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    // Copyright 2015-2017 Parity Technologies (UK) Ltd.
    // This file is part of Parity.

    // Parity is free software: you can redistribute it and/or modify
    // it under the terms of the GNU General Public License as published by
    // the Free Software Foundation, either version 3 of the License, or
    // (at your option) any later version.

    // Parity is distributed in the hope that it will be useful,
    // but WITHOUT ANY WARRANTY; without even the implied warranty of
    // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    // GNU General Public License for more details.

    // You should have received a copy of the GNU General Public License
    // along with Parity.  If not, see <http://www.gnu.org/licenses/>.

    use time::{self, Duration};

    use hyper::header;
    use hyper::server;
    use hyper::uri::RequestUri;
    use hyper::net::HttpStream;
    use hyper::status::StatusCode;
    use hyper::{Decoder, Encoder, Next};
    use endpoint::EndpointPath;
    use handlers::{ContentHandler, add_security_headers};

    /// Represents a file that can be sent to client.
    /// Implementation should keep track of bytes already sent internally.
    pub trait DappFile: Send {
    	/// Returns a content-type of this file.
    	fn content_type(&self) -> &str;

    	/// Checks if all bytes from that file were written.
    	fn is_drained(&self) -> bool;

    	/// Fetch next chunk to write to the client.
    	fn next_chunk(&mut self) -> &[u8];

    	/// How many files have been written to the client.
    	fn bytes_written(&mut self, bytes: usize);
    }

    /// Dapp as a (dynamic) set of files.
    pub trait Dapp: Send + 'static {
    	/// File type
    	type DappFile: DappFile;

    	/// Returns file under given path.
    	fn file(&self, path: &str) -> Option<Self::DappFile>;
    }

    /// Currently served by `PageHandler` file
    pub enum ServedFile<T: Dapp> {
    	/// File from dapp
    	File(T::DappFile),
    	/// Error (404)
    	Error(ContentHandler),
    }

    impl<T: Dapp> ServedFile<T> {
    	pub fn new(embeddable_on: Option<(String, u16)>) -> Self {
    		ServedFile::Error(ContentHandler::error(
    			StatusCode::NotFound,
    			"404 Not Found",
    			"Requested dapp resource was not found.",
    			None,
    			embeddable_on,
    		))
    	}
    }

    /// Defines what cache headers should be appended to returned resources.
    #[derive(Debug, Copy, Clone, PartialEq)]
    pub enum PageCache {
    	Enabled,
    	Disabled,
    }

    impl Default for PageCache {
    	fn default() -> Self {
    		PageCache::Disabled
    	}
    }

    /// A generic type for `PageHandler` allowing to set the URL.
    /// Used by dapps fetching to set the URL after the content was downloaded.
    pub trait PageHandlerWaiting: server::Handler<HttpStream> + Send {
    	fn set_uri(&mut self, uri: &RequestUri);
    }

    /// A handler for a single webapp.
    /// Resolves correct paths and serves as a plumbing code between
    /// hyper server and dapp.
    pub struct PageHandler<T: Dapp> {
    	/// A Dapp.
    	pub app: T,
    	/// File currently being served
    	pub file: ServedFile<T>,
    	/// Optional prefix to strip from path.
    	pub prefix: Option<String>,
    	/// Requested path.
    	pub path: EndpointPath,
    	/// Flag indicating if the file can be safely embeded (put in iframe).
    	pub safe_to_embed_on: Option<(String, u16)>,
    	/// Cache settings for this page.
    	pub cache: PageCache,
    }

    impl<T: Dapp> PageHandlerWaiting for PageHandler<T> {
    	fn set_uri(&mut self, uri: &RequestUri) {
    		trace!(target: "dapps", "Setting URI: {:?}", uri);
    		self.file = match *uri {
    			RequestUri::AbsolutePath { ref path, .. } => {
    				self.app.file(&self.extract_path(path))
    			},
    			RequestUri::AbsoluteUri(ref url) => {
    				self.app.file(&self.extract_path(url.path()))
    			},
    			_ => None,
    		}.map_or_else(|| ServedFile::new(self.safe_to_embed_on.clone()), |f| ServedFile::File(f));
    	}
    }

    impl<T: Dapp> PageHandler<T> {
    	fn extract_path(&self, path: &str) -> String {
    		let app_id = &self.path.app_id;
    		let prefix = "/".to_owned() + self.prefix.as_ref().unwrap_or(app_id);
    		let prefix_with_slash = prefix.clone() + "/";
    		let query_pos = path.find('?').unwrap_or_else(|| path.len());

    		// Index file support
    		match path == "/" || path == &prefix || path == &prefix_with_slash {
    			true => "index.html".to_owned(),
    			false => if path.starts_with(&prefix_with_slash) {
    				path[prefix_with_slash.len()..query_pos].to_owned()
    			} else if path.starts_with("/") {
    				path[1..query_pos].to_owned()
    			} else {
    				path[0..query_pos].to_owned()
    			}
    		}
    	}
    }

    impl<T: Dapp> server::Handler<HttpStream> for PageHandler<T> {
    	fn on_request(&mut self, req: server::Request<HttpStream>) -> Next {
    		self.set_uri(req.uri());
    		Next::write()
    	}

    	fn on_request_readable(&mut self, _decoder: &mut Decoder<HttpStream>) -> Next {
    		Next::write()
    	}

    	fn on_response(&mut self, res: &mut server::Response) -> Next {
    		match self.file {
    			ServedFile::File(ref f) => {
    				res.set_status(StatusCode::Ok);

    				if let PageCache::Enabled = self.cache {
    					let mut headers = res.headers_mut();
    					let validity = Duration::days(365);
    					headers.set(header::CacheControl(vec![
    						header::CacheDirective::Public,
    						header::CacheDirective::MaxAge(validity.num_seconds() as u32),
    					]));
    					headers.set(header::Expires(header::HttpDate(time::now() + validity)));
    				}

    				match f.content_type().parse() {
    					Ok(mime) => res.headers_mut().set(header::ContentType(mime)),
    					Err(()) => debug!(target: "dapps", "invalid MIME type: {}", f.content_type()),
    				}

    				// Security headers:
    				add_security_headers(&mut res.headers_mut(), self.safe_to_embed_on.clone());
    				Next::write()
    			},
    			ServedFile::Error(ref mut handler) => {
    				handler.on_response(res)
    			}
    		}
    	}

    	fn on_response_writable(&mut self, encoder: &mut Encoder<HttpStream>) -> Next {
    		match self.file {
    			ServedFile::Error(ref mut handler) => handler.on_response_writable(encoder),
    			ServedFile::File(ref f) if f.is_drained() => Next::end(),
    			ServedFile::File(ref mut f) => match encoder.write(f.next_chunk()) {
    				Ok(bytes) => {
    					f.bytes_written(bytes);
    					Next::write()
    				},
    				Err(e) => match e.kind() {
    					::std::io::ErrorKind::WouldBlock => Next::write(),
    					_ => Next::end(),
    				},
    			}
    		}
    	}
    }

    #[cfg(test)]
    mod test {
    	use super::*;

    	pub struct TestWebAppFile;

    	impl DappFile for TestWebAppFile {
    		fn content_type(&self) -> &str {
    			unimplemented!()
    		}

    		fn is_drained(&self) -> bool {
    			unimplemented!()
    		}

    		fn next_chunk(&mut self) -> &[u8] {
    			unimplemented!()
    		}

    		fn bytes_written(&mut self, _bytes: usize) {
    			unimplemented!()
    		}
    	}

    	#[derive(Default)]
    	pub struct TestWebapp;

    	impl Dapp for TestWebapp {
    		type DappFile = TestWebAppFile;

    		fn file(&self, _path: &str) -> Option<Self::DappFile> {
    			None
    		}
    	}
    }

    #[test]
    fn should_extract_path_with_appid() {

    	// given
    	let path1 = "/";
    	let path2= "/test.css";
    	let path3 = "/app/myfile.txt";
    	let path4 = "/app/myfile.txt?query=123";
    	let page_handler = PageHandler {
    		app: test::TestWebapp,
    		prefix: None,
    		path: EndpointPath {
    			app_id: "app".to_owned(),
    			host: "".to_owned(),
    			port: 8080,
    			using_dapps_domains: true,
    		},
    		file: ServedFile::new(None),
    		cache: Default::default(),
    		safe_to_embed_on: None,
    	};

    	// when
    	let res1 = page_handler.extract_path(path1);
    	let res2 = page_handler.extract_path(path2);
    	let res3 = page_handler.extract_path(path3);
    	let res4 = page_handler.extract_path(path4);

    	// then
    	assert_eq!(&res1, "index.html");
    	assert_eq!(&res2, "test.css");
    	assert_eq!(&res3, "myfile.txt");
    	assert_eq!(&res4, "myfile.txt");
    }

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