string_decoder: reimplement in C++

Implement string decoder in C++. The perks are a decent speed boost
(for decoding, whereas creation show some performance degradation),
that this can now be used more easily to add native decoding support
to C++ streams and (arguably) more readable variable names.

PR-URL: https://github.com/nodejs/node/pull/18537
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

1 files changed, 50 insertions, 0 deletions

diff --git a/src/string_decoder.h b/src/string_decoder.h
new file mode 100644
index 0000000000..9059eeaa9d
--- /dev/null
+++ b/src/string_decoder.h
@@ -0,0 +1,50 @@
+#ifndef SRC_STRING_DECODER_H_
+#define SRC_STRING_DECODER_H_
+
+#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
+
+#include "node.h"
+
+namespace node {
+
+class StringDecoder {
+ public:
+  StringDecoder() { state_[kEncodingField] = BUFFER; }
+  inline void SetEncoding(enum encoding encoding);
+  inline enum encoding Encoding() const;
+
+  inline char* IncompleteCharacterBuffer();
+  inline unsigned MissingBytes() const;
+  inline unsigned BufferedBytes() const;
+
+  // Decode a string from the specified encoding.
+  // The value pointed to by `nread` will be modified to reflect that
+  // less data may have been read because it ended on an incomplete character
+  // and more data may have been read because a previously incomplete character
+  // was finished.
+  v8::MaybeLocal<v8::String> DecodeData(v8::Isolate* isolate,
+                                        const char* data,
+                                        size_t* nread);
+  // Flush an incomplete character. For character encodings like UTF8 this
+  // means printing replacement characters, buf for e.g. Base64 the returned
+  // string contains more data.
+  v8::MaybeLocal<v8::String> FlushData(v8::Isolate* isolate);
+
+  enum Fields {
+    kIncompleteCharactersStart = 0,
+    kIncompleteCharactersEnd = 4,
+    kMissingBytes = 4,
+    kBufferedBytes = 5,
+    kEncodingField = 6,
+    kNumFields = 7
+  };
+
+ private:
+  uint8_t state_[kNumFields] = {};
+};
+
+}  // namespace node
+
+#endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
+
+#endif   // SRC_STRING_DECODER_H_