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/stringpiece.cc

@@ -0,0 +1,69 @@
+// Copyright 2004 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.
+
+#include "re2/stringpiece.h"
+
+#include <ostream>
+
+#include "util/util.h"
+
+namespace re2 {
+
+const StringPiece::size_type StringPiece::npos; // initialized in stringpiece.h
+
+StringPiece::size_type StringPiece::copy(char *buf, size_type n, size_type pos) const {
+    size_type ret = std::min(size_ - pos, n);
+    memcpy(buf, data_ + pos, ret);
+    return ret;
+}
+
+StringPiece StringPiece::substr(size_type pos, size_type n) const {
+    if (pos > size_)
+        pos = size_;
+    if (n > size_ - pos)
+        n = size_ - pos;
+    return StringPiece(data_ + pos, n);
+}
+
+StringPiece::size_type StringPiece::find(const StringPiece &s, size_type pos) const {
+    if (pos > size_)
+        return npos;
+    const_pointer result = std::search(data_ + pos, data_ + size_, s.data_, s.data_ + s.size_);
+    size_type xpos = result - data_;
+    return xpos + s.size_ <= size_ ? xpos : npos;
+}
+
+StringPiece::size_type StringPiece::find(char c, size_type pos) const {
+    if (size_ <= 0 || pos >= size_)
+        return npos;
+    const_pointer result = std::find(data_ + pos, data_ + size_, c);
+    return result != data_ + size_ ? result - data_ : npos;
+}
+
+StringPiece::size_type StringPiece::rfind(const StringPiece &s, size_type pos) const {
+    if (size_ < s.size_)
+        return npos;
+    if (s.size_ == 0)
+        return std::min(size_, pos);
+    const_pointer last = data_ + std::min(size_ - s.size_, pos) + s.size_;
+    const_pointer result = std::find_end(data_, last, s.data_, s.data_ + s.size_);
+    return result != last ? result - data_ : npos;
+}
+
+StringPiece::size_type StringPiece::rfind(char c, size_type pos) const {
+    if (size_ <= 0)
+        return npos;
+    for (size_t i = std::min(pos + 1, size_); i != 0;) {
+        if (data_[--i] == c)
+            return i;
+    }
+    return npos;
+}
+
+std::ostream &operator<<(std::ostream &o, const StringPiece &p) {
+    o.write(p.data(), p.size());
+    return o;
+}
+
+} // namespace re2