Fix #177

Author: cowtowncoder

avro/src/main/java/com/fasterxml/jackson/dataformat/avro/deser/AvroStructureReader.java

@@ -18,6 +18,26 @@ protected AvroStructureReader(AvroReadContext parent, int type, String typeId) {
         super(parent, typeId);
         _type = type;
     }
+
+    /*
+    /**********************************************************************
+    /* Metadata access
+    /**********************************************************************
+     */
+
+    /**
+     * Method that may be called to check if the values "read" by this reader
+     * are zero-length, that is, consume no content: most common example being
+     * Record with no fields.
+     *<p>
+     * Note: Arrays can not return {@code true} as they need to encode length
+     * even for "empty" arrays.
+     *
+     * @since 2.10
+     */
+    public boolean consumesNoContent() {
+        return false;
+    }
 
     /*
     /**********************************************************************

avro/src/main/java/com/fasterxml/jackson/dataformat/avro/deser/RecordReader.java

@@ -35,6 +35,14 @@ protected RecordReader(AvroReadContext parent, AvroFieldReader[] fieldReaders, A
     @Override
     public String getCurrentName() { return _currentName; }
 
+    @Override
+    public boolean consumesNoContent() {
+        // 26-Aug-2019, tatu: As per [dataformats-binary#177], 0-field Records consume
+        //   no content. It may be possible other variants exist too (fields with "Constant"
+        //   value?), but let's start with the simple case
+        return _fieldReaders.length == 0;
+    }
+
     @Override
     public final void skipValue(AvroParserImpl parser) throws IOException {
         for (int i = 0, end = _fieldReaders.length; i < end; ++i) {

avro/src/main/java/com/fasterxml/jackson/dataformat/avro/deser/RootReader.java

@@ -26,7 +26,11 @@ public JsonToken nextToken() throws IOException {
         // First: possibly we are at end. Could theoretically check against
         // empty streams but...
         if (_parser.checkInputEnd()) {
-            return null;
+            // 26-Aug-2019, tatu: As per [dataformats-binary#177], 0-field Records consume
+            //    no content, and if so we MUST NOT indicate end-of-content:
+            if (!_valueReader.consumesNoContent()) {
+                return null;
+            }
         }
         return _valueReader.newReader(this, _parser).nextToken();
     }

avro/src/test/java/com/fasterxml/jackson/dataformat/avro/failing/EmptyRecordRead177Test.java renamed to avro/src/test/java/com/fasterxml/jackson/dataformat/avro/RootEmptyRecord177Test.java

@@ -1,12 +1,11 @@
-package com.fasterxml.jackson.dataformat.avro.failing;
+package com.fasterxml.jackson.dataformat.avro;
 
 import com.fasterxml.jackson.annotation.JsonAutoDetect;
 
 import com.fasterxml.jackson.dataformat.avro.AvroMapper;
 import com.fasterxml.jackson.dataformat.avro.AvroSchema;
-import com.fasterxml.jackson.dataformat.avro.AvroTestBase;
 
-public class EmptyRecordRead177Test extends AvroTestBase
+public class RootEmptyRecord177Test extends AvroTestBase
 {
     private final AvroMapper MAPPER = getMapper();
 
@@ -25,7 +24,6 @@ public void testEmptyRecord() throws Exception {
         final Empty empty = new Empty();
 
         byte[] ser = MAPPER.writer().with(SCHEMA).writeValueAsBytes(empty);
-
         final Empty result = MAPPER.readerFor(Empty.class)
                 .with(SCHEMA)
                 .readValue(ser);

release-notes/VERSION-2.x

@@ -12,8 +12,10 @@ Project: jackson-datatypes-binaryModules:
 
 #168: (avro) `JsonMappingException` for union types with multiple Record types
  (reported by Juliana A; fix contributed by Marcos P)
-#173: (Avro) Improve Union type serialization performance
+#173: (avro) Improve Union type serialization performance
  (fix contributed by Marcos P)
+#177: (avro) Deserialization of "empty" Records as root values fails
+ (reported by Macros P)
 
 2.10.0.pr1 (19-Jul-2019)