# Struggling to use Mmap with ZipArchives

**URL:** <https://discourse.julialang.org/t/struggling-to-use-mmap-with-ziparchives/129839>\
**Category:** General Usage\
**Tags:** mmap, ziparchives\
**Created:** [June 12, 2025, 3:08pm UTC](https://discourse.julialang.org/t/struggling-to-use-mmap-with-ziparchives/129839 "2025-06-12T15:08:15Z")\
**Posts on this page:** 1\
**Showing post:** 19

<div class="post-metadata">

**Author:** ![fabiangans](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fabiangans/32/2624_2.png) [@fabiangans](https://discourse.julialang.org/u/fabiangans)\
**Post date:** [June 17, 2025, 4:22pm UTC](https://discourse.julialang.org/t/struggling-to-use-mmap-with-ziparchives/129839/19 "2025-06-17T16:22:26Z")

</div>

Maybe there would not be too many changes necessary to get option 3) running. I did a few small tests and the following seems to work at least for reading array without relying on Mmap or reading the whole archive, in case someone wants to experiment.

```julia
import DiskArrays: AbstractDiskArray, DiskArrays, Unchunked, Chunked, GridChunks

struct SimpleFileDiskArray{C<:Union{Int,Nothing}} <: AbstractDiskArray{UInt8,1}
    file::String
    s::Int
    chunksize::C
end
Base.size(s::SimpleFileDiskArray) = (s.s,)
function SimpleFileDiskArray(filename;chunksize=nothing)
    isfile(filename) || throw(ArgumentError("File $filename does not exist"))
    s = filesize(filename)
    SimpleFileDiskArray(filename, s, chunksize)
end
function DiskArrays.readblock!(a::SimpleFileDiskArray,aout,i::AbstractUnitRange)
    open(a.file) do f
        seek(f,first(i)-1)
        read!(f,aout)
    end
end
DiskArrays.haschunks(a::SimpleFileDiskArray) = a.chunksize === nothing ? Unchunked() : Chunked() 
function DiskArrays.eachchunk(a::SimpleFileDiskArray) 
    if a.chunksize === nothing
        DiskArrays.estimate_chunksize(a)
    else
        GridChunks((a.s,),(a.chunksize,))
    end
end

function Base.copyto!(dest::AbstractArray, desto::Int, src::SimpleFileDiskArray, so::Int,N::Int)
    destv = view(dest,range(desto,length=N))
    DiskArrays.readblock!(src,destv,range(so,length=N))
end

using ZipArchives
file = "../testzip.zip"
r = ZipReader(SimpleFileDiskArray(file))

entries = zip_names(r)
@time data = zip_readentry(r,entries[2])
Char.(data)

```

Maybe the SimpleFileDiskArray could be added to DiskArrays.jl in case it proves to be useful.

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