# Errors

> UCall for Python

A failed operation raises `ucall.Error`, a `RuntimeError` whose `status` is the `ucall.Status` it reported and whose `message` is a static detail beside it.
Each failing status raises a subclass of its own, named after the status, such as `ucall.ConnectionFailedError` or `ucall.NotFoundError`.
Where a built-in exception names the same fault, the subclass derives it too: `ConnectionError` for connection failures, `TimeoutError`, `MemoryError`, `OSError`, `ValueError` for invalid or malformed input, `KeyError`, `NotImplementedError`, `OverflowError` and `BlockingIOError`.
`str(error)` joins the two, as in "CONNECTION_FAILED: connection-failed".
Arguments of the wrong type raise `TypeError`, a key of the wrong length or an unknown enum name raises `ValueError`, and a reply while views over the body are alive raises `BufferError`.

```python
import ucall

client = ucall.Client(connections=1)
try:
    response = client.get("http://127.0.0.1:1/")
    print("answered", response.status_code)
except ucall.ConnectionFailedError as error:  # or: except ConnectionError
    assert error.status == ucall.Status.CONNECTION_FAILED
    print("nobody listens:", error)
```

`ucall.Status`, `Backend`, `CPUClass`, `Security`, `Verb`, `BodyDelivery` and `LogLevel` are `enum.IntEnum` classes, and every argument taking one also takes its name in any case, with "-" or "_" between words.
`ucall.Status.from_name("out-of-memory")` reads a status back from the spelling the library gives it, `ucall.version()` numbers the linked library, and `ucall.__version__` spells it with any candidate suffix.
A submitted call that fails completes with that status in `Completed.status`, such as `CONNECTION_FAILED`, `CONNECTION_CLOSED`, `TIMEOUT`, `HANDSHAKE_FAILED` or `PEER_REJECTED`, and HTTP error statuses are ordinary responses.
On the serving side, failures become replies rather than exceptions: 400 for parameters that do not bind, 500 for a handler that raised or a request released unanswered.

`import ucall`

`from ucall import Error`

## Status

The outcome of a verb, which [`Error.status`](#status) and [`Completed.status`](#status) carry.

```python
class Status(enum.IntEnum)
```

- `SUCCESS` = `0`
- `DEFERRED` = `1`
- `OUT_OF_MEMORY` = `2`
- `IO` = `7`
- `MALFORMED` = `9`
- `INTERNAL` = `10`
- `OVERFLOW` = `11`
- `UNINITIALIZED` = `12`
- `CONTENDED` = `14`
- `UNSUPPORTED` = `16`
- `INVALID_ARGUMENT` = `17`
- `NOT_FOUND` = `18`
- `ALREADY_EXISTS` = `19`
- `CONNECTION_FAILED` = `20`
- `CONNECTION_CLOSED` = `21`
- `TIMEOUT` = `22`
- `HANDSHAKE_FAILED` = `23`
- `PEER_REJECTED` = `24`
- `WOULD_BLOCK` = `25`

Examples: ```
>>> ucall.Status.CONTENDED.name
'CONTENDED'
```

## OutOfMemoryError

An allocation could not be satisfied.

```python
class OutOfMemoryError(Error, MemoryError)
```

## InputOutputError

A file or socket could not be opened, read, written, or closed.

```python
class InputOutputError(Error, OSError)
```

## MalformedError

The peer sent bytes that do not decode as the expected protocol.

```python
class MalformedError(Error, ValueError)
```

## InternalError

The library violated its contract, which points at a defect.

```python
class InternalError(Error)
```

## OverflowError

A requested size exceeds the representable range.

```python
class OverflowError(Error, builtins.OverflowError)
```

## UninitializedError

The call needs a handle that was never initialized.

```python
class UninitializedError(Error)
```

## ContendedError

The call was refused rather than waited for, like a submission to a full client.

```python
class ContendedError(Error)
```

## UnsupportedError

The build, backend, or machine does not implement the requested feature.

```python
class UnsupportedError(Error, NotImplementedError)
```

## InvalidArgumentError

An argument is missing, out of range, or contradicts another argument.

```python
class InvalidArgumentError(Error, ValueError)
```

## NotFoundError

The requested endpoint, header, parameter, or file does not exist.

```python
class NotFoundError(Error, KeyError)
```

## AlreadyExistsError

An endpoint with the same template and verb is already registered.

```python
class AlreadyExistsError(Error, ValueError)
```

## ConnectionFailedError

DNS lookup or connection establishment failed.

```python
class ConnectionFailedError(Error, ConnectionError)
```

## ConnectionClosedError

The connection closed before the exchange completed.

```python
class ConnectionClosedError(Error, ConnectionError)
```

## TimeoutError

The exchange did not finish within its deadline.

```python
class TimeoutError(Error, builtins.TimeoutError)
```

## HandshakeFailedError

The Noise handshake failed to authenticate or agree on keys.

```python
class HandshakeFailedError(Error)
```

## PeerRejectedError

The peer authorizer declined the authenticated static key.

```python
class PeerRejectedError(Error)
```

## WouldBlockError

Nothing was ready, like a body pull on the polling thread before any bytes arrived.

```python
class WouldBlockError(Error, BlockingIOError)
```

## Error

A failed verb, raised with the [`Status`](#Status) it reported and a static detail.

```python
class Error(RuntimeError)
```

Each failing status raises its own subclass, like [`ConnectionFailedError`](#ConnectionFailedError),
which derives the built-in naming the same fault, here `ConnectionError`.

Examples: ```
>>> error = ucall.Error(ucall.Status.TIMEOUT, "no reply")
>>> error.status, error.message, str(error)
(<Status.TIMEOUT: 22>, 'no reply', 'TIMEOUT: no reply')
```

## Error

```python
Error(status: Status, message: str, /)
```

## status

The [`Status`](#Status) of the failure.

```python
status: Status
```

## message

The detail of the failure.

```python
message: str
```