D'oh, ban copy/move constructors

Oops: if you ever passed a non-default compression level, we'd
try to create a new compressor. But because we were using the
default constructors, we'd happily create a temporary, copy its
pointer over to the `compressor` field, then destruct the temporary,
freeing the underlying native resource, and the world would end.

Instead, delete the default constructors and require an explicit
`setLevel` call.

Also update tests to verify that the different levels work.

src/helpers.cpp

@@ -32,12 +32,21 @@ class Compressor {
 	libdeflate_compressor* compressor;
 
 	Compressor(int level): level(level), compressor(NULL) {
+		setLevel(level);
+	}
+
+	void setLevel(int level) {
+		libdeflate_free_compressor(compressor);
+		this->level = level;
 		compressor = libdeflate_alloc_compressor(level);
 
 		if (!compressor)
 			throw std::runtime_error("libdeflate_alloc_compressor failed (level=" + std::to_string(level) + ")");
 	}
 
+	Compressor & operator=(const Compressor&) = delete;
+	Compressor(const Compressor&) = delete;
+
 	~Compressor() {
 		libdeflate_free_compressor(compressor);
 	}
@@ -54,6 +63,9 @@ class Decompressor {
 			throw std::runtime_error("libdeflate_alloc_decompressor failed");
 	}
 
+	Decompressor & operator=(const Decompressor&) = delete;
+	Decompressor(const Decompressor&) = delete;
+
 	~Decompressor() {
 		libdeflate_free_decompressor(decompressor);
 	}
@@ -88,15 +100,14 @@ std::vector<std::string> parseBox(const std::string& bbox) {
 }
 
 // Compress a STL string using zlib with given compression level, and return the binary data
-// TODO: consider returning a std::vector<char> ?
 std::string compress_string(const std::string& str,
                             int compressionlevel,
                             bool asGzip) {
 	if (compressionlevel == Z_DEFAULT_COMPRESSION)
 		compressionlevel = 6;
 
 	if (compressionlevel != compressor.level)
-		compressor = Compressor(compressionlevel);
+		compressor.setLevel(compressionlevel);
 
 	std::string rv;
 	if (asGzip) {

test/helpers.test.cpp

@@ -51,16 +51,31 @@ MU_TEST(test_get_chunks) {
 MU_TEST(test_compression_gzip) {
 	std::string input = "a random string to be compressed";
 
-	std::string gzipped = compress_string(input, 6, true);
+	for (int level = 1; level < 9; level++) {
+		std::string gzipped = compress_string(input, level, true);
+		std::string unzipped;
+		decompress_string(unzipped, gzipped.data(), gzipped.size(), true);
+		mu_check(unzipped == input);
+	}
+
+	std::string gzipped = compress_string(input, -1, true);
 	std::string unzipped;
 	decompress_string(unzipped, gzipped.data(), gzipped.size(), true);
 	mu_check(unzipped == input);
+
 }
 
 MU_TEST(test_compression_zlib) {
 	std::string input = "a random string to be compressed";
 
-	std::string gzipped = compress_string(input, 6, false);
+	for (int level = 1; level < 9; level++) {
+		std::string gzipped = compress_string(input, level, false);
+		std::string unzipped;
+		decompress_string(unzipped, gzipped.data(), gzipped.size(), false);
+		mu_check(unzipped == input);
+	}
+
+	std::string gzipped = compress_string(input, -1, false);
 	std::string unzipped;
 	decompress_string(unzipped, gzipped.data(), gzipped.size(), false);
 	mu_check(unzipped == input);