feat(openapi): support structured syntax suffixes in for JSON MIME types.

Author: outofcoffee

mock/openapi/build.gradle

@@ -17,6 +17,7 @@ dependencies {
 
     implementation "io.swagger.parser.v3:swagger-parser-v3:$version_swagger_parser"
     implementation "com.atlassian.oai:swagger-request-validator-core:$version_swagger_request_validator"
+    implementation 'jakarta.activation:jakarta.activation-api:2.1.3'
 
     implementation platform("com.amazonaws:aws-java-sdk-bom:$version_aws_sdk")
     implementation 'com.amazonaws:aws-java-sdk-s3'
@@ -26,6 +27,8 @@ dependencies {
     testImplementation project(':test:api-tests')
     testImplementation "org.testcontainers:testcontainers:$version_testcontainers"
     testImplementation "com.adobe.testing:s3mock-testcontainers:$version_s3mock"
+    testImplementation "org.mockito:mockito-core:$version_mockito"
+    testImplementation "org.mockito.kotlin:mockito-kotlin:$version_mockito_kotlin"
 
     // java 11 compatibility
     testImplementation ("javax.xml.bind:jaxb-api:$version_jaxb_api")

mock/openapi/src/main/java/io/gatehill/imposter/plugin/openapi/service/ResponseTransmissionServiceImpl.kt

@@ -42,17 +42,16 @@
  */
 package io.gatehill.imposter.plugin.openapi.service
 
-import com.fasterxml.jackson.core.JsonProcessingException
 import io.gatehill.imposter.http.HttpExchange
 import io.gatehill.imposter.plugin.openapi.model.ContentTypedHolder
 import io.gatehill.imposter.util.HttpUtil.CONTENT_TYPE
 import io.gatehill.imposter.util.LogUtil
 import io.gatehill.imposter.util.MapUtil
 import io.gatehill.imposter.util.MapUtil.YAML_MAPPER
 import io.swagger.v3.oas.models.examples.Example
+import jakarta.activation.MimeType
 import org.apache.logging.log4j.LogManager
 import java.util.Objects
-import javax.activation.MimeType
 
 /**
  * Serialises and transmits examples to the client.
@@ -174,26 +173,26 @@ class ResponseTransmissionServiceImpl : ResponseTransmissionService {
                 }
             }
             exampleResponse
-        } catch (e: JsonProcessingException) {
-            LOGGER.error("Error building example response", e)
-            ""
+        } catch (e: Exception) {
+            LOGGER.error("Error serialising response", e)
+            example.toString()
         }
     }
 
+    /**
+     * Extension method to check MIME type compatibility.
+     * Supports RFC 6838 structured syntax suffixes.
+     */
     private fun MimeType.compatibleWith(other: MimeType): Boolean {
-        return this.primaryType == other.primaryType && (
-                this.subType == other.subType
-                || this.subType.endsWith("+${other.subType}")
-                || other.subType.endsWith("+${this.subType}")
-                )
+        return (this.primaryType == other.primaryType && this.subType == other.subType) ||
+                this.subType.endsWith("+${other.subType}") ||
+                other.subType.endsWith("+${this.subType}")
     }
 
     companion object {
         private val LOGGER = LogManager.getLogger(ResponseTransmissionServiceImpl::class.java)
         private val JSON_CONTENT_TYPE = MimeType("application/json")
         private val YAML_CONTENT_TYPES = setOf("text/x-yaml", "application/yaml", "application/x-yaml")
-            .map{ MimeType(it) }
-
-
+            .map { MimeType(it) }
     }
 }

mock/openapi/src/test/java/io/gatehill/imposter/plugin/openapi/service/ResponseTransmissionServiceImplTest.kt

@@ -138,6 +138,25 @@ class ResponseTransmissionServiceImplTest {
         assertTrue(response.contains("\"data\""))
     }
 
+    @Test
+    fun `should serialise as JSON for non-application json types with json suffix`() {
+        val httpExchange = createMockHttpExchange()
+        val testData = mapOf("metadata" to "test")
+        val example = ContentTypedHolder("text/vnd.something+json", testData)
+
+        service.transmitExample(httpExchange, example)
+
+        verify(httpExchange.response).putHeader("Content-Type", "text/vnd.something+json")
+
+        val responseCaptor = argumentCaptor<String>()
+        verify(httpExchange.response).end(responseCaptor.capture())
+        val response = responseCaptor.firstValue
+
+        // Verify it's JSON format
+        assertTrue(response.contains("\"metadata\""))
+        assertTrue(response.contains("\"test\""))
+    }
+
     @Test
     fun `should serialise as YAML for YAML content types`() {
         val httpExchange = createMockHttpExchange()