Add qpdf-test-compare for comparing PDFs with different zlib

CMakeLists.txt

@@ -341,6 +341,7 @@ add_test(
 # add_subdirectory order affects test order
 add_subdirectory(include)
 add_subdirectory(libqpdf)
+add_subdirectory(compare-for-test)
 add_subdirectory(qpdf)
 add_subdirectory(libtests)
 add_subdirectory(examples)

compare-for-test/CMakeLists.txt

@@ -0,0 +1,15 @@
+# This directory is called compare-for-test rather than
+# qpdf-test-compare to make shell completion easier.
+add_executable(qpdf-test-compare qpdf-test-compare.cc)
+target_link_libraries(qpdf-test-compare libqpdf)
+
+add_test(
+  NAME compare-for-test
+  COMMAND ${RUN_QTEST}
+  --top ${qpdf_SOURCE_DIR}
+  --bin $<TARGET_FILE_DIR:qpdf-test-compare>
+  --bin $<TARGET_FILE_DIR:libqpdf>  # for Windows to find DLL
+  --code ${qpdf_SOURCE_DIR}/compare-for-test
+  --color ${QTEST_COLOR}
+  --show-on-failure ${SHOW_FAILED_TEST_OUTPUT}
+  --tc "${qpdf_SOURCE_DIR}/compare-for-test/*.cc")

compare-for-test/compare.testcov

@@ -0,0 +1,9 @@
+objects with different type 0
+different stream dictionaries 0
+uncompressing 0
+not uncompressing 0
+differing data size 1
+different data 1
+different non-stream 0
+different trailer 0
+ignore data for xref stream 0

compare-for-test/qpdf-test-compare.cc

@@ -0,0 +1,215 @@
+#include <qpdf/Pl_StdioFile.hh>
+#include <qpdf/QPDF.hh>
+#include <qpdf/QTC.hh>
+#include <qpdf/QUtil.hh>
+
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <iostream>
+
+static char const* whoami = nullptr;
+
+void
+usage()
+{
+    std::cerr << "Usage: " << whoami << " actual expected" << std::endl
+              << R"(Where "actual" is the actual output and "expected" is the expected)"
+              << std::endl
+              << "output of a test, compare the two PDF files. The files are considered"
+              << std::endl
+              << "to match if all their objects are identical except that, if a stream is"
+              << std::endl
+              << "compressed with FlateDecode, the uncompressed data must match." << std::endl
+              << std::endl
+              << "If the files match, the output is the expected file. Otherwise, it is"
+              << std::endl
+              << "the actual file. Read comments in the test suite for rationale." << std::endl;
+    exit(2);
+}
+
+void
+cleanEncryption(QPDF& q)
+{
+    auto enc = q.getTrailer().getKey("/Encrypt");
+    if (!enc.isDictionary()) {
+        return;
+    }
+    enc.removeKey("/O");
+    enc.removeKey("/OE");
+    enc.removeKey("/U");
+    enc.removeKey("/UE");
+    enc.removeKey("/Perms");
+}
+
+std::string
+compareObjects(std::string const& label, QPDFObjectHandle act, QPDFObjectHandle exp)
+{
+    if (act.getTypeCode() != exp.getTypeCode()) {
+        QTC::TC("compare", "objects with different type");
+        return label + ": different types";
+    }
+    if (act.isStream()) {
+        auto act_dict = act.getDict();
+        auto exp_dict = exp.getDict();
+        act_dict.removeKey("/Length");
+        exp_dict.removeKey("/Length");
+        if (act_dict.unparse() != exp_dict.unparse()) {
+            QTC::TC("compare", "different stream dictionaries");
+            return label + ": stream dictionaries differ";
+        }
+        if (act_dict.getKey("/Type").isNameAndEquals("/XRef")) {
+            QTC::TC("compare", "ignore data for xref stream");
+            return "";
+        }
+        auto act_filters = act_dict.getKey("/Filter");
+        bool uncompress = false;
+        if (act_filters.isName()) {
+            act_filters = act_filters.wrapInArray();
+        }
+        if (act_filters.isArray()) {
+            for (auto& filter: act_filters.aitems()) {
+                if (filter.isNameAndEquals("/FlateDecode")) {
+                    uncompress = true;
+                    break;
+                }
+            }
+        }
+        std::shared_ptr<Buffer> act_data;
+        std::shared_ptr<Buffer> exp_data;
+        if (uncompress) {
+            QTC::TC("compare", "uncompressing");
+            act_data = act.getStreamData();
+            exp_data = exp.getStreamData();
+        } else {
+            QTC::TC("compare", "not uncompressing");
+            act_data = act.getRawStreamData();
+            exp_data = exp.getRawStreamData();
+        }
+        if (act_data->getSize() != exp_data->getSize()) {
+            QTC::TC("compare", "differing data size", uncompress ? 0 : 1);
+            return label + ": stream data size differs";
+        }
+        auto act_buf = act_data->getBuffer();
+        auto exp_buf = exp_data->getBuffer();
+        if (memcmp(act_buf, exp_buf, act_data->getSize()) != 0) {
+            QTC::TC("compare", "different data", uncompress ? 0 : 1);
+            return label + ": stream data differs";
+        }
+    } else if (act.unparseResolved() != exp.unparseResolved()) {
+        QTC::TC("compare", "different non-stream");
+        return label + ": object contents differ";
+    }
+    return "";
+}
+
+std::string
+compare(char const* actual_filename, char const* expected_filename)
+{
+    QPDF actual;
+    actual.processFile(actual_filename);
+    QPDF expected;
+    expected.processFile(expected_filename);
+    // The motivation behind this program is to compare files in a way that allows for
+    // differences in the exact bytes of zlib compression. If all zlib implementations produced
+    // exactly the same output, we would just be able to use straight comparison, but since they
+    // don't, we use this. As such, we are enforcing a standard of "sameness" that goes beyond
+    // showing semantic equivalence. The only difference we are allowing is compressed data.
+
+    auto act_trailer = actual.getTrailer();
+    auto exp_trailer = expected.getTrailer();
+    act_trailer.removeKey("/Length");
+    exp_trailer.removeKey("/Length");
+    auto trailer_diff = compareObjects("trailer", act_trailer, exp_trailer);
+    if (!trailer_diff.empty()) {
+        QTC::TC("compare", "different trailer");
+        return trailer_diff;
+    }
+
+    cleanEncryption(actual);
+    cleanEncryption(expected);
+
+    auto actual_objects = actual.getAllObjects();
+    auto expected_objects = expected.getAllObjects();
+    if (actual_objects.size() != expected_objects.size()) {
+        // Not exercised in the test suite since the trailers will differ in this case.
+        return "different number of objects";
+    }
+    for (size_t i = 0; i < actual_objects.size(); ++i) {
+        auto act = actual_objects[i];
+        auto exp = expected_objects[i];
+        auto act_og = act.getObjGen();
+        auto exp_og = exp.getObjGen();
+        if (act_og != exp_og) {
+            // not reproduced in the test suite
+            return "different object IDs";
+        }
+        auto ret = compareObjects(act_og.unparse(), act, exp);
+        if (!ret.empty()) {
+            return ret;
+        }
+    }
+    return "";
+}
+
+int
+main(int argc, char* argv[])
+{
+    if ((whoami = strrchr(argv[0], '/')) == nullptr) {
+        whoami = argv[0];
+    } else {
+        ++whoami;
+    }
+
+    if ((argc == 2) && (strcmp(argv[1], "--version") == 0)) {
+        std::cout << whoami << " from qpdf version " << QPDF::QPDFVersion() << std::endl;
+        exit(0);
+    }
+
+    if (argc != 3) {
+        usage();
+    }
+
+    bool show_why = QUtil::get_env("QPDF_COMPARE_WHY");
+    try {
+        char const* to_output;
+        auto actual = argv[1];
+        auto expected = argv[2];
+        auto difference = compare(actual, expected);
+        if (difference.empty()) {
+            // The files are identical; write the expected file. This way, tests can be written
+            // that compare the output of this program to the expected file.
+            to_output = expected;
+        } else {
+            if (show_why) {
+                std::cerr << difference << std::endl;
+                exit(2);
+            }
+            // The files differ; write the actual file. If it is determined that the actual file
+            // is correct because of changes that result in intended differences, this enables
+            // the output of this program to replace the expected file in the test suite.
+            to_output = actual;
+        }
+        auto f = QUtil::safe_fopen(to_output, "rb");
+        QUtil::FileCloser fc(f);
+        QUtil::binary_stdout();
+        auto out = std::make_unique<Pl_StdioFile>("stdout", stdout);
+        unsigned char buf[2048];
+        bool done = false;
+        while (!done) {
+            size_t len = fread(buf, 1, sizeof(buf), f);
+            if (len <= 0) {
+                done = true;
+            } else {
+                out->write(buf, len);
+            }
+        }
+        if (!difference.empty()) {
+            exit(2);
+        }
+    } catch (std::exception& e) {
+        std::cerr << whoami << ": " << e.what() << std::endl;
+        exit(2);
+    }
+    return 0;
+}

compare-for-test/qtest/compare.test

@@ -0,0 +1,93 @@
+#!/usr/bin/env perl
+require 5.008;
+BEGIN { $^W = 1; }
+use strict;
+
+chdir("compare") or die "chdir testdir failed: $!\n";
+
+require TestDriver;
+
+my $td = new TestDriver('compare');
+
+# The comparison tool is designed so that you can write tests that run
+# `compare actual expected` and compare the result to expected. This
+# allows you to just replace the actual file in a comparison with the
+# comparison command. If the files match, the output is the expected
+# file, which means that if the actual file is the expected file with
+# different zlib compression, the test will pass. If the files differ,
+# the actual output shown will be the real actual output. If it is
+# determined to be correct and used to replace the expected output,
+# the test will pass next time regardless of whether the same zlib
+# implementation is used.
+
+# These files are the same file compressed with a different
+# compression level and/or a different zlib implementation.
+my @same = qw(zlib.pdf zlib-9.pdf zlib-ng.pdf);
+my $comparisons = (scalar(@same) * (scalar(@same) + 1))/2;
+my $n_tests = 2 * $comparisons;
+
+for (my $i = 0; $i < scalar(@same); $i++)
+{
+    for (my $j = $i; $j < scalar(@same); $j++)
+    {
+        # Make sure the files are byte-wise different (unless they are the same file).
+        $td->runtest("byte-wise compare $i and $j",
+                     {$td->COMMAND => "cmp $same[$i] $same[$j]"},
+                     {$td->REGEXP => ".*", $td->EXIT_STATUS => $i == $j ? 0 : "!0"});
+        # Make sure they match. This is how compare should be used:
+        # the expected output is the same file as the second argument
+        # to the command.
+        $td->runtest("compare $i and $j",
+                     {$td->COMMAND => "qpdf-test-compare $same[$i] $same[$j]"},
+                     {$td->FILE => $same[$j], $td->EXIT_STATUS => 0});
+    }
+}
+
+my @diff = (
+    ["diff-num-objects.pdf", "trailer: object contents differ"],
+    ["diff-non-stream.pdf", "3,0: object contents differ"],
+    ["diff-data-size.pdf", "4,0: stream data size differs"],
+    ["diff-data.pdf", "4,0: stream data differs"],
+    ["diff-data-size-unc.pdf", "5,0: stream data size differs"],
+    ["diff-data-unc.pdf", "5,0: stream data differs"],
+    ["diff-stream-dict.pdf", "4,0: stream dictionaries differ"],
+    ["diff-object-type.pdf", "6,0: different types"],
+    );
+$n_tests += 2 * scalar(@diff);
+
+foreach my $f (@diff)
+{
+    # In a real test, the expected output would be the expected file
+    # as above. Here, we are actually testing the comparison tool to
+    # verify that it returns a non-zero status and the actual file
+    # when there is mismatch. Don't copy this test.
+    $td->runtest("$f->[0] is different",
+                 {$td->COMMAND => "qpdf-test-compare $f->[0] zlib.pdf"},
+                 {$td->FILE => $f->[0], $td->EXIT_STATUS => 2});
+    $td->runtest("$f->[0] is different (why)",
+                 {$td->COMMAND => "env QPDF_COMPARE_WHY=1" .
+                      " qpdf-test-compare $f->[0] zlib.pdf"},
+                 {$td->STRING => "$f->[1]\n", $td->EXIT_STATUS => 2},
+                 $td->NORMALIZE_NEWLINES);
+}
+
+# Repeat for encrypted files.
+$n_tests += 3;
+$td->runtest("byte-wise compare encrypted files",
+             {$td->COMMAND => "cmp enc1.pdf enc2.pdf"},
+             {$td->REGEXP => ".*", $td->EXIT_STATUS => "!0"});
+$td->runtest("compare encrypted files (same)",
+             {$td->COMMAND => "env QPDF_COMPARE_WHY=1 qpdf-test-compare enc1.pdf enc2.pdf"},
+             {$td->FILE => "enc2.pdf", $td->EXIT_STATUS => 0});
+$td->runtest("compare encrypted files (different)",
+             {$td->COMMAND => "env QPDF_COMPARE_WHY=1 qpdf-test-compare enc1.pdf diff-data-enc.pdf"},
+             {$td->STRING => "4,0: stream data differs\n", $td->EXIT_STATUS => 2},
+             $td->NORMALIZE_NEWLINES);
+
+# Object streams
+$n_tests += 1;
+$td->runtest("compare object stream files (same)",
+             {$td->COMMAND => "env QPDF_COMPARE_WHY=1 qpdf-test-compare ostream1.pdf ostream2.pdf"},
+             {$td->FILE => "ostream2.pdf", $td->EXIT_STATUS => 0});
+
+$td->report($n_tests);

compare-for-test/qtest/compare/enc1.pdf

@@ -0,0 +1,41 @@
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+trailer << /Root 1 0 R /Size 8 /ID [<42841c13bbf709d79a200fa1691836f8><31415926535897932384626433832795>] /Encrypt 7 0 R >>
+startxref
+1189
+%%EOF

compare-for-test/qtest/compare/enc2.pdf

@@ -0,0 +1,41 @@
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+startxref
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+%%EOF

compare-for-test/qtest/compare/start.pdf

@@ -0,0 +1,47 @@
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+%¿÷¢þ
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+endobj
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