diff --git a/ChangeLog b/ChangeLog index bc052915..19be25a3 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,10 @@ +2023-12-16 Jay Berkenbilt + + * Add new C++ functions "qpdf_c_get_qpdf" and "qpdf_c_wrap" to + qpdf-c.h that make it possible to write your own extern "C" + functions in C++ that interoperate with the C API. See + examples/extend-c-api for more information. + 2023-12-10 Jay Berkenbilt * 11.6.4: release diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt index 9af85fe2..614047d5 100644 --- a/examples/CMakeLists.txt +++ b/examples/CMakeLists.txt @@ -34,6 +34,11 @@ foreach(PROG ${EXAMPLE_C_PROGRAMS}) endforeach() target_include_directories(pdf-create PRIVATE ${JPEG_INCLUDE}) +# extend-c-api contains a mixture of C and C++ files. +add_executable(extend-c-api extend-c-api-impl.cc extend-c-api.c) +set_property(TARGET extend-c-api PROPERTY LINKER_LANGUAGE CXX) +target_link_libraries(extend-c-api libqpdf) + add_test( NAME examples COMMAND ${RUN_QTEST} @@ -47,7 +52,7 @@ add_test( --tc "${qpdf_SOURCE_DIR}/examples/*.cc" --tc "${qpdf_SOURCE_DIR}/examples/*.c") -file(GLOB EXAMPLES_SRC "*.c" "*.cc") +file(GLOB EXAMPLES_SRC "*.c" "*.cc" "*.h") if(INSTALL_EXAMPLES) install(FILES ${EXAMPLES_SRC} DESTINATION ${CMAKE_INSTALL_DOCDIR}/examples diff --git a/examples/extend-c-api-impl.cc b/examples/extend-c-api-impl.cc new file mode 100644 index 00000000..680d957b --- /dev/null +++ b/examples/extend-c-api-impl.cc @@ -0,0 +1,29 @@ +// This is an example of how to write C++ functions and make them usable with the qpdf C API. It +// consists of three files: +// - extend-c-api.h -- a plain C header file +// - extend-c-api.c -- a C program that calls the function +// - extend-c-api.cc -- a C++ file that implements the function + +#include "extend-c-api.h" + +// Here, we add a function to get the number of pages in a PDF file and make it callable through the +// C API. + +// This is a normal C++ function that works with QPDF in a normal way. It doesn't do anything +// special to be callable from C. +int +numPages(std::shared_ptr qpdf) +{ + return qpdf->getRoot().getKey("/Pages").getKey("/Count").getIntValueAsInt(); +} + +// Now we define the glue that makes our function callable using the C API. + +// This is the C++ implementation of the C function. +QPDF_ERROR_CODE +num_pages(qpdf_data qc, int* npages) +{ + // Call qpdf_c_wrap to convert any exception our function might through to a QPDF_ERROR_CODE + // and attach it to the qpdf_data object in the same way as other functions in the C API. + return qpdf_c_wrap(qc, [&qc, &npages]() { *npages = numPages(qpdf_c_get_qpdf(qc)); }); +} diff --git a/examples/extend-c-api.c b/examples/extend-c-api.c new file mode 100644 index 00000000..aa603845 --- /dev/null +++ b/examples/extend-c-api.c @@ -0,0 +1,67 @@ +/* + * This is an example of how to write C++ functions and make them usable with the qpdf C API. It + * consists of three files: + * - extend-c-api.h -- a plain C header file + * - extend-c-api.c -- a C program that calls the function + * - extend-c-api.cc -- a C++ file that implements the function + */ + +#include "extend-c-api.h" +#include +#include +#include + +static char const* whoami = 0; + +static void +usage() +{ + fprintf(stderr, "Usage: %s infile\n", whoami); + exit(2); +} + +int +main(int argc, char* argv[]) +{ + char* infile = NULL; + qpdf_data qpdf = qpdf_init(); + int warnings = 0; + int errors = 0; + char* p = NULL; + + if ((p = strrchr(argv[0], '/')) != NULL) { + whoami = p + 1; + } else if ((p = strrchr(argv[0], '\\')) != NULL) { + whoami = p + 1; + } else { + whoami = argv[0]; + } + + if (argc != 2) { + usage(); + } + + infile = argv[1]; + + if ((qpdf_read(qpdf, infile, NULL) & QPDF_ERRORS) == 0) { + int npages; + if ((num_pages(qpdf, &npages) & QPDF_ERRORS) == 0) { + printf("num pages = %d\n", npages); + } + } + if (qpdf_more_warnings(qpdf)) { + warnings = 1; + } + if (qpdf_has_error(qpdf)) { + errors = 1; + printf("error: %s\n", qpdf_get_error_full_text(qpdf, qpdf_get_error(qpdf))); + } + qpdf_cleanup(&qpdf); + if (errors) { + return 2; + } else if (warnings) { + return 3; + } + + return 0; +} diff --git a/examples/extend-c-api.h b/examples/extend-c-api.h new file mode 100644 index 00000000..3b2d12d4 --- /dev/null +++ b/examples/extend-c-api.h @@ -0,0 +1,25 @@ +#ifndef EXAMPLE_C_EXTEND_H +#define EXAMPLE_C_EXTEND_H + +/* + * This is an example of how to write C++ functions and make them usable with the qpdf C API. It + * consists of three files: + * - extend-c-api.h -- a plain C header file + * - extend-c-api.c -- a C program that calls the function + * - extend-c-api.cc -- a C++ file that implements the function + */ +#include + +/* Declare your custom function to return QPDF_ERROR_CODE and take qpdf_data and anything else you + * need. Any errors are retrievable through the qpdf C APIs normal error-handling mechanism. + */ + +#ifdef __cplusplus +extern "C" { +#endif + QPDF_ERROR_CODE num_pages(qpdf_data qc, int* npages); +#ifdef __cplusplus +} +#endif + +#endif /* EXAMPLE_C_EXTEND_H */ diff --git a/examples/qtest/extend-c-api.test b/examples/qtest/extend-c-api.test new file mode 100644 index 00000000..3dd82193 --- /dev/null +++ b/examples/qtest/extend-c-api.test @@ -0,0 +1,30 @@ +#!/usr/bin/env perl +require 5.008; +use warnings; +use strict; + +chdir("extend-c-api") or die "chdir testdir failed: $!\n"; + +require TestDriver; + +cleanup(); + +my $td = new TestDriver('extend-c-api'); + +$td->runtest("extend C API (good)", + {$td->COMMAND => "extend-c-api good.pdf"}, + {$td->FILE => "good.out", $td->EXIT_STATUS => 0}, + $td->NORMALIZE_NEWLINES); +$td->runtest("extend C API (bad)", + {$td->COMMAND => "extend-c-api bad.pdf"}, + {$td->FILE => "bad.out", $td->EXIT_STATUS => 2}, + $td->NORMALIZE_NEWLINES); + +cleanup(); + +$td->report(2); + +sub cleanup +{ + unlink "a.pdf"; +} diff --git a/examples/qtest/extend-c-api/bad.out b/examples/qtest/extend-c-api/bad.out new file mode 100644 index 00000000..51f1d56b --- /dev/null +++ b/examples/qtest/extend-c-api/bad.out @@ -0,0 +1,5 @@ +WARNING: bad.pdf: can't find PDF header +WARNING: bad.pdf: file is damaged +WARNING: bad.pdf: can't find startxref +WARNING: bad.pdf: Attempting to reconstruct cross-reference table +error: bad.pdf: unable to find trailer dictionary while recovering damaged file diff --git a/examples/qtest/extend-c-api/bad.pdf b/examples/qtest/extend-c-api/bad.pdf new file mode 100644 index 00000000..a3d2d925 --- /dev/null +++ b/examples/qtest/extend-c-api/bad.pdf @@ -0,0 +1 @@ +not even a pdf file diff --git a/examples/qtest/extend-c-api/good.out b/examples/qtest/extend-c-api/good.out new file mode 100644 index 00000000..98205fae --- /dev/null +++ b/examples/qtest/extend-c-api/good.out @@ -0,0 +1 @@ +num pages = 1 diff --git a/examples/qtest/extend-c-api/good.pdf b/examples/qtest/extend-c-api/good.pdf new file mode 100644 index 00000000..42867b96 --- /dev/null +++ b/examples/qtest/extend-c-api/good.pdf @@ -0,0 +1,64 @@ +%PDF-2.0 +1 0 obj +<< + /Pages 2 0 R + /Type /Catalog +>> +endobj +2 0 obj +<< + /Count 1 + /Kids [ + 3 0 R + ] + /Type /Pages +>> +endobj +3 0 obj +<< + /Contents 4 0 R + /MediaBox [ 0 0 612 792 ] + /Parent 2 0 R + /Resources << + /Font << /F1 5 0 R >> + >> + /Type /Page +>> +endobj +4 0 obj +<< + /Length 44 +>> +stream +BT + /F1 24 Tf + 72 720 Td + (Potato) Tj +ET +endstream +endobj +5 0 obj +<< + /BaseFont /Helvetica + /Encoding /WinAnsiEncoding + /Subtype /Type1 + /Type /Font +>> +endobj + +xref +0 6 +0000000000 65535 f +0000000009 00000 n +0000000062 00000 n +0000000133 00000 n +0000000277 00000 n +0000000372 00000 n +trailer << + /Root 1 0 R + /Size 6 + /ID [<42841c13bbf709d79a200fa1691836f8>] +>> +startxref +478 +%%EOF diff --git a/include/qpdf/qpdf-c.h b/include/qpdf/qpdf-c.h index d4305602..f989ba15 100644 --- a/include/qpdf/qpdf-c.h +++ b/include/qpdf/qpdf-c.h @@ -21,21 +21,23 @@ #define QPDF_C_H /* - * This file defines a basic "C" API for qpdf. It provides access to a subset of the QPDF library's + * This file defines a basic "C" API for qpdf. It provides access to a subset of the QPDF library's * capabilities to make them accessible to callers who can't handle calling C++ functions or working - * with C++ classes. This may be especially useful to Windows users who are accessing the qpdf DLL + * with C++ classes. This may be especially useful to Windows users who are accessing the qpdf DLL * directly or to other people programming in non-C/C++ languages that can call C code but not C++ - * code. + * code. Starting with qpdf 11.7, it is possible to write your own `extern "C"` functions that + * interoperate with the C API. * * There are several things to keep in mind when using the C API. * * Error handling is tricky because the underlying C++ API uses exception handling. See "ERROR * HANDLING" below for a detailed explanation. * - * The C API is not as rich as the C++ API. For any operations that involve actually - * manipulating PDF objects, you must use the C++ API. The C API is primarily useful for doing - * basic transformations on PDF files similar to what you might do with the qpdf command-line - * tool. + * The C API is not as rich as the C++ API. For many operations, you must use the C++ API. The C + * API is primarily useful for doing basic transformations on PDF files similar to what you + * might do with the qpdf command-line tool. You can write your own `extern "C"` functions in + * C++ that interoperate with the C API by using qpdf_c_get_qpdf and qpdf_c_wrap which were + * introduced in qpdf 11.7.0. * * These functions store their state in a qpdf_data object. Individual instances of qpdf_data * are not thread-safe: although you may access different qpdf_data objects from different @@ -990,6 +992,23 @@ extern "C" { QPDF_ERROR_CODE qpdf_remove_page(qpdf_data qpdf, qpdf_oh page); #ifdef __cplusplus } + +// These C++ functions make it easier to write C++ code that interoperates with the C API. +// See examples/extend-c-api. + +# include +# include + +# include + +// Retrieve the real QPDF object attached to this qpdf_data. +QPDF_DLL +std::shared_ptr qpdf_c_get_qpdf(qpdf_data qpdf); + +// Wrap a C++ function that may throw an exception to translate the exception for retrieval using +// the normal QPDF C API methods. +QPDF_DLL +QPDF_ERROR_CODE qpdf_c_wrap(qpdf_data qpdf, std::function fn); #endif #endif /* QPDF_C_H */ diff --git a/libqpdf/qpdf-c.cc b/libqpdf/qpdf-c.cc index 1f7b85cb..b45b564b 100644 --- a/libqpdf/qpdf-c.cc +++ b/libqpdf/qpdf-c.cc @@ -1949,3 +1949,15 @@ qpdf_write_json( }); return status; } + +std::shared_ptr +qpdf_c_get_qpdf(qpdf_data qpdf) +{ + return qpdf->qpdf; +} + +QPDF_ERROR_CODE +qpdf_c_wrap(qpdf_data qpdf, std::function fn) +{ + return trap_errors(qpdf, [&fn](qpdf_data) { fn(); }); +} diff --git a/manual/release-notes.rst b/manual/release-notes.rst index 0ac5c005..7388f17d 100644 --- a/manual/release-notes.rst +++ b/manual/release-notes.rst @@ -38,6 +38,13 @@ Planned changes for future 12.x (subject to change): .. x.y.z: not yet released +11.7.0: not yet released + - Library Enhancements: + + - Add C++ functions ``qpdf_c_wrap`` and ``qpdf_c_get_qpdf`` to the + C API to enable custom C++ code to interoperate more easily with + the the C API. See ``examples/extend-c-api``. + 11.6.4: December 10, 2023 - Bug fixes: