URL Loading System Error Codes

App Transport Security disallowed a connection because there is no secure network connection.

An app or app extension attempted to connect to a background session that is already connected to a process.

The shared container identifier of the URL session configuration is needed but hasn’t been set.

The app is suspended or exits while a background data task is processing.

The URL Loading System received bad data from the server.

A malformed URL prevented a URL request from being initiated.

A connection was attempted while a phone call was active on a network that doesn’t support simultaneous phone and data communication, such as EDGE or GPRS.

An asynchronous load has been canceled.

A download task couldn’t close the downloaded file on disk.

An attempt to connect to a host failed.

A download task couldn’t create the downloaded file on disk because of an I/O failure.

Content data received during a connection request had an unknown content encoding.

Content data received during a connection request couldn’t be decoded for a known content encoding.

The host name for a URL couldn’t be resolved.

A specific request to load an item only from the cache couldn't be satisfied.

A downloaded file on disk couldn’t be moved.

A downloaded file on disk couldn’t be opened.

A response to a connection request couldn’t be parsed.

A downloaded file couldn’t be removed from disk.

A download task couldn’t write the file to disk.

A server certificate was rejected.

A client certificate was required to authenticate an SSL connection during a connection request.

The length of the resource data exceeded the maximum allowed.

The cellular network disallowed a connection.

The host address couldn’t be found via DNS lookup.

A download task failed to decode an encoded file during the download.

A download task failed to decode an encoded file after downloading.

The specified file doesn’t exist.

A request for an FTP file resulted in the server responding that the file is not a plain file, but a directory.

An internal file operation failed.

A redirect loop was detected or the threshold for number of allowable redirects was exceeded (currently 16).

The attempted connection required activating a data context while roaming, but international roaming is disabled.

A client or server connection was severed in the middle of an in-progress load.

A resource couldn’t be read because of insufficient permissions.

A network resource was requested, but an internet connection has not been established and can’t be established automatically.

A redirect was specified by way of server response code, but the server didn’t accompany this code with a redirect URL.

A body stream was needed but the client did not provide one.

A requested resource couldn’t be retrieved.

An attempt to establish a secure connection failed for reasons that can’t be expressed more specifically.

A server certificate is expired, or is not yet valid.

A server certificate wasn’t signed by any root server.

A server certificate isn’t valid yet.

A server certificate was signed by a root server that isn’t trusted.

An asynchronous operation timed out.

The URL Loading System encountered an error that it can’t interpret.

A properly formed URL couldn’t be handled by the framework.

Authentication was required to access a resource.

An asynchronous request for authentication has been canceled by the user.

A server reported that a URL has a non-zero content length, but terminated the network connection gracefully without sending any data.

Recognize these keys from the user info dictionary of error objects produced by URL Loading APIs.