[package]
name = "tmpfile"
version = "0.0.2"
version = "0.0.3"
edition = "2021"
license = "0BSD"
categories = [ "filesystem" ]
keywords = [ "tmpfile", "tempfile" ]
repository = "https://repos.qrnch.tech/pub/tmpfile"
description = "A temporary file writer with an option to persist."
rust-version = "1.56"
exclude = [
  ".fossil-settings",
  ".efiles",
  ".fslckout",
  "examples",
  "www",
  "bacon.toml",
  "rustfmt.toml"
]

[features]
defer-persist = ["dep:swctx"]

[dependencies]
swctx = { version = "0.2.2", optional = true }
swctx = { version = "0.3.0", optional = true }

[dev-dependencies]
hex = { version = "0.4.3" }
rand = { version = "0.8.5" }
sha2 =  { version = "0.10.8" }

[package.metadata.docs.rs]
all-features = true
rustdoc-args = ["--cfg", "docsrs", "--generate-link-to-definition"]

[lints.clippy]
all = { level = "deny", priority = -1 }
pedantic = { level = "warn", priority = -1 }
nursery = { level = "warn", priority = -1 }
cargo = { level = "warn", priority = -1 }

# This is a configuration file for the bacon tool
#
# Bacon repository: https://github.com/Canop/bacon
# Complete help on configuration: https://dystroy.org/bacon/config/
# You can also check bacon's own bacon.toml file
#  as an example: https://github.com/Canop/bacon/blob/main/bacon.toml

default_job = "clippy-all"

[jobs.check]
command = ["cargo", "check", "--color", "always"]
need_stdout = false

[jobs.check-all]
command = ["cargo", "check", "--all-targets", "--color", "always"]
need_stdout = false

# Run clippy on the default target
[jobs.clippy]
command = [
    "cargo", "clippy",
    "--all-features",
    "--color", "always",
]
need_stdout = false

# Run clippy on all targets
# To disable some lints, you may change the job this way:
#    [jobs.clippy-all]
#    command = [
#        "cargo", "clippy",
#        "--all-targets",
#        "--color", "always",
#    	 "--",
#    	 "-A", "clippy::bool_to_int_with_if",
#    	 "-A", "clippy::collapsible_if",
#    	 "-A", "clippy::derive_partial_eq_without_eq",
#    ]
# need_stdout = false
[jobs.clippy-all]
command = [
    "cargo", "clippy",
    "--all-features",
    "--all-targets",
    "--color", "always",
]
need_stdout = false

# This job lets you run
# - all tests: bacon test
# - a specific test: bacon test -- config::test_default_files
# - the tests of a package: bacon test -- -- -p config
[jobs.test]
command = [
    "cargo", "test", "--color", "always",
    "--", "--color", "always", # see https://github.com/Canop/bacon/issues/124
]
need_stdout = true

[jobs.doc]
command = ["cargo", "doc", "--color", "always", "--no-deps"]
need_stdout = false

# If the doc compiles, then it opens in your browser and bacon switches
# to the previous job
[jobs.doc-open]
command = ["cargo", "doc", "--color", "always", "--no-deps", "--open"]
need_stdout = false
on_success = "back" # so that we don't open the browser at each change

# You can run your application and have the result displayed in bacon,
# *if* it makes sense for this crate.
# Don't forget the `--color always` part or the errors won't be
# properly parsed.
# If your program never stops (eg a server), you may set `background`
# to false to have the cargo run output immediately displayed instead
# of waiting for program's end.
[jobs.run]
command = [
    "cargo", "run",
    "--color", "always",
    # put launch parameters for your program behind a `--` separator
]
need_stdout = true
allow_warnings = true
background = true

# This parameterized job runs the example of your choice, as soon
# as the code compiles.
# Call it as
#    bacon ex -- my-example
[jobs.ex]
command = ["cargo", "run", "--color", "always", "--example"]
need_stdout = true
allow_warnings = true

# You may define here keybindings that would be specific to
# a project, for example a shortcut to launch a specific job.
# Shortcuts to internal functions (scrolling, toggling, etc.)
# should go in your personal global prefs.toml file instead.
[keybindings]
# alt-m = "job:my-job"
c = "job:clippy-all" # comment this to have 'c' run clippy on only the default target

#[cfg(feature = "defer-persist")]
mod inner {
  use std::{
    io::Write,
    path::{Path, PathBuf},
    thread
  };

  use tmpfile::{TmpFile, TmpProc};

  use sha2::{Digest, Sha256};

  use rand::Rng;

  #[derive(Debug)]
  enum MyError {
    IO(())
  }

  impl From<std::io::Error> for MyError {
    fn from(_err: std::io::Error) -> Self {
      Self::IO(())
    }
  }

  struct Hasher {
    inner: Sha256
  }

  impl TmpProc for Hasher {
    type Output = Vec<u8>;
    type Error = MyError;

    /// Called when a buffer is about to be written.
    fn update(&mut self, buf: &[u8]) {
      self.inner.update(buf);
    }

    fn finalize(
      &mut self,
      _tmpfile: Option<&Path>
    ) -> Result<(Self::Output, Option<PathBuf>), std::io::Error> {
    ) -> Result<(Self::Output, Option<PathBuf>), Self::Error> {
      let result = self.inner.clone().finalize();
      let hash = result.to_vec();

      let hexhash = hex::encode(&hash);
      let (subdir1, rest) = hexhash.split_at(2);
      let (subdir2, fname) = rest.split_at(2);
      let subdirs = PathBuf::from(subdir1).join(subdir2);
      if !subdirs.exists() {
        std::fs::create_dir_all(&subdirs)?;
      let dir = PathBuf::from(subdir1).join(subdir2);
      if !dir.exists() {
        std::fs::create_dir_all(&dir)?;
      }
      Ok((hash, Some(subdirs.join(fname))))
      Ok((hash, Some(dir.join(fname))))
    }
  }


  pub(super) fn main() {
  pub fn main() {
    let mut buf = vec![0u8; 65536];
    rand::thread_rng().fill(&mut buf[..]);

    let tp = Hasher {
      inner: Sha256::new()
    };
    let tp = Box::new(tp);

use std::{
  io::Write,
  path::{Path, PathBuf}
};

use tmpfile::{TmpFile, TmpProc};

use sha2::{Digest, Sha256};

use rand::Rng;

#[derive(Debug)]
enum MyError {
  IO(())
}

impl From<std::io::Error> for MyError {
  fn from(_err: std::io::Error) -> Self {
    Self::IO(())
  }
}

struct Hasher {
  inner: Sha256
}

impl TmpProc for Hasher {
  type Output = Vec<u8>;
  type Error = MyError;

  /// Called when a buffer is about to be written.
  fn update(&mut self, buf: &[u8]) {
    self.inner.update(buf);
  }

  fn finalize(
    &mut self,
    tmpfile: Option<&Path>
  ) -> Result<(Self::Output, Option<PathBuf>), std::io::Error> {
  ) -> Result<(Self::Output, Option<PathBuf>), Self::Error> {
    let result = self.inner.clone().finalize();
    let hash = result.to_vec();
    if tmpfile.is_some() {
      // The temporary file is stored in the file system.
      // We need to return a target location for it.
      let hexhash = hex::encode(&hash);
      let (subdir1, rest) = hexhash.split_at(2);
      let (subdir2, fname) = rest.split_at(2);
      let subdirs = PathBuf::from(subdir1).join(subdir2);
      if !subdirs.exists() {
        std::fs::create_dir_all(&subdirs)?;
      let dir = PathBuf::from(subdir1).join(subdir2);
      if !dir.exists() {
        std::fs::create_dir_all(&dir)?;
      }
      Ok((hash, Some(subdirs.join(fname))))
      Ok((hash, Some(dir.join(fname))))
    } else {
      // The content is stored in memory
      Ok((hash, None))
    }
  }
}

use std::{
  io::Write,
  path::{Path, PathBuf}
};

use tmpfile::{TmpFile, TmpProc};

use sha2::{Digest, Sha256};

use rand::Rng;

#[derive(Debug)]
enum MyError {
  IO(())
}

impl From<std::io::Error> for MyError {
  fn from(_err: std::io::Error) -> Self {
    Self::IO(())
  }
}

struct Hasher {
  inner: Sha256
}

impl TmpProc for Hasher {
  type Output = Vec<u8>;
  type Error = MyError;

  /// Called when a buffer is about to be written.
  fn update(&mut self, buf: &[u8]) {
    self.inner.update(buf);
  }

  fn finalize(
    &mut self,
    _tmpfile: Option<&Path>
  ) -> Result<(Self::Output, Option<PathBuf>), std::io::Error> {
  ) -> Result<(Self::Output, Option<PathBuf>), Self::Error> {
    let result = self.inner.clone().finalize();
    let hash = result.to_vec();

    let hexhash = hex::encode(&hash);
    let (subdir1, rest) = hexhash.split_at(2);
    let (subdir2, fname) = rest.split_at(2);
    let subdirs = PathBuf::from(subdir1).join(subdir2);
    if !subdirs.exists() {
      std::fs::create_dir_all(&subdirs)?;
    let dir = PathBuf::from(subdir1).join(subdir2);
    if !dir.exists() {
      std::fs::create_dir_all(&dir)?;
    }
    Ok((hash, Some(subdirs.join(fname))))
    Ok((hash, Some(dir.join(fname))))
  }
}


fn main() {
  let mut buf = vec![0u8; 65536];
  rand::thread_rng().fill(&mut buf[..]);

//! Representation of a temporary file that can be persisted.
//! Temporary file object that can be persisted.
//!
//! # Usage overview
//! The main type of this crate is [`TmpFile`], which represents a (temporary)
//! file being written to, that may optionally be persisted (or it will be
//! removed).
//!
//! To use `TmpFile` an application must first implement the [`TmpProc`] trait
//! on a type.  [`TmpProc::update()`] will be called each time a block of data
//! is written to the `TmpFile`.  [`TmpProc::finalize()`] will be called if the
//! This is intended to be used in an application that needs to receive a file
//! to persistent storage, but doesn't know its final target file name until it
//! has received the entire file (such as if the file's name should be its
//! content's hash).
//! application chooses to persist the `TmpFile`.
//!
//! When a `TmpFile` is created, the application must pass along the file's
//! _temporary_ location and an object whose type implements `TmpProc`.  The
//! instantiated `TmpFile` object implements [`std::io::Write`], which is used
//! to write data to it.
//!
//! If the entire file can not be completed, the `TmpFile` object is dropped,
//! which will automatically remove the temporary file.
//!
//! If the entire file has been written, and the application wants to persist
//! it, it calls [`TmpFile::persist()`].  This will call the
//! `TmpProc::finalize()` trait method, whose responsibility it is to return
//! the file's persistent location (and application-defined data).  Information
//! about the persisted file is finally returned to the application via an
//! instantion of [`Persisted`].
//!
//! # Minimum size
//! In some cases an application may not want to store small files in its
//! filesystem based data store.  For this purpose, the `TmpFile` can be set up
//! to have a minimum file size.  If a `TmpFile` does not reach this size
//! before being persisted, a buffer of the file's contents will be returned
//! instead of a file name of the persisted file.
//! # "Small file" special case
//! An application may not want to store small files in its filesystem.
//! For this purpose, the `TmpFile` can be set up to have a minimum file size.
//! If a `TmpFile` does not reach this size before being persisted, a memory
//! buffer of the file's contents will be returned instead of a file name of
//! the persisted file.
//!
//! The [`TmpFile::with_minsize()`] factory method can be used to use this
//! feature.
//!
//! # Deferred persist
//! There may be cases where it's impractical to call [`TmpFile::persist()`] on
//! a `TmpFile`, but where the originator of the `TmpFile` wants to manage the
//! results from the `TmpFile` when it is pesisted.  This crate has means to
//! handle such situations, but it drastically changes the semantics of
//! `TmpFile`:  The `defer_persist()` method returns a wait context that can be
//! used to wait for the `TmpFile` to finalize and send its results.  In this
//! scenario, the finalization occurrs implicitly when the `TmpFile` is
//! dropped.
//!
//! This means that deferred persist shifts the default assumption of
//! "drop-before-persist implies failure" to "drop means persist", with no
//! means to trigger "abort without finalization" (unless the `TmpProc`'s
//! finalization is able to determine that the file is incomplete).
//!
//! # Features
//! | Feature         | Function
//! |-----------------|----------
//! | `defer-persist` | Allow `Drop` to finalize `TmpFile`.

#![cfg_attr(docsrs, feature(doc_cfg))]

use std::{
  fs,
  io::Write,
  path::{Path, PathBuf},
  time::{Duration, Instant}
};


/// Used to inspect content as it is being fed to the temporary file.
/// Used to inspect contents as it is being fed to the temporary file and to
/// finalize the temporary file when it is being persisted.
pub trait TmpProc {
  /// Application-defined data to be returned on successful finalization.
  type Output;

  /// Application-defined error type.
  type Error;

  /// Called when a buffer has been written to the `TmpFile` storage.
  fn update(&mut self, buf: &[u8]);

  /// Called when the application has chosen to persist the file.
  ///
  /// The role of this method is to:
  /// - Return its application-specific data of the associated type `Output`.
  /// - If `src` is `Some()` it means that the `TmpFile` is backed by a file,
  ///   and the implementation of this method should return, as the second
  ///   tuple member, `Some(PathBuf)`, pointing out the target file that the
  ///   temporary file should be persisted to.  If `src` is `None` the
  ///   temporary buffer is not stored in the file system and thus `None`
  ///   should be returned instead.
  ///
  /// # Errors
  /// Returns application-specific errors.
  fn finalize(
    &mut self,
    src: Option<&Path>
  ) -> Result<(Self::Output, Option<PathBuf>), std::io::Error>;
  ) -> Result<(Self::Output, Option<PathBuf>), Self::Error>;
}


/// A [`TmpProc`] implementation which does nothing.
pub struct NullProc<'a>(&'a Path);

impl TmpProc for NullProc<'_> {
  type Output = ();
  type Error = ();

  #[allow(unused_variables)]
  fn update(&mut self, buf: &[u8]) {}

  #[allow(unused_variables)]
  fn finalize(
    &mut self,
    src: Option<&Path>
  ) -> Result<(Self::Output, Option<PathBuf>), std::io::Error> {
  ) -> Result<(Self::Output, Option<PathBuf>), Self::Error> {
    Ok(((), Some(self.0.to_path_buf())))
  }
}

/// Temporary file contents container returned after successful persist.
#[derive(Debug)]
pub enum Output {
  /// The temporary file's contents have been persisted to a file.
  File(PathBuf),

  /// The temporary file's contents weren't large enough to be written to disk
  /// and are returned in this buffer.
  ///
  /// This variant can only occur if a minimum size threshold has been set.
  Buf(Vec<u8>)
}

impl Output {
  /// Fallibly convert `Output` to a `PathBuf`.
  ///
  /// # Errors
  /// If the `Output` does not represent a file name, then return the `Output`.
  pub fn try_into_fname(self) -> Result<PathBuf, Output> {
  pub fn try_into_fname(self) -> Result<PathBuf, Self> {
    match self {
      Self::File(fname) => Ok(fname),
      r => Err(r)
      r @ Self::Buf(_) => Err(r)
    }
  }

  /// Unwrap `PathBuf`.
  ///
  /// # Panics
  /// The `Output` must represent a file name.
  #[must_use]
  pub fn unwrap_fname(self) -> PathBuf {
    let Output::File(fname) = self else {
    let Self::File(fname) = self else {
      panic!("Not a file name");
    };
    fname
  }

  /// Fallibly convert `Output` to a buffer.
  ///
  /// # Errors
  /// If the `Output` does not represent a buffer, then return the `Output`.
  pub fn try_into_buf(self) -> Result<Vec<u8>, Output> {
  pub fn try_into_buf(self) -> Result<Vec<u8>, Self> {
    match self {
      Self::Buf(buf) => Ok(buf),
      r => Err(r)
      r @ Self::File(_) => Err(r)
    }
  }

  /// Unwrap buffer.
  ///
  /// # Panics
  /// The `Output` must represent a buffer.
  #[must_use]
  pub fn unwrap_buf(self) -> Vec<u8> {
    let Output::Buf(buf) = self else {
    let Self::Buf(buf) = self else {
      panic!("Not a buffer");
    };
    buf
  }
}

/// The final results of successfully persisting a [`TmpFile`].

struct MemBuf {
  buf: Vec<u8>,
  idx: usize
}

/// Temporary file contents generator.
pub struct TmpFile<T> {
/// File writer used to write to a temporary file that can be persisted.
pub struct TmpFile<T, E>
where
  E: From<std::io::Error>
{
  tmpfile: PathBuf,
  f: Option<Box<dyn Write + Send>>,
  tp: Box<dyn TmpProc<Output = T> + Send>,
  tp: Box<dyn TmpProc<Output = T, Error = E> + Send>,
  size: u64,
  start_time: Instant,
  membuf: Option<MemBuf>,
  #[cfg(feature = "defer-persist")]
  sctx: Option<swctx::SetCtx<Persisted<T>, (), std::io::Error>>
  sctx: Option<swctx::SetCtx<Persisted<T>, (), E>>
}

impl<T> TmpFile<T> {
  fn inner_persist(&mut self) -> Result<Persisted<T>, std::io::Error> {
impl<T, E> TmpFile<T, E>
where
  E: From<std::io::Error>
{
  fn inner_persist(&mut self) -> Result<Persisted<T>, E> {
    // Force close file, if open
    if let Some(f) = self.f.take() {
      drop(f);
    }

    let (output, t) = if let Some(ref mut membuf) = self.membuf {
      let mut buf = std::mem::take(&mut membuf.buf);

      (Output::File(outfile), t)
    };

    Ok(Persisted {
      output,
      size: self.size,
      procres: t,
      duration: Instant::now() - self.start_time
      duration: self.start_time.elapsed()
    })
  }
}

impl<T> TmpFile<T> {
impl<T, E> TmpFile<T, E>
where
  E: From<std::io::Error>
{
  /// Create a new [`TmpFile`].
  ///
  /// # Errors
  /// If the temporary file could not be opened for writing `std::io::Error` is
  /// returned.
  pub fn new<P>(
    fname: P,
    tp: Box<dyn TmpProc<Output = T> + Send>
    tp: Box<dyn TmpProc<Output = T, Error = E> + Send>
  ) -> Result<Self, std::io::Error>
  where
    P: AsRef<Path>
  {
    let tmpfile = fname.as_ref().to_path_buf();
    let f = fs::File::create(&tmpfile)?;
    let f = Box::new(f);

      #[cfg(feature = "defer-persist")]
      sctx: None
    })
  }

  /// Create a new [`TmpFile`] that will not write to file unless the size
  /// exceeds a specified size.
  ///
  /// # Errors
  /// If the temporary file could not be opened for writing `std::io::Error` is
  /// returned.
  pub fn with_minsize<P>(
    fname: P,
    tp: Box<dyn TmpProc<Output = T> + Send>,
    tp: Box<dyn TmpProc<Output = T, Error = E> + Send>,
    minsize: usize
  ) -> Result<Self, std::io::Error>
  where
    P: AsRef<Path>
  {
    let tmpfile = fname.as_ref().to_path_buf();
    let f = fs::File::create(&tmpfile)?;

  }


  /// Persist the hitherto temporary file.
  ///
  /// The location of the persisted file will be determined by the [`TmpProc`]
  /// object that was passed into [`TmpFile::new()`].
  ///
  /// # Errors
  /// If it was not possible to persist, the application-defined error `E` will
  /// be returned.
  #[cfg_attr(
    feature = "defer-persist",
    doc = r#"
# Panic
If the `TmpFile` has previously registered to receive the finalization
results via a channel using [`TmpFile::defer_persist()`] this method will
# Panics
If the `defer-persist` feature is used: If the `TmpFile` has previously
registered to receive the finalization results via a channel using
[`TmpFile::defer_persist()`] this method will cause a panic.
cause a panic.
"#
  )]
  pub fn persist(mut self) -> Result<Persisted<T>, std::io::Error> {
  pub fn persist(mut self) -> Result<Persisted<T>, E> {
    #[cfg(feature = "defer-persist")]
    assert!(
    if self.sctx.is_some() {
      self.sctx.is_none(),
      panic!(
        "Con not persist TmpFile that has been configured for deferred \
      "Con not persist TmpFile that has been configured for deferred persist"
         persist"
      );
    );
    }

    self.inner_persist()
  }

  /// Persist this temporary file on `Drop`, but report the finalized results
  /// using a one-shot channel.
  ///
  /// This method can be used if the `TmpFile` is type-erase cast into a
  /// `dyn std::io::Write` (which loses access to [`TmpFile::persist()`]).
  ///
  /// # Caveat
  /// When using a deferred persist, the semantics of the `TmpFile` changes
  /// from "assume failure" to "assume success".  If an error occurs which
  /// should cause the temporary file to no longer be persisted, the owner of
  /// the `TmpFile` must call [`TmpFile::cancel()`] on it.
  ///
  /// # Panic
  /// # Panics
  /// This method must only be called once per `TmpFile` object.  Calling it
  /// a second time will cause a panic.
  #[cfg(feature = "defer-persist")]
  #[cfg_attr(docsrs, doc(cfg(feature = "defer-persist")))]
  pub fn defer_persist(
    &mut self
  pub fn defer_persist(&mut self) -> swctx::WaitCtx<Persisted<T>, (), E> {
    assert!(
  ) -> swctx::WaitCtx<Persisted<T>, (), std::io::Error> {
    if self.sctx.is_some() {
      panic!("TmpFile already configured for deferred persist");
      self.sctx.is_none(),
      "TmpFile already configured for deferred persist"
    }
    );

    let (sctx, wctx) = swctx::mkpair();

    self.sctx = Some(sctx);

    wctx
  }

  /// Cancel a deferred persist request.
  #[cfg(feature = "defer-persist")]
  #[cfg_attr(docsrs, doc(cfg(feature = "defer-persist")))]
  pub fn cancel(mut self) {
    // Take out the SetCtx so the Drop handler doesn't attempt to
    // finalize/persist.
    let _ = self.sctx.take();
  }
}


impl<T> Write for TmpFile<T> {
impl<T, E> Write for TmpFile<T, E>
where
  E: From<std::io::Error>
{
  fn write(&mut self, buf: &[u8]) -> Result<usize, std::io::Error> {
    // If there's a memory buffer, then append to it.  Unless this write would
    // overflow the membuf, in which case switch to using a file.
    if let Some(ref mut membuf) = self.membuf {
      if membuf.idx + buf.len() > membuf.buf.len() {
        // Current write index + size of input buffer would exceed maximum
        // buffer size.

        // Update TmpProc
        self.tp.update(buf);

        return Ok(buf.len());
      }
    }

    // At this point the Tmpfile is writing to a file in the file system.  The
    // memory buffer case should have returned early.
    let Some(ref mut f) = self.f else {
      panic!("No file?");
    };

    let n = f.write(buf)?;
    self.tp.update(&buf[..n]);
    self.size += n as u64;

    Ok(n)
  }

  fn flush(&mut self) -> Result<(), std::io::Error> {
    if let Some(ref mut f) = self.f {
      f.flush()?;
    };
    Ok(())
  }
}

impl<T> Drop for TmpFile<T> {
impl<T, E> Drop for TmpFile<T, E>
where
  E: From<std::io::Error>
{
  fn drop(&mut self) {
    // Close file if it hasn't been already
    if let Some(f) = self.f.take() {
      drop(f);
    }

    // If deferred persist has been requested, then handle it here.
    #[cfg(feature = "defer-persist")]
    if let Some(sctx) = self.sctx.take() {
      match self.inner_persist() {
        Ok(res) => sctx.set(res),
        Err(e) => sctx.fail(e)
        Ok(res) => {
          // ToDo: Log error?
          let _ = sctx.set(res);
        }
        Err(e) => {
          // ToDo: Log error?
          let _ = sctx.fail(e);
        }
      }
    }

    if let Err(_e) = fs::remove_file(&self.tmpfile) {
      // ToDo: Log error?
    }
  }
}

// vim: set ft=rust et sw=2 ts=2 sts=2 cinoptions=2 tw=79 :

# Change Log

## [Unreleased]

[Details](/vdiff?from=tmpfile-0.0.2&to=trunk)

### Added

### Changed

- Previously several error cases returned `std::io::Error`.  Now use an
  application-specific error type:  The `TmpProc` trait now has an `Error`
  type, and `TmpFile` uses a generic `E`, which has a `From<std::io::Error>`
  bound.
- Update to `swctx` `0.3.0`.

### Removed

---

## [0.0.2] - 2024-01-30

[Details](/vdiff?from=tmpfile-0.0.1&to=trunk)
[Details](/vdiff?from=tmpfile-0.0.1&to=tmpfile-0.0.2)

### Added

- Allow a "minimum file content size" to be specified.  If, at the point of
  persisting a `TmpFile` the total size of it is smaller than the configured
  threshold value, the file's contents will be returned as a memory buffer
  rather than to be persisted into a file.

# tmpfile

`TmpFile` is an object representing a temporary file that can optionally be
persisted to a new location.
persisted.  It can be useful if a file being received over the network should
be named according to its contents, but the name can not be determined until
the entire file has been received.

This library was created to provide a prepackaged solution where:

- An application wants to write a new (temporary) file, but wants it to be
  automatically removed if not explicitly requested to persist.  (For instance,
  receive a file over network, and automatically remove it if the connection is
  lost before the entire file could be received).
- The contents of a file is inspected as it is being received.  (For instance,
  while receiving a file over a network, calculate the file's hash as it is
  being received).
- An application may want the file to be written to a temporary location, and
  only moved to its permanent name once the entire file has been received.
  (For instance, the name of the file may be its hash, which is unavailable
  until the entire file has been processed).
- A small file isn't written to the file system at all, and is returned as a
  memory buffer instead.


## Feature labels in documentation

The crate's documentation uses automatically generated feature labels, which
currently requires nightly featuers.  To build the documentation locally use: