Add new SQL parser to support S3 Select syntax (#7102)

- New parser written from scratch, allows easier and complete parsing
  of the full S3 Select SQL syntax. Parser definition is directly
  provided by the AST defined for the SQL grammar.

- Bring support to parse and interpret SQL involving JSON path
  expressions; evaluation of JSON path expressions will be
  subsequently added.

- Bring automatic type inference and conversion for untyped
  values (e.g. CSV data).

pkg/s3select/sql/utils.go

@@ -0,0 +1,87 @@
+/*
+ * Minio Cloud Storage, (C) 2019 Minio, 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 sql
+
+import (
+	"fmt"
+	"strings"
+)
+
+// String functions
+
+// String - returns the JSONPath representation
+func (e *JSONPath) String() string {
+	parts := make([]string, len(e.PathExpr)+1)
+	parts[0] = e.BaseKey.String()
+	for i, pe := range e.PathExpr {
+		parts[i+1] = pe.String()
+	}
+	return strings.Join(parts, "")
+}
+
+func (e *JSONPathElement) String() string {
+	switch {
+	case e.Key != nil:
+		return e.Key.String()
+	case e.Index != nil:
+		return fmt.Sprintf("[%d]", *e.Index)
+	case e.ObjectWildcard:
+		return ".*"
+	case e.ArrayWildcard:
+		return "[*]"
+	}
+	return ""
+}
+
+// Removes double quotes in quoted identifiers
+func (i *Identifier) String() string {
+	if i.Unquoted != nil {
+		return *i.Unquoted
+	}
+	return string(*i.Quoted)
+}
+
+func (o *ObjectKey) String() string {
+	if o.Lit != nil {
+		return fmt.Sprintf("['%s']", string(*o.Lit))
+	}
+	return fmt.Sprintf(".%s", o.ID.String())
+}
+
+// getLastKeypathComponent checks if the given expression is a path
+// expression, and if so extracts the last dot separated component of
+// the path. Otherwise it returns false.
+func getLastKeypathComponent(e *Expression) (string, bool) {
+	if len(e.And) > 1 ||
+		len(e.And[0].Condition) > 1 ||
+		e.And[0].Condition[0].Not != nil ||
+		e.And[0].Condition[0].Operand.ConditionRHS != nil {
+		return "", false
+	}
+
+	operand := e.And[0].Condition[0].Operand.Operand
+	if operand.Right != nil ||
+		operand.Left.Right != nil ||
+		operand.Left.Left.Negated != nil ||
+		operand.Left.Left.Primary.JPathExpr == nil {
+		return "", false
+	}
+
+	keypath := operand.Left.Left.Primary.JPathExpr.String()
+	ps := strings.Split(keypath, ".")
+	return ps[len(ps)-1], true
+}