Fix #2081: Apply zstd compression level reliably across the documente… (#2113)

* Fix #2081: Apply zstd compression level reliably across the documented range

* Fix flaky zstd compression-level test

The test compared output sizes for levels 1 vs 10 on a 20KB pcap; on
inputs that small, zstd produces identical output for both levels, so
the GREATER_THAN assertion always failed. Switch to a larger input
(EXAMPLE2_PCAPNG_PATH, ~26KB) and widen the gap to levels 1 vs 22
(zstd's documented max), which produces a clear size delta.

Also brace the single-statement while body per review nit.

* Skip zstd compression-level test when zstd is not configured

---------

Co-authored-by: Liam Merino <merino@uber.com>
Co-authored-by: seladb <pcapplusplus@gmail.com>

Author: 3 people

3rdParty/LightPcapNg/LightPcapNg/src/light_zstd_compression.c

@@ -57,8 +57,13 @@ _compression_t * get_zstd_compression_context(int compression_level)
 	context->buffer_out_max_size = max(ZSTD_CStreamOutSize(), COMPRESSION_BUFFER_IN_MAX_SIZE);
 	context->buffer_in = malloc(context->buffer_in_max_size);
 	context->buffer_out = malloc(context->buffer_out_max_size);
-	context->compression_level = compression_level * 2; //Input is scale 0-10 but zstd goes 0 - 20!
-	assert(!ZSTD_isError(ZSTD_CCtx_setParameter(context->cctx, ZSTD_c_compressionLevel, compression_level)));
+	// Map 0-10 input scale onto zstd's 1-22 range; preserve 0 as the "default
+	// compression" sentinel. setParameter must run outside assert() so its
+	// side effect is not stripped under NDEBUG.
+	context->compression_level = compression_level > 0 ? (compression_level * 2) + 1 : 0;
+	size_t const set_param_result = ZSTD_CCtx_setParameter(context->cctx, ZSTD_c_compressionLevel, context->compression_level);
+	assert(!ZSTD_isError(set_param_result));
+	(void)set_param_result;
 
 	return context;
 }

Tests/Pcap++Test/Common/PcapFileNamesDef.h

@@ -20,6 +20,7 @@
 #define EXAMPLE_PCAPNG_WRITE_PATH "PcapExamples/many_interfaces_copy.pcapng"
 #define EXAMPLE2_PCAPNG_WRITE_PATH "PcapExamples/pcapng-example-write.pcapng"
 #define EXAMPLE_PCAPNG_ZSTD_WRITE_PATH "PcapExamples/many_interfaces_copy.pcapng.zstd"
+#define EXAMPLE_PCAPNG_ZSTD_LEVELS_WRITE_PATH "PcapExamples/many_interfaces_levels.pcapng.zstd"
 #define EXAMPLE2_PCAPNG_ZSTD_WRITE_PATH "PcapExamples/pcapng-example-write.pcapng.zstd"
 #define EXAMPLE2_PCAPNG_ZST_WRITE_PATH "PcapExamples/pcapng-example-write.pcapng.zst"
 #define EXAMPLE_PCAPNG_INTERFACES_PATH "PcapExamples/too_many_interfaces.pcapng"

Tests/Pcap++Test/TestDefinition.h

@@ -30,6 +30,7 @@ PTF_TEST_CASE(TestPcapFileReadAdv);
 PTF_TEST_CASE(TestPcapFileWriteAdv);
 PTF_TEST_CASE(TestPcapFileAppend);
 PTF_TEST_CASE(TestPcapNgFileReadWrite);
+PTF_TEST_CASE(TestPcapNgZstdCompressionLevels);
 PTF_TEST_CASE(TestPcapNgFileReadWriteAdv);
 PTF_TEST_CASE(TestPcapNgFileTooManyInterfaces);
 PTF_TEST_CASE(TestPcapFileReadLinkTypeIPv6);

Tests/Pcap++Test/Tests/FileTests.cpp

@@ -1314,6 +1314,41 @@ PTF_TEST_CASE(TestPcapNgFileReadWrite)
 
 }  // TestPcapNgFileReadWrite
 
+PTF_TEST_CASE(TestPcapNgZstdCompressionLevels)
+{
+#ifdef USE_Z_STD
+	// If the compression level is silently ignored, low and high levels
+	// produce identical output sizes. PcapPlusPlus exposes levels 0-10,
+	// which the zstd wrapper maps to zstd's native 1-22 range. Test three
+	// points to verify the level scales monotonically, not just that the
+	// endpoints differ.
+	std::array<int, 3> sizes = { 0, 0, 0 };
+	const std::array<int, 3> levels = { 1, 5, 10 };
+	for (int i = 0; i < 3; i++)
+	{
+		pcpp::PcapNgFileReaderDevice readerDev(EXAMPLE2_PCAPNG_PATH);
+		PTF_ASSERT_TRUE(readerDev.open());
+
+		pcpp::PcapNgFileWriterDevice writerDev(EXAMPLE_PCAPNG_ZSTD_LEVELS_WRITE_PATH, levels[i]);
+		PTF_ASSERT_TRUE(writerDev.open());
+
+		pcpp::RawPacket rawPacket;
+		while (readerDev.getNextPacket(rawPacket))
+		{
+			PTF_ASSERT_TRUE(writerDev.writePacket(rawPacket));
+		}
+		readerDev.close();
+		writerDev.close();
+
+		sizes[i] = getFileLength(EXAMPLE_PCAPNG_ZSTD_LEVELS_WRITE_PATH);
+	}
+	PTF_ASSERT_GREATER_THAN(sizes[0], sizes[1]);
+	PTF_ASSERT_GREATER_THAN(sizes[1], sizes[2]);
+#else
+	PTF_SKIP_TEST("Zstd is not configured");
+#endif
+}  // TestPcapNgZstdCompressionLevels
+
 PTF_TEST_CASE(TestPcapNgFileReadWriteAdv)
 {
 	pcpp::PcapNgFileReaderDevice readerDev(EXAMPLE2_PCAPNG_PATH);

Tests/Pcap++Test/main.cpp

@@ -230,6 +230,7 @@ int main(int argc, char* argv[])
 	PTF_RUN_TEST(TestPcapFileReadAdv, "no_network;pcap");
 	PTF_RUN_TEST(TestPcapFileWriteAdv, "no_network;pcap");
 	PTF_RUN_TEST(TestPcapNgFileReadWrite, "no_network;pcap;pcapng");
+	PTF_RUN_TEST(TestPcapNgZstdCompressionLevels, "no_network;pcap;pcapng");
 	PTF_RUN_TEST(TestPcapNgFileReadWriteAdv, "no_network;pcap;pcapng");
 	PTF_RUN_TEST(TestPcapNgFileTooManyInterfaces, "no_network;pcap;pcapng");
 	PTF_RUN_TEST(TestPcapNgFilePrecision, "no_network;pcapng");