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Error handling

content/develop/clients/rust/error-handling.md

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redis-rs uses Result types following Rust's idiomatic error handling pattern. Code examples in the documentation often omit error handling for brevity, but it is essential in production code. This page explains how error handling works in redis-rs and how to apply some common error handling patterns. For an overview of error types and handling strategies, see [Error handling]({{< relref "/develop/clients/error-handling" >}}).

Error handling in Rust

In Rust, functions return errors using the Result<T, E> type. You can check for errors explicitly with code like the following:

rust
use redis::Commands;

let client = redis::Client::open("redis://127.0.0.1/")?;
let mut con = client.get_connection()?;

match con.get::<_, String>("key") {
    Ok(value) => println!("Value: {}", value),
    Err(e) => {
        // Handle the error
        eprintln!("Error: {}", e);
    }
}

Error types

redis-rs provides a RedisError type with various error kinds. Common error kinds include:

Error KindWhen it occursRecoverableRecommended action
ErrorKind::IoNetwork or I/O error✅Retry with backoff or fall back to alternative
ErrorKind::AuthenticationFailedInvalid credentials❌Fix credentials and fail
ErrorKind::UnexpectedReturnTypeType mismatch❌Fix the command or type conversion
ErrorKind::ServerRedis server error response⚠️Check specific server error; some are retryable
ErrorKind::ParseFailed to parse server response❌Report as a bug

See [Categories of errors]({{< relref "/develop/clients/error-handling#categories-of-errors" >}}) for a more detailed discussion of these errors and their causes.

Applying error handling patterns

The [Error handling]({{< relref "/develop/clients/error-handling" >}}) overview describes four main patterns. The sections below show how to implement them in redis-rs:

Pattern 1: Fail fast

Return the error immediately if it represents an unrecoverable situation (see [Pattern 1: Fail fast]({{< relref "/develop/clients/error-handling#pattern-1-fail-fast" >}}) for a full description):

rust
use redis::{Commands, RedisResult};

fn get_value(con: &mut redis::Connection, key: &str) -> RedisResult<String> {
    // Using ? operator to propagate errors immediately
    let value: String = con.get(key)?;
    Ok(value)
}

Pattern 2: Graceful degradation

Check for specific errors and fall back to an alternative (see [Pattern 2: Graceful degradation]({{< relref "/develop/clients/error-handling#pattern-2-graceful-degradation" >}}) for a full description):

rust
use redis::{Commands, ErrorKind};

fn get_with_fallback(
    con: &mut redis::Connection,
    key: &str,
) -> Result<String, Box<dyn std::error::Error>> {
    match con.get::<_, String>(key) {
        Ok(value) => Ok(value),
        Err(e) => {
            if e.kind() == ErrorKind::Io {
                // Network error, use fallback
                log::warn!("Cache unavailable, using database");
                database_get(key)
            } else {
                Err(Box::new(e))
            }
        }
    }
}

Pattern 3: Retry with backoff

Retry on temporary errors such as timeouts (see [Pattern 3: Retry with backoff]({{< relref "/develop/clients/error-handling#pattern-3-retry-with-backoff" >}}) for a full description):

rust
use redis::{Commands, ErrorKind};
use std::thread;
use std::time::Duration;

fn get_with_retry(
    con: &mut redis::Connection,
    key: &str,
    max_attempts: u32,
) -> redis::RedisResult<String> {
    let mut delay = Duration::from_millis(100);
    
    for attempt in 0..max_attempts {
        match con.get::<_, String>(key) {
            Ok(value) => return Ok(value),
            Err(e) => {
                if attempt < max_attempts - 1 && e.kind() == ErrorKind::Io {
                    thread::sleep(delay);
                    delay *= 2; // Exponential backoff
                    continue;
                }
                return Err(e);
            }
        }
    }
    
    unreachable!()
}

Pattern 4: Log and continue

Log non-critical errors and continue (see [Pattern 4: Log and continue]({{< relref "/develop/clients/error-handling#pattern-4-log-and-continue" >}}) for a full description):

rust
use redis::{Commands, ErrorKind};

fn cache_value(con: &mut redis::Connection, key: &str, value: &str) {
    if let Err(e) = con.set_ex::<_, _, _, ()>(key, value, 3600) {
        if e.kind() == ErrorKind::Io {
            log::warn!("Failed to cache {}, continuing without cache", key);
            // Application continues normally
        } else {
            log::error!("Unexpected error caching {}: {}", key, e);
        }
    }
}

Async error handling

Error handling works the same way when you use async/await with redis-rs, as shown in the example below:

rust
use redis::AsyncCommands;

async fn get_with_fallback_async(
    con: &mut redis::aio::MultiplexedConnection,
    key: &str,
) -> Result<String, Box<dyn std::error::Error>> {
    match con.get::<_, String>(key).await {
        Ok(value) => Ok(value),
        Err(e) => {
            if e.kind() == redis::ErrorKind::Io {
                log::warn!("Cache unavailable");
                database_get_async(key).await
            } else {
                Err(Box::new(e))
            }
        }
    }
}

See also