S3 Select API Support for CSV (#6127)

Add support for trivial where clause cases

vendor/github.com/xwb1989/sqlparser/dependency/hack/hack.go

@@ -0,0 +1,79 @@
+/*
+Copyright 2017 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package hack gives you some efficient functionality at the cost of
+// breaking some Go rules.
+package hack
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+// StringArena lets you consolidate allocations for a group of strings
+// that have similar life length
+type StringArena struct {
+	buf []byte
+	str string
+}
+
+// NewStringArena creates an arena of the specified size.
+func NewStringArena(size int) *StringArena {
+	sa := &StringArena{buf: make([]byte, 0, size)}
+	pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&sa.buf))
+	pstring := (*reflect.StringHeader)(unsafe.Pointer(&sa.str))
+	pstring.Data = pbytes.Data
+	pstring.Len = pbytes.Cap
+	return sa
+}
+
+// NewString copies a byte slice into the arena and returns it as a string.
+// If the arena is full, it returns a traditional go string.
+func (sa *StringArena) NewString(b []byte) string {
+	if len(b) == 0 {
+		return ""
+	}
+	if len(sa.buf)+len(b) > cap(sa.buf) {
+		return string(b)
+	}
+	start := len(sa.buf)
+	sa.buf = append(sa.buf, b...)
+	return sa.str[start : start+len(b)]
+}
+
+// SpaceLeft returns the amount of space left in the arena.
+func (sa *StringArena) SpaceLeft() int {
+	return cap(sa.buf) - len(sa.buf)
+}
+
+// String force casts a []byte to a string.
+// USE AT YOUR OWN RISK
+func String(b []byte) (s string) {
+	if len(b) == 0 {
+		return ""
+	}
+	pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
+	pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
+	pstring.Data = pbytes.Data
+	pstring.Len = pbytes.Len
+	return
+}
+
+// StringPointer returns &s[0], which is not allowed in go
+func StringPointer(s string) unsafe.Pointer {
+	pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
+	return unsafe.Pointer(pstring.Data)
+}