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// Copyright (c) 2016 The Rouille developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://opensource.org/licenses/MIT>,
// at your option. All files in the project carrying such
// notice may not be copied, modified, or distributed except
// according to those terms.

//! Parsing JSON data in the body of a request.
//!
//! Returns an error if the content-type of the request is not JSON, if the JSON is malformed,
//! or if a field is missing or fails to parse.
//!
//! # Example
//!
//! ```
//! # extern crate serde;
//! # #[macro_use] extern crate serde_derive;
//! # #[macro_use] extern crate rouille;
//! # use rouille::{Request, Response};
//! # fn main() {}
//!
//! fn route_handler(request: &Request) -> Response {
//!     #[derive(Deserialize)]
//!     struct Json {
//!         field1: String,
//!         field2: i32,
//!     }
//!
//!     let json: Json = try_or_400!(rouille::input::json_input(request));
//!     Response::text(format!("field1's value is {}", json.field1))
//! }
//! ```
//!

use std::error;
use std::fmt;
use std::io::Error as IoError;
use serde;
use serde_json;
use Request;

/// Error that can happen when parsing the JSON input.
#[derive(Debug)]
pub enum JsonError {
    /// Can't parse the body of the request because it was already extracted.
    BodyAlreadyExtracted,

    /// Wrong content type.
    WrongContentType,

    /// Could not read the body from the request. Also happens if the body is not valid UTF-8.
    IoError(IoError),

    /// Error while parsing.
    ParseError(serde_json::Error),
}

impl From<IoError> for JsonError {
    fn from(err: IoError) -> JsonError {
        JsonError::IoError(err)
    }
}

impl From<serde_json::Error> for JsonError {
    fn from(err: serde_json::Error) -> JsonError {
        JsonError::ParseError(err)
    }
}

impl error::Error for JsonError {
    #[inline]
    fn description(&self) -> &str {
        match *self {
            JsonError::BodyAlreadyExtracted => {
                "the body of the request was already extracted"
            },
            JsonError::WrongContentType => {
                "the request didn't have a JSON content type"
            },
            JsonError::IoError(_) => {
                "could not read the body from the request, or could not execute the CGI program"
            },
            JsonError::ParseError(_) => {
                "error while parsing the JSON body"
            },
        }
    }

    #[inline]
    fn cause(&self) -> Option<&error::Error> {
        match *self {
            JsonError::IoError(ref e) => Some(e),
            JsonError::ParseError(ref e) => Some(e),
            _ => None
        }
    }
}

impl fmt::Display for JsonError {
    #[inline]
    fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        write!(fmt, "{}", error::Error::description(self))
    }
}

/// Attempts to parse the request's body as JSON.
///
/// Returns an error if the content-type of the request is not JSON, or if the JSON is malformed.
///
/// # Example
///
/// ```
/// # extern crate serde;
/// # #[macro_use] extern crate serde_derive;
/// # #[macro_use] extern crate rouille;
/// # use rouille::{Request, Response};
/// fn main() {}
///
/// fn route_handler(request: &Request) -> Response {
///     #[derive(Deserialize)]
///     struct Json {
///         field1: String,
///         field2: i32,
///     }
///
///     let json: Json = try_or_400!(rouille::input::json_input(request));
///     Response::text(format!("field1's value is {}", json.field1))
/// }
/// ```
///
pub fn json_input<O>(request: &Request) -> Result<O, JsonError> where O: serde::de::DeserializeOwned {
    // TODO: add an optional bytes limit

    if let Some(header) = request.header("Content-Type") {
        if !header.starts_with("application/json") {
            return Err(JsonError::WrongContentType);
        }
    } else {
        return Err(JsonError::WrongContentType);
    }

    if let Some(b) = request.data() {
        serde_json::from_reader::<_, O>(b).map_err(From::from)
    } else {
        Err(JsonError::BodyAlreadyExtracted)
    }
}