Expand description
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:
use std::fs::{self, File};
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");
/* ... */
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())?;
}
};
Example for checking whether a file has changed since its metadata was last updated:
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.
Structs§
- File
Http Metadata - 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.
- Metadata
Format - Information about the format of the JSON-serialized metadata.
- Metadata
Format Version - The version of the format of the serialized metadata.
Enums§
- Error
- An error that occurred during processing the metadata.
Functions§
- build_
req - Add the
If-Modified-Since
and/orIf-None-Match
headers to an HTTP request if needed. - match_
meta - Verify that a file has not been changed since the last time the metadata was stored.
- match_
meta_ with_ source - 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. - mtime_
to_ unix - Unwrap a
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.