Fix JSON parser handling for certain objects (#7162)

This PR also adds some comments and simplifies
the code. Primary handling is done to ensure
that we make sure to honor cached buffer.

Added unit tests as well

Fixes #7141

vendor/github.com/bcicen/jstream/errors.go

@@ -0,0 +1,41 @@
+package jstream
+
+import (
+	"fmt"
+	"strconv"
+)
+
+// Predefined errors
+var (
+	ErrSyntax        = SyntaxError{msg: "invalid character"}
+	ErrUnexpectedEOF = SyntaxError{msg: "unexpected end of JSON input"}
+)
+
+type errPos [2]int // line number, byte offset where error occurred
+
+type SyntaxError struct {
+	msg     string // description of error
+	context string // additional error context
+	pos     errPos
+	atChar  byte
+}
+
+func (e SyntaxError) Error() string {
+	loc := fmt.Sprintf("%s [%d,%d]", quoteChar(e.atChar), e.pos[0], e.pos[1])
+	return fmt.Sprintf("%s %s: %s", e.msg, e.context, loc)
+}
+
+// quoteChar formats c as a quoted character literal
+func quoteChar(c byte) string {
+	// special cases - different from quoted strings
+	if c == '\'' {
+		return `'\''`
+	}
+	if c == '"' {
+		return `'"'`
+	}
+
+	// use quoted string with different quotation marks
+	s := strconv.Quote(string(c))
+	return "'" + s[1:len(s)-1] + "'"
+}