Refactor content encoding interceptor out into a separate class

src/main/java/com/commafeed/backend/ContentEncodingInterceptor.java

@@ -0,0 +1,60 @@
+package com.commafeed.backend;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Locale;
+import java.util.Set;
+
+import org.apache.http.Header;
+import org.apache.http.HeaderElement;
+import org.apache.http.HttpEntity;
+import org.apache.http.HttpException;
+import org.apache.http.HttpResponse;
+import org.apache.http.HttpResponseInterceptor;
+import org.apache.http.entity.HttpEntityWrapper;
+import org.apache.http.protocol.HttpContext;
+
+class ContentEncodingInterceptor implements HttpResponseInterceptor {
+	
+	private static final Set<String> ALLOWED_CONTENT_ENCODINGS = new HashSet<>(Arrays.asList("gzip", "x-gzip", "deflate", "identity"));
+
+	@Override
+	public void process(HttpResponse response, HttpContext context) throws HttpException, IOException {
+		if (hasContent(response)) {
+			Header contentEncodingHeader = response.getEntity().getContentEncoding();
+			if (contentEncodingHeader != null && doesNotContainAllowedEncodings(contentEncodingHeader)) {
+				overrideContentEncoding(response);
+			}
+		}
+	}
+	
+	private boolean doesNotContainAllowedEncodings(Header contentEncodingHeader) {
+		HeaderElement[] codecs = contentEncodingHeader.getElements();
+		
+		for (final HeaderElement codec : codecs) {
+			String codecName = codec.getName().toLowerCase(Locale.US);
+			if (!ALLOWED_CONTENT_ENCODINGS.contains(codecName)) {
+				return true;
+			}
+		}
+		
+		return false;
+	}
+
+	private void overrideContentEncoding(HttpResponse response) {
+		HttpEntity wrapped = new HttpEntityWrapper(response.getEntity()) {
+			@Override
+			public Header getContentEncoding() {
+				return null;
+			};
+		};
+		
+		response.setEntity(wrapped);
+	}
+
+	private boolean hasContent(HttpResponse response) {
+		return response.getEntity() != null && response.getEntity().getContentLength() != 0;
+	}
+
+}