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  1. jclouds
  2. JCLOUDS-1521

Automatic computation of content length for input streams

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    Details

    • Type: Improvement
    • Status: Open
    • Priority: Major
    • Resolution: Unresolved
    • Affects Version/s: 2.1.1
    • Fix Version/s: None
    • Component/s: jclouds-blobstore
    • Labels:
      None

      Description

      I have a REST API that allows upload of potentially large files (up to 4GBs). Due to the size, I cannot load these files in-memory, as that could quickly crash my application. I also don't want to store them as temporary files, since that could fill up my disk if a lot of people decide to upload at the same time.

      Instead, I want to process the incoming files as InputStreams and forward them to the S3 object store. I understand that this is not possible directly, since S3 requires the content length to be known before the upload. However, I saw on StackOverflow (https://stackoverflow.com/questions/8653146/can-i-stream-a-file-upload-to-s3-without-a-content-length-header) that it's possible to workaround this problem by reading the InputStream in memory in chunks of 5 (or more) MBs and uploading these chunks via the S3 multipart upload API. As a result, I assume that I'll be able to upload a 4GB file, by having no more than 5 MBs of its content stored in-memory at any given time.

      I tried to do so with JClouds (version 2.1.1), but I've hit a problem. I have the following code:

      Blob blob = blobStore.blobBuilder(name)
          .payload(inputStream)
          ...
          .build();
      blobStore.putBlob(container, blob, PutOptions.Builder.multipart());
      

      If I run it like this, I get a NullPointerException, because I didn't specify the content's length:

      java.lang.NullPointerException: while trying to invoke the method java.lang.Long.longValue() of a null object returned from org.jclouds.io.MutableContentMetadata.getContentLength()
         at org.jclouds.blobstore.internal.BaseBlobStore.putMultipartBlob(BaseBlobStore.java:356)
         at org.jclouds.blobstore.internal.BaseBlobStore.putMultipartBlob(BaseBlobStore.java:347)
         at org.jclouds.aws.s3.blobstore.AWSS3BlobStore.putBlob(AWSS3BlobStore.java:79)
      

      I think it would be possible for JClouds to compute the size of the InputStream dynamically:

      1. Slice the stream into chunks of X MBs and store the chunks in-memory (where X has a default value but is also configurable).
      2. Upload the chunks sequentially - the content length header can be set to X MBs.
      3. Finalize the multipart upload.

      That way, no more than X MBs will be stored in memory for any given upload.

      Would you accept a pull request for this?

      PS: I've set the priority to blocker, because we really can't use JClouds for our upload right now, because of the memory and disk space concerns listed above.

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            • Assignee:
              Unassigned
              Reporter:
              nictas Alexander Tsvetkov
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              • Created:
                Updated: