an efficient binary archive format
update spec
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SPEC.md
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SPEC.md
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| `0x00` | **Header** | 8-byte magic identification string. |
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| `0x08` | **Data Payload** | Sequential blobs of raw or compressed data. |
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| `Variable` | **Index** | A sequence of metadata entries and filenames. |
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| `EOF - 20` | **Footer** | Pointer to the index and file count. |
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| `EOF - 16` | **Footer** | Pointer to the index and file count. |
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---
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···
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| `name_len` | 2 bytes | u16 | Length of the following filename string. |
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| `comp_type` | 1 byte | u8 | `0` = Raw, `1` = Zstd. |
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| `reserved` | 1 byte | u8 | Alignment padding. |
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| `filename` | variable | utf8 | Filename string
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**Padding:** After the filename string, the file MUST be padded with null bytes until the next 8-byte boundary is reached.
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### 2.4 Footer
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The last 20 bytes of the file contain the lookup information required to parse the archive.
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The last 16 bytes of the file contain the lookup information required to parse the archive.
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| Field | Size | Type | Description |
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| :--- | :--- | :--- | :--- |
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| `index_offset` | 8 bytes | u64 | Absolute offset to the start of the Index. |
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| `entry_count` | 4 bytes | u32 | Total number of entries in the file. |
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| `entry_count` | 8 bytes | u32 | Total number of entries in the file. |
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---
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···
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To read a Bindle file:
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1. Validate the file size (must be at least 28 bytes).
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2. Read the first 8 bytes and the last 8 bytes to verify the `BINDL001` magic.
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3. Read the `index_offset` from the footer (EOF - 20).
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3. Read the `index_offset` from the footer (EOF - 16).
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4. Seek to `index_offset` and iterate `entry_count` times to populate an in-memory map of files.
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### 3.2 Writing Logic (Atomic Updates)
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src/lib.rs
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src/lib.rs
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#[derive(FromBytes, Unaligned, IntoBytes, Immutable, Debug)]
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struct Footer {
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pub index_offset: [u8; 8],
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pub entry_count: [u8; 4],
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pub entry_count: [u8; 8],
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}
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pub struct Bindle {
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// If magic is valid, proceed to parse the index
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let data_end = u64::from_le_bytes(footer.index_offset);
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let count = u32::from_le_bytes(footer.entry_count);
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let count = u64::from_le_bytes(footer.entry_count);
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let mut entries = Vec::with_capacity(count as usize);
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let mut cursor = data_end as usize;
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let footer = Footer {
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index_offset: index_start.to_le_bytes(),
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entry_count: (self.entries.len() as u32).to_le_bytes(),
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entry_count: (self.entries.len() as u64).to_le_bytes(),
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};
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self.file.write_all(footer.as_bytes())?;