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Archives.ArchiveFactory.Open returns a ZipArchive but ZipArchive.IsZipFile is false #593

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opened 2026-01-29 22:14:19 +00:00 by claunia · 3 comments
claunia commented 2026-01-29 22:14:19 +00:00
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Originally created by @njlr on GitHub (Oct 4, 2023).

#r "nuget: SharpCompress, 0.34.1"

open SharpCompress

let filePath = "./example.zip"

let isZipFile = Archives.Zip.ZipArchive.IsZipFile(filePath)

printfn $"isZipFile? %b{isZipFile}"

let archive = Archives.ArchiveFactory.Open(filePath)

printfn $"Archive type: %s{archive.GetType().FullName}"

printfn "Entries:"

for x in archive.Entries do
  printfn "%s" x.Key

Output:

isZipFile? false
Archive type: SharpCompress.Archives.Zip.ZipArchive
Entries:
Foo/
Foo/Bar.txt
System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at SharpCompress.Archives.Zip.ZipArchive.LoadEntries(IEnumerable`1 volumes)+MoveNext()
   at SharpCompress.LazyReadOnlyCollection`1.LazyLoader.MoveNext()
   at <StartupCode$FSI_0002>.$FSI_0002.main@() in /home/runner/Scratch.fsx:line 13
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr)
Stopped due to error

This suggests a bug in ArchiveFactory.Open to me - it shouldn't return a ZipArchive for a file where ZipArchive.IsZipFile is false.

I cannot share the zip file, unfortunately.

Originally created by @njlr on GitHub (Oct 4, 2023). ```fsharp #r "nuget: SharpCompress, 0.34.1" open SharpCompress let filePath = "./example.zip" let isZipFile = Archives.Zip.ZipArchive.IsZipFile(filePath) printfn $"isZipFile? %b{isZipFile}" let archive = Archives.ArchiveFactory.Open(filePath) printfn $"Archive type: %s{archive.GetType().FullName}" printfn "Entries:" for x in archive.Entries do printfn "%s" x.Key ``` Output: ``` isZipFile? false Archive type: SharpCompress.Archives.Zip.ZipArchive Entries: Foo/ Foo/Bar.txt System.IndexOutOfRangeException: Index was outside the bounds of the array. at SharpCompress.Archives.Zip.ZipArchive.LoadEntries(IEnumerable`1 volumes)+MoveNext() at SharpCompress.LazyReadOnlyCollection`1.LazyLoader.MoveNext() at <StartupCode$FSI_0002>.$FSI_0002.main@() in /home/runner/Scratch.fsx:line 13 at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor) at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr) Stopped due to error ``` This suggests a bug in `ArchiveFactory.Open` to me - it shouldn't return a `ZipArchive` for a file where `ZipArchive.IsZipFile` is `false`. I cannot share the zip file, unfortunately.
claunia added the bugup for grabs labels 2026-01-29 22:14:19 +00:00
claunia commented 2026-01-29 22:14:19 +00:00
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@btomblinson commented on GitHub (Nov 12, 2023):

@njlr do you have any way to share the .zip in question for reproducing this?

@btomblinson commented on GitHub (Nov 12, 2023): @njlr do you have any way to share the .zip in question for reproducing this?
claunia commented 2026-01-29 22:14:20 +00:00
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@DannyBoyk commented on GitHub (Jan 29, 2024):

The fact it can extract any entries at all implies it has at least some zip headers in it, even if IsZipFile returns false. This seems too specific to the zip file to be able to debug without it. I'm afraid you'll need to step through the headers in the file manually in something like HxD. The Wikipedia Zip file format article is a good reference. You need to try to figure out where things go off track.

@DannyBoyk commented on GitHub (Jan 29, 2024): The fact it can extract any entries at all implies it has at least some zip headers in it, even if `IsZipFile` returns false. This seems too specific to the zip file to be able to debug without it. I'm afraid you'll need to step through the headers in the file manually in something like HxD. The [Wikipedia Zip file format article ](https://en.wikipedia.org/wiki/ZIP_(file_format)) is a good reference. You need to try to figure out where things go off track.
claunia commented 2026-01-29 22:14:20 +00:00
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@adamhathcock commented on GitHub (Jan 29, 2024):

IsZipFile just checks if there is a valid header. This should probably change to use the magic bytes for the format. However, it can be a valid zip without the magic bytes

@adamhathcock commented on GitHub (Jan 29, 2024): IsZipFile just checks if there is a valid header. This should probably change to use the magic bytes for the format. However, it can be a valid zip without the magic bytes
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Reference: starred/sharpcompress#593
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