Add request logging

src/main/java/com/imgfloat/app/config/TwitchOAuth2ErrorResponseErrorHandler.java

@@ -1,6 +1,7 @@
 package com.imgfloat.app.config;
 
 import java.io.IOException;
+import java.io.ByteArrayInputStream;
 import java.nio.charset.StandardCharsets;
 
 import org.slf4j.Logger;
@@ -26,23 +27,72 @@ class TwitchOAuth2ErrorResponseErrorHandler extends OAuth2ErrorResponseErrorHand
 
     @Override
     public void handleError(ClientHttpResponse response) throws IOException {
+        byte[] bodyBytes = StreamUtils.copyToByteArray(response.getBody());
+        String body = new String(bodyBytes, StandardCharsets.UTF_8);
+
+        if (body.isBlank()) {
+            LOG.warn("Failed to parse Twitch OAuth error response (status: {}, headers: {}): <empty body>",
+                    response.getStatusCode(),
+                    response.getHeaders());
+            throw asAuthorizationException(body, null);
+        }
+
         try {
-            super.handleError(response);
-        } catch (HttpMessageNotReadableException ex) {
-            String body = StreamUtils.copyToString(response.getBody(), StandardCharsets.UTF_8);
+            super.handleError(new CachedBodyClientHttpResponse(response, bodyBytes));
+        } catch (HttpMessageNotReadableException | IllegalArgumentException ex) {
             LOG.warn("Failed to parse Twitch OAuth error response (status: {}, headers: {}): {}",
                     response.getStatusCode(),
                     response.getHeaders(),
-                    body.isBlank() ? "<empty body>" : body,
+                    body,
                     ex);
             throw asAuthorizationException(body, ex);
         }
     }
 
-    private OAuth2AuthorizationException asAuthorizationException(String body,
-                                                                   HttpMessageNotReadableException ex) {
+    private OAuth2AuthorizationException asAuthorizationException(String body, Exception ex) {
         String description = "Failed to parse Twitch OAuth error response" + (body.isBlank() ? "." : ": " + body);
         OAuth2Error oauth2Error = new OAuth2Error("invalid_token_response", description, null);
         return new OAuth2AuthorizationException(oauth2Error, ex);
     }
+
+    private static final class CachedBodyClientHttpResponse implements ClientHttpResponse {
+
+        private final ClientHttpResponse delegate;
+        private final byte[] body;
+
+        private CachedBodyClientHttpResponse(ClientHttpResponse delegate, byte[] body) {
+            this.delegate = delegate;
+            this.body = body;
+        }
+
+        @Override
+        public org.springframework.http.HttpStatusCode getStatusCode() throws IOException {
+            return delegate.getStatusCode();
+        }
+
+        @Override
+        public int getRawStatusCode() throws IOException {
+            return delegate.getRawStatusCode();
+        }
+
+        @Override
+        public String getStatusText() throws IOException {
+            return delegate.getStatusText();
+        }
+
+        @Override
+        public void close() {
+            delegate.close();
+        }
+
+        @Override
+        public java.io.InputStream getBody() throws IOException {
+            return new ByteArrayInputStream(body);
+        }
+
+        @Override
+        public org.springframework.http.HttpHeaders getHeaders() {
+            return delegate.getHeaders();
+        }
+    }
 }

src/test/java/com/imgfloat/app/config/TwitchOAuth2ErrorResponseErrorHandlerTest.java

@@ -0,0 +1,58 @@
+package com.imgfloat.app.config;
+
+import java.net.URI;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.http.RequestEntity;
+import org.springframework.http.ResponseEntity;
+import org.springframework.mock.http.client.MockClientHttpResponse;
+import org.springframework.security.oauth2.core.OAuth2AuthorizationException;
+import org.springframework.security.oauth2.core.endpoint.OAuth2AccessTokenResponse;
+import org.springframework.test.web.client.MockRestServiceServer;
+import org.springframework.web.client.RestTemplate;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+class TwitchOAuth2ErrorResponseErrorHandlerTest {
+
+    private final TwitchOAuth2ErrorResponseErrorHandler handler = new TwitchOAuth2ErrorResponseErrorHandler();
+
+    @Test
+    void fallsBackToSyntheticErrorWhenErrorBodyIsMissing() throws Exception {
+        MockClientHttpResponse response = new MockClientHttpResponse(new byte[0], HttpStatus.BAD_REQUEST);
+        response.getHeaders().setContentType(MediaType.APPLICATION_JSON);
+
+        OAuth2AuthorizationException exception = assertThrows(OAuth2AuthorizationException.class,
+                () -> handler.handleError(response));
+
+        assertThat(exception.getError().getErrorCode()).isEqualTo("invalid_token_response");
+        assertThat(exception.getError().getDescription())
+                .contains("Failed to parse Twitch OAuth error response");
+    }
+
+    @Test
+    void successfulResponsesStillParseNormally() {
+        RestTemplate restTemplate = OAuth2RestTemplateFactory.create();
+        restTemplate.setErrorHandler(new TwitchOAuth2ErrorResponseErrorHandler());
+        MockRestServiceServer server = MockRestServiceServer.bindTo(restTemplate).build();
+
+        server.expect(requestTo("https://id.twitch.tv/oauth2/token"))
+                .andRespond(withSuccess(
+                        "{\"access_token\":\"abc\",\"token_type\":\"bearer\",\"expires_in\":3600,\"scope\":[]}",
+                        MediaType.APPLICATION_JSON));
+
+        RequestEntity<Void> request = RequestEntity.post(URI.create("https://id.twitch.tv/oauth2/token")).build();
+        ResponseEntity<OAuth2AccessTokenResponse> response = restTemplate.exchange(request, OAuth2AccessTokenResponse.class);
+
+        assertThat(response.getStatusCode()).isEqualTo(HttpStatus.OK);
+        assertThat(response.getBody()).isNotNull();
+        assertThat(response.getBody().getAccessToken().getTokenValue()).isEqualTo("abc");
+
+        server.verify();
+    }
+}