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// Package main demonstrates error wrapping and chaining using the errors package from
// github.com/olekukonko/errors. It simulates a layered application (API, business logic,
// database) where errors are created, enriched with context, and wrapped, then inspected
// to show the full error chain and specific error checks.
package main
import (
"fmt"
"github.com/olekukonko/errors"
)
// databaseQuery simulates a database operation that fails, returning an error with context.
// It represents the lowest layer where an error originates, enriched with database-specific details.
func databaseQuery() error {
// Create a base error with database failure details
return errors.New("connection timeout").
With("timeout_sec", 5). // Add timeout duration context
With("server", "db01.prod") // Add server identifier context
}
// businessLogic processes a user request and handles database errors, wrapping them with business context.
// It represents an intermediate layer that adds its own context without modifying the original error.
func businessLogic(userID string) error {
err := databaseQuery()
if err != nil {
// Create a new error specific to business logic failure
return errors.New("failed to process user "+userID).
With("user_id", userID). // Add user ID context
With("stage", "processing"). // Add processing stage context
Wrap(err) // Wrap the database error for chaining
}
return nil
}
// apiHandler simulates an API request handler that wraps business logic errors with API context.
// It represents the top layer, adding a status code and stack trace for debugging.
func apiHandler() error {
err := businessLogic("12345")
if err != nil {
// Create a new error specific to API failure
return errors.New("API request failed").
WithCode(500). // Set HTTP-like status code
WithStack(). // Capture stack trace at API level
Wrap(err) // Wrap the business logic error
}
return nil
}
// main is the entry point, demonstrating error creation, wrapping, and inspection.
// It prints the combined error message, unwraps the error chain, and checks for a specific error.
func main() {
err := apiHandler()
// Print the full error message combining all wrapped errors
fmt.Println("=== Combined Message ===")
fmt.Println(err)
// Unwrap and display each error in the chain with its details
fmt.Println("\n=== Error Chain ===")
for i, e := range errors.UnwrapAll(err) {
fmt.Printf("%d. %T\n", i+1, e) // Show error index and type
if err, ok := e.(*errors.Error); ok {
fmt.Println(err.Format()) // Print formatted details for custom errors
} else {
fmt.Println(e) // Print standard error message for non-custom errors
}
}
// Check if the error chain contains a specific error
fmt.Println("\n=== Error Checks ===")
if errors.Is(err, errors.New("connection timeout")) {
fmt.Println("✓ Matches connection timeout error") // Confirm match with database error
}
}
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