Building out schema comparison mechanism

Which has led to a new wider hashing capability for the low level API. hashing makes it very easy to determine changes quickly, without having to run comparisons to discover changes, could really speed things up moving forward.

datamodel/low/base/external_doc.go

@@ -4,9 +4,11 @@
 package base
 
 import (
+	"crypto/sha256"
 	"github.com/pb33f/libopenapi/datamodel/low"
 	"github.com/pb33f/libopenapi/index"
 	"gopkg.in/yaml.v3"
+	"strings"
 )
 
 // ExternalDoc represents a low-level External Documentation object as defined by OpenAPI 2 and 3
@@ -38,3 +40,12 @@ func (ex *ExternalDoc) GetExtensions() map[low.KeyReference[string]]low.ValueRef
 	}
 	return ex.Extensions
 }
+
+func (ex *ExternalDoc) Hash() [32]byte {
+	// calculate a hash from every property.
+	d := []string{
+		ex.Description.Value,
+		ex.URL.Value,
+	}
+	return sha256.Sum256([]byte(strings.Join(d, "|")))
+}