Change request/error handling

Fixes DE-955.

CHANGELOG.md

@@ -16,8 +16,121 @@ This driver uses semantic versioning:
 
 ## [Unreleased]
 
+### Changed
+
+- Errors encountered before a request completes are now wrapped in a `NetworkError`
+
+  This should help making it easier to diagnose network issues and distinguish
+  the relevant error conditions.
+
+  The originating error can still be accessed using the `cause` property of the
+  `NetworkError` error.
+
+- `HttpError` now extends the `NetworkError` type
+
+  This allows treating all non-`ArangoError` errors as one category of errors,
+  even when there is no server response available.
+
+- `db.waitForPropagation` now throws a `PropagationTimeoutError` error when
+  invoked with a `timeout` option and the timeout duration is exceeded
+
+  The method would previously throw the most recent error encountered while
+  waiting for replication. The originating error can still be accessed using
+  the `cause` property of the `PropagationTimeoutError` error.
+
+- `db.waitForPropagation` now respects the `timeout` option more strictly
+
+  Previously the method would only time out if the timeout duration was
+  exceeded after the most recent request failed. Now the timeout is
+  recalculated and passed on to each request, preventing it from exceeding
+  the specified duration.
+
+  If the propagation timed out due to an underlying request exceeding the
+  timeout duration, the `cause` property of the `PropagationTimeoutError`
+  error will be a `ResponseTimeoutError` error.
+
+- `config.beforeRequest` and `config.afterResponse` callbacks can now return
+  promises
+
+  If the callback returns a promise, it will be awaited before the request
+  and response cycle proceeds. If either callback throws an error or returns
+  a promise that is rejected, that error will be thrown instead.
+
+- `config.afterResponse` callback signature changed
+
+  The callback signature previously used the internal `ArangojsResponse` type.
+  The new signature uses the `Response` type of the Fetch API with an
+  additional `request` property to more accurately represent the actual value
+  it receives as the `parsedBody` property will never be present.
+
+- `response` property on `ArangoError` is now optional
+
+  This property should always be present but this allows using the error in
+  situations where a response might not be available.
+
 ### Added
 
+- Added `onError` option to `Config` (DE-955)
+
+  This option can be used to specify a callback function that will be invoked
+  whenever a request results in an error. Unlike `afterResponse`, this callback
+  will be invoked even if the request completed but returned an error status.
+  In this case the error will be the `HttpError` or `ArangoError` representing
+  the error response.
+
+  If the `onError` callback throws an error or returns a promise that is
+  rejected, that error will be thrown instead.
+
+- Added `NetworkError` error type
+
+  This is the common base class for all errors (including `HttpError`) that
+  occur while making a request. The originating error can be accessed using the
+  `cause` property. The request object can be accessed using the `request`
+  property.
+
+  Note that `ArangoError` and the new `PropagationTimeoutError` error type
+  do not extend `NetworkError` but may wrap an underlying error, which can
+  be accessed using the `cause` property.
+
+- Added `ResponseTimeoutError` error type
+
+  This error extends `NetworkError` and is thrown when a request deliberately
+  times out using the `timeout` option.
+
+- Added `RequestAbortedError` error type
+
+  This error extends `NetworkError` and is thrown when a request is aborted
+  by using the `db.close` method.
+
+- Added `FetchFailedError` error type
+
+  This error extends `NetworkError` and is thrown when a request fails because
+  the underlying `fetch` call fails (usually with a `TypeError`).
+
+  In Node.js the root cause of this error (e.g. a network failure) can often be
+  found in the `cause` property of the originating error, i.e. the `cause`
+  property of the `cause` property of this error.
+
+  In browsers the root cause is usually not exposed directly but can often
+  be diagnosed by examining the developer console or network tab.
+
+- Added `PropagationTimeoutError` error type
+
+  This error does not extend `NetworkError` but wraps the most recent error
+  encountered while waiting for replication, which can be accessed using the
+  `cause` property. This error is only thrown when `db.waitForPropagation`
+  is invoked with a `timeout` option and the timeout duration is exceeded.
+
+- Added `ProcessedResponse` type
+
+  This type replaces the previously internal `ArangojsResponse` type and
+  extends the native `Response` type with additional properties.
+
+- Added optional `request` property to `ArangoError`
+
+  This property is always present if the error has a `response` property. In
+  normal use this should always be the case.
+
 - Added `database` property to `Analyzer`, `ArrayCursor`, `BatchedArrayCursor`,
   `Collection`, `Graph`, `Job`, `Route`, `Transaction` and `View` types (DE-935)