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/re2/unicode_casefold.h

@@ -0,0 +1,78 @@
+// Copyright 2008 The RE2 Authors.  All Rights Reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#ifndef RE2_UNICODE_CASEFOLD_H_
+#define RE2_UNICODE_CASEFOLD_H_
+
+// Unicode case folding tables.
+
+// The Unicode case folding tables encode the mapping from one Unicode point
+// to the next largest Unicode point with equivalent folding.  The largest
+// point wraps back to the first.  For example, the tables map:
+//
+//     'A' -> 'a'
+//     'a' -> 'A'
+//
+//     'K' -> 'k'
+//     'k' -> 'K'  (Kelvin symbol)
+//     'K' -> 'K'
+//
+// Like everything Unicode, these tables are big.  If we represent the table
+// as a sorted list of uint32_t pairs, it has 2049 entries and is 16 kB.
+// Most table entries look like the ones around them:
+// 'A' maps to 'A'+32, 'B' maps to 'B'+32, etc.
+// Instead of listing all the pairs explicitly, we make a list of ranges
+// and deltas, so that the table entries for 'A' through 'Z' can be represented
+// as a single entry { 'A', 'Z', +32 }.
+//
+// In addition to blocks that map to each other (A-Z mapping to a-z)
+// there are blocks of pairs that individually map to each other
+// (for example, 0100<->0101, 0102<->0103, 0104<->0105, ...).
+// For those, the special delta value EvenOdd marks even/odd pairs
+// (if even, add 1; if odd, subtract 1), and OddEven marks odd/even pairs.
+//
+// In this form, the table has 274 entries, about 3kB.  If we were to split
+// the table into one for 16-bit codes and an overflow table for larger ones,
+// we could get it down to about 1.5kB, but that's not worth the complexity.
+//
+// The grouped form also allows for efficient fold range calculations
+// rather than looping one character at a time.
+
+#include <stdint.h>
+
+#include "util/utf.h"
+#include "util/util.h"
+
+namespace re2 {
+
+enum {
+    EvenOdd = 1,
+    OddEven = -1,
+    EvenOddSkip = 1 << 30,
+    OddEvenSkip,
+};
+
+struct CaseFold {
+    Rune lo;
+    Rune hi;
+    int32_t delta;
+};
+
+extern const CaseFold unicode_casefold[];
+extern const int num_unicode_casefold;
+
+extern const CaseFold unicode_tolower[];
+extern const int num_unicode_tolower;
+
+// Returns the CaseFold* in the tables that contains rune.
+// If rune is not in the tables, returns the first CaseFold* after rune.
+// If rune is larger than any value in the tables, returns NULL.
+extern const CaseFold *LookupCaseFold(const CaseFold *, int, Rune rune);
+
+// Returns the result of applying the fold f to the rune r.
+extern Rune ApplyFold(const CaseFold *f, Rune r);
+
+} // namespace re2
+
+#endif // RE2_UNICODE_CASEFOLD_H_