// Copyright 2019-2021 Parity Technologies (UK) Ltd.
//
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//! Utility methods relying on hyper

use crate::error::GenericTransportError;
use futures_util::stream::StreamExt;

/// Read a data from a [`hyper::Body`] and return the data if it is valid and within the allowed size range.
///
/// Returns `Ok((bytes, single))` if the body was in valid size range; and a bool indicating whether the JSON-RPC
/// request is a single or a batch.
/// Returns `Err` if the body was too large or the body couldn't be read.
pub async fn read_body(
	headers: &hyper::HeaderMap,
	mut body: hyper::Body,
	max_request_body_size: u32,
) -> Result<(Vec<u8>, bool), GenericTransportError<hyper::Error>> {
	// NOTE(niklasad1): Values bigger than `u32::MAX` will be turned into zero here. This is unlikely to occur in
	// practice and for that case we fallback to allocating in the while-loop below instead of pre-allocating.
	let body_size = read_header_content_length(headers).unwrap_or(0);

	if body_size > max_request_body_size {
		return Err(GenericTransportError::TooLarge);
	}

	let first_chunk =
		body.next().await.ok_or(GenericTransportError::Malformed)?.map_err(GenericTransportError::Inner)?;

	if first_chunk.len() > max_request_body_size as usize {
		return Err(GenericTransportError::TooLarge);
	}

	let first_non_whitespace = first_chunk.iter().find(|byte| !byte.is_ascii_whitespace());

	let single = match first_non_whitespace {
		Some(b'{') => true,
		Some(b'[') => false,
		_ => return Err(GenericTransportError::Malformed),
	};

	let mut received_data = Vec::with_capacity(body_size as usize);
	received_data.extend_from_slice(&first_chunk);

	while let Some(chunk) = body.next().await {
		let chunk = chunk.map_err(GenericTransportError::Inner)?;
		let body_length = chunk.len() + received_data.len();
		if body_length > max_request_body_size as usize {
			return Err(GenericTransportError::TooLarge);
		}
		received_data.extend_from_slice(&chunk);
	}
	Ok((received_data, single))
}

/// Read the `Content-Length` HTTP Header. Must fit into a `u32`; returns `None` otherwise.
///
/// NOTE: There's no specific hard limit on `Content_length` in HTTP specification.
/// Thus this method might reject valid `content_length`
fn read_header_content_length(headers: &hyper::header::HeaderMap) -> Option<u32> {
	let length = read_header_value(headers, "content-length")?;
	// HTTP Content-Length indicates number of bytes in decimal.
	length.parse::<u32>().ok()
}

/// Returns a string value when there is exactly one value for the given header.
pub fn read_header_value<'a>(headers: &'a hyper::header::HeaderMap, header_name: &str) -> Option<&'a str> {
	let mut values = headers.get_all(header_name).iter();
	let val = values.next()?;
	if values.next().is_none() {
		val.to_str().ok()
	} else {
		None
	}
}

/// Returns an iterator of all values for a given a header name
pub fn read_header_values<'a>(
	headers: &'a hyper::header::HeaderMap,
	header_name: &str,
) -> hyper::header::GetAll<'a, hyper::header::HeaderValue> {
	headers.get_all(header_name)
}

/// Get the header values from the `access-control-request-headers` header.
pub fn get_cors_request_headers<'a>(headers: &'a hyper::header::HeaderMap) -> impl Iterator<Item = &str> {
	const ACCESS_CONTROL_REQUEST_HEADERS: &str = "access-control-request-headers";

	read_header_values(headers, ACCESS_CONTROL_REQUEST_HEADERS)
		.iter()
		.filter_map(|val| val.to_str().ok())
		.flat_map(|val| val.split(','))
		// The strings themselves might contain leading and trailing whitespaces
		.map(|s| s.trim())
}

#[cfg(test)]
mod tests {
	use super::{get_cors_request_headers, read_body, read_header_content_length};

	#[tokio::test]
	async fn body_to_bytes_size_limit_works() {
		let headers = hyper::header::HeaderMap::new();
		let body = hyper::Body::from(vec![0; 128]);
		assert!(read_body(&headers, body, 127).await.is_err());
	}

	#[test]
	fn read_content_length_works() {
		let mut headers = hyper::header::HeaderMap::new();
		headers.insert(hyper::header::CONTENT_LENGTH, "177".parse().unwrap());
		assert_eq!(read_header_content_length(&headers), Some(177));

		headers.append(hyper::header::CONTENT_LENGTH, "999".parse().unwrap());
		assert_eq!(read_header_content_length(&headers), None);
	}

	#[test]
	fn read_content_length_too_big_value() {
		let mut headers = hyper::header::HeaderMap::new();
		headers.insert(hyper::header::CONTENT_LENGTH, "18446744073709551616".parse().unwrap());
		assert_eq!(read_header_content_length(&headers), None);
	}

	#[test]
	fn get_cors_headers_works() {
		let mut headers = hyper::header::HeaderMap::new();

		// access-control-request-headers
		headers.insert(hyper::header::ACCESS_CONTROL_REQUEST_HEADERS, "Content-Type,x-requested-with".parse().unwrap());

		let values: Vec<&str> = get_cors_request_headers(&headers).collect();
		assert_eq!(values, vec!["Content-Type", "x-requested-with"]);

		headers.insert(
			hyper::header::ACCESS_CONTROL_REQUEST_HEADERS,
			"Content-Type,               x-requested-with                  ".parse().unwrap(),
		);

		let values: Vec<&str> = get_cors_request_headers(&headers).collect();
		assert_eq!(values, vec!["Content-Type", "x-requested-with"]);
	}
}