RAGFlow go API server (#13240)

# RAGFlow Go Implementation Plan 🚀

This repository tracks the progress of porting RAGFlow to Go. We'll
implement core features and provide performance comparisons between
Python and Go versions.

## Implementation Checklist

- [x] User Management APIs
- [x] Dataset Management Operations
- [x] Retrieval Test
- [x] Chat Management Operations
- [x] Infinity Go SDK

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>
Co-authored-by: Yingfeng Zhang <yingfeng.zhang@gmail.com>

internal/cpp/util/utf.h

@@ -0,0 +1,43 @@
+/*
+ * The authors of this software are Rob Pike and Ken Thompson.
+ *              Copyright (c) 2002 by Lucent Technologies.
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose without fee is hereby granted, provided that this entire notice
+ * is included in all copies of any software which is or includes a copy
+ * or modification of this software and in all copies of the supporting
+ * documentation for such software.
+ * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHORS NOR LUCENT TECHNOLOGIES MAKE ANY
+ * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
+ * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
+ *
+ * This file and rune.cc have been converted to compile as C++ code
+ * in name space re2.
+ */
+
+#ifndef UTIL_UTF_H_
+#define UTIL_UTF_H_
+
+#include <stdint.h>
+
+namespace re2 {
+
+typedef signed int Rune; /* Code-point values in Unicode 4.0 are 21 bits wide.*/
+
+enum {
+    UTFmax = 4,         /* maximum bytes per rune */
+    Runesync = 0x80,    /* cannot represent part of a UTF sequence (<) */
+    Runeself = 0x80,    /* rune and UTF sequences are the same (<) */
+    Runeerror = 0xFFFD, /* decoding error in UTF */
+    Runemax = 0x10FFFF, /* maximum rune value */
+};
+
+int runetochar(char *s, const Rune *r);
+int chartorune(Rune *r, const char *s);
+int fullrune(const char *s, int n);
+int utflen(const char *s);
+char *utfrune(const char *, Rune);
+
+} // namespace re2
+
+#endif // UTIL_UTF_H_