Avoids InputStream.available when determining if a stream is empty

Adrian Cole · Adrian Cole · commit 2b79b93a4e8e · 2015-08-02T11:23:55.000-07:00
InputStream.available isn't a reliable api. This uses an alternative approach, which is to read the first byte to see if it is present. This allows us to continue to avoid "No content to map due to end-of-input" errors, but in a more supportable way. Fixes OpenFeign#250
diff --git a/jackson/src/main/java/feign/jackson/JacksonDecoder.java b/jackson/src/main/java/feign/jackson/JacksonDecoder.java
@@ -20,8 +20,9 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.RuntimeJsonMappingException;
 
+import java.io.BufferedReader;
 import java.io.IOException;
-import java.io.InputStream;
+import java.io.Reader;
 import java.lang.reflect.Type;
 import java.util.Collections;
 
@@ -50,12 +51,18 @@ public Object decode(Response response, Type type) throws IOException {
     if (response.body() == null) {
       return null;
     }
-    InputStream inputStream = response.body().asInputStream();
+    Reader reader = response.body().asReader();
+    if (!reader.markSupported()) {
+      reader = new BufferedReader(reader, 1);
+    }
     try {
-      if (inputStream.available() <= 0){
-        return null;
+      // Read the first byte to see if we have any data
+      reader.mark(1);
+      if (reader.read() == -1) {
+        return null; // Eagerly returning null avoids "No content to map due to end-of-input"
       }
-      return mapper.readValue(inputStream, mapper.constructType(type));
+      reader.reset();
+      return mapper.readValue(reader, mapper.constructType(type));
     } catch (RuntimeJsonMappingException e) {
       if (e.getCause() != null && e.getCause() instanceof IOException) {
         throw IOException.class.cast(e.getCause());
