[GitHub] [avro] steveloughran commented on a diff in pull request #1639: AVRO-3482: Reuse MAGIC in DataFileReader

[GitBox <gi...@apache.org>]

steveloughran commented on code in PR #1639:
URL: https://github.com/apache/avro/pull/1639#discussion_r852210974


##########
lang/java/avro/src/main/java/org/apache/avro/file/DataFileReader12.java:
##########
@@ -61,6 +61,7 @@ public DataFileReader12(SeekableInput sin, DatumReader<D> reader) throws IOExcep
     this.in = new DataFileReader.SeekableInputStream(sin);
 
     byte[] magic = new byte[4];
+    in.seek(0); // seek to 0 to read magic header
     in.read(magic);

Review Comment:
   what if fewer bytes come back? why not a readFully()? 



##########
lang/java/avro/src/main/java/org/apache/avro/file/DataFileStream.java:
##########
@@ -97,18 +97,30 @@ protected DataFileStream(DatumReader<D> reader) throws IOException {
     this.reader = reader;
   }
 
-  /** Initialize the stream by reading from its head. */
-  void initialize(InputStream in) throws IOException {
-    this.header = new Header();
-    this.vin = DecoderFactory.get().binaryDecoder(in, vin);
+  byte[] readMagic() throws IOException {
+    if (this.vin == null) {
+      throw new IOException("InputStream is not initialized");
+    }
     byte[] magic = new byte[DataFileConstants.MAGIC.length];
     try {
       vin.readFixed(magic); // read magic
     } catch (IOException e) {
       throw new IOException("Not an Avro data file.", e);

Review Comment:
   always nice to include the error string of the nested exception, as there may be many other causes of problems than just file type



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