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lyse
lyse.isobeef.org
 (2y ago)

Question to all you Gophers out there: How do you deal with custom errors that include more information and different kinds of matching them?

I started with a simple var ErrPermissionNotAllowed = errors.New("permission not allowed"). In my function I then wrap that using fmt.Errorf("%w: %v", ErrPermissionNotAllowed, failedPermissions). I can match this error using errors.Is(err, ErrPermissionNotAllowed). So far so good.

Now for display purposes I’d also like to access the individual permissions that could not be assigned. Parsing the error message is obviously not an option. So I thought, I create a custom error type, e.g. type PermissionNotAllowedError []Permission and give it some func (e PermissionNotAllowedError) Error() string { return fmt.Sprintf("permission not allowed: %v", e) }. My function would then return this error instead: PermissionNotAllowedError{failedPermissions}

At some layers I don’t care about the exact permissions that failed, but at others I do, at least when accessing them. A custom func (e PermissionNotAllowedError) Is(target err) bool could match both the general ErrPermissionNotAllowed as well as the PermissionNotAllowedError. Same with As(…). For testing purposes the PermissionNotAllowedError would then also try to match the included permissions, so assertions in tests would work nicely. But having two different errors for different matching seems not very elegant at all.

Did you ever encounter this scenario before? How did you address this? Is my thinking flawed?

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prologic
twtxt.net
 (2y ago)
↳ In-reply-to » I've never liked the idea of having everything displayed all of the time for all of history.

@eldersnake@we.loveprivacy.club Several reasons:

  • It’s another language to learn (SQL)
  • It adds another dependency to your system
  • It’s another failure mode (database blows up, scheme changes, indexs, etc)
  • It increases security problems (now you have to worry about being SQL-safe)

And most of all, in my experience, it doesn’t actually solve any problems that a good key/value store can solve with good indexes and good data structures. I’m just no longer a fan, I used to use MySQL, SQLite, etc back in the day, these days, nope I wouldn’t even go anywhere near a database (for my own projects) if I can help it – It’s just another thing that can fail, another operational overhead.

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prologic
twtxt.net
 (2y ago)

Anyone know what this might be about?

[1134036.271114] ata1.00: exception Emask 0x0 SAct 0x4 SErr 0x880000 action 0x6 frozen
[1134036.271478] ata1: SError: { 10B8B LinkSeq }
[1134036.271829] ata1.00: failed command: WRITE FPDMA QUEUED
[1134036.272182] ata1.00: cmd 61/20:10:e0:75:6e/00:00:11:00:00/40 tag 2 ncq 16384 out
                          res 40/00:01:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
[1134036.272895] ata1.00: status: { DRDY }
[1134036.273245] ata1: hard resetting link
[1134037.447033] ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[1134038.747174] ata1.00: configured for UDMA/133
[1134038.747179] ata1.00: device reported invalid CHS sector 0
[1134038.747185] ata1: EH complete

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xuu
txt.sour.is
 (2y ago)
↳ In-reply-to » I made a thing. Its a multi password type checker. Using the PHC string format we can identify a password hashing format from the prefix $name$ and then dispatch the hashing or checking to its specific format.

Here is an example of usage:

func Example() {
	pass := "my_pass"
	hash := "my_pass"

	pwd := passwd.New(
		&unix.MD5{}, // first is preferred type.
		&plainPasswd{},
	)

	_, err := pwd.Passwd(pass, hash)
	if err != nil {
		fmt.Println("fail: ", err)
	}

	// Check if we want to update.
	if !pwd.IsPreferred(hash) {
		newHash, err := pwd.Passwd(pass, "")
		if err != nil {
			fmt.Println("fail: ", err)
		}

		fmt.Println("new hash:", newHash)
	}

	// Output:
	//  new hash: $1$81ed91e1131a3a5a50d8a68e8ef85fa0
}

This shows how one would set a preferred hashing type and if the current version of ones password is not the preferred type updates it to enhance the security of the hashed password when someone logs in.

https://github.com/sour-is/go-passwd/blob/main/passwd_test.go#L33-L59

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niplav
niplav.site
 (2y ago)

In this House — We might fail, but never with abandon — Every moment is fresh, unimpeded by the one before — We remove as many obligations as we add — There is something to protect, something to give everything for — Tsuyoku Naritai!

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xuu
txt.sour.is
 (3y ago)
↳ In-reply-to » Progress! so i have moved into working on aggregates. Which are a grouping of events that replayed on an object set the current state of the object. I came up with this little bit of generic wonder.

(cont.)

Just to give some context on some of the components around the code structure.. I wrote this up around an earlier version of aggregate code. This generic bit simplifies things by removing the need of the Crud functions for each aggregate.

Domain Objects

A domain object can be used as an aggregate by adding the event.AggregateRoot struct and finish implementing event.Aggregate. The AggregateRoot implements logic for adding events after they are either Raised by a command or Appended by the eventstore Load or service ApplyFn methods. It also tracks the uncommitted events that are saved using the eventstore Save method.

type User struct {
  Identity string ```json:"identity"`

  CreatedAt time.Time

  event.AggregateRoot
}

// StreamID for the aggregate when stored or loaded from ES.
func (a *User) StreamID() string {
	return "user-" + a.Identity
}
// ApplyEvent to the aggregate state.
func (a *User) ApplyEvent(lis ...event.Event) {
	for _, e := range lis {
		switch e := e.(type) {
		case *UserCreated:
			a.Identity = e.Identity
			a.CreatedAt = e.EventMeta().CreatedDate
        /* ... */
		}
	}
}
Events

Events are applied to the aggregate. They are defined by adding the event.Meta and implementing the getter/setters for event.Event

type UserCreated struct {
	eventMeta event.Meta

	Identity string
}

func (c *UserCreated) EventMeta() (m event.Meta) {
	if c != nil {
		m = c.eventMeta
	}
	return m
}
func (c *UserCreated) SetEventMeta(m event.Meta) {
	if c != nil {
		c.eventMeta = m
	}
}
Reading Events from EventStore

With a domain object that implements the event.Aggregate the event store client can load events and apply them using the Load(ctx, agg) method.

// GetUser populates an user from event store.
func (rw *User) GetUser(ctx context.Context, userID string) (*domain.User, error) {
	user := &domain.User{Identity: userID}

	err := rw.es.Load(ctx, user)
	if err != nil {
		if err != nil {
			if errors.Is(err, eventstore.ErrStreamNotFound) {
				return user, ErrNotFound
			}
			return user, err
		}
		return nil, err
	}
	return user, err
}
OnX Commands

An OnX command will validate the state of the domain object can have the command performed on it. If it can be applied it raises the event using event.Raise() Otherwise it returns an error.

// OnCreate raises an UserCreated event to create the user.
// Note: The handler will check that the user does not already exsist.
func (a *User) OnCreate(identity string) error {
    event.Raise(a, &UserCreated{Identity: identity})
    return nil
}

// OnScored will attempt to score a task.
// If the task is not in a Created state it will fail.
func (a *Task) OnScored(taskID string, score int64, attributes Attributes) error {
	if a.State != TaskStateCreated {
		return fmt.Errorf("task expected created, got %s", a.State)
	}
	event.Raise(a, &TaskScored{TaskID: taskID, Attributes: attributes, Score: score})
	return nil
}
Crud Operations for OnX Commands

The following functions in the aggregate service can be used to perform creation and updating of aggregates. The Update function will ensure the aggregate exists, where the Create is intended for non-existent aggregates. These can probably be combined into one function.

// Create is used when the stream does not yet exist.
func (rw *User) Create(
  ctx context.Context,
  identity string,
  fn func(*domain.User) error,
) (*domain.User, error) {
	session, err := rw.GetUser(ctx, identity)
	if err != nil && !errors.Is(err, ErrNotFound) {
		return nil, err
	}

	if err = fn(session); err != nil {
		return nil, err
	}

	_, err = rw.es.Save(ctx, session)

	return session, err
}

// Update is used when the stream already exists.
func (rw *User) Update(
  ctx context.Context,
  identity string,
  fn func(*domain.User) error,
) (*domain.User, error) {
	session, err := rw.GetUser(ctx, identity)
	if err != nil {
		return nil, err
	}

	if err = fn(session); err != nil {
		return nil, err
	}

	_, err = rw.es.Save(ctx, session)
	return session, err
}

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