tap_reader/

lib.rs

//! Tapped reader
//!
//! Wraps an existing reader and copies the read bytes into it's own buffer
//!
//! This can be useful for when you are deserializing a stream of bytes, and want to be able to
//! provide the original input for log messages, error messages, etc
//!
//! # Example
//!
//! ```
//! extern crate tap_reader;
//! extern crate serde_json;
//! extern crate serde;
//! #[macro_use] extern crate serde_derive;
//!
//! # use std::error::Error;
//! use std::io::Cursor;
//! use tap_reader::Tap;
//!
//! # fn main() -> Result<(), ()> {
//! #[derive(Debug, Deserialize, PartialEq)]
//! struct Foo {
//!     foo: String,
//!     bar: usize,
//! }
//!
//! let input = r#"{"foo":"hello, world!","bar":42}"#;
//! let bytes = input.as_bytes();
//! let reader = Cursor::new(bytes);
//! let mut reader = Tap::new(reader);

//! let foo: Foo = match serde_json::from_reader(&mut reader) {
//!     Ok(foo) => foo,
//!     Err(e) => {
//!         eprintln!("Error serializing Foo from input: '{}'\n error was: {}",
//!                   String::from_utf8_lossy(&reader.bytes),
//!                   e.description());
//!         return Err(());
//!     }
//! };
//! assert_eq!(foo, Foo { foo: "hello, world!".to_string(), bar: 42 });
//! assert_eq!(reader.bytes, bytes);
//! #   Ok(())
//! # }
//!
//! ```
//!
//! ```
//! extern crate tap_reader;
//!
//! use std::io::{Cursor, Read};
//!
//! use tap_reader::Tap;
//!
//! # fn main() -> ::std::io::Result<()> {
//! let input = "hello, world!".to_string();
//! let bytes = input.as_bytes();
//! let cursor = Cursor::new(bytes);
//! let mut reader = Tap::new(cursor);
//!
//! let mut output = String::new();
//!
//! reader.read_to_string(&mut output)?;
//!
//! assert_eq!(output, input);
//! assert_eq!(bytes, &reader.bytes[..]);
//!
//! #     Ok(())
//! # }
//! ```

#[cfg(test)]
extern crate serde;
#[cfg(test)]
extern crate serde_json;

#[cfg(test)]
#[cfg_attr(test, macro_use)]
extern crate serde_derive;

use std::io::{self, Read};

/// `Read` adaptor
///
/// Takes a `Read` as input and copies all read bytes into it's own buffer
///
/// # Example
///
/// ```
/// # extern crate tap_reader;
/// use tap_reader::Tap;
/// # use std::io;
/// use std::io::{Cursor, Read};
///
/// # fn main() -> io::Result<()> {
/// let input = "hello, world!";
/// let bytes = input.as_bytes();
/// let cursor = Cursor::new(bytes);
/// let mut reader = Tap::new(cursor);
///
/// let mut output = String::new();
/// reader.read_to_string(&mut output)?;
///
/// assert_eq!(output, String::from_utf8_lossy(&reader.bytes));
/// #   Ok(())
/// # }
/// ```
pub struct Tap<R> {
    pub bytes: Vec<u8>,
    reader: R,
}

impl<R: Read> Tap<R> {
    /// Construct a `Tap` reader from an existing reader
    ///
    /// # Example
    ///
    /// ```
    /// # extern crate tap_reader;
    /// use std::io::Cursor;
    /// use tap_reader::Tap;
    /// let input = "hello, world!";
    /// let bytes = input.as_bytes();
    /// let cursor = Cursor::new(bytes);
    /// let mut reader = Tap::new(cursor);
    /// ```
    pub fn new(r: R) -> Tap<R> {
        Tap { bytes: vec![], reader: r }
    }
}

impl<R: Read> Read for Tap<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let num = self.reader.read(buf)?;
        self.bytes.extend_from_slice(&buf[..num]);
        Ok(num)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Cursor;

    #[derive(Deserialize, Debug, PartialEq)]
    struct Foo {
        foo: String,
        bar: u64,
    }

    #[test]
    fn tap_serde_deser() {
        let input = r#"{"foo":"hello, world!","bar":42}"#;
        let bytes = input.as_bytes();
        let reader = Cursor::new(bytes);
        let mut reader = Tap::new(reader);

        let foo: Foo = serde_json::from_reader(&mut reader).expect("Couldn't deserialize");
        assert_eq!(
            foo,
            Foo {
                foo: "hello, world!".to_string(),
                bar: 42
            }
        );
        assert_eq!(reader.bytes, bytes);
    }

    #[test]
    fn tap_cursor() {
        let s = String::from("foo bar");
        let bytes = s.as_bytes();
        let reader = Cursor::new(bytes);

        let mut reader = Tap::new(reader);

        let mut output = String::new();
        reader.read_to_string(&mut output).expect("Could not read");

        let tapped = reader.bytes;
        assert_eq!(output, String::from_utf8(bytes.to_vec()).expect("Couldn't create string from bytes"));
        assert_eq!(tapped, bytes);
    }

    #[test]
    fn test_large_string() {
        let text = r#"Demicyclic Disease: Because there is no repeating stage in the life cycle of demicyclic
        fungi, removal of the primary or the alternate host will disrupt the disease cycle. This method, however,
        is not highly effective in managing all demicyclic diseases. Cedar-apple rust disease, for example, can
        persist despite removal of one of the hosts since spores can be disseminated from long distances. The 
        severity of Cedar-apple rust disease can be managed by removal of basidiospore producing galls from 
        junipers or the application of protective fungicides to junipers."#;

        let bytes = text.as_bytes();
        let cursor = Cursor::new(bytes);
        let mut reader = Tap::new(cursor);

        let mut output = String::new();
        reader.read_to_string(&mut output).expect("Could not read");

        let tapped = reader.bytes;
        assert_eq!(output, String::from_utf8(bytes.to_vec()).expect("Couldn't create string from bytes"));
        assert_eq!(tapped, bytes);
    }
}