NSURLErrorDomain error codes description

The NSURLErrorDomain error codes are listed here https://developer.apple.com/documentation/foundation/1508628-url_loading_system_error_codes

However, 400 is just the http status code (http://www.w3.org/Protocols/HTTP/HTRESP.html) being returned which means you've got something wrong with your request.

I was unable to find name of an error for given code when developing in Swift. For that reason I paste minus codes for NSURLErrorDomain taken from NSURLError.h

/*!    @enum NSURL-related Error Codes    @abstract Constants used by NSError to indicate errors in the NSURL domain*/NS_ENUM(NSInteger){    NSURLErrorUnknown =             -1,    NSURLErrorCancelled =           -999,    NSURLErrorBadURL =              -1000,    NSURLErrorTimedOut =            -1001,    NSURLErrorUnsupportedURL =          -1002,    NSURLErrorCannotFindHost =          -1003,    NSURLErrorCannotConnectToHost =         -1004,    NSURLErrorNetworkConnectionLost =       -1005,    NSURLErrorDNSLookupFailed =         -1006,    NSURLErrorHTTPTooManyRedirects =        -1007,    NSURLErrorResourceUnavailable =         -1008,    NSURLErrorNotConnectedToInternet =      -1009,    NSURLErrorRedirectToNonExistentLocation =   -1010,    NSURLErrorBadServerResponse =       -1011,    NSURLErrorUserCancelledAuthentication =     -1012,    NSURLErrorUserAuthenticationRequired =  -1013,    NSURLErrorZeroByteResource =        -1014,    NSURLErrorCannotDecodeRawData =             -1015,    NSURLErrorCannotDecodeContentData =         -1016,    NSURLErrorCannotParseResponse =             -1017,    NSURLErrorAppTransportSecurityRequiresSecureConnection NS_ENUM_AVAILABLE(10_11, 9_0) = -1022,    NSURLErrorFileDoesNotExist =        -1100,    NSURLErrorFileIsDirectory =         -1101,    NSURLErrorNoPermissionsToReadFile =     -1102,    NSURLErrorDataLengthExceedsMaximum NS_ENUM_AVAILABLE(10_5, 2_0) =   -1103,    // SSL errors    NSURLErrorSecureConnectionFailed =      -1200,    NSURLErrorServerCertificateHasBadDate =     -1201,    NSURLErrorServerCertificateUntrusted =  -1202,    NSURLErrorServerCertificateHasUnknownRoot = -1203,    NSURLErrorServerCertificateNotYetValid =    -1204,    NSURLErrorClientCertificateRejected =   -1205,    NSURLErrorClientCertificateRequired =   -1206,    NSURLErrorCannotLoadFromNetwork =       -2000,    // Download and file I/O errors    NSURLErrorCannotCreateFile =        -3000,    NSURLErrorCannotOpenFile =          -3001,    NSURLErrorCannotCloseFile =         -3002,    NSURLErrorCannotWriteToFile =       -3003,    NSURLErrorCannotRemoveFile =        -3004,    NSURLErrorCannotMoveFile =          -3005,    NSURLErrorDownloadDecodingFailedMidStream = -3006,    NSURLErrorDownloadDecodingFailedToComplete =-3007,    NSURLErrorInternationalRoamingOff NS_ENUM_AVAILABLE(10_7, 3_0) =         -1018,    NSURLErrorCallIsActive NS_ENUM_AVAILABLE(10_7, 3_0) =                    -1019,    NSURLErrorDataNotAllowed NS_ENUM_AVAILABLE(10_7, 3_0) =                  -1020,    NSURLErrorRequestBodyStreamExhausted NS_ENUM_AVAILABLE(10_7, 3_0) =      -1021,    NSURLErrorBackgroundSessionRequiresSharedContainer NS_ENUM_AVAILABLE(10_10, 8_0) = -995,    NSURLErrorBackgroundSessionInUseByAnotherProcess NS_ENUM_AVAILABLE(10_10, 8_0) = -996,    NSURLErrorBackgroundSessionWasDisconnected NS_ENUM_AVAILABLE(10_10, 8_0)= -997,};

IN SWIFT 3.Here are the NSURLErrorDomain error codes description in a Swift 3 enum:(copied from answer above and converted what i can).

enum NSURLError: Int {    case unknown = -1    case cancelled = -999    case badURL = -1000    case timedOut = -1001    case unsupportedURL = -1002    case cannotFindHost = -1003    case cannotConnectToHost = -1004    case connectionLost = -1005    case lookupFailed = -1006    case HTTPTooManyRedirects = -1007    case resourceUnavailable = -1008    case notConnectedToInternet = -1009    case redirectToNonExistentLocation = -1010    case badServerResponse = -1011    case userCancelledAuthentication = -1012    case userAuthenticationRequired = -1013    case zeroByteResource = -1014    case cannotDecodeRawData = -1015    case cannotDecodeContentData = -1016    case cannotParseResponse = -1017    //case NSURLErrorAppTransportSecurityRequiresSecureConnection NS_ENUM_AVAILABLE(10_11, 9_0) = -1022    case fileDoesNotExist = -1100    case fileIsDirectory = -1101    case noPermissionsToReadFile = -1102    //case NSURLErrorDataLengthExceedsMaximum NS_ENUM_AVAILABLE(10_5, 2_0) =   -1103    // SSL errors    case secureConnectionFailed = -1200    case serverCertificateHasBadDate = -1201    case serverCertificateUntrusted = -1202    case serverCertificateHasUnknownRoot = -1203    case serverCertificateNotYetValid = -1204    case clientCertificateRejected = -1205    case clientCertificateRequired = -1206    case cannotLoadFromNetwork = -2000    // Download and file I/O errors    case cannotCreateFile = -3000    case cannotOpenFile = -3001    case cannotCloseFile = -3002    case cannotWriteToFile = -3003    case cannotRemoveFile = -3004    case cannotMoveFile = -3005    case downloadDecodingFailedMidStream = -3006    case downloadDecodingFailedToComplete = -3007    /*     case NSURLErrorInternationalRoamingOff NS_ENUM_AVAILABLE(10_7, 3_0) =         -1018     case NSURLErrorCallIsActive NS_ENUM_AVAILABLE(10_7, 3_0) =                    -1019     case NSURLErrorDataNotAllowed NS_ENUM_AVAILABLE(10_7, 3_0) =                  -1020     case NSURLErrorRequestBodyStreamExhausted NS_ENUM_AVAILABLE(10_7, 3_0) =      -1021     case NSURLErrorBackgroundSessionRequiresSharedContainer NS_ENUM_AVAILABLE(10_10, 8_0) = -995     case NSURLErrorBackgroundSessionInUseByAnotherProcess NS_ENUM_AVAILABLE(10_10, 8_0) = -996     case NSURLErrorBackgroundSessionWasDisconnected NS_ENUM_AVAILABLE(10_10, 8_0)= -997     */}

Direct link to URLError.Code in the Swift github repository, which contains the up to date list of error codes being used (github link).