archive support

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title: Archive Support permalink: /archive-support parent: Deep Dives nav_order: 10

Archive Support

Supported formats

Detected by file extension (ArchiveFormats):

Extension	Format
.zip	ZIP
.7z	7-Zip
.rar	RAR
.tar	TAR
.tar.gz, .tgz	GZIP-compressed TAR
.tar.bz2, .tbz2	BZIP2-compressed TAR
.tar.xz, .txz	XZ-compressed TAR
.cbz, .cbr, .cb7	Comic-book archives (ZIP/RAR/7Z containers)

Everything else is rejected with "The file 'X' is not a supported archive" and the list of expected extensions. The mount is read-only — archives are never modified.

Decompression paths

Situation	Path
ZIP stored entry (no compression, not encrypted/solid)	Zero-copy direct read — no decompression, no cache (details)
Compressed entry ≤ per-file RAM limit (512 MB default)	Decompress once into the shared memory cache
Compressed entry above the limit	Extract once to the disk cache
SharpCompress fails to decompress	7-Zip fallback (below)

Password-protected archives

• Encryption is detected by entry flags plus a test read of up to 1 KB per encrypted entry (some ZIP tools set the encryption flag incorrectly, so the app verifies instead of trusting the flag).
• A verified-encrypted archive shows the Password Required dialog before mounting.
• The password is verified by reading 1 KB from every encrypted entry — a wrong password is caught at mount time, not mid-file.
• 3 attempts maximum, then "Mount aborted after 3 attempts." Cancelling the dialog cancels the mount.
• Corrupt archives are deliberately not treated as password problems: a truncated/corrupt RAR surfaces as a corruption error instead of looping the password dialog (fixed in 2.9.0).
• The password is kept only for the duration of the mount session and cleared after use.

Corrupt or unsupported archives

• Unparseable archives: "The archive file appears to be corrupted, incomplete, or uses an unsupported format/feature that could not be parsed."
• Corruption found while enumerating entries: "Archive data corruption detected during initialization." — mounting aborts.
• Individual entries that fail to decompress are marked failed and return read errors instead of poisoning the whole mount; the log names the entry and the failure.

The 7-Zip fallback

When SharpCompress (the primary extraction library) fails to decompress an entry, SimpleZipDrive retries with the 7-Zip engine via SharpSevenZip:

• Requires the native 7z.dll (x64) or 7z_arm64.dll (ARM64) beside the executable — both ship in every release package, one process-appropriate library is selected automatically.
• Only available when the archive is a real file (not a pipe) so the library can open it by path.
• The fallback receives the same password (if any) as the primary path.
• If the fallback also fails: "SevenZip fallback also failed for '…'" and the entry is marked failed.

Packaging note: the fallback libraries must stay next to the .exe. Bundling them inside a single-file executable made them invisible to the library-path probe in older releases — fixed in 2.9.0 (Building & Packaging).

Practical notes

• ZIP64 archives (over 4 GB / 65 535 entries) are handled by SharpCompress.
• Solid archives (common in 7Z/RAR) cannot use the zero-copy path; reads decompress through the cache tiers, so first-access cost is higher.
• Multi-volume/split archives are not supported.
• For best performance with large game images, store them as uncompressed ZIP (see Performance).