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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 zip;
    use std::{fs, fmt};
    use std::io::{self, Read, Write};
    use std::path::PathBuf;
    use fetch::{self, Mime};
    use util::H256;

    use util::sha3::sha3;
    use page::{LocalPageEndpoint, PageCache};
    use handlers::{ContentValidator, ValidatorResponse};
    use apps::manifest::{MANIFEST_FILENAME, deserialize_manifest, serialize_manifest, Manifest};

    type OnDone = Box<Fn(Option<LocalPageEndpoint>) + Send>;

    fn write_response_and_check_hash(
    	id: &str,
    	mut content_path: PathBuf,
    	filename: &str,
    	response: fetch::Response
    ) -> Result<(fs::File, PathBuf), ValidationError> {
    	// try to parse id
    	let id = id.parse().map_err(|_| ValidationError::InvalidContentId)?;

    	// check if content exists
    	if content_path.exists() {
    		warn!(target: "dapps", "Overwriting existing content at 0x{:?}", id);
    		fs::remove_dir_all(&content_path)?
    	}

    	// create directory
    	fs::create_dir_all(&content_path)?;

    	// append filename
    	content_path.push(filename);

    	// Now write the response
    	let mut file = io::BufWriter::new(fs::File::create(&content_path)?);
    	let mut reader = io::BufReader::new(response);
    	io::copy(&mut reader, &mut file)?;
    	file.flush()?;

    	// Validate hash
    	// TODO [ToDr] calculate sha3 in-flight while reading the response
    	let mut file = io::BufReader::new(fs::File::open(&content_path)?);
    	let hash = sha3(&mut file)?;
    	if id == hash {
    		Ok((file.into_inner(), content_path))
    	} else {
    		Err(ValidationError::HashMismatch {
    			expected: id,
    			got: hash,
    		})
    	}
    }

    pub struct Content {
    	id: String,
    	mime: Mime,
    	content_path: PathBuf,
    	on_done: OnDone,
    }

    impl Content {
    	pub fn new(id: String, mime: Mime, content_path: PathBuf, on_done: OnDone) -> Self {
    		Content {
    			id: id,
    			mime: mime,
    			content_path: content_path,
    			on_done: on_done,
    		}
    	}
    }

    impl ContentValidator for Content {
    	type Error = ValidationError;

    	fn validate_and_install(&self, response: fetch::Response) -> Result<ValidatorResponse, ValidationError> {
    		let validate = |content_path: PathBuf| {
    			// Create dir
    			let (_, content_path) = write_response_and_check_hash(self.id.as_str(), content_path.clone(), self.id.as_str(), response)?;

    			Ok(LocalPageEndpoint::single_file(content_path, self.mime.clone(), PageCache::Enabled))
    		};

    		// Prepare path for a file
    		let content_path = self.content_path.join(&self.id);
    		// Make sure to always call on_done (even in case of errors)!
    		let result = validate(content_path.clone());
    		// remove the file if there was an error
    		if result.is_err() {
    			// Ignore errors since the file might not exist
    			let _ = fs::remove_dir_all(&content_path);
    		}
    		(self.on_done)(result.as_ref().ok().cloned());
    		result.map(ValidatorResponse::Local)
    	}
    }

    pub struct Dapp {
    	id: String,
    	dapps_path: PathBuf,
    	on_done: OnDone,
    	embeddable_on: Option<(String, u16)>,
    }

    impl Dapp {
    	pub fn new(id: String, dapps_path: PathBuf, on_done: OnDone, embeddable_on: Option<(String, u16)>) -> Self {
    		Dapp {
    			id: id,
    			dapps_path: dapps_path,
    			on_done: on_done,
    			embeddable_on: embeddable_on,
    		}
    	}

    	fn find_manifest(zip: &mut zip::ZipArchive<fs::File>) -> Result<(Manifest, PathBuf), ValidationError> {
    		for i in 0..zip.len() {
    			let mut file = zip.by_index(i)?;

    			if !file.name().ends_with(MANIFEST_FILENAME) {
    				continue;
    			}

    			// try to read manifest
    			let mut manifest = String::new();
    			let manifest = file
    				.read_to_string(&mut manifest).ok()
    				.and_then(|_| deserialize_manifest(manifest).ok());

    			if let Some(manifest) = manifest {
    				let mut manifest_location = PathBuf::from(file.name());
    				manifest_location.pop(); // get rid of filename
    				return Ok((manifest, manifest_location));
    			}
    		}

    		Err(ValidationError::ManifestNotFound)
    	}
    }

    impl ContentValidator for Dapp {
    	type Error = ValidationError;

    	fn validate_and_install(&self, response: fetch::Response) -> Result<ValidatorResponse, ValidationError> {
    		let validate = |dapp_path: PathBuf| {
    			let (file, zip_path) = write_response_and_check_hash(self.id.as_str(), dapp_path.clone(), &format!("{}.zip", self.id), response)?;
    			trace!(target: "dapps", "Opening dapp bundle at {:?}", zip_path);
    			// Unpack archive
    			let mut zip = zip::ZipArchive::new(file)?;
    			// First find manifest file
    			let (mut manifest, manifest_dir) = Self::find_manifest(&mut zip)?;
    			// Overwrite id to match hash
    			manifest.id = self.id.clone();

    			// Unpack zip
    			for i in 0..zip.len() {
    				let mut file = zip.by_index(i)?;
    				let is_dir = file.name().chars().rev().next() == Some('/');

    				let file_path = PathBuf::from(file.name());
    				let location_in_manifest_base = file_path.strip_prefix(&manifest_dir);
    				// Create files that are inside manifest directory
    				if let Ok(location_in_manifest_base) = location_in_manifest_base {
    					let p = dapp_path.join(location_in_manifest_base);
    					// Check if it's a directory
    					if is_dir {
    						fs::create_dir_all(p)?;
    					} else {
    						let mut target = fs::File::create(p)?;
    						io::copy(&mut file, &mut target)?;
    					}
    				}
    			}

    			// Remove zip
    			fs::remove_file(&zip_path)?;

    			// Write manifest
    			let manifest_str = serialize_manifest(&manifest).map_err(ValidationError::ManifestSerialization)?;
    			let manifest_path = dapp_path.join(MANIFEST_FILENAME);
    			let mut manifest_file = fs::File::create(manifest_path)?;
    			manifest_file.write_all(manifest_str.as_bytes())?;
    			// Create endpoint
    			let endpoint = LocalPageEndpoint::new(dapp_path, manifest.clone().into(), PageCache::Enabled, self.embeddable_on.clone());
    			Ok(endpoint)
    		};

    		// Prepare directory for dapp
    		let target = self.dapps_path.join(&self.id);
    		// Validate the dapp
    		let result = validate(target.clone());
    		// remove the file if there was an error
    		if result.is_err() {
    			// Ignore errors since the file might not exist
    			let _ = fs::remove_dir_all(&target);
    		}
    		(self.on_done)(result.as_ref().ok().cloned());
    		result.map(ValidatorResponse::Local)
    	}
    }

    #[derive(Debug)]
    pub enum ValidationError {
    	Io(io::Error),
    	Zip(zip::result::ZipError),
    	InvalidContentId,
    	ManifestNotFound,
    	ManifestSerialization(String),
    	HashMismatch { expected: H256, got: H256, },
    }

    impl fmt::Display for ValidationError {
    	fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
    		match *self {
    			ValidationError::Io(ref io) => write!(f, "Unexpected IO error occured: {:?}", io),
    			ValidationError::Zip(ref zip) => write!(f, "Unable to read ZIP archive: {:?}", zip),
    			ValidationError::InvalidContentId => write!(f, "ID is invalid. It should be 256 bits keccak hash of content."),
    			ValidationError::ManifestNotFound => write!(f, "Downloaded Dapp bundle did not contain valid manifest.json file."),
    			ValidationError::ManifestSerialization(ref err) => {
    				write!(f, "There was an error during Dapp Manifest serialization: {:?}", err)
    			},
    			ValidationError::HashMismatch { ref expected, ref got } => {
    				write!(f, "Hash of downloaded content did not match. Expected:{:?}, Got:{:?}.", expected, got)
    			},
    		}
    	}
    }

    impl From<io::Error> for ValidationError {
    	fn from(err: io::Error) -> Self {
    		ValidationError::Io(err)
    	}
    }

    impl From<zip::result::ZipError> for ValidationError {
    	fn from(err: zip::result::ZipError) -> Self {
    		ValidationError::Zip(err)
    	}
    }

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