C-API: drop ZXing_ReadBarcode() + new heap allocation optimization

Use a trick from the C# playbook: return a static empty vector that
does not need to be allocated and deleted on every call.

Author: axxel

core/src/ZXingC.cpp

@@ -18,6 +18,7 @@
 using namespace ZXing;
 
 static thread_local std::string lastErrorMsg;
+static Barcodes emptyBarcodes{}; // used to prevent new heap allocation for each empty result
 
 template<typename R, typename T> R transmute_cast(const T& v) noexcept
 {
@@ -66,19 +67,6 @@ static uint8_t* copy(const ByteArray& ba, int* len) noexcept
 	ZX_CATCH({})
 
 
-static std::tuple<Barcodes, bool> ReadBarcodesAndSetLastError(const ZXing_ImageView* iv, const ZXing_ReaderOptions* opts,
-															  int maxSymbols)
-{
-	ZX_CHECK(iv, "ImageView param is NULL")
-	try {
-		auto o = opts ? *opts : ReaderOptions{};
-		if (maxSymbols)
-			o.setMaxNumberOfSymbols(maxSymbols);
-		return {ReadBarcodes(*iv, o), true};
-	}
-	ZX_CATCH({Barcodes{}, false})
-}
-
 extern "C" {
 /*
  * ZXing/ImageView.h
@@ -238,7 +226,8 @@ void ZXing_Barcode_delete(ZXing_Barcode* barcode)
 
 void ZXing_Barcodes_delete(ZXing_Barcodes* barcodes)
 {
-	delete barcodes;
+	if (barcodes != &emptyBarcodes)
+		delete barcodes;
 }
 
 int ZXing_Barcodes_size(const ZXing_Barcodes* barcodes)
@@ -314,16 +303,14 @@ ZX_ENUM_PROPERTY(TextMode, textMode, TextMode)
  * ZXing/ReadBarcode.h
  */
 
-ZXing_Barcode* ZXing_ReadBarcode(const ZXing_ImageView* iv, const ZXing_ReaderOptions* opts)
-{
-	auto [res, ok] = ReadBarcodesAndSetLastError(iv, opts, 1);
-	return !res.empty() ? new Barcode(std::move(res.front())) : NULL;
-}
-
 ZXing_Barcodes* ZXing_ReadBarcodes(const ZXing_ImageView* iv, const ZXing_ReaderOptions* opts)
 {
-	auto [res, ok] = ReadBarcodesAndSetLastError(iv, opts, 0);
-	return !res.empty() || ok ? new Barcodes(std::move(res)) : NULL;
+	ZX_CHECK(iv, "ImageView param is NULL")
+	try {
+		auto res = ReadBarcodes(*iv, opts ? *opts : ReaderOptions{});
+		return res.empty() ? &emptyBarcodes : new Barcodes(std::move(res));
+	}
+	ZX_CATCH(NULL);
 }
 
 

core/src/ZXingC.h

@@ -257,7 +257,6 @@ int ZXing_ReaderOptions_getMaxNumberOfSymbols(const ZXing_ReaderOptions* opts);
  */
 
 /** Note: opts is optional, i.e. it can be NULL, which will imply default settings. */
-ZXing_Barcode* ZXing_ReadBarcode(const ZXing_ImageView* iv, const ZXing_ReaderOptions* opts);
 ZXing_Barcodes* ZXing_ReadBarcodes(const ZXing_ImageView* iv, const ZXing_ReaderOptions* opts);
 
 #ifdef ZXING_EXPERIMENTAL_API

wrappers/rust/src/bindings.rs

@@ -197,7 +197,6 @@ extern "C" {
 	pub fn ZXing_ReaderOptions_getTextMode(opts: *const ZXing_ReaderOptions) -> ZXing_TextMode;
 	pub fn ZXing_ReaderOptions_getMinLineCount(opts: *const ZXing_ReaderOptions) -> ::core::ffi::c_int;
 	pub fn ZXing_ReaderOptions_getMaxNumberOfSymbols(opts: *const ZXing_ReaderOptions) -> ::core::ffi::c_int;
-	pub fn ZXing_ReadBarcode(iv: *const ZXing_ImageView, opts: *const ZXing_ReaderOptions) -> *mut ZXing_Barcode;
 	pub fn ZXing_ReadBarcodes(iv: *const ZXing_ImageView, opts: *const ZXing_ReaderOptions) -> *mut ZXing_Barcodes;
 	pub fn ZXing_CreatorOptions_new(format: ZXing_BarcodeFormat) -> *mut ZXing_CreatorOptions;
 	pub fn ZXing_CreatorOptions_delete(opts: *mut ZXing_CreatorOptions);