Apple NSURLError and CFNetworkError codes

CFNetworkErrors.h

typedef CF_ENUM(int, CFNetworkErrors) {

  kCFHostErrorHostNotFound = 1,
  kCFHostErrorUnknown = 2, // Query the kCFGetAddrInfoFailureKey to get the value returned from getaddrinfo; lookup in netdb.h
  // SOCKS errors; in all cases you may query kCFSOCKSStatusCodeKey to recover the status code returned by the server
  kCFSOCKSErrorUnknownClientVersion = 100,
  kCFSOCKSErrorUnsupportedServerVersion = 101, // Query the kCFSOCKSVersionKey to find the version requested by the server
  // SOCKS4-specific errors
  kCFSOCKS4ErrorRequestFailed = 110,  // request rejected or failed by the server
  kCFSOCKS4ErrorIdentdFailed = 111,  // request rejected because SOCKS server cannot connect to identd on the client
  kCFSOCKS4ErrorIdConflict = 112,  // request rejected because the client program and identd report different user-ids
  kCFSOCKS4ErrorUnknownStatusCode = 113,
  // SOCKS5-specific errors
  kCFSOCKS5ErrorBadState = 120,
  kCFSOCKS5ErrorBadResponseAddr = 121,
  kCFSOCKS5ErrorBadCredentials = 122,
  kCFSOCKS5ErrorUnsupportedNegotiationMethod = 123, // query kCFSOCKSNegotiationMethodKey to find the method requested
  kCFSOCKS5ErrorNoAcceptableMethod = 124,
  // FTP errors; query the kCFFTPStatusCodeKey to get the status code returned by the server
  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,
	
  // Error codes for CFURLConnection and CFURLProtocol
  kCFURLErrorBackgroundSessionInUseByAnotherProcess = -996,
  kCFURLErrorBackgroundSessionWasDisconnected = -997,
  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,
  kCFURLErrorAppTransportSecurityRequiresSecureConnection = -1022,
  kCFURLErrorFileDoesNotExist = -1100,
  kCFURLErrorFileIsDirectory = -1101,
  kCFURLErrorNoPermissionsToReadFile = -1102,
  kCFURLErrorDataLengthExceedsMaximum = -1103,
  kCFURLErrorFileOutsideSafeArea = -1104,
  // 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 // An error from DNS discovery; look at kCFDNSServiceFailureKey to get the error number and interpret using dns_sd.h	
};

NSURLError.h

NS_ERROR_ENUM(NSURLErrorDomain)
{
    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 API_AVAILABLE(macos(10.11), ios(9.0), watchos(2.0), tvos(9.0)) = -1022,
    NSURLErrorFileDoesNotExist = 		-1100,
    NSURLErrorFileIsDirectory = 		-1101,
    NSURLErrorNoPermissionsToReadFile = 	-1102,
    NSURLErrorDataLengthExceedsMaximum API_AVAILABLE(macos(10.5), ios(2.0), watchos(2.0), tvos(9.0)) =	-1103,
    NSURLErrorFileOutsideSafeArea API_AVAILABLE(macos(10.12.4), ios(10.3), watchos(3.2), tvos(10.2)) = -1104,
    
    // 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 API_AVAILABLE(macos(10.7), ios(3.0), watchos(2.0), tvos(9.0)) =         -1018,
    NSURLErrorCallIsActive API_AVAILABLE(macos(10.7), ios(3.0), watchos(2.0), tvos(9.0)) =                    -1019,
    NSURLErrorDataNotAllowed API_AVAILABLE(macos(10.7), ios(3.0), watchos(2.0), tvos(9.0)) =                  -1020,
    NSURLErrorRequestBodyStreamExhausted API_AVAILABLE(macos(10.7), ios(3.0), watchos(2.0), tvos(9.0)) =      -1021,
    
    NSURLErrorBackgroundSessionRequiresSharedContainer API_AVAILABLE(macos(10.10), ios(8.0), watchos(2.0), tvos(9.0)) = -995,
    NSURLErrorBackgroundSessionInUseByAnotherProcess API_AVAILABLE(macos(10.10), ios(8.0), watchos(2.0), tvos(9.0)) = -996,
    NSURLErrorBackgroundSessionWasDisconnected API_AVAILABLE(macos(10.10), ios(8.0), watchos(2.0), tvos(9.0))= -997,
};

Jesus lord, just what I needed

@isaac-weisberg this Gist is super old: from 2017. I don't even remember what was it used for.

I suggest you check our the latest NSURLError.h and CFNetworkErrors.h in Xcode or, if you're searching for an error by code, use a wonderful https://www.osstatus.com/ for that.

For those looking for a tool to find these codes, check out a repo I just published: https://github.com/AvdLee/WhatTheErrorCode