68 lines
1.9 KiB
Rust
68 lines
1.9 KiB
Rust
use bytes::BufMut;
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use super::{Block, SIZEOF_U16};
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/// Builds a block.
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pub struct BlockBuilder {
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/// Offsets of each key-value entries.
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offsets: Vec<u16>,
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/// All serialized key-value pairs in the block.
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data: Vec<u8>,
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/// The expected block size.
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block_size: usize,
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}
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impl BlockBuilder {
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/// Creates a new block builder.
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pub fn new(block_size: usize) -> Self {
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Self {
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offsets: Vec::new(),
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data: Vec::new(),
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block_size,
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}
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}
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fn estimated_size(&self) -> usize {
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SIZEOF_U16 /* number of key-value pairs in the block */ + self.offsets.len() * SIZEOF_U16 /* offsets */ + self.data.len()
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// key-value pairs
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}
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/// Adds a key-value pair to the block. Returns false when the block is full.
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#[must_use]
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pub fn add(&mut self, key: &[u8], value: &[u8]) -> bool {
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assert!(!key.is_empty(), "key must not be empty");
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if self.estimated_size() + key.len() + value.len() + SIZEOF_U16 * 3 /* key_len, value_len and offset */ > self.block_size
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&& !self.is_empty()
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{
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return false;
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}
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// Add the offset of the data into the offset array.
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self.offsets.push(self.data.len() as u16);
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// Encode key length.
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self.data.put_u16(key.len() as u16);
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// Encode key content.
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self.data.put(key);
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// Encode value length.
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self.data.put_u16(value.len() as u16);
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// Encode value content.
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self.data.put(value);
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true
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}
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/// Check if there are no key-value pairs in the block.
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pub fn is_empty(&self) -> bool {
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self.offsets.is_empty()
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}
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/// Finalize the block.
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pub fn build(self) -> Block {
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if self.is_empty() {
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panic!("block should not be empty");
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}
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Block {
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data: self.data,
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offsets: self.offsets,
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}
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}
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}
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