README
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SARchive
Solid ARchive is a very simple compressed archive format.
Documentation
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Overview ¶
Package sarchive implements a simple 'solid' archive format which contains a separately extractable table of contents, somewhat comparable to ZIP or XAR. Unlike ZIP, the table of contents is compressed, and the file data is compressed in a single solid block (allowing better compression ratios for archives of similar files). Unlike XAR, the table of contents uses a relatively efficient and easy-to-manipulate protobuf instead of XML.
Unlike ZIP and XAR both, the SAR format does not attempt to preserve or restore specific file ACLs (i.e. user ownership ids, posix mode, etc.), but instead allows files to set platform-specific mode bits (like the 'system' bit on windows), and express a small handful of cross-platform concepts (like 'read-only'). The reasoning is that, in this burgeoning age of the internet, porting user ids or mode flags across systems is silly, at best, and possibly harmful.
It has a fairly basic format:
- file magic header ("SAR" + byte(API_VERSION)). API_VERSION current == 1.
- block_header + table_of_contents
- block_header + archive_data
- checksum
block_headers define the compression type and length of subsequent block.
table_of_contents is a protobuf defined in toc/toc.proto.
archive_data is all of the file data noted in the table_of_contents, concatenated and compressed. The offsets and sizes in table_of_contents refer to locations in the uncompressed archive_data stream.
checksum indicates the type of checksum, followed by the bytes of the checksum, followed by the length of the checksum (as a single byte). The checksum covers all bytes in the archive which preceed the checksum type inidicator. The length at the end of the checksum allows the checksum to be validated simply by reading from the end of the archive without parsing it.
TODO(riannucci): implement better compression scheme like brotli or zstd... this depends on better compression support becoming available in golang.
TODO(riannucci): if the format requires greater extensibility, implement a PNG-like chunk scheme (i.e. with FourCC identifiers for sections).
Source Files
Directories
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| Path | Synopsis |
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Package sar implements a high level interface to manipulate SARchive files.
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Package sar implements a high level interface to manipulate SARchive files. |
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sardata
Package sardata implements IO routines for reading and writing various chunks of the SARchive format, including checksums, blocks (table of contents and archive data), and the 'magic' bytes.
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Package sardata implements IO routines for reading and writing various chunks of the SARchive format, including checksums, blocks (table of contents and archive data), and the 'magic' bytes. |
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sardata/toc
Package toc defines the Table of Contents format for SARchives (as proto).
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Package toc defines the Table of Contents format for SARchives (as proto). |