Struct zbox::File [−][src]
pub struct File { /* fields omitted */ }
Expand description
A reference to an opened file in the repository.
An instance of a File
can be read and/or written depending on what options
it was opened with. Files also implement Seek
to alter the logical
cursor that the file contains internally.
Files are automatically closed when they go out of scope.
As ZboxFS internally cached file content, it is no need to use buffered
reader, such as BufReader<R>
.
Examples
Create a new file and write bytes to it:
use std::io::prelude::*;
let mut file = repo.create_file("/foo.txt")?;
file.write_all(b"Hello, world!")?;
file.finish()?;
Read the content of a file into a String
:
use std::io::prelude::*;
let mut file = repo.open_file("/foo.txt")?;
let mut content = String::new();
file.read_to_string(&mut content)?;
assert_eq!(content, "Hello, world!");
Versioning
File
contents support up to 255 revision versions. Version
is
immutable once it is created.
By default, the maximum number of versions of a File
is 1
, which is
configurable by version_limit
on both Repo
and File
level. File
level option takes precedence.
After reaching this limit, the oldest Version
will be automatically
deleted after adding a new one.
Version number starts from 1
and continuously increases by 1.
Writing
File content is cached internally for deduplication and will be handled
automatically, thus calling flush
is not recommended.
File
can be sent to multiple threads, but only one thread can modify it at
a time, which is similar to a RwLock
.
File
is multi-versioned, each time updating its content will create a new
permanent Version
. There are two ways of writing data to a file:
-
Multi-part Write
This is done by updating
File
usingWrite
trait multiple times. After all writing operations,finish
must be called to create a new version. Unlessfinish
was successfully returned, no data will be written to the file.Internally, a transaction is created when writing to the file first time and calling
finish
will commit that transaction. If any errors happened duringwrite
, that transaction will be aborted. Thus, you should not callfinish
after any failedwrite
.Because transactions is thread local, multi-part write should be done in one transaction.
Examples
use std::io::prelude::*; use std::io::SeekFrom; let mut file = OpenOptions::new() .create(true) .open(&mut repo, "/foo.txt")?; file.write_all(b"foo ")?; file.write_all(b"bar")?; file.finish()?; let mut content = String::new(); file.seek(SeekFrom::Start(0))?; file.read_to_string(&mut content)?; assert_eq!(content, "foo bar");
-
Single-part Write
This can be done by calling
write_once
, which will callfinish
internally to create a new version. Unless this method was successfully returned, no data will be written to the file.Examples
use std::io::{Read, Seek, SeekFrom}; let mut file = OpenOptions::new() .create(true) .open(&mut repo, "/foo.txt")?; file.write_once(b"foo bar")?; let mut content = String::new(); file.seek(SeekFrom::Start(0))?; file.read_to_string(&mut content)?; assert_eq!(content, "foo bar");
To gurantee atomicity, ZboxFS uses transaction when updating file so the data either be wholly persisted or nothing has been written.
- For multi-part write, the transaction begins in the first-time
write
and will be committed infinish
. Any failure inwrite
will abort the transaction, thusfinish
should not be called after that. If error happened duringfinish
, the transaction will also be aborted. - For single-part write,
write_once
itself is transactional. The transaction begins and will be committed inside this method.
Keep in mind of those characteristics, especially when writing a large amount of data to file, because any uncomitted transactions will abort and data in those transactions won’t be persisted.
Reading
As File
can contain multiple versions, Read
operation can be
associated with different versions. By default, reading on File
object is
always bound to the latest version. To read a specific version, a
VersionReader
, which supports Read
trait as well, can be used.
Examples
Read the file content while it is in writing, notice that reading is always bound to latest content version.
use std::io::prelude::*;
use std::io::SeekFrom;
// create a file and write data to it
let mut file = OpenOptions::new().create(true).open(&mut repo, "/foo.txt")?;
file.write_once(&[1, 2, 3, 4, 5, 6])?;
// read the first 2 bytes
let mut buf = [0; 2];
file.seek(SeekFrom::Start(0))?;
file.read_exact(&mut buf)?;
assert_eq!(&buf[..], &[1, 2]);
// create a new version, now the file content is [1, 2, 7, 8, 5, 6]
file.write_once(&[7, 8])?;
// notice that reading is on the latest version
file.seek(SeekFrom::Current(-2))?;
file.read_exact(&mut buf)?;
assert_eq!(&buf[..], &[7, 8]);
Read multiple versions using VersionReader
.
use std::io::prelude::*;
// create a file and write 2 versions
let mut file = OpenOptions::new()
.version_limit(4)
.create(true)
.open(&mut repo, "/foo.txt")?;
file.write_once(b"foo")?;
file.write_once(b"bar")?;
// get latest version number
let curr_ver = file.curr_version()?;
// create a version reader and read latest version of content
let mut rdr = file.version_reader(curr_ver)?;
let mut content = String::new();
rdr.read_to_string(&mut content)?;
assert_eq!(content, "foobar");
// create another version reader and read previous version of content
let mut rdr = file.version_reader(curr_ver - 1)?;
let mut content = String::new();
rdr.read_to_string(&mut content)?;
assert_eq!(content, "foo");
Implementations
Returns the current content version number.
Complete multi-part write to file and create a new version.
This method will try to commit the transaction internally, no data will
be persisted if it failed. Do not call this method if any previous
write
failed.
Errors
Calling this method without writing data before will return
Error::NotWrite
error.
Truncates or extends the underlying file, create a new version of
content which size to become size
.
If the size is less than the current content size, then the new
content will be shrunk. If it is greater than the current content size,
then the content will be extended to size
and have all of the
intermediate data filled in with 0s.
This method is atomic.
Errors
This method will return an error if the file is not opened for writing or not finished writing.
Trait Implementations
Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
Like read
, except that it reads into a slice of buffers. Read more
can_vector
)Determines if this Read
er has an efficient read_vectored
implementation. Read more
read_initializer
)Determines if this Read
er can work with buffers of uninitialized
memory. Read more
Read all bytes until EOF in this source, placing them into buf
. Read more
Read all bytes until EOF in this source, appending them to buf
. Read more
Read the exact number of bytes required to fill buf
. Read more
Creates a “by reference” adapter for this instance of Read
. Read more
Creates an adapter which will chain this stream with another. Read more
Write a buffer into this writer, returning how many bytes were written. Read more
Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
can_vector
)Determines if this Write
r has an efficient write_vectored
implementation. Read more
Attempts to write an entire buffer into this writer. Read more
write_all_vectored
)Attempts to write multiple buffers into this writer. Read more
Writes a formatted string into this writer, returning any error encountered. Read more
Auto Trait Implementations
impl RefUnwindSafe for File
impl UnwindSafe for File
Blanket Implementations
Mutably borrows from an owned value. Read more
Reads an unsigned 8 bit integer from the underlying reader. Read more
Reads a signed 8 bit integer from the underlying reader. Read more
Reads an unsigned 16 bit integer from the underlying reader. Read more
Reads a signed 16 bit integer from the underlying reader. Read more
Reads an unsigned 24 bit integer from the underlying reader. Read more
Reads a signed 24 bit integer from the underlying reader. Read more
Reads an unsigned 32 bit integer from the underlying reader. Read more
Reads a signed 32 bit integer from the underlying reader. Read more
Reads an unsigned 48 bit integer from the underlying reader. Read more
Reads a signed 48 bit integer from the underlying reader. Read more
Reads an unsigned 64 bit integer from the underlying reader. Read more
Reads a signed 64 bit integer from the underlying reader. Read more
Reads an unsigned 128 bit integer from the underlying reader. Read more
Reads a signed 128 bit integer from the underlying reader. Read more
Reads an unsigned n-bytes integer from the underlying reader. Read more
Reads a signed n-bytes integer from the underlying reader. Read more
fn read_uint128<T>(&mut self, nbytes: usize) -> Result<u128, Error> where
T: ByteOrder,
fn read_uint128<T>(&mut self, nbytes: usize) -> Result<u128, Error> where
T: ByteOrder,
Reads an unsigned n-bytes integer from the underlying reader.
fn read_int128<T>(&mut self, nbytes: usize) -> Result<i128, Error> where
T: ByteOrder,
fn read_int128<T>(&mut self, nbytes: usize) -> Result<i128, Error> where
T: ByteOrder,
Reads a signed n-bytes integer from the underlying reader.
Reads a IEEE754 single-precision (4 bytes) floating point number from the underlying reader. Read more
Reads a IEEE754 double-precision (8 bytes) floating point number from the underlying reader. Read more
Reads a sequence of unsigned 16 bit integers from the underlying reader. Read more
Reads a sequence of unsigned 32 bit integers from the underlying reader. Read more
Reads a sequence of unsigned 64 bit integers from the underlying reader. Read more
Reads a sequence of unsigned 128 bit integers from the underlying reader. Read more
Reads a sequence of signed 8 bit integers from the underlying reader. Read more
Reads a sequence of signed 16 bit integers from the underlying reader. Read more
Reads a sequence of signed 32 bit integers from the underlying reader. Read more
Reads a sequence of signed 64 bit integers from the underlying reader. Read more
Reads a sequence of signed 128 bit integers from the underlying reader. Read more
Reads a sequence of IEEE754 single-precision (4 bytes) floating point numbers from the underlying reader. Read more
Reads a sequence of IEEE754 double-precision (8 bytes) floating point numbers from the underlying reader. Read more
Writes an unsigned 8 bit integer to the underlying writer. Read more
Writes a signed 8 bit integer to the underlying writer. Read more
Writes an unsigned 16 bit integer to the underlying writer. Read more
Writes a signed 16 bit integer to the underlying writer. Read more
Writes an unsigned 24 bit integer to the underlying writer. Read more
Writes a signed 24 bit integer to the underlying writer. Read more
Writes an unsigned 32 bit integer to the underlying writer. Read more
Writes a signed 32 bit integer to the underlying writer. Read more
Writes an unsigned 48 bit integer to the underlying writer. Read more
Writes a signed 48 bit integer to the underlying writer. Read more
Writes an unsigned 64 bit integer to the underlying writer. Read more
Writes a signed 64 bit integer to the underlying writer. Read more
fn write_u128<T>(&mut self, n: u128) -> Result<(), Error> where
T: ByteOrder,
fn write_u128<T>(&mut self, n: u128) -> Result<(), Error> where
T: ByteOrder,
Writes an unsigned 128 bit integer to the underlying writer.
fn write_i128<T>(&mut self, n: i128) -> Result<(), Error> where
T: ByteOrder,
fn write_i128<T>(&mut self, n: i128) -> Result<(), Error> where
T: ByteOrder,
Writes a signed 128 bit integer to the underlying writer.
Writes an unsigned n-bytes integer to the underlying writer. Read more
Writes a signed n-bytes integer to the underlying writer. Read more
Writes an unsigned n-bytes integer to the underlying writer. Read more
Writes a signed n-bytes integer to the underlying writer. Read more
Writes a IEEE754 single-precision (4 bytes) floating point number to the underlying writer. Read more