Compile pattern on validate

.github/workflows/go.yml

@@ -65,6 +65,9 @@ jobs:
       run: git --no-pager diff && [[ $(git --no-pager diff --name-only | wc -l) = 0 ]]
 
     - run: go test ./...
+    - run: go test -v -run TestRaceyPatternSchema -race ./...
+      env:
+        CGO_ENABLED: '1'
     - run: |
         cd openapi3/testdata
         go get -u -v github.com/getkin/kin-openapi

openapi3/race_test.go

@@ -0,0 +1,26 @@
+package openapi3_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/getkin/kin-openapi/openapi3"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRaceyPatternSchema(t *testing.T) {
+	schema := openapi3.Schema{
+		Pattern: "^test|for|race|condition$",
+	}
+
+	err := schema.Validate(context.Background())
+	require.NoError(t, err)
+
+	visit := func() {
+		err := schema.VisitJSONString("test")
+		require.NoError(t, err)
+	}
+
+	go visit()
+	visit()
+}

openapi3/schema.go

@@ -666,6 +666,11 @@ func (schema *Schema) validate(ctx context.Context, stack []*Schema) (err error)
 			case "byte", "binary", "date", "date-time", "password":
 				// In JSON Draft-07 (not validated yet though):
 			case "regex":
+				if !SchemaFormatValidationDisabled {
+					if err = schema.compilePattern(); err != nil {
+						return err
+					}
+				}
 			case "time", "email", "idn-email":
 			case "hostname", "idn-hostname", "ipv4", "ipv6":
 			case "uri", "uri-reference", "iri", "iri-reference", "uri-template":
@@ -1141,13 +1146,7 @@ func (schema *Schema) visitJSONString(settings *schemaValidationSettings, value
 	// "pattern"
 	if pattern := schema.Pattern; pattern != "" && schema.compiledPattern == nil {
 		var err error
-		if schema.compiledPattern, err = regexp.Compile(pattern); err != nil {
-			err = &SchemaError{
-				Value:       value,
-				Schema:      schema,
-				SchemaField: "pattern",
-				Reason:      fmt.Sprintf("cannot compile pattern %q: %v", pattern, err),
-			}
+		if err = schema.compilePattern(); err != nil {
 			if !settings.multiError {
 				return err
 			}
@@ -1461,6 +1460,20 @@ func (schema *Schema) expectedType(settings *schemaValidationSettings, typ strin
 	}
 }
 
+func (schema *Schema) compilePattern() (err error) {
+	if schema.Pattern == "" {
+		return nil
+	}
+	if schema.compiledPattern, err = regexp.Compile(schema.Pattern); err != nil {
+		return &SchemaError{
+			Schema:      schema,
+			SchemaField: "pattern",
+			Reason:      fmt.Sprintf("cannot compile pattern %q: %v", schema.Pattern, err),
+		}
+	}
+	return nil
+}
+
 type SchemaError struct {
 	Value       interface{}
 	reversePath []string