Test that the 3MF we write is actually compressed

include/openscad_cpp_evaluator/export.hpp

@@ -39,7 +39,10 @@ void writeObj(const std::string& path, const std::vector<ColoredBody>& bodies);
 void writeOff(const std::string& path, const std::vector<ColoredBody>& bodies);
 
 // 3MF: one mesh object + a base-color colorgroup per body (skipping empty
-// bodies), written as a stored (uncompressed) ZIP -- see zip_stored.hpp.
+// bodies), written as a DEFLATE-compressed ZIP (writeDeflateZip, see
+// zip_stored.hpp) -- the XML is highly compressible, so storing it would
+// make the file several times larger for nothing. An entry that does not
+// actually shrink is stored raw, as any ZIP writer would.
 // Mirrors export.py's write_3mf's XML shape exactly (core + material
 // namespaces, %.6g vertex formatting); throws std::runtime_error if there's
 // no geometry to export.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "scikit_build_core.build"
 
 [project]
 name = "openscad_cpp_evaluator"
-version = "0.29.1"
+version = "0.29.2"
 description = "C++ OpenSCAD evaluator with Python bindings"
 readme = "README.md"
 requires-python = ">=3.12"

tests/test_import_export.cpp

@@ -77,6 +77,40 @@ TEST(ImportModuleContext, ThreeMfRoundTripPreservesVolume) {
     std::filesystem::remove(path);
 }
 
+// The .3mf writeThreeMf() produces is DEFLATE-compressed, not stored. The
+// round-trip test above passes either way -- the reader accepts both
+// methods -- so without this a regression to STORED would show up only as
+// files several times bigger than they need to be.
+TEST(ImportModuleContext, ThreeMfIsDeflateCompressed) {
+    const auto path = tempPath("cube_compressed.3mf");
+    writeCubeAs(path, &writeThreeMf);
+
+    std::ifstream in(path, std::ios::binary);
+    ASSERT_TRUE(in);
+    std::vector<uint8_t> buf((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
+    in.close();
+
+    bool sawModel = false;
+    for (size_t i = 0; i + 46 <= buf.size(); ++i) {
+        if (!(buf[i] == 0x50 && buf[i + 1] == 0x4B && buf[i + 2] == 0x01 && buf[i + 3] == 0x02)) continue;
+        const uint16_t method = static_cast<uint16_t>(buf[i + 10] | (buf[i + 11] << 8));
+        const uint32_t compressedSize =
+            static_cast<uint32_t>(buf[i + 20] | (buf[i + 21] << 8) | (buf[i + 22] << 16) | (buf[i + 23] << 24));
+        const uint32_t rawSize =
+            static_cast<uint32_t>(buf[i + 24] | (buf[i + 25] << 8) | (buf[i + 26] << 16) | (buf[i + 27] << 24));
+        const uint16_t nameLen = static_cast<uint16_t>(buf[i + 28] | (buf[i + 29] << 8));
+        if (i + 46 + nameLen > buf.size()) continue;
+        const std::string name(reinterpret_cast<const char*>(&buf[i + 46]), nameLen);
+        if (name.find("3dmodel.model") == std::string::npos) continue;
+        sawModel = true;
+        EXPECT_EQ(method, 8) << "3dmodel.model stored uncompressed";
+        EXPECT_LT(compressedSize, rawSize) << "compressed " << compressedSize << " vs raw " << rawSize;
+    }
+    EXPECT_TRUE(sawModel) << "no 3dmodel.model entry in the archive";
+
+    std::filesystem::remove(path);
+}
+
 TEST(ImportModuleContext, UnsupportedExtensionErrors) {
     Evaluator ev;
     auto ast = parseSrc("import(\"nope.xyz\");");

tests/test_zip_stored.cpp

@@ -1,6 +1,12 @@
 // Direct tests for zip_stored.hpp -- writeStoredZip()'s own STORED-entry
 // round trip, plus reading a DEFLATE-compressed (method 8) entry, which is
 // what most third-party ZIP/3MF writers actually emit.
+//
+// Also what writeDeflateZip() and writeThreeMf() put in the archive. That
+// went untested: the round-trip tests pass either way, since the reader
+// handles both methods, so a silent regression to STORED would only show
+// up as files several times larger. The method byte is read out of the
+// central directory here so it cannot regress unnoticed.
 
 #include "openscad_cpp_evaluator/zip_stored.hpp"
 
@@ -169,3 +175,81 @@ TEST(ZipStored, UnsupportedCompressionMethodThrows) {
     EXPECT_THROW(readStoredZipEntry(path.string(), "hello.txt"), std::runtime_error);
     std::filesystem::remove(path);
 }
+
+
+// --- what we WRITE, not just what we can read -------------------------
+
+namespace {
+
+// The compression method of the first central-directory entry whose name
+// ends with `suffix`. Read from the central directory rather than the local
+// header, since that is the authoritative copy.
+uint16_t centralDirMethodBySuffix(const std::string& path, const std::string& suffix) {
+    std::ifstream in(path, std::ios::binary);
+    EXPECT_TRUE(in) << "cannot open " << path;
+    std::vector<uint8_t> buf((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
+    // Walk central-directory headers by signature; these archives are small
+    // and have no ZIP comment, so a forward scan is enough.
+    for (size_t i = 0; i + 46 <= buf.size(); ++i) {
+        if (!(buf[i] == 0x50 && buf[i + 1] == 0x4B && buf[i + 2] == 0x01 && buf[i + 3] == 0x02)) continue;
+        const uint16_t method = static_cast<uint16_t>(buf[i + 10] | (buf[i + 11] << 8));
+        const uint16_t nameLen = static_cast<uint16_t>(buf[i + 28] | (buf[i + 29] << 8));
+        if (i + 46 + nameLen > buf.size()) continue;
+        const std::string name(reinterpret_cast<const char*>(&buf[i + 46]), nameLen);
+        if (name.size() >= suffix.size() && name.compare(name.size() - suffix.size(), suffix.size(), suffix) == 0)
+            return method;
+    }
+    ADD_FAILURE() << "no central-directory entry ending in " << suffix;
+    return 0xFFFF;
+}
+
+// Compressible: long runs, which is what 3MF's indented XML looks like.
+std::vector<uint8_t> compressibleBytes(size_t n) {
+    std::vector<uint8_t> out;
+    out.reserve(n);
+    const std::string unit = "\t\t\t\t\t<vertex x=\"0\" y=\"0\" z=\"0\" />\n";
+    while (out.size() < n) out.insert(out.end(), unit.begin(), unit.end());
+    out.resize(n);
+    return out;
+}
+
+}  // namespace
+
+TEST(ZipStored, DeflateZipReallyWritesMethod8) {
+    const auto path = tempPath("deflate_method.zip");
+    const auto data = compressibleBytes(64 * 1024);
+    writeDeflateZip(path.string(), {ZipEntry{"3D/3dmodel.model", data}});
+    EXPECT_EQ(centralDirMethodBySuffix(path.string(), "3dmodel.model"), 8);
+    // And it still reads back byte for byte.
+    EXPECT_EQ(readStoredZipEntry(path.string(), "3D/3dmodel.model"), data);
+    std::filesystem::remove(path);
+}
+
+TEST(ZipStored, DeflateZipActuallyShrinksCompressibleData) {
+    const auto path = tempPath("deflate_size.zip");
+    const auto data = compressibleBytes(256 * 1024);
+    writeDeflateZip(path.string(), {ZipEntry{"3D/3dmodel.model", data}});
+    const auto onDisk = std::filesystem::file_size(path);
+    // Highly repetitive input; anything near its original size means the
+    // compressor did not run.
+    EXPECT_LT(onDisk, data.size() / 4) << "archive " << onDisk << " for " << data.size() << " bytes of input";
+    std::filesystem::remove(path);
+}
+
+TEST(ZipStored, DeflateZipStoresDataThatWouldNotShrink) {
+    const auto path = tempPath("deflate_tiny.zip");
+    const std::vector<uint8_t> tiny{'x'};
+    writeDeflateZip(path.string(), {ZipEntry{"a.txt", tiny}});
+    EXPECT_EQ(centralDirMethodBySuffix(path.string(), "a.txt"), 0);
+    EXPECT_EQ(readStoredZipEntry(path.string(), "a.txt"), tiny);
+    std::filesystem::remove(path);
+}
+
+TEST(ZipStored, StoredZipWritesMethod0) {
+    // The control for the tests above: same call shape, opposite method.
+    const auto path = tempPath("stored_method.zip");
+    const auto data = compressibleBytes(64 * 1024);
+    writeStoredZip(path.string(), {ZipEntry{"3D/3dmodel.model", data}});
+    EXPECT_EQ(centralDirMethodBySuffix(path.string(), "3dmodel.model"), 0);
+    std::filesystem::remove(path);
+}