Upgrade gjson to bring in new performance improvements (#6106)

vendor/github.com/tidwall/gjson/gjson_ngae.go

@@ -0,0 +1,73 @@
+//+build !appengine
+
+package gjson
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+// getBytes casts the input json bytes to a string and safely returns the
+// results as uniquely allocated data. This operation is intended to minimize
+// copies and allocations for the large json string->[]byte.
+func getBytes(json []byte, path string) Result {
+	var result Result
+	if json != nil {
+		// unsafe cast to string
+		result = Get(*(*string)(unsafe.Pointer(&json)), path)
+		result = fromBytesGet(result)
+	}
+	return result
+}
+
+func fromBytesGet(result Result) Result {
+	// safely get the string headers
+	rawhi := *(*reflect.StringHeader)(unsafe.Pointer(&result.Raw))
+	strhi := *(*reflect.StringHeader)(unsafe.Pointer(&result.Str))
+	// create byte slice headers
+	rawh := reflect.SliceHeader{Data: rawhi.Data, Len: rawhi.Len}
+	strh := reflect.SliceHeader{Data: strhi.Data, Len: strhi.Len}
+	if strh.Data == 0 {
+		// str is nil
+		if rawh.Data == 0 {
+			// raw is nil
+			result.Raw = ""
+		} else {
+			// raw has data, safely copy the slice header to a string
+			result.Raw = string(*(*[]byte)(unsafe.Pointer(&rawh)))
+		}
+		result.Str = ""
+	} else if rawh.Data == 0 {
+		// raw is nil
+		result.Raw = ""
+		// str has data, safely copy the slice header to a string
+		result.Str = string(*(*[]byte)(unsafe.Pointer(&strh)))
+	} else if strh.Data >= rawh.Data &&
+		int(strh.Data)+strh.Len <= int(rawh.Data)+rawh.Len {
+		// Str is a substring of Raw.
+		start := int(strh.Data - rawh.Data)
+		// safely copy the raw slice header
+		result.Raw = string(*(*[]byte)(unsafe.Pointer(&rawh)))
+		// substring the raw
+		result.Str = result.Raw[start : start+strh.Len]
+	} else {
+		// safely copy both the raw and str slice headers to strings
+		result.Raw = string(*(*[]byte)(unsafe.Pointer(&rawh)))
+		result.Str = string(*(*[]byte)(unsafe.Pointer(&strh)))
+	}
+	return result
+}
+
+// fillIndex finds the position of Raw data and assigns it to the Index field
+// of the resulting value. If the position cannot be found then Index zero is
+// used instead.
+func fillIndex(json string, c *parseContext) {
+	if len(c.value.Raw) > 0 && !c.calcd {
+		jhdr := *(*reflect.StringHeader)(unsafe.Pointer(&json))
+		rhdr := *(*reflect.StringHeader)(unsafe.Pointer(&(c.value.Raw)))
+		c.value.Index = int(rhdr.Data - jhdr.Data)
+		if c.value.Index < 0 || c.value.Index >= len(json) {
+			c.value.Index = 0
+		}
+	}
+}