Struct Header

Source

pub struct Header { /* private fields */ }

Expand description

Defines and validates the metadata associated with a channel.

Implementations§

Source §

impl Header

Source

pub fn new( writer_id: u64, channel_id: u64, capacity_hint: u32, max_msg_len_hint: u32, timeout: u64, tick_unit: TickUnit, ) -> Header

Defines a new channel header.

Return a struct that contains all the metadata required to be associated with a new channel.

§Arguments

writer_id - Channel’s writer identifier
channel_id - Channel’s identifier
capacity_hint - Hint for the size of the channel - the maximum amount of data that can be wrote into the channel. Usually a successfully created channel will have a size very close to this hint, probably a little larger.
max_msg_len_hint - Hint for the maximum size of a message wrote into the channel. This cannot be larger than a certain fraction. of the channel’s capacity(1/128th), so the new created channel may have max message length value smaller than this hint.
timeout - Specifies the write inactivity time interval after each the reader will consider the channel abandoned by the writer.
tick_unit - Time unit used by the timeout and creation time attributes.

§Example

use kekbit_core::tick::TickUnit::Nanos;
use kekbit_core::header::*;
     
let producer_id: u64 = 111;
let channel_id: u64 = 101;
let capacity: u32 = 10_001;
let max_msg_len: u32 = 100;
let timeout: u64 = 10_000;
let tick_unit = Nanos;
let header = Header::new(channel_id, producer_id, capacity, max_msg_len, timeout, tick_unit);
println!("{:?}", &header);

Source

pub fn read(header: &[u8]) -> Result<Header, ChannelError>

Reads and validates the metadata from an existing memory mapped channel.

Returns the metadata associated with the channel.

§Arguments

header - Reference to a byte array which should contain metadata associated with a given channel. Usually points at the beginning of a memory mapped file used as storage for a kekbit channel.

§Errors

An error will occur if data is corrupted or points to an incompatible version of kekbit channel.

§Example

 use memmap::MmapOptions;
 use std::fs::OpenOptions;

 use kekbit_core::shm::*;
 let writer_id = 1850;
 let channel_id = 4242;
 let test_tmp_dir = tempdir::TempDir::new("kektest").unwrap();
 let dir_path = test_tmp_dir.path();

 let kek_file_name = storage_path(dir_path, channel_id);
 let kek_file = OpenOptions::new()
  .write(true)
  .read(true)
  .open(&kek_file_name).unwrap();
  let mut mmap = unsafe { MmapOptions::new().map_mut(&kek_file) }.unwrap();
  let buf = &mut mmap[..];
  let header = Header::read(buf).unwrap();
  println!("{:?}", &header);

Source

pub fn write_to(&self, header: &mut [u8]) -> usize

Writes kekbit metadata to a memory mapepd file.

Returns the lenght of the metadata

§Arguments

header - Reference to a byte slice where metadata must be written. Usually points at the beginning of a memory mapped file used as storage for a kekbit channel.

§Example

 use memmap::MmapOptions;
 use std::fs::OpenOptions;

 use kekbit_core::tick::TickUnit::Nanos;
 use kekbit_core::header::Header;
 use kekbit_core::shm::*;
 use std::fs::DirBuilder;

 const FOREVER: u64 = 99_999_999_999;
 let writer_id = 1850;
 let channel_id = 42;
 let test_tmp_dir = tempdir::TempDir::new("keksample").unwrap();
 let dir_path = test_tmp_dir.path().join(writer_id.to_string());
 let mut builder = DirBuilder::new();
 builder.recursive(true);
 builder.create(&dir_path).or_else(|err| Err(err.to_string())).unwrap();

 let kek_file_name = dir_path.join(format!("{}.kekbit", channel_id));
 let kek_file = OpenOptions::new()
 .write(true)
 .read(true)
 .create(true)
 .open(&kek_file_name)
 .or_else(|err| Err(err.to_string())).unwrap();

 let header = Header::new(writer_id, channel_id, 300_000, 1000, FOREVER, Nanos);
 let total_len = (header.capacity() + header.len() as u32) as u64;
 kek_file.set_len(total_len).or_else(|err| Err(err.to_string())).unwrap();
 let mut mmap = unsafe { MmapOptions::new().map_mut(&kek_file) }.unwrap();
 let buf = &mut mmap[..];
 header.write_to(buf);
 mmap.flush().unwrap();