diff --git a/README.md b/README.md index ffc49bbe..e98b8eb5 100755 --- a/README.md +++ b/README.md @@ -83,9 +83,20 @@ Stream-based compressor/decompressor `SnappyOutputStream`/`SnappyInputStream` ar * See also [Javadoc API](https://oss.sonatype.org/service/local/repositories/releases/archive/org/xerial/snappy/snappy-java/1.1.3-M1/snappy-java-1.1.3-M1-javadoc.jar/!/index.html) #### Compatibility Notes - * `SnappyOutputStream` and `SnappyInputStream` use `[magic header:16 bytes]([block size:int32][compressed data:byte array])*` format. You can read the result of `Snappy.compress` with `SnappyInputStream`, but you cannot read the compressed data generated by `SnappyOutputStream` with `Snappy.uncompress`. Here is the data format compatibility matrix: + +The original Snappy format definition did not define a file format. It later added +a "framing" format to define a file format, but by this point major software was +already using an industry standard instead -- represented in this library by the +`SnappyOutputStream` and `SnappyInputStream` methods. + +For interoperability with other libraries, check that compatible formats are used. +Note that not all libraries support all variants. + + * `SnappyOutputStream` and `SnappyInputStream` use `[magic header:16 bytes]([block size:int32][compressed data:byte array])*` format. You can read the result of `Snappy.compress` with `SnappyInputStream`, but you cannot read the compressed data generated by `SnappyOutputStream` with `Snappy.uncompress`. * `SnappyHadoopCompatibleOutputStream` does not emit a file header but write out the current block size as a preemble to each block +#### Data format compatibility matrix: + | Write\Read | `Snappy.uncompress` | `SnappyInputStream` | `SnappyFramedInputStream` | `org.apache.hadoop.io.compress.SnappyCodec` | | --------------- |:-------------------:|:------------------:|:-----------------------:|:-------------------------------------------:| | `Snappy.compress` | ok | ok | x | x |