feat: Add support for refs in request bodies (#7)

Author: thced

README.md

@@ -104,6 +104,12 @@ The library uses a flexible JSON mapping system that automatically detects and p
 - JSON arrays (`[...]`)
 - JSON objects (`{...}`)
 
-## Known limitations (not exhaustive..)
+## Local development
 
-- OpenAPI refs are not supported yet.
+To test the server in isolation, you can start an example server (`src/test/java/com/retailsvc/http/start/ServerLauncher.java`).
+Schemas are located under test resources folder.
+
+- Example requests can be found under `acceptance/k6` that can be a base for exploring the functionality.
+- The logger in the configuration needs to be enabled to get some insight into the code.
+
+## Known limitations or missing features

acceptance/k6/script.js

@@ -10,7 +10,7 @@ export const options = {
   ],
 };
 
-const body = JSON.stringify({
+const exampleObjectRequest = {
   id: 'some-id',
   age: 42,
   random: 'd5af5004-8b5a-4db6-838e-38be773eac34',
@@ -31,12 +31,15 @@ const body = JSON.stringify({
   ],
   aDate: '2025-03-02',
   aDateTime: '2025-03-02T12:34:56Z'
-});
+};
 
-const listOfObjects = JSON.stringify([
+const exampleListRequest = [
   { value: 42 },
   { value: 43 }
-]);
+];
+
+const objectBody = JSON.stringify(exampleObjectRequest);
+const listBody = JSON.stringify(exampleListRequest);
 
 export default function () {
   group('get request', () => {
@@ -52,7 +55,7 @@ export default function () {
 
   group('post request', () => {
     const url = 'http://localhost:8080/api/v1/data';
-    const res = http.post(url, body, {
+    const res = http.post(url, objectBody, {
       headers: {
         'Content-Type':'application/json',
       }
@@ -67,7 +70,7 @@ export default function () {
 
   group('post list-of-objects request', () => {
     const url = 'http://localhost:8080/api/v1/list/objects';
-    const res = http.post(url, listOfObjects, {
+    const res = http.post(url, listBody, {
       headers: {
         'Content-Type':'application/json',
       }

pom.xml

@@ -43,6 +43,7 @@
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-api</artifactId>
       <version>2.0.16</version>
+      <scope>provided</scope>
     </dependency>
 
     <dependency>

src/main/java/com/retailsvc/http/OpenApiServer.java

@@ -65,6 +65,8 @@ public OpenApiServer(
       throws IOException {
 
     long t0 = System.currentTimeMillis();
+    LOG.debug("Starting server...");
+
     requireNonNull(specification, "OpenAPI specification must not be null");
     requireNonNull(jsonMapper, "Request body mapper must not be null");
     requireNonNull(requestHandlers, "Request handlers must not be null");
@@ -95,10 +97,10 @@ private HttpServer initializeServer(
     context.setHandler(new RequestDispatchingHandler(specification, requestHandlers));
 
     server.createContext("/", notFoundHandler());
-
-    LOG.debug("Starting server...");
     server.start();
+
     LOG.info("Server started (port {}) in {}ms", PORT, System.currentTimeMillis() - t0);
+
     return server;
   }
 

src/main/java/com/retailsvc/http/openapi/OpenApiValidationFilter.java

@@ -1,6 +1,7 @@
 package com.retailsvc.http.openapi;
 
 import static java.net.HttpURLConnection.HTTP_BAD_REQUEST;
+import static java.util.Objects.nonNull;
 
 import com.retailsvc.http.openapi.exceptions.OperationIdNotFoundException;
 import com.retailsvc.http.openapi.model.GetRequestBody;
@@ -36,7 +37,7 @@ public class OpenApiValidationFilter extends Filter implements GetRequestBody {
   private final Validator validator;
 
   public OpenApiValidationFilter(OpenApi spec, JsonMapper mapper) {
-    this(spec, mapper, new ValidatorImpl());
+    this(spec, mapper, new ValidatorImpl(spec::getResolvedSchema));
   }
 
   protected OpenApiValidationFilter(OpenApi spec, JsonMapper mapper, Validator validator) {
@@ -101,6 +102,10 @@ public void doFilter(HttpExchange exchange, Chain chain) throws IOException {
       MediaType mediaType = operation.requestBody().content().get(contentType);
       Schema schema = mediaType.schema();
 
+      if (nonNull(schema.$ref())) {
+        schema = specification.getResolvedSchema(schema.$ref());
+      }
+
       boolean isValid = validator.validate(mappedBody, schema);
 
       LOG.debug("Overall validation is {}", isValid ? "VALID" : "INVALID");

src/main/java/com/retailsvc/http/openapi/model/OpenApi.java

@@ -13,6 +13,7 @@
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Function;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -23,10 +24,15 @@
  * @author thced
  */
 public record OpenApi(
-    String openapi, Info info, Collection<Server> servers, Map<String, PathItem> paths) {
+    String openapi,
+    Info info,
+    Collection<Server> servers,
+    Map<String, PathItem> paths,
+    Components components) {
 
   private static final Logger LOG = LoggerFactory.getLogger(OpenApi.class);
   private static final Set<String> SUPPORTED_VERSIONS = Set.of("3.1.0");
+  private static final Map<String, Schema> SCHEMAS_CACHE = new ConcurrentHashMap<>();
 
   public static OpenApi parse(Function<String, OpenApi> fn, String spec) {
     return fn.apply(spec);
@@ -69,6 +75,20 @@ public Optional<Operation> getOperation(String method, String path) {
         .findFirst();
   }
 
+  /**
+   * Used to get access to the referenced schema components. It will strip off the
+   * '#/components/schemas/' prefix and cache the found {@link Schema} instance.
+   *
+   * @param ref The "full" ref name
+   * @return The found schema, or null
+   */
+  public Schema getResolvedSchema(String ref) {
+    String name = ref.replace("#/components/schemas/", "");
+    Schema found = SCHEMAS_CACHE.computeIfAbsent(name, components::getSchema);
+    LOG.debug("Found resolved schema: {} -> {}", ref, found);
+    return found;
+  }
+
   /**
    * The 'info' object.
    *
@@ -155,6 +175,7 @@ public record RequestBody(
   public record MediaType(Schema schema) {}
 
   public record Schema(
+      String $ref,
       String type,
       String format,
       Map<String, Object> properties,
@@ -163,18 +184,35 @@ public record Schema(
       Number maximum,
       Number minimum) {
 
+    /**
+     * If Schema has a $ref, we do not set any properties. The properties will be resolved later via
+     * the referenced component {@link Components}.
+     */
     public Schema {
-      if (type == null || type.isBlank()) {
-        throw new LoadSpecificationException("Type is missing");
-      }
-      if (isNull(format) && isNumber()) {
-        format = "int32";
+      if (isNull($ref)) {
+        if (type == null || type.isBlank()) {
+          throw new LoadSpecificationException("Type is missing");
+        }
+        if (isNull(format) && isNumber()) {
+          format = "int32";
+        }
+        required = Objects.requireNonNullElse(required, List.of());
+        items = Objects.requireNonNullElse(items, Map.of());
+        properties = Objects.requireNonNullElse(properties, Map.of());
+        maximum = Objects.requireNonNullElse(maximum, Double.MAX_VALUE);
+        minimum = Objects.requireNonNullElse(minimum, Double.MIN_VALUE);
       }
-      required = Objects.requireNonNullElse(required, List.of());
-      items = Objects.requireNonNullElse(items, Map.of());
-      properties = Objects.requireNonNullElse(properties, Map.of());
-      maximum = Objects.requireNonNullElse(maximum, Double.MAX_VALUE);
-      minimum = Objects.requireNonNullElse(minimum, Double.MIN_VALUE);
+    }
+
+    public Schema(
+        String type,
+        String format,
+        Map<String, Object> properties,
+        Map<String, Object> items,
+        List<String> required,
+        Number maximum,
+        Number minimum) {
+      this(null, type, format, properties, items, required, maximum, minimum);
     }
 
     public boolean isString() {
@@ -205,4 +243,10 @@ public boolean isArray() {
       return "array".equalsIgnoreCase(type);
     }
   }
+
+  public record Components(Map<String, Schema> schemas) {
+    public Schema getSchema(String name) {
+      return schemas.get(name);
+    }
+  }
 }

src/main/java/com/retailsvc/http/openapi/validation/ArrayValidator.java

@@ -5,16 +5,25 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.function.Function;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 public class ArrayValidator implements Validator {
 
   private static final Logger LOG = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
   private final Validator rootValidator;
+  private final Function<String, Schema> referencedSchema;
 
-  public ArrayValidator(Validator rootValidator) {
+  /**
+   * Validate lists
+   *
+   * @param rootValidator The parent that delegates types to correct validator
+   * @param referencedSchema Referenced schema registry
+   */
+  public ArrayValidator(Validator rootValidator, Function<String, Schema> referencedSchema) {
     this.rootValidator = rootValidator;
+    this.referencedSchema = referencedSchema;
   }
 
   @Override
@@ -29,27 +38,28 @@ public boolean validate(Object json, Schema schema) {
 
     Map<String, Object> items = schema.items();
     String type = (String) items.get("type");
+    String $ref = (String) items.get("$ref");
     Map<String, Object> props = (Map<String, Object>) items.get("properties");
     String format = (String) items.get("format");
     List<String> required = (List<String>) items.get("required");
-    var maximum =
-        Optional.ofNullable(props)
-            .map(p -> p.get("maximum"))
-            .map(Number.class::cast)
-            .orElse(Double.MAX_VALUE);
-    var minimum =
-        Optional.ofNullable(props)
-            .map(p -> p.get("minimum"))
-            .map(Number.class::cast)
-            .orElse(Double.MIN_VALUE);
+    var max = getLimitForNumber(props, "maximum", Double.MAX_VALUE);
+    var min = getLimitForNumber(props, "minimum", Double.MIN_VALUE);
 
     for (Object entry : iterable) {
-      if (!rootValidator.validate(
-          entry, new Schema(type, format, props, items, required, maximum, minimum))) {
+      Schema propertySchema =
+          Optional.ofNullable($ref)
+              .map(referencedSchema)
+              .orElseGet(() -> new Schema($ref, type, format, props, items, required, max, min));
+
+      if (!rootValidator.validate(entry, propertySchema)) {
         LOG.debug("Failed to validate '{}'", entry);
         return false;
       }
     }
     return true;
   }
+
+  private static Number getLimitForNumber(Map<String, Object> props, String name, double limit) {
+    return Optional.ofNullable(props).map(p -> p.get(name)).map(Number.class::cast).orElse(limit);
+  }
 }