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Update README instructions for setting compression_level.

This commit is contained in:
Robert Haines 2020-09-13 16:45:10 +01:00
parent f1dd724a3a
commit 2ff313da26
1 changed files with 14 additions and 4 deletions
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README.md
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@ -288,15 +288,25 @@ Zip.validate_entry_sizes = false
Note that if you use the lower level `Zip::InputStream` interface, `rubyzip` does *not* check the entry `size`s. In this case, the caller is responsible for making sure it does not read more data than expected from the input stream.
### Default Compression
### Compression level
You can set the default compression level like so:
When adding entries to a zip archive you can set the compression level to trade-off compressed size against compression speed. By default this is set to the same as the underlying Zlib library's default (`Zlib::DEFAULT_COMPRESSION`), which is somewhere in the middle.
You can configure the default compression level with:
```ruby
Zip.default_compression = Zlib::DEFAULT_COMPRESSION
Zip.default_compression = X
```
It defaults to `Zlib::DEFAULT_COMPRESSION`. Possible values are `Zlib::BEST_COMPRESSION`, `Zlib::DEFAULT_COMPRESSION` and `Zlib::NO_COMPRESSION`
Where X is an integer between 0 and 9, inclusive. If this option is set to 0 (`Zlib::NO_COMPRESSION`) then entries will be stored in the zip archive uncompressed. A value of 1 (`Zlib::BEST_SPEED`) gives the fastest compression and 9 (`Zlib::BEST_COMPRESSION`) gives the smallest compressed file size.
This can also be set for each archive as an option to `Zip::File`:
```ruby
Zip::File.open('foo.zip', Zip::File::CREATE, {compression_level: 9}) do |zip|
zip.add ...
end
```
### Zip64 Support