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//! This crate allows you to specify an offset for reads and writes, without changing the current //! position in a file. This is similar to [`pread()` and `pwrite()`][pread] in C. //! //! The major advantages of this type of I/O are: //! //! * You don't need to seek before doing a random-access read or write, which is convenient. //! * Reads don't modify the file at all, so don't require mutability. //! //! [pread]: http://man7.org/linux/man-pages/man2/pread.2.html //! //! The repository is at https://github.com/vasi/positioned-io //! //! //! # Examples //! //! Read the fifth 512-byte sector of a file: //! //! ```no_run //! # use std::io; //! # use std::fs::File; //! use positioned_io::ReadAt; //! //! # fn foo() -> io::Result<()> { //! // Note that file does not need to be mut! //! let file = try!(File::open("foo.data")); //! let mut buf = vec![0; 512]; //! let bytes_read = try!(file.read_at(2048, &mut buf)); //! # Ok(()) //! # } //! ``` //! //! Write an integer to the middle of a file: //! //! ```no_run //! # extern crate positioned_io; //! # extern crate byteorder; //! # use std::io; //! # use std::fs::OpenOptions; //! use positioned_io::WriteAt; //! use byteorder::{ByteOrder, LittleEndian}; //! //! # fn foo() -> io::Result<()> { //! // Put the integer in a buffer. //! let mut buf = vec![0; 4]; //! LittleEndian::write_u32(&mut buf, 1234); //! //! // Write it to the file. //! let mut file = try!(OpenOptions::new().write(true).open("foo.data")); //! try!(file.write_all_at(1 << 20, &buf)); //! # Ok(()) //! # } //! # fn main() { foo().unwrap() } //! ``` //! //! Or, more simply: //! //! ```no_run //! # extern crate positioned_io; //! # extern crate byteorder; //! # use std::io; //! # use std::fs::OpenOptions; //! # use byteorder::LittleEndian; //! // Extend files with writing integers at offsets. //! use positioned_io::WriteBytesExt; //! //! # fn foo() -> io::Result<()> { //! let mut file = try!(OpenOptions::new().write(true).open("foo.data")); //! try!(file.write_u32_at::<LittleEndian>(1 << 20, 1234)); //! # Ok(()) //! # } //! # fn main() { foo().unwrap() } //! ``` //! //! Read from anything else that supports ReadAt, like a byte array: //! //! ```rust //! # extern crate positioned_io; //! # extern crate byteorder; //! # use std::io; //! # use byteorder::BigEndian; //! use positioned_io::ReadBytesExt; //! //! # fn foo() -> io::Result<()> { //! let buf = [0, 5, 254, 212, 0, 3]; //! let n = try!(buf.as_ref().read_i16_at::<BigEndian>(2)); //! assert_eq!(n, -300); //! # Ok(()) //! # } //! # fn main() { foo().unwrap() } //! ``` mod byteorder; pub use byteorder::{ReadBytesExt, WriteBytesExt}; pub use byteorder::byteio::{ByteIo, ReadInt, WriteInt, ReadIntAt, WriteIntAt}; mod cursor; pub use cursor::{Cursor, SizeCursor}; mod slice; pub use slice::Slice; extern crate byteorder as extbyteorder; use std::io::{Error, ErrorKind, Result}; use std::fs::File; /// Trait for reading at an offset. /// /// Implementations should be able to read bytes without changing any sort of read-position. /// Self should not change at all. Buffering reads is unlikely to be useful, since each time /// `read_at()` is called, the position may be completely different. /// /// # Examples /// /// Read the fifth 512-byte sector of a file: /// /// ```no_run /// # use std::io; /// # use std::fs::File; /// use positioned_io::ReadAt; /// /// # fn foo() -> io::Result<()> { /// let file = try!(File::open("foo.data")); /// let mut buf = vec![0; 512]; /// let bytes_read = try!(file.read_at(2048, &mut buf)); /// # Ok(()) /// # } /// ``` pub trait ReadAt { /// Read bytes from an offset in this source into a buffer, returning how many bytes were read. /// /// This function may yield fewer bytes than the size of `buf`, if it was interrupted or hit /// end-of-file. /// /// See [`Read::read()`](https://doc.rust-lang.org/std/io/trait.Read.html#tymethod.read). fn read_at(&self, pos: u64, buf: &mut [u8]) -> Result<usize>; /// Read the exact number of bytes required to fill `buf`, from an offset. /// /// If only a lesser number of bytes can be read, will yield an error. fn read_exact_at(&self, mut pos: u64, mut buf: &mut [u8]) -> Result<()> { while !buf.is_empty() { match self.read_at(pos, buf) { Ok(0) => break, Ok(n) => { let tmp = buf; buf = &mut tmp[n..]; pos += n as u64; } Err(ref e) if e.kind() == ErrorKind::Interrupted => {} Err(e) => return Err(e), } } if !buf.is_empty() { Err(Error::new(ErrorKind::UnexpectedEof, "failed to fill whole buffer")) } else { Ok(()) } } } /// Trait for writing at an offset. /// /// Implementations should be able to write bytes at an offset, without changing any sort of /// write-position. Self should not change at all. /// /// # Examples /// /// ```no_run /// # extern crate positioned_io; /// # extern crate byteorder; /// # use std::io; /// # use std::fs::OpenOptions; /// use positioned_io::WriteAt; /// use byteorder::{ByteOrder, LittleEndian}; /// /// # fn foo() -> io::Result<()> { /// // Put the integer in a buffer. /// let mut buf = vec![0; 4]; /// LittleEndian::write_u32(&mut buf, 1234); /// /// // Write it to the file. /// let mut file = try!(OpenOptions::new().write(true).open("foo.data")); /// try!(file.write_all_at(1 << 20, &buf)); /// # Ok(()) /// # } /// # fn main() { foo().unwrap() } /// ``` pub trait WriteAt { /// Write a buffer at an offset, returning the number of bytes written. /// /// This function may write fewer bytes than the size of `buf`, for example if it is /// interrupted. /// /// See [`Write::write()`](https://doc.rust-lang.org/std/io/trait.Write.html#tymethod.write). fn write_at(&mut self, pos: u64, buf: &[u8]) -> Result<usize>; /// Write a complete buffer at an offset. /// /// If only a lesser number of bytes can be written, will yield an error. fn write_all_at(&mut self, mut pos: u64, mut buf: &[u8]) -> Result<()> { while !buf.is_empty() { match self.write_at(pos, buf) { Ok(0) => break, Ok(n) => { let tmp = buf; buf = &tmp[n..]; pos += n as u64; } Err(ref e) if e.kind() == ErrorKind::Interrupted => {} Err(e) => return Err(e), } } Ok(()) } /// Flush this writer, ensuring that any buffered data is written. /// /// This should rarely do anything, since buffering is not very useful for positioned writes. fn flush(&mut self) -> Result<()>; } /// Trait to get the size of an I/O object. /// /// Implementing this for a ReadAt or WriteAt makes it easier for users to predict whether they /// will read past end-of-file. However, it may not be possible to implement for certain readers /// or writers that have unknown size. /// /// # Examples /// /// ```no_run /// # use std::io; /// # use std::fs::File; /// use positioned_io::Size; /// /// # fn foo() -> io::Result<()> { /// let file = try!(File::open("foo.txt")); /// let size = try!(file.size()); /// assert_eq!(size, Some(22)); /// /// // Special files probably don't have a size. /// let file = try!(File::open("/dev/stdin")); /// let size = try!(file.size()); /// assert_eq!(size, None); /// # Ok(()) /// # } /// ``` pub trait Size { /// Get the size of this object, in bytes. /// /// This function may return Ok(None) if the size is unknown, for example if a file is a pipe. /// /// If a positive value is returned, it should be the value such that reading at greater /// offsets always yields end-of-file. fn size(&self) -> Result<Option<u64>>; } impl Size for File { fn size(&self) -> Result<Option<u64>> { let md = try!(self.metadata()); if md.is_file() { Ok(Some(md.len())) } else { Ok(None) } } } // Implementation for Unix files. #[cfg(unix)] mod unix; // Implementation for Windows files. #[cfg(windows)] mod windows; // Implementation for arrays, vectors. mod array; mod vec; mod refs; #[cfg(test)] mod test;