Return response body in FeignException from errorReading (#2618)

FeignException.errorReading passed request.body() and request.headers()
into the constructor's responseBody/responseHeaders parameters, so
FeignException.responseBody()/contentUTF8()/responseHeaders() exposed the
request data instead of the response when a read failure occurred while
decoding a response.

Read the response body (mirroring errorStatus, tolerating a streamed or
already-consumed body) and pass the response headers instead.

Signed-off-by: seonwoo_jung <79202163+seonwooj0810@users.noreply.github.com>

Author: seonwooj0810

core/src/main/java/feign/FeignException.java

@@ -177,13 +177,20 @@ public String contentUTF8() {
   }
 
   static FeignException errorReading(Request request, Response response, IOException cause) {
+    byte[] body = {};
+    try {
+      if (response.body() != null) {
+        body = Util.toByteArray(response.body().asInputStream());
+      }
+    } catch (IOException ignored) { // NOPMD
+    }
     return new FeignException(
         response.status(),
         format("%s reading %s %s", cause.getMessage(), request.httpMethod(), request.url()),
         request,
         cause,
-        request.body(),
-        request.headers());
+        body,
+        response.headers());
   }
 
   public static FeignException errorStatus(String methodKey, Response response) {

core/src/test/java/feign/FeignExceptionTest.java

@@ -43,16 +43,22 @@ void canCreateWithRequestAndResponse() {
             StandardCharsets.UTF_8,
             null);
 
+    Map<String, Collection<String>> responseHeaders =
+        Collections.singletonMap("content-type", Collections.singletonList("application/json"));
     Response response =
         Response.builder()
             .status(400)
             .body("response".getBytes(StandardCharsets.UTF_8))
+            .headers(responseHeaders)
             .request(request)
             .build();
 
     FeignException exception =
         FeignException.errorReading(request, response, new IOException("socket closed"));
     assertThat(exception.responseBody()).isNotEmpty();
+    // the exception must carry the response body, not the request body (gh-2618)
+    assertThat(exception.contentUTF8()).isEqualTo("response");
+    assertThat(exception.responseHeaders()).containsKeys("content-type");
     assertThat(exception.hasRequest()).isTrue();
     assertThat(exception.request()).isNotNull();
   }