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Create file format for format version 1

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This is in preparation of improving compression by concatenating files
together before compressing them to reduce the per-file overhead.

Discussed in
#18
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Stephen Seo 2024-09-24 18:43:47 +09:00
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file_format.md
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@ -76,3 +76,105 @@ Following the file-count bytes, the following bytes are added for each file:
1. 8 bytes 64-bit unsigned integer "size of filename in this archive file" 1. 8 bytes 64-bit unsigned integer "size of filename in this archive file"
in big-endian. in big-endian.
2. X bytes file data (length defined by previous value). 2. X bytes file data (length defined by previous value).
## Format Version 1
File extension is "*.simplearchive" but this isn't really checked.
First 18 bytes of file will be (in ascii):
SIMPLE_ARCHIVE_VER
Next 2 bites is a 16-bit unsigned integer "version" in big-endian. It will be:
0x00 0x01
Next 4 bytes are bit-flags.
1. The first byte
1. The first bit is set if de/compressor is set for this archive.
The remaining unused flags in the previous bit-flags bytes are reserved for
future revisions and are currently ignored.
If the previous "de/compressor is set" flag is enabled, then the next section is
added:
1. 2 bytes is 16-bit unsigned integer "compressor cmd+args" in big-endian. This
does not include the NULL at the end of the string.
2. X bytes of "compressor cmd+args" (length defined by previous value). Is a
NULL-terminated string.
3. 2 bytes is 16-bit unsigned integer "decompressor cmd+args" in big-endian.
This does not include the NULL at the end of the string.
4. X bytes of "decompressor cmd+args" (length defined by previous value). Is a
NULL-terminated string.
The next 4 bytes is a 32-bit unsigned integer "link count" in big-endian which
will indicate the number of symbolic links in this archive.
Following the link-count bytes, the following bytes are added for each symlink:
1. 2 bytes bit-flags:
1. The first byte.
1. The first bit is UNSET if relative links are preferred, and is SET if
absolute links are preferred.
2. The second byte.
1. Currently unused.
2. 2 bytes is 16-bit unsigned integer "link target absolute path" in
big-endian. This does not include the NULL at the end of the string.
3. X bytes of link-target-absolute-path (length defined by previous value).
Is a NULL-terminated string. If the previous "size" value is 0, then
this entry does not exist and should be skipped.
4. 2 bytes is 16-bit unsigned integer "link target relative path" in
big-endian. This does not include the NULL at the end of the string.
5. X bytes of link-target-relative-path (length defined by previous value).
Is a NULL-terminated string. If the previous "size" value is 0, then
this entry does not exist and should be skipped.
After the symlink related data, the next 4 bytes is a 32-bit unsigned integer
"chunk count" in big-endian which will indicate the number of chunks in this
archive.
Following the chunk-count bytes, the following bytes are added for each chunk:
1. 2 bytes that are a 16-bit unsigned integer "file count" in big-endian.
The following bytes are added for each file within each chunk:
1. 2 bytes that are a 16-bit unsigned integer "filename length" in big-endian.
This does not include the NULL at the end of the string.
2. X bytes of filename (length defined by previous value). Is a NULL-terminated
string.
3. 4 bytes bit-flags.
1. The first byte.
1. The first bit is "user read permission".
2. The second bit is "user write permission".
3. The third bit is "user execute permission".
4. The fourth bit is "group read permission".
5. The fifth bit is "group write permission".
6. The sixth bit is "group execute permission".
7. The seventh bit is "other read permission".
8. The eighth bit is "other write permission".
2. The second byte.
1. The first bit is "other execute permission".
3. The third byte.
1. Currently unused.
4. The fourth byte.
1. Currently unused.
4. Two 4-byte unsigned integers in big-endian for UID and GID.
1. A 32-bit unsigned integer in big endian that specifies the UID of the
file. Note that during extraction, if the user is not root, then this
value will be ignored.
2. A 32-bit unsigned integer in big endian that specifies the GID of the
file. Note that during extraction, if the user is not root, then this
value will be ignored.
5. A 64-bit unsigned integer in big endian for the "size of file".
After the files' metadata are the current chunk's data:
1. A 64-bit unsigned integer in big endian for the "size of chunk".
2. X bytes of data for the current chunk of the previously specified size. If
not using de/compressor, this section is the previously mentioned files
concatenated with each other. If using de/compressor, this section is the
previously mentioned files concatenated and compressed into a single blob of
data.