mirror of
https://github.com/rust-lang-nursery/rust-cookbook
synced 2025-02-16 12:18:27 +00:00
Ludwig PACIFICI
Michał Budzyński
parent
b31b7a7688
commit
b8aab7930c
3 changed files with 104 additions and 3 deletions
102
src/basics.md
102
src/basics.md
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@ -24,7 +24,7 @@
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| [Define and operate on a type represented as a bitfield][ex-bitflags] | [![bitflags-badge]][bitflags] | [![cat-no-std-badge]][cat-no-std] |
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| [Access a file randomly using a memory map][ex-random-file-access] | [![memmap-badge]][memmap] | [![cat-filesystem-badge]][cat-filesystem] |
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| [Check number of logical cpu cores][ex-check-cpu-cores] | [![num_cpus-badge]][num_cpus] | [![cat-hardware-support-badge]][cat-hardware-support] |
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| [Obtain backtrace of complex error scenarios][ex-error-chain-backtrace] | [![error-chain-badge]][error-chain] | [![cat-rust-patterns-badge]][cat-rust-patterns] |
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[ex-std-read-lines]: #ex-std-read-lines
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<a name="ex-std-read-lines"></a>
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@ -866,7 +866,7 @@ Uses [`ring::hmac`] to creates a [`hmac::Signature`] of a string then verifies t
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# #[macro_use]
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# extern crate error_chain;
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extern crate ring;
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#
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#
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# error_chain! {
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# foreign_links {
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# Ring(ring::error::Unspecified);
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@ -1092,14 +1092,112 @@ fn main() {
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}
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```
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[ex-error-chain-backtrace]: #ex-error-chain-backtrace
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<a name="ex-error-chain-backtrace"></a>
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## Obtain backtrace of complex error scenarios
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[![error-chain-badge]][error-chain] [![cat-rust-patterns-badge]][cat-rust-patterns]
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This recipe shows how to handle a complex error scenario and then
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print a backtrace. It relies on [`chain_err`] to extend errors by
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appending new errors. The error stack can be unwinded, thus providing
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a better context to understand why an error was raised.
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The below recipes attemps to deserialize the value `256` into a
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`u8`. An error will bubble up from Serde then csv and finaly up to the
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user code.
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```rust
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# extern crate csv;
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#[macro_use]
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extern crate error_chain;
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# #[macro_use]
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# extern crate serde_derive;
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#
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# use std::fmt;
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#
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# error_chain! {
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# foreign_links {
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# Reader(csv::Error);
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# }
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# }
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#[derive(Debug, Deserialize)]
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struct Rgb {
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red: u8,
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blue: u8,
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green: u8,
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}
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impl Rgb {
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fn from_reader(csv_data: &[u8]) -> Result<Rgb> {
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let color: Rgb = csv::Reader::from_reader(csv_data)
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.deserialize()
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.nth(0)
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.ok_or("Cannot deserialize the first CSV record")?
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.chain_err(|| "Cannot deserialize RGB color")?;
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Ok(color)
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}
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}
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# impl fmt::UpperHex for Rgb {
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# fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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# let hexa = u32::from(self.red) << 16 | u32::from(self.blue) << 8 | u32::from(self.green);
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# write!(f, "{:X}", hexa)
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# }
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# }
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#
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fn run() -> Result<()> {
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let csv = "red,blue,green
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102,256,204";
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let rgb = Rgb::from_reader(csv.as_bytes()).chain_err(|| "Cannot read CSV data")?;
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println!("{:?} to hexadecimal #{:X}", rgb, rgb);
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Ok(())
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}
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fn main() {
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if let Err(ref errors) = run() {
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eprintln!("Error level - description");
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errors
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.iter()
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.enumerate()
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.for_each(|(index, error)| eprintln!("└> {} - {}", index, error));
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if let Some(backtrace) = errors.backtrace() {
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eprintln!("{:?}", backtrace);
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}
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#
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# // In a real use case, errors should handled. For example:
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# // ::std::process::exit(1);
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}
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}
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```
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Backtrace error rendered:
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```text
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Error level - description
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└> 0 - Cannot read CSV data
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└> 1 - Cannot deserialize RGB color
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└> 2 - CSV deserialize error: record 1 (line: 2, byte: 15): field 1: number too large to fit in target type
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└> 3 - field 1: number too large to fit in target type
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```
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Run the recipe with `RUST_BACKTRACE=1` to display a detailed [`backtrace`] associated with this error.
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{{#include links.md}}
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<!-- API Reference -->
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[`backtrace`]: https://docs.rs/error-chain/*/error_chain/trait.ChainedError.html#tymethod.backtrace
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[`bitflags!`]: https://docs.rs/bitflags/*/bitflags/macro.bitflags.html
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[`BufRead::lines`]: https://doc.rust-lang.org/std/io/trait.BufRead.html#method.lines
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[`BufRead`]: https://doc.rust-lang.org/std/io/trait.BufRead.html
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[`BufReader`]: https://doc.rust-lang.org/std/io/struct.BufReader.html
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[`chain_err`]: https://docs.rs/error-chain/*/error_chain/index.html#chaining-errors
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[`Command`]: https://doc.rust-lang.org/std/process/struct.Command.html
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[`digest::Context`]: https://docs.rs/ring/*/ring/digest/struct.Context.html
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[`digest::Digest`]: https://docs.rs/ring/*/ring/digest/struct.Digest.html
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@ -42,7 +42,7 @@ community. It needs and welcomes help. For details see
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| [Define and operate on a type represented as a bitfield][ex-bitflags] | [![bitflags-badge]][bitflags] | [![cat-no-std-badge]][cat-no-std] |
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| [Access a file randomly using a memory map][ex-random-file-access] | [![memmap-badge]][memmap] | [![cat-filesystem-badge]][cat-filesystem] |
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| [Check number of logical cpu cores][ex-check-cpu-cores] | [![num_cpus-badge]][num_cpus] | [![cat-hardware-support-badge]][cat-hardware-support] |
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| [Obtain backtrace of complex error scenarios][ex-error-chain-backtrace] | [![error-chain-badge]][error-chain] | [![cat-rust-patterns-badge]][cat-rust-patterns] |
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## [Encoding](encoding.html)
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@ -159,6 +159,7 @@ community. It needs and welcomes help. For details see
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[ex-threadpool-fractal]: concurrency.html#ex-threadpool-fractal
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[ex-threadpool-walk]: concurrency.html#ex-threadpool-walk
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[ex-dedup-filenames]: app.html#ex-dedup-filenames
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[ex-error-chain-backtrace]: basics.html#ex-error-chain-backtrace
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[ex-extract-links-webpage]: net.html#ex-extract-links-webpage
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[ex-extract-hashtags]: basics.html#ex-extract-hashtags
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[ex-extract-mediawiki-links]: net.html#ex-extract-mediawiki-links
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@ -64,6 +64,8 @@ Keep lines sorted.
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[data-encoding]: https://docs.rs/data-encoding/
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[env_logger-badge]: https://badge-cache.kominick.com/crates/v/env_logger.svg?label=env_logger
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[env_logger]: https://docs.rs/env_logger/
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[error-chain-badge]: https://badge-cache.kominick.com/crates/v/error-chain.svg?label=error-chain
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[error-chain]: https://docs.rs/error-chain/
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[flate2-badge]: https://badge-cache.kominick.com/crates/v/flate2.svg?label=flate2
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[flate2]: https://docs.rs/flate2/
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[glob-badge]:https://badge-cache.kominick.com/crates/v/glob.svg?label=glob
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