Add support for error aggregation for request/response validation (#259)

Author: zlozano

openapi3/errors.go

@@ -0,0 +1,43 @@
+package openapi3
+
+import (
+	"bytes"
+	"errors"
+)
+
+// MultiError is a collection of errors, intended for when
+// multiple issues need to be reported upstream
+type MultiError []error
+
+func (me MultiError) Error() string {
+	buff := &bytes.Buffer{}
+	for _, e := range me {
+		buff.WriteString(e.Error())
+		buff.WriteString(" | ")
+	}
+	return buff.String()
+}
+
+//Is allows you to determine if a generic error is in fact a MultiError using `errors.Is()`
+//It will also return true if any of the contained errors match target
+func (me MultiError) Is(target error) bool {
+	if _, ok := target.(MultiError); ok {
+		return true
+	}
+	for _, e := range me {
+		if errors.Is(e, target) {
+			return true
+		}
+	}
+	return false
+}
+
+//As allows you to use `errors.As()` to set target to the first error within the multi error that matches the target type
+func (me MultiError) As(target interface{}) bool {
+	for _, e := range me {
+		if errors.As(e, target) {
+			return true
+		}
+	}
+	return false
+}