commands that take a very long to run. If you want to run only a specific test file in a specific test suite, you can set the `TESTS` environment variable (used by `qtest-driver`) and pass the `-R` parameter to `ctest`. For example:

    TESTS=qutil ctest --verbose -R libtests

would run only `qutil.test` from the `libtests` test suite.

### Installation and Packaging

Installation can be performed using `cmake --install` or `cpack`. For most normal use cases, `cmake --install` or `cpack` can be run in the normal way as described in CMake documentation. qpdf follows all normal installation conventions and uses CMake-defined variables for standard behavior.

There are several components that can be installed separately:

Installation Components
cli | Command-line tools
lib | The runtime libraries; required if you built with shared libraries
dev | Static libraries, header files, and other files needed by developers
doc | Documentation and, if selected for installation, the manual
examples | Example source files

Note that the `lib` component installs only runtime libraries, not header files or other files/links needed to build against qpdf. For that, you need `dev`. If you are using shared libraries, the `dev` will install files or create symbolic links that depend on files installed by `lib`, so you will need to install both. If you wanted to build software against the qpdf library and only wanted to install the files you needed for that purpose, here are some examples:

- Install development files with static libraries only:

      cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo -DBUILD_SHARED_LIBS=OFF
      cmake --build build --parallel --target libqpdf
      cmake --install build --component dev

- Install development files with shared libraries only:

      cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo -DBUILD_STATIC_LIBS=OFF
      cmake --build build --parallel --target libqpdf
      cmake --install build --component lib
      cmake --install build --component dev

- Install development files with shared and static libraries:

      cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo
      cmake --build build --parallel --target libqpdf libqpdf_static
      cmake --install build --component lib
      cmake --install build --component dev

There are also separate options, discussed in Build Options, that control how certain specific parts of the software are installed.

## Build Options

All available build options are defined in the the top-level `CMakeLists.txt` file and have help text. You can see them using any standard cmake front-end (like `cmake-gui` or `ccmake`). This section describes options that apply to most users. If you are trying to map autoconf options (from prior to qpdf 11) to cmake options, please see Converting From autoconf to cmake.

If you are packaging qpdf for a distribution, you should also read Notes for Packagers.

### Basic Build Options

BUILD_DOC

  Whether to build documentation with sphinx. You must have the required tools installed.

BUILD_DOC_HTML

  Visible when BUILD_DOC is selected. This option controls building HTML documentation separately from PDF documentation since the sphinx theme is only needed for the HTML documentation.

BUILD_DOC_PDF

  Visible when BUILD_DOC is selected. This option controls building PDF documentation separately from HTML documentation since additional tools are required to build the PDF documentation.

BUILD_SHARED_LIBS, BUILD_STATIC_LIBS

  You can configure whether to build shared libraries, static libraries, or both. You must select at least one of these options. For rapid iteration, select only one as this cuts the build time in half.

  On Windows, if you build with shared libraries, you must have the output directory for libqpdf (e.g. `libqpdf/Release` or `libqpdf` within the build directory) in your path so that the compiled executables can find the DLL. Updating your path is not necessary if you build with static libraries only.

FUTURE

  This option enables changes planned for the next major release to be included. They are NOT part of the stable API. These changes are ABI breaking and are subject to change, which means code linked against a qpdf built with this option may not be binary compatible with installed qpdf libraries. Set this if you want to test your code with proposed QPDF API changes and provide feedback prior to the inclusion of those changes in a release. Packagers should never distribute packages built with this option.

QTEST_COLOR

  Turn this on or off to control whether qtest uses color in its output.

### Options for Working on qpdf

CHECK_SIZES

  The source file `qpdf/sizes.cc` is used to display the sizes of all objects in the public API. Consistency of its output between releases is used as part of the check against accidental breakage of the binary interface (ABI). Turning this on causes a test to be run that ensures an exact match between classes in `sizes.cc` and classes in the library’s public API. This option requires Python 3.

ENABLE_COVERAGE

  Compile with `--coverage`. See README-maintainer.md for information about generating coverage reports.

ENABLE_QTC

  This is off by default, except in maintainer mode. When off, `QTC::TC` calls are compiled out by having `QTC::TC` be an empty inline function. The underlying `QTC::TC` remains in the library, so it is possible to build and package the qpdf library with `ENABLE_QTC` turned off while still allowing developer code to use `QTC::TC` if desired. If you are modifying qpdf code, it’s a good idea to have this on for more robust automated testing. Otherwise, there’s no reason to have it on.

GENERATE_AUTO_JOB

  Some qpdf source files are automatically generated from `job.yml` and the CLI documentation. If you are adding new command-line arguments to the qpdf CLI or updating `manual/cli.rst` in the qpdf sources, you should turn this on. This option requires Python 3.

WERROR

  Make any compiler warnings into errors. We want qpdf to compile free of warnings whenever possible, but there’s always a chance that a compiler upgrade or tool change may cause warnings to appear that weren’t there before. If you are testing qpdf with a new compiler, you should turn this on.

### Environment-Specific Options

SHOW_FAILED_TEST_OUTPUT

  Ordinarily, qtest (which drives qpdf’s test suite) writes detailed information about its output to the file `qtest.log` in the build output directory. If you are running a build in a continuous integration or automated environment where you can’t get to those files, you should enable this option and also run `ctest --verbose` or `ctest --output-on-failure`. This will cause detailed test failure output to be written into the build log.

CI_MODE

  Turning this on sets options used in qpdf’s continuous integration environment to ensure we catch as many problems as possible. Specifically, this option enables `SHOW_FAILED_TEST_OUTPUT` and `WERROR` and forces the native crypto provider to be built.

MAINTAINER_MODE

  Turning this option on sets options that should be on if you are maintaining qpdf. In turns on the following:

  - `BUILD_DOC`

  - `CHECK_SIZES`

  - `ENABLE_QTC`

  - `GENERATE_AUTO_JOB`

  - `WERROR`

  - `REQUIRE_NATIVE_CRYPTO`

  It is possible to turn `BUILD_DOC` off in maintainer mode so that the extra requirements for building documentation don’t have to be available.

### Build-time Crypto Selection

Since version 9.1.0, qpdf can use external crypto providers in addition to its native provider. For a general discussion, see Crypto Providers. This section discusses how to configure which crypto providers are compiled into qpdf.

In nearly all cases, external crypto providers should be preferred over the native one. However, if you are not concerned about working with encrypted files and want to reduce the number of dependencies, the native crypto provider is fully supported.

By default, qpdf’s build enables every external crypto providers whose dependencies are available and only enables the native crypto provider if no external providers are available. You can change this behavior with the options described here.

USE_IMPLICIT_CRYPTO

  This is on by default. If turned off, only explicitly selected crypto providers will be built. You must use at least one of the `REQUIRE` options below.

ALLOW_CRYPTO_NATIVE

  This option is only available when USE_IMPLICIT_CRYPTO is selected, in which case it is on by default. Turning it off prevents qpdf from falling back to the native crypto provider when no external provider is available.

REQUIRE_CRYPTO_NATIVE

  Build the native crypto provider even if other options are available.

REQUIRE_CRYPTO_GNUTLS

  Require the gnutls crypto provider. Turning this on makes in an error if the gnutls library is not available.

REQUIRE_CRYPTO_OPENSSL

  Require the openssl crypto provider. Turning this on makes in an error if the openssl library is not available.

DEFAULT_CRYPTO

  Explicitly select which crypto provider is used by default. See Runtime Crypto Provider Selection for information about run-time selection of the crypto provider. If not specified, qpdf will pick gnutls if available, otherwise openssl if available, and finally native as a last priority.

Example: if you wanted to build with only the gnutls crypto provider, you should run cmake with `-DUSE_IMPLICIT_CRYPTO=0 -DREQUIRE_CRYPTO_GNUTLS=1`.

### Advanced Build Options

These options are used only for special purposes and are not relevant to most users.

AVOID_WINDOWS_HANDLE

  Disable use of the `HANDLE` type in Windows. This can be useful if you are building for certain embedded Windows environments. Some functionality won’t work, but you can still process PDF files from memory in this configuration.

BUILD_DOC_DIST, INSTALL_MANUAL

  By default, installing qpdf does not include a pre-built copy of the manual. Instead, it installs a README file that tells people where to find the manual online. If you want to install the manual, you must enable the `INSTALL_MANUAL` option, and you must have a `doc-dist` directory in the manual directory of the build. The `doc-dist` directory is created if `BUILD_DOC_DIST` is selected and `BUILD_DOC_PDF` and `BUILD_DOC_HTML` are both on.

  The `BUILD_DOC_DIST` and `INSTALL_MANUAL` options are separate and independent because of the additional tools required to build documentation. In particular, for qpdf’s official release preparation, a `doc-dist` directory is built in Linux and then extracted into the Windows builds so that it can be included in the Windows installers. This prevents us from having to build the documentation in a Windows environment. For additional discussion, see Documentation Packaging Rationale.

INSTALL_CMAKE_PACKAGE

  Controls whether or not to install qpdf’s cmake configuration file (on by default).

INSTALL_EXAMPLES

  Controls whether or not to install qpdf’s example source files with documentation (on by default).

INSTALL_PKGCONFIG

  Controls whether or not to install qpdf’s pkg-config configuration file (on by default).

OSS_FUZZ

  Turning this option on changes the build of the fuzzers in a manner specifically required by Google’s oss-fuzz project. There is no reason to turn this on for any other reason. It is enabled by the build script that builds qpdf from that context.

SKIP_OS_SECURE_RANDOM, USE_INSECURE_RANDOM

  The native crypto implementation uses the operating systems’s secure random number source when available. It is not used when an external crypto provider is in use. If you are building in a very specialized environment where you are not using an external crypto provider but can’t use the OS-provided secure random number generator, you can turn both of these options on. This will cause qpdf to fall back to an insecure random number generator, which may generate guessable random numbers. The resulting qpdf is still secure, but encrypted files may be more subject to brute force attacks. Unless you know you need these options for a specialized purpose, you don’t need them. These options were added to qpdf in response to a special request from a user who needed to run a specialized PDF-related task in an embedded environment that didn’t have a secure random number source.

### Building without wchar_t

It is possible to build qpdf on a system that doesn’t have `wchar_t`. The resulting build of qpdf is not API-compatible with a regular qpdf build, so this option cannot be selected from cmake. This option was added to qpdf to support installation on a very stripped down embedded environment that included only a partial implementation of the standard C++ library.

You can disable use of `wchar_t` in qpdf’s code by defining the `QPDF_NO_WCHAR_T` preprocessor symbol in your build (e.g. by including `-DQPDF_NO_WCHAR_T` in `CFLAGS` and `CXXFLAGS`).

While `wchar_t` is part of the C++ standard library and should be present on virtually every system, there are some stripped down systems, such as those targeting certain embedded environments, that lack `wchar_t`. Internally, qpdf uses UTF-8 encoding for everything, so there is nothing important in qpdf’s API that uses `wchar_t`. However, there are some helper methods for converting between `wchar_t*` and `char*`.

If you are building in an environment that does not support `wchar_t`, you can define the preprocessor symbol `QPDF_NO_WCHAR_T` in your build. This will work whether you are building qpdf and need to avoid compiling the code that uses wchar_t or whether you are building client code that uses qpdf.

Note that, when you build code with libqpdf, it is not necessary to have the definition of `QPDF_NO_WCHAR_T` in your build match what was defined when the library was built as long as you are not calling any of the methods that use `wchar_t`.

## Crypto Providers

Starting with qpdf 9.1.0, the qpdf library can be built with multiple implementations of providers of cryptographic functions, which we refer to as “crypto providers.” At the time of writing, a crypto implementation must provide MD5 and SHA2 (256, 384, and 512-bit) hashes and RC4 and AES256 with and without CBC encryption. In the future, if digital signature is added to qpdf, there may be additional requirements beyond this. Some of these are weak cryptographic algorithms. For a discussion of why they’re needed, see Weak Cryptography.

The available crypto provider implementations are `gnutls`, `openssl`, and `native`. OpenSSL support was added in qpdf 10.0.0 with support for OpenSSL added in 10.4.0. GnuTLS support was introduced in qpdf 9.1.0. Additional implementations can be added as needed. It is also possible for a developer to provide their own implementation without modifying the qpdf library.

For information about selecting which crypto providers are compiled into qpdf, see Build-time Crypto Selection.

### Runtime Crypto Provider Selection

You can use the `--show-crypto` option to qpdf to get a list of available crypto providers. The default provider is always listed first, and the rest are listed in lexical order. Each crypto provider is listed on a line by itself with no other text, enabling the output of this command to be used easily in scripts.

You can override which crypto provider is used by setting the `QPDF_CRYPTO_PROVIDER` environment variable. There are few reasons to ever do this, but you might want to do it if you were explicitly trying to compare behavior of two different crypto providers while testing performance or reproducing a bug. It could also be useful for people who are implementing their own crypto providers.

### Crypto Provider Information for Developers

If you are writing code that uses libqpdf and you want to force a certain crypto provider to be used, you can call the method `QPDFCryptoProvider::setDefaultProvider`. The argument is the name of a built-in or developer-supplied provider. To add your own crypto provider, you have to create a class derived from `QPDFCryptoImpl` and register it with `QPDFCryptoProvider`. For additional information, see comments in `include/qpdf/QPDFCryptoImpl.hh`.

### Crypto Provider Design Notes

This section describes a few bits of rationale for why the crypto provider interface was set up the way it was. You don’t need to know any of this information, but it’s provided for the record and in case it’s interesting.

As a general rule, I want to avoid as much as possible including large blocks of code that are conditionally compiled such that, in most builds, some code is never built. This is dangerous because it makes it very easy for invalid code to creep in unnoticed. As such, I want it to be possible to build qpdf with all available crypto providers, and this is the way I build qpdf for local development. At the same time, if a particular packager feels that it is a security liability for qpdf to use crypto functionality from other than a library that gets considerable scrutiny for this specific purpose (such as gnutls, openssl, or nettle), then I want to give that packager the ability to completely disable qpdf’s native implementation. Or if someone wants to avoid adding a dependency on one of the external crypto providers, I don’t want the availability of the provider to impose additional external dependencies within that environment. Both of these are situations that I know to be true for some users of qpdf.

I want registration and selection of crypto providers to be thread-safe, and I want it to work deterministically for a developer to provide their own crypto provider and be able to set it up as the default. This was the primary motivation behind requiring C++-11 as doing so enabled me to exploit the guaranteed thread safety of local block static initialization. The `QPDFCryptoProvider` class uses a singleton pattern with thread-safe initialization to create the singleton instance of `QPDFCryptoProvider` and exposes only static methods in its public interface. In this way, if a developer wants to call any `QPDFCryptoProvider` methods, the library guarantees the `QPDFCryptoProvider` is fully initialized and all built-in crypto providers are registered. Making `QPDFCryptoProvider` actually know about all the built-in providers may seem a bit sad at first, but this choice makes it extremely clear exactly what the initialization behavior is. There’s no question about provider implementations automatically registering themselves in a nondeterministic order. It also means that implementations do not need to know anything about the provider interface, which makes them easier to test in isolation. Another advantage of this approach is that a developer who wants to develop their own crypto provider can do so in complete isolation from the qpdf library and, with just two calls, can make qpdf use their provider in their application. If they decided to contribute their code, plugging it into the qpdf library would require a very small change to qpdf’s source code.

The decision to make the crypto provider selectable at runtime was one I struggled with a little, but I decided to do it for various reasons. Allowing an end user to switch crypto providers easily could be very useful for reproducing a potential bug. If a user reports a bug that some cryptographic thing is broken, I can easily ask that person to try with the `QPDF_CRYPTO_PROVIDER` variable set to different values. The same could apply in the event of a performance problem. This also makes it easier for qpdf’s own test suite to exercise code with different providers without having to make every program that links with qpdf aware of the possibility of multiple providers. In qpdf’s continuous integration environment, the entire test suite is run for each supported crypto provider. This is made simple by being able to select the provider using an environment variable.

Finally, making crypto providers selectable in this way establish a pattern that I may follow again in the future for stream filter providers. One could imagine a future enhancement where someone could provide their own implementations for basic filters like `/FlateDecode` or for other filters that qpdf doesn’t support. Implementing the registration functions and internal storage of registered providers was also easier using C++-11’s functional interfaces, which was another reason to require C++-11 at this time.

## Converting From autoconf to cmake

Versions of qpdf before qpdf 11 were built with `autoconf` and a home-grown GNU Make-based build system. If you built qpdf with special `./configure` options, this section can help you switch them over to `cmake`.

In most cases, there is a one-to-one mapping between configure options and cmake options. There are a few exceptions:

- The cmake build behaves differently with respect to whether or not to include support for the native crypto provider. Specifically, it is not implicitly enabled unless explicitly requested if there are other options available. You can force it to be included by enabling `REQUIRE_CRYPTO_NATIVE`. For details, see Build-time Crypto Selection.

- The `--enable-external-libs` option is no longer available. The cmake build detects the presence of `external-libs` automatically. See `README-windows.md` in the source distribution for a more in-depth discussion.

- The sense of the option representing use of the OS-provided secure random number generator has been reversed: the `--enable-os-secure-random`, which was on by default, has been replaced by the `SKIP_OS_SECURE_RANDOM` option, which is off by default. The option’s new name and behavior match the preprocessor symbol that it turns on.

- Non-default test configuration is selected with environment variables rather than cmake. The old `./configure` options just set environment variables. Note that the sense of the variable for image comparison tests has been reversed. It used to be that you had to set `QPDF_SKIP_TEST_COMPARE_IMAGES` to `1` to disable image comparison tests. This was done by default. Now you have to set `QPDF_TEST_COMPARE_IMAGES` to `1` to enable image comparison tests. Either way, they are off by default.

- Non-user-visible change: the preprocessor symbol that triggers the export of functions into the public ABI (application binary interface) has been changed from `DLL_EXPORT` to `libqpdf_EXPORTS`. This detail is encapsulated in the build and is only relevant to people who are building qpdf on their own or who may have previously needed to work around a collision between qpdf’s use of `DLL_EXPORT` and someone else’s use of the same symbol.

- A handful of options that were specific to autoconf or the old build system have been dropped.

- `cmake --install` installs example source code in `doc/qpdf/examples` in the `examples` installation component. Packagers are encouraged to package this with development files if there is no separate doc package. This can be turned off by disabling the `INSTALL_EXAMPLES` build option.

There are some new options available in the cmake build that were not available in the autoconf build. This table shows the old options and their equivalents in cmake.

configure flags to cmake options
enable-avoid-windows-handle | AVOID_WINDOWS_HANDLE
enable-check-autofiles | none – not relevant to cmake
enable-crypto-gnutls | REQUIRE_CRYPTO_GNUTLS
enable-crypto-native | REQUIRE_CRYPTO_NATIVE (but see above)
enable-crypto-openssl | REQUIRE_CRYPTO_OPENSSL
enable-doc-maintenance | BUILD_DOC
enable-external-libs | none – detected automatically
enable-html-doc | BUILD_DOC_HTML
enable-implicit-crypto | USE_IMPLICIT_CRYPTO
enable-insecure-random | USE_INSECURE_RANDOM
enable-ld-version-script | none – detected automatically
enable-maintainer-mode | MAINTAINER_MODE (slight differences)
enable-os-secure-random (on by default) | SKIP_OS_SECURE_RANDOM (off by default)
enable-oss-fuzz | OSS_FUZZ
enable-pdf-doc | BUILD_DOC_PDF
enable-rpath | none – cmake handles rpath correctly
enable-show-failed-test-output | SHOW_FAILED_TEST_OUTPUT
enable-test-compare-images | set the `QPDF_TEST_COMPARE_IMAGES` environment variable
enable-werror | WERROR
with-buildrules | none – not relevant to cmake
with-default-crypto | DEFAULT_CRYPTO
large-file-test-path | set the `QPDF_LARGE_FILE_TEST_PATH` environment variable