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#![warn(missing_docs)] //! Store a file's metadata for caching purposes. //! //! The [`FileHttpMetadata`] structure may be serialized and //! stored in a JSON file alongside the real file, e.g. one with //! ".meta" appended to the file name. Then either the [`match_meta`] //! function may be used directly, or the [`build_req`] one may be //! used to modify an HTTP request, adding the necessary headers to //! make sure that the file is not downloaded if there have been //! no changes on the remote server. //! //! Example for checking whether a file needs to be downloaded: //! ```rust //! # use std::error; //! use std::fs; //! # use std::io::{self, Read, Write}; //! # use std::path; //! //! # fn main() -> Result<(), Box<dyn error::Error>> { //! # let agent = ureq::agent(); //! # let tempd_obj = tempfile::tempdir()?; //! # let destdir: &path::Path = tempd_obj.as_ref(); //! let dst = destdir.join("data.json"); //! let dst_meta = destdir.join("data.json.meta"); //! let (req, stored_meta) = file_with_meta::build_req( //! agent.get("https://example.com/"), //! &dst, //! &dst_meta, //! ); //! let resp = req.call()?; //! match resp.status() { //! 304 => println!("Nothing was fetched"), //! _ => { //! println!("Storing the content"); //! /* ... */ //! # let mut reader = resp.into_reader(); //! # let mut outfile = fs::File::create(&dst)?; //! # let mut writer = io::BufWriter::new(&outfile); //! # loop { //! # let mut buf = [0; 8192]; //! # let n = reader.read(&mut buf[..])?; //! # if n == 0 { //! # break; //! # } //! # writer.write_all(&buf[..n])?; //! # } //! # writer.flush()?; //! # outfile.sync_all()?; //! //! println!("Updating the file's metadata"); //! let meta = file_with_meta::FileHttpMetadata::from_file(&dst)?; //! fs::write(&dst_meta, serde_json::to_string(&meta).unwrap())?; //! } //! }; //! # Ok(()) //! # } //! ``` //! //! Example for checking whether a file has changed since its metadata //! was last updated: //! ```rust //! let dst = "/path/to/file.dat"; //! let dst_meta = "/path/to/file.dat.meta"; //! //! match file_with_meta::match_meta(&dst, &dst_meta).is_some() { //! true => println!("No change"), //! false => println!("Somebody touched our file, recreate it?"), //! }; //! ``` //! //! The [`match_meta_with_source`] function may be used to additionally //! make sure that a "source" file has not been modified since this file //! was last generated from its data. #[doc(html_root_url = "https://docs.rs/file-with-meta/0.1.0")] /* * Copyright (c) 2021 Peter Pentchev <roam@ringlet.net> * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ use std::error; use std::fmt; use std::fs; use std::path; use std::time; use serde::{Deserialize, Serialize}; #[cfg(test)] mod tests; /// An error that occurred during loading the metadata. #[derive(Debug)] pub struct MetadataError { /// The error message. msg: String, } impl fmt::Display for MetadataError { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "{}", self.msg) } } impl error::Error for MetadataError {} impl MetadataError { /// Return a boxed error with the specified message. pub fn boxed(msg: String) -> Box<Self> { Box::new(Self { msg }) } } /// The version of the format of the serialized metadata. #[derive(Debug, Serialize, Deserialize, PartialEq)] pub struct MetadataFormatVersion { /// The major version number; bumped when a field is removed or /// its type is changed. major: u32, /// The minor version number; bumped when a new field is added. minor: u32, } impl Default for MetadataFormatVersion { /// The default format version is the most recent one. fn default() -> Self { Self { major: 0, minor: 1 } } } /// Information about the format of the JSON-serialized metadata. #[derive(Debug, Default, Serialize, Deserialize, PartialEq)] pub struct MetadataFormat { /// The version of the metadata format, currently 0.x. version: MetadataFormatVersion, } #[derive(Debug, Serialize, Deserialize)] struct MetadataTopLevelFormatOnly { format: MetadataFormat, } /// Information about a single file's last modification time and, /// if specified, some relevant HTTP headers returned by the server /// that the file was fetched from. #[derive(Debug, Default, Serialize, Deserialize, PartialEq)] pub struct FileHttpMetadata { /// The version of the metadata as stored in a JSON string. pub format: MetadataFormat, /// The size of the file. pub file_size: u64, /// The modification time of the file as a Unix timestamp. pub file_mtime: u64, /// The "Last-Modified" header as returned by an HTTP server. pub hdr_last_modified: Option<String>, /// The "ETag" header as returned by an HTTP server. pub hdr_etag: Option<String>, /// The size of the source file if applicable. pub source_file_size: Option<u64>, /// The modification time of the source file if applicable. pub source_file_mtime: Option<u64>, /// A hook for external users to store information about whether /// the file's contents has been validated. pub verified: bool, } impl FileHttpMetadata { /// Examine an existing file and return a metadata structure /// recording its size and last modification time. pub fn from_file<P>(path: P) -> Result<Self, Box<dyn error::Error>> where P: AsRef<path::Path>, { match fs::metadata(&path) { Ok(meta) => Ok(Self { file_size: meta.len(), file_mtime: mtime_to_unix(&meta), ..Self::default() }), Err(err) => Err(MetadataError::boxed(format!( "Could not examine {}: {}", path.as_ref().to_string_lossy(), err ))), } } /// Examine an existing file and return a metadata structure /// recording its size and last modification time, as well as /// that of the specified "source" file. pub fn from_file_with_source<P1, P2>(path: P1, src: P2) -> Result<Self, Box<dyn error::Error>> where P1: AsRef<path::Path>, P2: AsRef<path::Path>, { let meta = Self::from_file(path)?; match fs::metadata(&src) { Ok(src_meta) => Ok(Self { source_file_size: Some(src_meta.len()), source_file_mtime: Some(mtime_to_unix(&src_meta)), ..meta }), Err(err) => Err(MetadataError::boxed(format!( "Could not examine {}: {}", src.as_ref().to_string_lossy(), err ))), } } /// Examine an existing file and return a metadata structure /// recording its size and last modification time, as well as /// the previously-stored one for a "source" file. pub fn from_file_with_source_meta<P>( path: P, src_meta: &FileHttpMetadata, ) -> Result<Self, Box<dyn error::Error>> where P: AsRef<path::Path>, { let meta = Self::from_file(path)?; Ok(Self { source_file_size: Some(src_meta.file_size), source_file_mtime: Some(src_meta.file_mtime), ..meta }) } /// Parse a metadata structure from the supplied JSON string. /// Verify the version specified in the "format" element, do not /// even attempt to parse unknown versions. pub fn parse(contents: &str) -> Result<Self, Box<dyn error::Error>> { match serde_json::from_str::<MetadataTopLevelFormatOnly>(contents) { Ok(header) => match header.format.version.major { 0 => serde_json::from_str::<Self>(contents) .map_err(|err| -> Box<dyn error::Error> { Box::new(err) }), _ => Err(MetadataError::boxed(format!( "Unsupported metadata format version {}", header.format.version.major ))), }, Err(err) => Err(Box::new(err)), } } } /// Unwrap a [`fs::Metadata`] object's last modified timestamp, /// assume it may be converted to a Unix timestamp, and return /// the number of seconds since the Unix epoch. pub fn mtime_to_unix(metadata: &fs::Metadata) -> u64 { metadata .modified() .unwrap() .duration_since(time::SystemTime::UNIX_EPOCH) .unwrap() .as_secs() } /// Verify that a file has not been changed since the last time /// the metadata was stored. pub fn match_meta<P1, P2>(dst: P1, dst_meta: P2) -> Option<FileHttpMetadata> where P1: AsRef<path::Path>, P2: AsRef<path::Path>, { match fs::metadata(&dst) { Ok(file_meta) => match fs::read_to_string(&dst_meta) { Ok(contents) => match FileHttpMetadata::parse(&contents) { Ok(meta) => match file_meta.is_file() && file_meta.len() == meta.file_size && mtime_to_unix(&file_meta) == meta.file_mtime { true => Some(meta), false => None, }, Err(_) => None, }, Err(_) => None, }, Err(_) => None, } } /// Verify that a file has not been changed, and additionally verify /// that its source file, specified by the `src` local path, has /// also not been changed. Useful when e.g. uncompressing or otherwise /// processing downloaded files. pub fn match_meta_with_source<P1, P2, P3>( dst: P1, dst_meta: P2, src: P3, ) -> Option<FileHttpMetadata> where P1: AsRef<path::Path>, P2: AsRef<path::Path>, P3: AsRef<path::Path>, { match_meta(dst, dst_meta).and_then(|meta| match fs::metadata(src) { Ok(src_meta) => { let src_len = src_meta.len(); match meta.source_file_size.or(Some(src_len)).unwrap() == src_len { true => { let src_mtime = mtime_to_unix(&src_meta); match meta.source_file_mtime.or(Some(src_mtime)).unwrap() == src_mtime { true => Some(meta), false => None, } } false => None, } } Err(_) => match meta.source_file_size.is_some() || meta.source_file_mtime.is_some() { false => Some(meta), true => None, }, }) } #[cfg(feature = "ureq")] /// Add the "If-Modified-Since" and/or "If-None-Match" headers to /// an HTTP request if the relevant fields ("Last-Modified" and "ETag" /// respectively) have been returned in the last response from /// the server when the file has been downloaded. pub fn build_req<P1, P2>( orig_req: ureq::Request, dst: P1, dst_meta: P2, ) -> (ureq::Request, Option<FileHttpMetadata>) where P1: AsRef<path::Path>, P2: AsRef<path::Path>, { let stored_meta = match_meta(dst, dst_meta); let req = match &stored_meta { None => orig_req, Some(meta) => match &meta.hdr_etag { Some(etag) => orig_req.set("If-None-Match", &etag), None => match &meta.hdr_last_modified { Some(last_modified) => orig_req.set("If-Modified-Since", &last_modified), None => orig_req, }, }, }; (req, stored_meta) }