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#![crate_name = "bodyparser"]

//! Body Parser Plugin for Iron
//!
//! This plugin parses JSON out of an incoming Request.

extern crate iron;
extern crate rustc_serialize;
extern crate plugin;
extern crate persistent;

use rustc_serialize::{json, Decodable};

use iron::mime;
use iron::prelude::*;
use iron::headers;
use iron::typemap::{Key};
use std::io::Read;
use std::any::Any;
use std::marker;

pub use self::errors::{BodyError, BodyErrorCause};
pub use self::limit_reader::{LimitReader};

mod errors;
mod limit_reader;

fn read_body_as_utf8(req: &mut Request, limit: usize) -> Result<String, errors::BodyError> {
    let mut bytes = Vec::new();
    match LimitReader::new(req.body.by_ref(), limit).read_to_end(&mut bytes) {
        Ok(_) => {
             match String::from_utf8(bytes) {
                Ok(e) => Ok(e),
                Err(err) => Err(errors::BodyError {
                    detail: "Invalid UTF-8 sequence".to_string(),
                    cause: errors::BodyErrorCause::Utf8Error(err.utf8_error())
                })
            }
        },
        Err(err) => Err(errors::BodyError {
            detail: "Can't read request body".to_string(),
            cause: errors::BodyErrorCause::IoError(err)
        })
    }
}

/// Use this key to modify the default body limit.
pub struct MaxBodyLength;
impl Key for MaxBodyLength {
    type Value = usize;
}

/// Raw is a plugin to read a request body into UTF-8 String.
/// Doesn't read `multipart/form-data`.
pub struct Raw;

impl Key for Raw {
    type Value = Option<String>;
}

const DEFAULT_BODY_LIMIT: usize = 1024 * 1024 * 100;

impl<'a, 'b> plugin::Plugin<Request<'a, 'b>> for Raw {
    type Error = BodyError;

    fn eval(req: &mut Request) -> Result<Option<String>, BodyError> {
        let need_read = req.headers.get::<headers::ContentType>().map(|header| {
            match **header {
                mime::Mime(mime::TopLevel::Multipart, mime::SubLevel::FormData, _) => false,
                _ => true
            }
        }).unwrap_or(false);

        if need_read {
            let max_length = req
                .get::<persistent::Read<MaxBodyLength>>()
                .ok()
                .map(|x| *x)
                .unwrap_or(DEFAULT_BODY_LIMIT);

            let body = try!(read_body_as_utf8(req, max_length));
            Ok(Some(body))
        } else {
            Ok(None)
        }
    }
}

/// Json is a plugin to parse a request body into JSON.
/// Uses Raw plugin to parse the body with limit.
#[derive(Clone)]
pub struct Json;
impl Key for Json {
    type Value = Option<json::Json>;
}

impl<'a, 'b> plugin::Plugin<Request<'a, 'b>> for Json {
    type Error = BodyError;

    fn eval(req: &mut Request) -> Result<Option<json::Json>, BodyError> {
        req.get::<Raw>()
            .and_then(|maybe_body| {
                reverse_option(maybe_body.map(|body| body.parse()))
                    .map_err(|err| {
                        BodyError {
                            detail: "Can't parse body to JSON".to_string(),
                            cause: BodyErrorCause::ParserError(err)
                        }
                    })
            })
    }
}

/// Struct is a plugin to parse a request body into a struct.
/// Uses Raw plugin to parse the body with limit.
pub struct Struct<T: Decodable> {
    marker: marker::PhantomData<T>
}
impl<T> Key for Struct<T> where T: Decodable + Any {
    type Value = Option<T>;
}

impl<'a, 'b, T> plugin::Plugin<Request<'a, 'b>> for Struct<T>
where T: Decodable + Any {
    type Error = BodyError;

    fn eval(req: &mut Request) -> Result<Option<T>, BodyError> {
        req.get::<Json>()
            .and_then(|maybe_body| {
                reverse_option(maybe_body.map(|body| Decodable::decode(&mut json::Decoder::new(body))))
                    .map_err(|err| BodyError {
                        detail: "Can't parse body to the struct".to_string(),
                        cause: BodyErrorCause::DecoderError(err)
                    })
            })
    }
}

fn reverse_option<T,E>(value: Option<Result<T, E>>) -> Result<Option<T>, E> {
    match value {
        Some(Ok(val)) => Ok(Some(val)),
        Some(Err(err)) => Err(err),
        None => Ok(None),
    }
}