requires GET and Streaming on SSE adapters

Author: MukjepScarlet

retrofit-adapters/sse/core/src/main/java/retrofit2/adapter/sse/EventSourceCallAdapterFactory.kt

@@ -20,6 +20,7 @@ import java.lang.reflect.Type
 import retrofit2.CallAdapter
 import retrofit2.Retrofit
 import retrofit2.adapter.sse.internal.EventSourceCallAdapter
+import retrofit2.http.GET
 import retrofit2.http.Streaming
 
 object EventSourceCallAdapterFactory : CallAdapter.Factory() {
@@ -44,6 +45,10 @@ object EventSourceCallAdapterFactory : CallAdapter.Factory() {
       error("SSE endpoint must be annotated with @Streaming")
     }
 
+    if (annotations.none { it is GET }) {
+      error("SSE endpoint must use @GET method")
+    }
+
     val idType = getParameterUpperBound(0, returnType)
     val typeType = getParameterUpperBound(1, returnType)
     val dataType = getParameterUpperBound(2, returnType)

retrofit-adapters/sse/juc-flow/src/main/java/retrofit2/adapter/sse/java9/SseJucFlowCallAdapterFactory.kt

@@ -22,6 +22,7 @@ import java.util.concurrent.Flow
 import retrofit2.CallAdapter
 import retrofit2.Retrofit
 import retrofit2.adapter.sse.ServerSentEvent
+import retrofit2.http.GET
 import retrofit2.http.Streaming
 
 class SseJucFlowCallAdapterFactory private constructor(
@@ -68,6 +69,10 @@ class SseJucFlowCallAdapterFactory private constructor(
       error("SSE endpoint must be annotated with @Streaming")
     }
 
+    if (annotations.none { it is GET }) {
+      error("SSE endpoint must use @GET method")
+    }
+
     val idType = getParameterUpperBound(0, innerType)
     val typeType = getParameterUpperBound(1, innerType)
     val dataType = getParameterUpperBound(2, innerType)

retrofit-adapters/sse/ktx-flow/src/main/java/retrofit2/adapter/sse/kotlinx/SseKtxFlowCallAdapterFactory.kt

@@ -21,6 +21,7 @@ import kotlinx.coroutines.flow.Flow
 import retrofit2.CallAdapter
 import retrofit2.Retrofit
 import retrofit2.adapter.sse.ServerSentEvent
+import retrofit2.http.GET
 import retrofit2.http.Streaming
 
 object SseKtxFlowCallAdapterFactory : CallAdapter.Factory() {
@@ -57,6 +58,10 @@ object SseKtxFlowCallAdapterFactory : CallAdapter.Factory() {
       error("SSE endpoint must be annotated with @Streaming")
     }
 
+    if (annotations.none { it is GET }) {
+      error("SSE endpoint must use @GET method")
+    }
+
     val idType = getParameterUpperBound(0, innerType)
     val typeType = getParameterUpperBound(1, innerType)
     val dataType = getParameterUpperBound(2, innerType)