goof

Overview ¶

Package goof is a drop-in replacement for the go stdlib `errors` package, providing enhanced error construction capabilities and formatting capabilities.

Plays Golf ¶

Errors can be created with the standard `New` or `Newf` constructors in order to create new error instances. However, the methods `WithField`, `WithFields`, `WithFieldE`, and `WithFieldsE` also exist. These methods enable the construction of new error instances with additional information about the error injected at the time and location of when the error was created.

These fields then become available to the Golf framework (https://github.com/akutz/golf) in order to extract more information about an error than just a simple error message.

Structured Logging ¶

The support for fields as a backing-store in conjunction with Golf support enable the ability to seamlessly integrate with the structured logging framework Logrus (https://github.com/Sirupsen/logrus).

The advantage of this marriage between error objects and a structured logging framework is that information about an error is stored *with* an error, at the time of the error's construction. This alleviates the question of whether or not to log an error and the contextual information surrounding it when an error is created.

Logging Errors Sans Goof ¶

The file `ex1-nogoof.go` in the `examples/example1-nogoof` folder demonstrates how traditional error handling and logging looks without Goof:

package main

import (
    "fmt"
    "os"

    log "github.com/Sirupsen/logrus"
)

func getDividend() int {
    return 2
}

func getDivisor() int {
    return 0
}

func divide() (int, error) {
    x := getDividend()
    y := getDivisor()

    if y == 0 {
        log.Errorf("error dividing by 0 with %d / %d", x, y)
        return -1, fmt.Errorf("error dividing by 0 with %d / %d", x, y)
    }

    return x / y, nil
}

func calculate(op string) error {
    switch op {
    case "divide":
        z, err := divide()
        if err != nil {
            log.Errorf("division error %v", err)
            return fmt.Errorf("division error %v", err)
        }
        fmt.Printf("division = %d\n", z)
        return nil
    }
    return nil
}

func main() {
    if err := calculate("divide"); err != nil {
        log.Errorf("calculation error %v", err)
        os.Exit(1)
    }
}

Running the above example results in the above output:

$ go run examples/example1-nogoof/ex1-nogoof.go
ERRO[0000] error dividing by 0 with 2 / 0
ERRO[0000] division error error dividing by 0 with 2 / 0
ERRO[0000] calculation error division error error dividing by 0 with 2 / 0
exit status 1

In the example above the `main` function asks `calculate` to do division, and so `calculate` forwards that request to `divide`. The `divide` function then fetches the dividend and the divisor from some data store via the (undefined) methods `getDividend` and `getDivisor` and proceeds to perform the operation.

However, if the divisor is zero then a *divide-by-zero* is logged and an error is returned to `calculate` which in turn logs and returns the error to `main` which also logs the error.

The problem is neither the `divide` or `calculate` functions should really be logging anything regarding errors. Error logging should be as centralized as possible in order to avoid cluttering logs with duplicate information. This often means logging errors at the outer-most areas of a program.

Yet this choice also means you can, and often do, lose contextual information about the errors. In this case neither `calculate` or `main` know what the dividend or divisor were. True, the error object can format a string that includes that information, but the logging framework Logrus (https://github.com/Sirupsen/logrus) articulates a very intelligent case for structured logging.

Logging Errors With Goof ¶

Goof on the other hand makes creating errors that can be logged by a structured logger as simple as can be. Let's revisit the previous example using the file `ex2-goof.go` in the `examples/example2-goof` folder:

package main

import (
    "fmt"
    "os"

    log "github.com/Sirupsen/logrus"
    "github.com/akutz/goof"
)

func divide() int, error {
    x := getDividend()
    y := getDivisor()
    if y == 0 {
        return -1, goof.WithFields(goof.Fields{
            "dividend": x,
            "divisor": y,
            }, "divide by zero")
    }

    return x / y
}

func calculate(op string) error {
    switch op {
        case "divide":
            if z, err := divide(); err != nil {
                return err
            } else {
                fmt.Printf("division = %d\n", z)
                return nil
            }
    }
}

func main() {
    if err := calculate("divide"); err != nil {
        log.Error(err)
        os.Exit(1)
    }
}

In the refactored example no errors are logged in the `divide` or `calculate` functions. Instead, an error is created with fields labeled as "divisor" and "dividend" with those fields set to the values to which they relate. The error is also created with a brief, but sufficient, message, describing the issue.

This error is then returned all the way to the main function where it is logged via the structured logging framework Logrus. Because the main function also instructs Logrus to use the Golf formatter for logging, this is what is emitted to the console:

$ go run examples/example2-goof/ex2-goof.go
ERRO[0000] divide by zero                               dividend=2 divisor=0
exit status 1

The log output is now much cleaner, concise, and without losing any information regarding the context of the error and that may be helpful to debugging.