# How to decompress .xz files/ How to use streams?
**URL:** https://discourse.julialang.org/t/how-to-decompress-xz-files-how-to-use-streams/86307
**Category:** General Usage
**Tags:** question, package, codecxz
**Created:** [August 25, 2022, 7:31am UTC](https://discourse.julialang.org/t/how-to-decompress-xz-files-how-to-use-streams/86307 "2022-08-25T07:31:52Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [August 25, 2022, 7:31am UTC](https://discourse.julialang.org/t/how-to-decompress-xz-files-how-to-use-streams/86307/1 "2022-08-25T07:31:52Z")
I have the following code for unpacking .xz compressed files:
```julia
using CodecXz
function decompress(in, out)
stream = open(in)
output = open(out,"w")
for line in eachline(XzDecompressorStream(stream))
println(output, line)
end
close(stream)
close(output)
end
```
This does not always work due to the use of eachline and println…
How can I do this in a more generic form?
@aplavin suggested to use `read(XzDecompressorStream(stream))`, but I do not want to do that because it creates a huge vector in RAM. I would prefer to do the decompression in chunks.
How can I do that in Julia?
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [August 25, 2022, 7:41am UTC](https://discourse.julialang.org/t/how-to-decompress-xz-files-how-to-use-streams/86307/2 "2022-08-25T07:41:05Z")
I guess my main problem is that I don’t fully understand how to use streams.
How can I for example copy a binary file using an input and an output stream?
```julia
function copyfile(input_file, output_file)
in_stream = open(input_file)
out_stream = open(output_file,"w")
# What to put here?
close(in_stream)
close(out_stream)
end
```
---
### Author:  [@pfitzseb](https://discourse.julialang.org/u/pfitzseb)
#### Post date: [August 25, 2022, 7:51am UTC](https://discourse.julialang.org/t/how-to-decompress-xz-files-how-to-use-streams/86307/3 "2022-08-25T07:51:36Z")
```julia
function copyfile(input_file, output_file)
in_stream = open(input_file)
out_stream = open(output_file,"w")
while !eof(in_stream)
write(out_stream, read(in_stream, 10000))
end
close(in_stream)
close(out_stream)
end
```
Something like that (maybe even exactly that) should work for your original question as well.
---
### Author:  [@cjdoris](https://discourse.julialang.org/u/cjdoris)
#### Post date: [August 25, 2022, 8:55am UTC](https://discourse.julialang.org/t/how-to-decompress-xz-files-how-to-use-streams/86307/4 "2022-08-25T08:55:16Z")
Or simply
```julia
write(out_stream, in_stream)
```
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [August 25, 2022, 9:46am UTC](https://discourse.julialang.org/t/how-to-decompress-xz-files-how-to-use-streams/86307/5 "2022-08-25T09:46:18Z")
Not working:
```julia
function decompress1(in, out)
stream = open(in)
output = open(out,"w")
while !eof(stream)
write(output, read(XzDecompressorStream(stream), 10000))
end
close(stream)
close(output)
end
```
It fails with:
```julia
ERROR: LoadError: lzma error: code = 7
Stacktrace:
[1] changemode!(stream::TranscodingStreams.TranscodingStream{XzDecompressor, IOStream}, newmode::Symbol)
@ TranscodingStreams ~/.julia/packages/TranscodingStreams/TsaT2/src/stream.jl:724
[2] callprocess(stream::TranscodingStreams.TranscodingStream{XzDecompressor, IOStream}, inbuf::TranscodingStreams.Buffer, outbuf::TranscodingStreams.Buffer)
@ TranscodingStreams ~/.julia/packages/TranscodingStreams/TsaT2/src/stream.jl:654
[3] fillbuffer(stream::TranscodingStreams.TranscodingStream{XzDecompressor, IOStream}; eager::Bool)
@ TranscodingStreams ~/.julia/packages/TranscodingStreams/TsaT2/src/stream.jl:582
[4] fillbuffer
@ ~/.julia/packages/TranscodingStreams/TsaT2/src/stream.jl:568 [inlined]
[5] eof(stream::TranscodingStreams.TranscodingStream{XzDecompressor, IOStream})
@ TranscodingStreams ~/.julia/packages/TranscodingStreams/TsaT2/src/stream.jl:191
[6] readbytes!(stream::TranscodingStreams.TranscodingStream{XzDecompressor, IOStream}, b::Vector{UInt8}, nb::Int64)
@ TranscodingStreams ~/.julia/packages/TranscodingStreams/TsaT2/src/stream.jl:375
[7] read(s::TranscodingStreams.TranscodingStream{XzDecompressor, IOStream}, nb::Int64)
@ Base ./io.jl:1000
[8] decompress(in::String, out::String)
@ Main ~/repos/CanAnalyzer/src/process_log.jl:97
[9] main(logfile_name::String)
@ Main ~/repos/CanAnalyzer/src/process_log.jl:500
[10] top-level scope
@ ~/repos/CanAnalyzer/src/process_log.jl:595
[11] include(fname::String)
@ Base.MainInclude ./client.jl:476
[12] top-level scope
@ REPL[1]:1
in expression starting at ...
```
Working:
```julia
function decompress(in, out)
stream = open(in)
output = open(out,"w")
write(output, read(XzDecompressorStream(stream)))
close(stream)
close(output)
end
```
So I have a working solution, but it allocates the full size of the output file in RAM…
---
### Author:  [@cjdoris](https://discourse.julialang.org/u/cjdoris)
#### Post date: [August 25, 2022, 10:27am UTC](https://discourse.julialang.org/t/how-to-decompress-xz-files-how-to-use-streams/86307/6 "2022-08-25T10:27:25Z")
```julia
function decompress(in, out)
stream = open(in)
output = open(out,"w")
write(output, XzDecompressorStream(stream))
close(stream)
close(output)
end
```
Also you should use the do-block version of `open` to ensure the streams are closed even if an error occurs.
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [September 3, 2022, 11:00pm UTC](https://discourse.julialang.org/t/how-to-decompress-xz-files-how-to-use-streams/86307/7 "2022-09-03T23:00:32Z")
Is this better?
```julia
function decompress(input, output)
open(input) do inp
open(output,"w") do out
write(out, read(XzDecompressorStream(inp)))
end
end
end
```