Why Do Java and Go Produce Different GZIP Compressed Outputs?

Why do gzip of Java and Go get different results?

When using gzip to compress data, Java and Go may produce different results. This discrepancy is due to several factors:

Byte representation

Java's byte type is signed, allowing values between -128 and 127. Go's byte type, on the other hand, is an alias for uint8, covering the range from 0 to 255. Consequently, comparisons between Java's byte values and Go's uint8 values require an adjustment by adding 256 to negative Java values.

Compression level

Gzip's compression level can vary across implementations and releases. While both Java and Go default to level 6, this level is not standardized, potentially leading to different results.

Compression algorithms

Gzip utilizes LZ77 and Huffman coding, which employ probability-based trees to assign output codes. Differences in input character frequencies or bit patterns can result in varying codes, influencing the final output.

Headers

Gzip includes optional headers that store additional information. Go sets and inserts these headers, while Java does not. This difference contributes to further variations in output.

Achieving similar outputs

If identical outputs are desired, setting the compression level to 0 (no compression) is the only solution. In Java, use Deflater.NO_COMPRESSION; in Go, use gzip.NoCompression.

Implications

尽管存在差异，但压缩数据并不能影响解压缩过程。使用不同的压缩库不会影响解压缩结果，因为 gzip 标准确保了兼容性。

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