feat: Add TypeMapper interface

Author: thced

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

@@ -0,0 +1,21 @@
+package com.retailsvc.http;
+
+/**
+ * Reads and writes request/response bodies for a specific media type. Registered on {@link
+ * OpenApiServer.Builder#bodyMapper(String, TypeMapper)} keyed by media type. The library ships
+ * built-in mappers for {@code application/x-www-form-urlencoded} and {@code text/plain}; an {@code
+ * application/json} mapper must be supplied by the caller or auto-detected via Gson on the
+ * classpath.
+ */
+public interface TypeMapper {
+
+  /**
+   * @param body raw request body bytes
+   * @param contentTypeHeader the full raw {@code Content-Type} header, used for charset and other
+   *     parameters (the JSON mapper ignores it)
+   */
+  Object readFrom(byte[] body, String contentTypeHeader);
+
+  /** Serializes {@code value} to bytes suitable for writing as the response body. */
+  byte[] writeTo(Object value);
+}

src/test/java/com/retailsvc/http/TypeMapperShapeTest.java

@@ -0,0 +1,29 @@
+package com.retailsvc.http;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.nio.charset.StandardCharsets;
+import org.junit.jupiter.api.Test;
+
+class TypeMapperShapeTest {
+
+  @Test
+  void roundTripsViaInlineImplementation() {
+    TypeMapper identity =
+        new TypeMapper() {
+          @Override
+          public Object readFrom(byte[] body, String contentTypeHeader) {
+            return new String(body, StandardCharsets.UTF_8);
+          }
+
+          @Override
+          public byte[] writeTo(Object value) {
+            return ((String) value).getBytes(StandardCharsets.UTF_8);
+          }
+        };
+
+    Object read = identity.readFrom("hi".getBytes(StandardCharsets.UTF_8), "text/plain");
+    assertThat(read).isEqualTo("hi");
+    assertThat(identity.writeTo("hi")).containsExactly('h', 'i');
+  }
+}