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// Package main demonstrates the use of context in the errors package from
// github.com/olekukonko/errors. It showcases adding context to custom errors,
// accessing context through wrapped and converted errors, handling standard library
// errors, and working with complex context data structures.
package main
import (
"fmt"
"github.com/olekukonko/errors"
)
// processData simulates a data processing operation that fails, returning an error with context.
// It attaches retry-related metadata to the error for demonstration purposes.
func processData(id string, attempt int) error {
// Create an error with processing-specific context
return errors.New("processing failed").
With("id", id). // Add data identifier
With("attempt", attempt). // Add attempt number
With("retryable", true) // Mark as retryable
}
// main is the entry point, illustrating various ways to work with error context.
// It demonstrates basic context addition, context preservation through wrapping,
// handling standard errors, and managing complex context data.
func main() {
// 1. Basic context example
// Create and display an error with simple key-value context
err := processData("123", 3)
fmt.Println("Error:", err) // Print error message
fmt.Println("Full context:", errors.Context(err)) // Print all context as a map
// 2. Accessing context through conversion
// Wrap the error with fmt.Errorf and show context preservation
rawErr := fmt.Errorf("wrapped: %w", err)
fmt.Println("\nAfter wrapping with fmt.Errorf:")
fmt.Println("Direct context access:", errors.Context(rawErr)) // Show context is unavailable directly
e := errors.Convert(rawErr)
fmt.Println("After conversion - context:", e.Context()) // Show context restored via conversion
// 3. Standard library errors
// Demonstrate that standard errors lack context
stdErr := fmt.Errorf("standard error")
if errors.Context(stdErr) == nil {
fmt.Println("\nStandard library errors have no context") // Confirm no context exists
}
// 4. Adding context to standard errors
// Convert a standard error and enrich it with context
converted := errors.Convert(stdErr).
With("source", "legacy"). // Add source information
With("severity", "high") // Add severity level
fmt.Println("\nConverted standard error:")
fmt.Println("Message:", converted.Error()) // Print original message
fmt.Println("Context:", converted.Context()) // Print added context
// 5. Complex context example
// Create an error with nested and varied context data
complexErr := errors.New("database operation failed").
With("query", "SELECT * FROM users"). // Add SQL query string
With("params", map[string]interface{}{
"limit": 100, // Nested parameter: result limit
"offset": 0, // Nested parameter: result offset
}).
With("duration_ms", 45.2) // Add execution time in milliseconds
fmt.Println("\nComplex error context:")
for k, v := range errors.Context(complexErr) {
fmt.Printf("%s: %v (%T)\n", k, v, v) // Print each context key-value pair with type
}
}
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