Looks like Apple have removed a number of their development articles that outline the error codes, below is quite useful for troubleshooting iOS and macOS connectivity issues.
CFNetworkErrors
kCFHostErrorHostNotFound = 1,
kCFHostErrorUnknown = 2,
SOCKS Errors
kCFSOCKSErrorUnknownClientVersion = 100,
kCFSOCKSErrorUnsupportedServerVersion = 101,
SOCKS4-Specific Errors
kCFSOCKS4ErrorRequestFailed = 110,
kCFSOCKS4ErrorIdentdFailed = 111,
kCFSOCKS4ErrorIdConflict = 112,
kCFSOCKS4ErrorUnknownStatusCode = 113,
SOCKS5-specific errors
kCFSOCKS5ErrorBadState = 120,
kCFSOCKS5ErrorBadResponseAddr = 121,
kCFSOCKS5ErrorBadCredentials = 122,
kCFSOCKS5ErrorUnsupportedNegotiationMethod = 123,
kCFSOCKS5ErrorNoAcceptableMethod = 124,
FTP Errors
kCFFTPErrorUnexpectedStatusCode = 200,
HTTP Errors
kCFErrorHTTPAuthenticationTypeUnsupported = 300,
kCFErrorHTTPBadCredentials = 301,
kCFErrorHTTPConnectionLost = 302,
kCFErrorHTTPParseFailure = 303,
kCFErrorHTTPRedirectionLoopDetected = 304,
kCFErrorHTTPBadURL = 305,
kCFErrorHTTPProxyConnectionFailure = 306,
kCFErrorHTTPBadProxyCredentials = 307,
kCFErrorPACFileError = 308,
kCFErrorPACFileAuth = 309,
kCFErrorHTTPSProxyConnectionFailure = 310,
kCFStreamErrorHTTPSProxyFailureUnexpectedResponseToCONNECTMethod = 311,
CFURL and CRUFLConnection Errors
These error codes also match NSURLErrorDomain error codes
kCFURLErrorUnknown = -998,
kCFURLErrorCancelled = -999,
kCFURLErrorBadURL = -1000,
kCFURLErrorTimedOut = -1001,
kCFURLErrorUnsupportedURL = -1002,
kCFURLErrorCannotFindHost = -1003,
kCFURLErrorCannotConnectToHost = -1004,
kCFURLErrorNetworkConnectionLost = -1005,
kCFURLErrorDNSLookupFailed = -1006,
kCFURLErrorHTTPTooManyRedirects = -1007,
kCFURLErrorResourceUnavailable = -1008,
kCFURLErrorNotConnectedToInternet = -1009,
kCFURLErrorRedirectToNonExistentLocation = -1010,
kCFURLErrorBadServerResponse = -1011,
kCFURLErrorUserCancelledAuthentication = -1012,
kCFURLErrorUserAuthenticationRequired = -1013,
kCFURLErrorZeroByteResource = -1014,
kCFURLErrorCannotDecodeRawData = -1015,
kCFURLErrorCannotDecodeContentData = -1016,
kCFURLErrorCannotParseResponse = -1017,
kCFURLErrorInternationalRoamingOff = -1018,
kCFURLErrorCallIsActive = -1019,
kCFURLErrorDataNotAllowed = -1020,
kCFURLErrorRequestBodyStreamExhausted = -1021,
kCFURLErrorFileDoesNotExist = -1100,
kCFURLErrorFileIsDirectory = -1101,
kCFURLErrorNoPermissionsToReadFile = -1102,
kCFURLErrorDataLengthExceedsMaximum = -1103,
SSL Errors
kCFURLErrorSecureConnectionFailed = -1200,
kCFURLErrorServerCertificateHasBadDate = -1201,
kCFURLErrorServerCertificateUntrusted = -1202,
kCFURLErrorServerCertificateHasUnknownRoot = -1203,
kCFURLErrorServerCertificateNotYetValid = -1204,
kCFURLErrorClientCertificateRejected = -1205,
kCFURLErrorClientCertificateRequired = -1206,
kCFURLErrorCannotLoadFromNetwork = -2000,
Download and file I/O errors
kCFURLErrorCannotCreateFile = -3000,
kCFURLErrorCannotOpenFile = -3001,
kCFURLErrorCannotCloseFile = -3002,
kCFURLErrorCannotWriteToFile = -3003,
kCFURLErrorCannotRemoveFile = -3004,
kCFURLErrorCannotMoveFile = -3005,
kCFURLErrorDownloadDecodingFailedMidStream = -3006,
kCFURLErrorDownloadDecodingFailedToComplete = -3007,
Cookie Errors
kCFHTTPCookieCannotParseCookieFile = -4000,
Errors Originating from CFNetServices
kCFNetServiceErrorUnknown = -72000L,
kCFNetServiceErrorCollision = -72001L,
kCFNetServiceErrorNotFound = -72002L,
kCFNetServiceErrorInProgress = -72003L,
kCFNetServiceErrorBadArgument = -72004L,
kCFNetServiceErrorCancel = -72005L,
kCFNetServiceErrorInvalid = -72006L,
kCFNetServiceErrorTimeout = -72007L,
kCFNetServiceErrorDNSServiceFailure = -73000L,
| Error | Description | OSX Version |
|---|---|---|
kCFHostErrorHostNotFound |
Indicates that the DNS lookup failed. | 10.5 and later |
| kCFHostErrorUnknown | An unknown error occurred (a name server failure, for example). For additional information, you can query the kCFGetAddrInfoFailureKey key to obtain the value returned by getaddrinfo and look up the value in /usr/include/netdb.h. | 10.5 and later |
| kCFSOCKSErrorUnknownClientVersion | The SOCKS server rejected access because it does not support connections with the requested SOCKS version. SOCKS client version. You can query the kCFSOCKSVersionKey key to find out what version the server requested. | 10.5 and later |
| kCFSOCKSErrorUnsupportedServerVersion | The version of SOCKS requested by the server is not supported. You can query the kCFSOCKSVersionKeykey to find out what version the server requested. | 10.5 and later |
| kCFSOCKS4ErrorRequestFailed | Request rejected by the server or request failed. This error is specific to SOCKS4. | 10.5 and later |
| kCFSOCKS4ErrorIdentdFailed | Request rejected by the server because it could not connect to the identd daemon on the client. This error is specific to SOCKS4. | 10.5 and later |
| kCFSOCKS4ErrorIdConflict | Request rejected by the server because the client program and the identd daemon reported different user IDs. This error is specific to SOCKS4. | 10.5 and later |
| kCFSOCKS4ErrorUnknownStatusCode | The status code returned by the server is unknown. This error is specific to SOCKS4. | 10.5 and later |
| kCFSOCKS5ErrorBadState | The stream is not in a state that allows the requested operation. | 10.5 and later |
| kCFSOCKS5ErrorBadResponseAddr | The address type returned is not supported | 10.5 and later |
| kCFSOCKS5ErrorBadCredentials | The SOCKS server refused the client connection because of bad login credentials. | 10.5 and later |
| kCFSOCKS5ErrorUnsupportedNegotiationMethod | The requested method is not supported. You can query the kCFSOCKSNegotiationMethodKey key to find out which method the server requested. | 10.5 and later |
| kCFSOCKS5ErrorNoAcceptableMethod | The client and server could not find a mutually agreeable authentication method. | 10.5 and later |
| kCFFTPErrorUnexpectedStatusCode | The server returned an unexpected status code. | 10.5 and later |
| kCFErrorHTTPAuthenticationTypeUnsupported | The client and server could not agree on a supported authentication type. | 10.5 and later |
| kCFErrorHTTPBadCredentials | The credentials provided for an authenticated connection were rejected by the server | 10.5 and later |
| kCFErrorHTTPConnectionLost | The connection to the server was dropped. This usually indicates a highly overloaded server | 10.5 and later |
| kCFErrorHTTPParseFailure | The HTTP server response could not be parsed. | 10.5 and later. |
| kCFErrorHTTPRedirectionLoopDetected | Too many HTTP redirects occurred before reaching a page that did not redirect the client to another page. This usually indicates a redirect loop | 10.5 and later. |
| kCFErrorHTTPBadURL | The requested URL could not be retrieved. | 10.5 and later. |
| kCFErrorHTTPProxyConnectionFailure | A connection could not be established to the HTTP proxy. | v10.5 and later. |
| kCFErrorHTTPBadProxyCredentials | The authentication credentials provided for logging into the proxy were rejected. | 10.5 and later. |
| kCFErrorPACFileError | An error occurred with the proxy autoconfiguration file. | 10.5 and later. |
| kCFErrorPACFileAuth | The authentication credentials provided by the proxy autoconfiguration file were rejected. | 10.6 and later. |
| kCFErrorHTTPSProxyConnectionFailure | A connection could not be established to the HTTPS proxy. | 10.6 and later. |
| kCFStreamErrorHTTPSProxyFailureUnexpectedResponseToCONNECTMethod | The HTTPS proxy returned an unexpected status code, such as a 3xx redirect. | 10.7 and later |
| kCFURLErrorUnknown | An unknown error occurred. | 10.6 and later |
| kCFURLErrorCancelled | The connection was cancelled. | 10.6 and later |
| kCFURLErrorBadURL | The connection failed due to a malformed URL. | 10.6 and later |
| kCFURLErrorTimedOut | The connection timed out. | 10.6 and later |
| kCFURLErrorUnsupportedURL | The connection failed due to an unsupported URL scheme. | 10.6 and later |
| kCFURLErrorCannotFindHost | The connection failed because the host could not be found. | 10.6 and later |
| kCFURLErrorCannotConnectToHost | The connection failed because a connection cannot be made to the host. | 10.6 and later |
| kCFURLErrorNetworkConnectionLost | The connection failed because the network connection was lost. | 10.6 and later |
| kCFURLErrorDNSLookupFailed | The connection failed because the DNS lookup failed. | 10.6 and later |
| kCFURLErrorHTTPTooManyRedirects | The HTTP connection failed due to too many redirects. | 10.6 and later |
| kCFURLErrorResourceUnavailable | The connection’s resource is unavailable. | 10.6 and later |
| kCFURLErrorNotConnectedToInternet | The connection failed because the device is not connected to the internet. | 10.6 and later |
| kCFURLErrorRedirectToNonExistentLocation | The connection was redirected to a nonexistent location. | 10.6 and later |
| kCFURLErrorBadServerResponse | The connection received an invalid server response. | 10.6 and later. |
| kCFURLErrorUserCancelledAuthentication | The connection failed because the user cancelled required authentication. | 10.6 and later. |
| kCFURLErrorUserAuthenticationRequired | The connection failed because authentication is required. | 10.6 and later |
| kCFURLErrorZeroByteResource | The resource retrieved by the connection is zero bytes. | 10.6 and later |
| kCFURLErrorCannotDecodeRawData | The connection cannot decode data encoded with a known content encoding. | 10.6 and later |
| kCFURLErrorCannotDecodeContentData | The connection cannot decode data encoded with an unknown content encoding. | 10.6 and later |
| kCFURLErrorCannotParseResponse | The connection cannot parse the server’s response. | 10.6 and later |
| kCFURLErrorInternationalRoamingOff | The connection failed because international roaming is disabled on the device. | 10.6 and later. |
| kCFURLErrorCallIsActive | The connection failed because a call is active. | 10.6 and later. |
| kCFURLErrorDataNotAllowed | The connection failed because data use is currently not allowed on the device. | 10.6 and later. |
| kCFURLErrorRequestBodyStreamExhausted | The connection failed because its request’s body stream was exhausted. | 10.6 and later |
| kCFURLErrorFileDoesNotExist | The file operation failed because the file does not exist. | 10.6 and later |
| kCFURLErrorFileIsDirectory | The file operation failed because the file is a directory. | v10.6 and later |
| kCFURLErrorNoPermissionsToReadFile | The file operation failed because it does not have permission to read the file. | v10.6 and later |
| kCFURLErrorDataLengthExceedsMaximum | The file operation failed because the file is too large. | 10.6 and later |
| kCFURLErrorSecureConnectionFailed | The secure connection failed for an unknown reason | 10.6 and later |
| kCFURLErrorServerCertificateHasBadDate | The secure connection failed because the server’s certificate has an invalid date. | 10.6 and later |
| kCFURLErrorServerCertificateUntrusted | The secure connection failed because the server’s certificate is not trusted. | 10.6 and later |
| kCFURLErrorServerCertificateHasUnknownRoot | The secure connection failed because the server’s certificate has an unknown root. | 10.6 and later |
| kCFURLErrorServerCertificateNotYetValid | The secure connection failed because the server’s certificate is not yet valid. | 10.6 and later |
| kCFURLErrorClientCertificateRejected | The secure connection failed because the client’s certificate was rejected. | 10.6 and later |
| kCFURLErrorClientCertificateRequired | The secure connection failed because the server requires a client certificate. | 10.6 and later |
| kCFURLErrorCannotLoadFromNetwork | The connection failed because it is being required to return a cached resource, but one is not available. | 10.6 and later |
| kCFURLErrorCannotCreateFile | The file cannot be created. | 10.6 and later |
| kCFURLErrorCannotOpenFile | The file cannot be opened | 10.6 and later |
| kCFURLErrorCannotCloseFile | The file cannot be closed | 10.6 and later |
| kCFURLErrorCannotWriteToFile | The file cannot be written. | 10.6 and later |
| kCFURLErrorCannotRemoveFile | The file cannot be removed. | 10.6 and later |
| kCFURLErrorCannotMoveFile | The file cannot be moved. | 10.6 and later |
| kCFURLErrorDownloadDecodingFailedMidStream | The download failed because decoding of the downloaded data failed mid-stream. | 10.6 and later |
| kCFURLErrorDownloadDecodingFailedToComplete | The download failed because decoding of the downloaded data failed to complete. | 10.6 and later |
| kCFHTTPCookieCannotParseCookieFile | The cookie file cannot be parsed. | 10.6 and later |
| kCFNetServiceErrorUnknown | An unknown error occurred. | 10.2 and later |
| kCFNetServiceErrorCollision | An attempt was made to use a name that is already in use. | 10.2 and later. |
| kCFNetServiceErrorNotFound | Not used. | 10.2 and later. |
| kCFNetServiceErrorInProgress | A new search could not be started because a search is already in progress. | 10.2 and later |
| kCFNetServiceErrorBadArgument | A required argument was not provided or was not valid. | 10.2 and later. |
| kCFNetServiceErrorCancel | The search or service was cancelled. | 10.2 and later |
| kCFNetServiceErrorInvalid | Invalid data was passed to a CFNetServices function. | 10.2 and later |
| kCFNetServiceErrorTimeout | A search failed because it timed out. | 10.2 and later |
| kCFNetServiceErrorDNSServiceFailure | DNS service discovery returned an error. You can query the kCFDNSServiceFailureKey key to find out the error returned by DNS service discovery and look up the code in /usr/include/dns_sd.h or DNS Service Discovery C Reference. | 10.5 and later |