First implementation

vendor/github.com/mattn/go-pointer/LICENSE

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+The MIT License (MIT)
+
+Copyright (c) 2019 Yasuhiro Matsumoto
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

vendor/github.com/mattn/go-pointer/README.md

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+# go-pointer
+
+Utility for cgo
+
+## Usage
+
+https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md
+
+In go 1.6, cgo argument can't be passed Go pointer.
+
+```
+var s string
+C.pass_pointer(pointer.Save(&s))
+v := *(pointer.Restore(C.get_from_pointer()).(*string))
+```
+
+## Installation
+
+```
+go get github.com/mattn/go-pointer
+```
+
+## License
+
+MIT
+
+## Author
+
+Yasuhiro Matsumoto (a.k.a mattn)

vendor/github.com/mattn/go-pointer/doc.go

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+package pointer

vendor/github.com/mattn/go-pointer/pointer.go

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+package pointer
+
+// #include <stdlib.h>
+import "C"
+import (
+	"sync"
+	"unsafe"
+)
+
+var (
+	mutex sync.RWMutex
+	store = map[unsafe.Pointer]interface{}{}
+)
+
+func Save(v interface{}) unsafe.Pointer {
+	if v == nil {
+		return nil
+	}
+
+	// Generate real fake C pointer.
+	// This pointer will not store any data, but will bi used for indexing purposes.
+	// Since Go doest allow to cast dangling pointer to unsafe.Pointer, we do rally allocate one byte.
+	// Why we need indexing, because Go doest allow C code to store pointers to Go data.
+	var ptr unsafe.Pointer = C.malloc(C.size_t(1))
+	if ptr == nil {
+		panic("can't allocate 'cgo-pointer hack index pointer': ptr == nil")
+	}
+
+	mutex.Lock()
+	store[ptr] = v
+	mutex.Unlock()
+
+	return ptr
+}
+
+func Restore(ptr unsafe.Pointer) (v interface{}) {
+	if ptr == nil {
+		return nil
+	}
+
+	mutex.RLock()
+	v = store[ptr]
+	mutex.RUnlock()
+	return
+}
+
+func Unref(ptr unsafe.Pointer) {
+	if ptr == nil {
+		return
+	}
+
+	mutex.Lock()
+	delete(store, ptr)
+	mutex.Unlock()
+
+	C.free(ptr)
+}