1 files changed, 74 insertions, 0 deletions
diff --git a/library/cpp/yson_pull/detail/byte_reader.h b/library/cpp/yson_pull/detail/byte_reader.h
new file mode 100644
index 0000000000..7cea50d323
--- /dev/null
+++ b/library/cpp/yson_pull/detail/byte_reader.h
@@ -0,0 +1,74 @@
+#pragma once
+
+#include "cescape.h"
+#include "fail.h"
+#include "stream_counter.h"
+
+#include <library/cpp/yson_pull/input.h>
+
+namespace NYsonPull {
+    namespace NDetail {
+        template <class StreamCounter>
+        class byte_reader {
+            NYsonPull::NInput::IStream& stream_;
+            StreamCounter stream_counter_;
+
+        public:
+            byte_reader(NYsonPull::NInput::IStream& stream)
+                : stream_(stream)
+            {
+            }
+
+            // const-ness added to prevent direct stream mutation
+            const NYsonPull::NInput::IStream& stream() {
+                return stream_;
+            }
+
+            template <typename... Args>
+            ATTRIBUTE(noinline, cold)
+            void fail[[noreturn]](const char* msg, Args&&... args) {
+                NYsonPull::NDetail::fail(
+                    stream_counter_.info(),
+                    msg,
+                    std::forward<Args>(args)...);
+            }
+
+            template <bool AllowFinish>
+            void fill_buffer() {
+                stream_.fill_buffer();
+
+                if (!AllowFinish) {
+                    auto& buf = stream_.buffer();
+                    if (Y_UNLIKELY(buf.is_empty() && stream_.at_end())) {
+                        fail("Premature end of stream");
+                    }
+                }
+            }
+
+            void fill_buffer() {
+                return fill_buffer<true>();
+            }
+
+            template <bool AllowFinish>
+            ui8 get_byte() {
+                fill_buffer<AllowFinish>();
+                auto& buf = stream_.buffer();
+                return !buf.is_empty()
+                           ? *buf.pos()
+                           : ui8{'\0'};
+            }
+
+            ui8 get_byte() {
+                return get_byte<true>();
+            }
+
+            void advance(size_t bytes) {
+                auto& buf = stream_.buffer();
+                stream_counter_.update(
+                    buf.pos(),
+                    buf.pos() + bytes);
+                buf.advance(bytes);
+            }
+        };
+    }
+}