harmos-storage 0.1.2

Harmos storage: durable journals, snapshots and Arrow-backed stream storage.
Documentation 
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/* ***
 *
 * Harmos
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * ***
 */

/* === Modules === */

/* === Re-Exports === */

/* === Imports === */

// Standard Library Imports
use std::num::NonZeroUsize;
// Third Party Imports
use tokio::sync::watch;
// Local Imports
use super::capacity::{Held, Pool, Refusal, Reservation};
use super::{ErasedCatalog, FileBatch, FilePhase, FileProgress, StagedFile, StorageManager};
use crate::{Error, MemorySize, Result};

/* === Constants === */

/* === Macros === */

/* === Type Aliases === */

/* === Structs === */

pub struct FileFollower {
    manager: StorageManager<ErasedCatalog>,
    file: StagedFile,
    offset: u64,
    progress: FileProgress,
    changed: watch::Receiver<u64>,
    held: Held,
    _metadata: Reservation,
}

/* === Enums === */

/* === Traits === */

/* === Implementations === */

impl<C> StorageManager<C> {
    pub async fn follow_file(&self, file: &StagedFile, offset: u64) -> Result<FileFollower> {
        self.inner.primary.history().check(&file.history)?;
        let held = Held::default();
        let metadata =
            Reservation::wait(&self.inner, Pool::Read, &held, file.memory_size().saturating_add(std::mem::size_of::<FileFollower>()), None)
                .await
                .map_err(Refusal::into_error)?;
        let changed = self.inner.changed.subscribe();
        let progress = self.file_progress(file).await?;
        if offset > progress.length {
            tracing::error!(file = %file.id, offset, available = progress.length, reason = "offset exceeds retained bytes", "file following rejected");
            return Err(Error::InvalidInput { field: "file offset", reason: "offset exceeds retained bytes" });
        }
        Ok(FileFollower { manager: self.erased(), file: file.clone(), offset, progress, changed, held, _metadata: metadata })
    }

    pub async fn file_progress(&self, file: &StagedFile) -> Result<FileProgress> {
        self.inner.primary.history().check(&file.history)?;
        let _lifecycle = self.inner.lifecycle.read().await;
        {
            let state = self.inner.state.lock().unwrap();
            if state.status.closing || !state.ready {
                return Err(Error::Closing { domain: "storage file reader" });
            }
            if let Some(progress) = state.files.values().find_map(|active| active.production(file)) {
                return progress;
            }
        }
        self.inner.bounded(self.inner.primary.file_progress(file)).await
    }
}

impl FileFollower {
    pub fn offset(&self) -> u64 {
        self.offset
    }

    pub fn progress(&self) -> FileProgress {
        self.progress
    }

    pub async fn next_batch(&mut self, max_bytes: NonZeroUsize) -> Result<Option<FileBatch>> {
        loop {
            self.changed.borrow_and_update();
            let progress = self.manager.file_progress(&self.file).await?;
            if self.offset > progress.length {
                return Err(Error::InvalidInput { field: "file offset", reason: "retained bytes moved behind reader offset" });
            }
            self.progress = progress;
            if self.offset < progress.length {
                let size = max_bytes
                    .get()
                    .min(self.manager.inner.settings.response.batch_bytes.get())
                    .min(usize::try_from(progress.length - self.offset).unwrap_or(usize::MAX));
                let maximum = NonZeroUsize::new(size).expect("nonempty file prefix");
                let _transfer =
                    Reservation::wait(&self.manager.inner, Pool::Read, &self.held, size, None).await.map_err(Refusal::into_error)?;
                let _lifecycle = self.manager.inner.lifecycle.read().await;
                if self.manager.inner.state.lock().unwrap().status.closing {
                    return Err(Error::Closing { domain: "storage file reader" });
                }
                let bytes =
                    self.manager.inner.bounded(self.manager.inner.primary.read_production(&self.file, self.offset, maximum)).await?;
                if bytes.is_empty() || bytes.len() > size || bytes.capacity() > size {
                    return Err(Error::InvalidInput {
                        field: "file batch",
                        reason: "backend returned an empty or oversized retained prefix",
                    });
                }
                let offset = self.offset;
                self.offset += bytes.len() as u64;
                return Ok(Some(FileBatch { offset, bytes }));
            }
            if progress.phase != FilePhase::Producing {
                return Ok(None);
            }
            self.changed.changed().await.map_err(|_| Error::Closing { domain: "storage file reader" })?;
        }
    }
}

impl Drop for FileFollower {
    fn drop(&mut self) {
        tracing::debug!(file = %self.file.id, offset = self.offset, reason = "viewer disconnected", "file following stopped");
    }
}

/* === Public Functions === */

/* === Private Functions === */

/* === Tests === */