Содержание
How Socket Error Codes Depend on Runtime and Operating System
Rider consists of several processes that send messages to each other via sockets. To ensure the reliability of the whole application, it’s important to properly handle all the socket errors. In our codebase, we had the following code which was adopted from Mono Debugger Libs and helps us communicate with debugger processes:
In the case of a failed connection because of a “ConnectionRefused” error, we are retrying the connection attempt. It works fine with .NET Framework and Mono. However, once we migrated to .NET Core, this method no longer correctly detects the “connection refused” situation on Linux and macOS. If we open the SocketException documentation, we will learn that this class has three different properties with error codes: - SocketError SocketErrorCode : Gets the error code that is associated with this exception.
- int ErrorCode : Gets the error code that is associated with this exception.
- int NativeErrorCode : Gets the Win32 error code associated with this exception.
Digging into the problem
Let’s start with the following program, which prints error code property values for SocketError.ConnectionRefused :
If we run it on Windows, we will get the same value on .NET Framework, Mono, and .NET Core:
SocketErrorCode
SocketException.SocketErrorCode returns a value from the SocketError enum. The numerical values of the enum elements are the same on all the runtimes (see its implementation in .NET Framework, .NET Core 3.1.3, and Mono 6.8.0.105):
These values correspond to the Windows Sockets Error Codes.
NativeErrorCode
In .NET Core, the native code is calculated in the constructor (see SocketException.cs#L20): The Windows implementation of GetNativeErrorForSocketError is trivial (see SocketException.Windows.cs):
The Unix implementation is more complicated (see SocketException.Unix.cs): TryGetNativeErrorForSocketError should convert SocketError to the native Unix error code. Unfortunately, there exists no unequivocal mapping between Windows and Unix error codes. As such, the .NET team decided to create a Dictionary that maps error codes in the best possible way (see SocketErrorPal.Unix.cs):
Once we have an instance of Interop.Error , we call interopErr.Info().RawErrno . The implementation of RawErrno can be found in Interop.Errors.cs: Here we are jumping to the native function SystemNative_ConvertErrorPalToPlatform that maps Error to the native integer code that is defined in errno.h. You can get all the values using the errno util. Here is a typical output on Linux: Note that errno may be not available by default in your Linux distro. For example, on Debian, you should call sudo apt-get install moreutils to get this utility. Here is a typical output on macOS:
Hooray! We’ve finished our fascinating journey into the internals of socket error codes. Now you know where .NET is getting the native error code for each SocketException from!
ErrorCode
The ErrorCode property is the most boring one, as it always returns NativeErrorCode . .NET Framework, Mono 6.8.0.105:
Circling back to the original method we started this post with, we rewrote ShouldRetryConnection as follows:
There was a lot of work involved in tracking down the error code to check against, but in the end, our code is much more readable now. Adding to that, this method is now also completely cross-platform, and works correctly on any runtime.
Overview of the native error codes
In some situations, you may want to have a table with native error codes on different operating systems. We can get these values with the following code snippet:
| |"We executed this program on Windows, Linux, and macOS. Here are the aggregated results:
| SocketError | Windows | Linux | macOS |
| Success | 0 | 0 | 0 |
| OperationAborted | 995 | 125 | 89 |
| IOPending | 997 | 115 | 36 |
| Interrupted | 10004 | 4 | 4 |
| AccessDenied | 10013 | 13 | 13 |
| Fault | 10014 | 14 | 14 |
| InvalidArgument | 10022 | 22 | 22 |
| TooManyOpenSockets | 10024 | 23 | 23 |
| WouldBlock | 10035 | 11 | 35 |
| InProgress | 10036 | 115 | 36 |
| AlreadyInProgress | 10037 | 114 | 37 |
| NotSocket | 10038 | 88 | 38 |
| DestinationAddressRequired | 10039 | 89 | 39 |
| MessageSize | 10040 | 90 | 40 |
| ProtocolType | 10041 | 91 | 41 |
| ProtocolOption | 10042 | 92 | 42 |
| ProtocolNotSupported | 10043 | 93 | 43 |
| SocketNotSupported | 10044 | 94 | 44 |
| OperationNotSupported | 10045 | 95 | 45 |
| ProtocolFamilyNotSupported | 10046 | 96 | 46 |
| AddressFamilyNotSupported | 10047 | 97 | 47 |
| AddressAlreadyInUse | 10048 | 98 | 48 |
| AddressNotAvailable | 10049 | 99 | 49 |
| NetworkDown | 10050 | 100 | 50 |
| NetworkUnreachable | 10051 | 101 | 51 |
| NetworkReset | 10052 | 102 | 52 |
| ConnectionAborted | 10053 | 103 | 53 |
| ConnectionReset | 10054 | 104 | 54 |
| NoBufferSpaceAvailable | 10055 | 105 | 55 |
| IsConnected | 10056 | 106 | 56 |
| NotConnected | 10057 | 107 | 57 |
| Shutdown | 10058 | 32 | 32 |
| TimedOut | 10060 | 110 | 60 |
| ConnectionRefused | 10061 | 111 | 61 |
| HostDown | 10064 | 112 | 64 |
| HostUnreachable | 10065 | 113 | 65 |
| ProcessLimit | 10067 | 10067 | 10067 |
| SystemNotReady | 10091 | 10091 | 10091 |
| VersionNotSupported | 10092 | 10092 | 10092 |
| NotInitialized | 10093 | 10093 | 10093 |
| Disconnecting | 10101 | 108 | 58 |
| TypeNotFound | 10109 | 10109 | 10109 |
| HostNotFound | 11001 | -131073 | -131073 |
| TryAgain | 11002 | 11 | 35 |
| NoRecovery | 11003 | 11003 | 11003 |
| NoData | 11004 | 61 | 96 |
| SocketError | -1 | -1 | -1 |
This table may be useful if you work with native socket error codes.
Summary
- SocketException.SocketErrorCode returns a value from the SocketError enum. The numerical values of the enum elements always correspond to the Windows socket error codes.
- SocketException.ErrorCode always returns SocketException.NativeErrorCode .
- SocketException.NativeErrorCode on .NET Framework and Mono always corresponds to the Windows error codes (even if you are using Mono on Unix). On .NET Core, SocketException.NativeErrorCode equals the corresponding native error code from the current operating system.
A few practical recommendations:
- If you want to write portable code, always use SocketException.SocketErrorCode and compare it with the values of SocketError . Never use raw numerical error codes.
- If you want to get the native error code on .NET Core (e.g., for passing to another native program), use SocketException.NativeErrorCode . Remember that different Unix-based operating systems (e.g., Linux, macOS, Solaris) have different native code sets. You can get the exact values of the native error codes by using the errno command.
References
gabrielfalcao / tcp-socket-error-codes-errno.txt
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| 0 = Success |
| 1 = Operation not permitted |
| 2 = No such file or directory |
| 3 = No such process |
| 4 = Interrupted system call |
| 5 = Input/output error |
| 6 = No such device or address |
| 7 = Argument list too long |
| 8 = Exec format error |
| 9 = Bad file descriptor |
| 10 = No child processes |
| 11 = Resource temporarily unavailable |
| 12 = Cannot allocate memory |
| 13 = Permission denied |
| 14 = Bad address |
| 15 = Block device required |
| 16 = Device or resource busy |
| 17 = File exists |
| 18 = Invalid cross-device link |
| 19 = No such device |
| 20 = Not a directory |
| 21 = Is a directory |
| 22 = Invalid argument |
| 23 = Too many open files in system |
| 24 = Too many open files |
| 25 = Inappropriate ioctl for device |
| 26 = Text file busy |
| 27 = File too large |
| 28 = No space left on device |
| 29 = Illegal seek |
| 30 = Read-only file system |
| 31 = Too many links |
| 32 = Broken pipe |
| 33 = Numerical argument out of domain |
| 34 = Numerical result out of range |
| 35 = Resource deadlock avoided |
| 36 = File name too long |
| 37 = No locks available |
| 38 = Function not implemented |
| 39 = Directory not empty |
| 40 = Too many levels of symbolic links |
| 41 = Unknown error 41 |
| 42 = No message of desired type |
| 43 = Identifier removed |
| 44 = Channel number out of range |
| 45 = Level 2 not synchronized |
| 46 = Level 3 halted |
| 47 = Level 3 reset |
| 48 = Link number out of range |
| 49 = Protocol driver not attached |
| 50 = No CSI structure available |
| 51 = Level 2 halted |
| 52 = Invalid exchange |
| 53 = Invalid request descriptor |
| 54 = Exchange full |
| 55 = No anode |
| 56 = Invalid request code |
| 57 = Invalid slot |
| 58 = Unknown error 58 |
| 59 = Bad font file format |
| 60 = Device not a stream |
| 61 = No data available |
| 62 = Timer expired |
| 63 = Out of streams resources |
| 64 = Machine is not on the network |
| 65 = Package not installed |
| 66 = Object is remote |
| 67 = Link has been severed |
| 68 = Advertise error |
| 69 = Srmount error |
| 70 = Communication error on send |
| 71 = Protocol error |
| 72 = Multihop attempted |
| 73 = RFS specific error |
| 74 = Bad message |
| 75 = Value too large for defined data type |
| 76 = Name not unique on network |
| 77 = File descriptor in bad state |
| 78 = Remote address changed |
| 79 = Can not access a needed shared library |
| 80 = Accessing a corrupted shared library |
| 81 = .lib section in a.out corrupted |
| 82 = Attempting to link in too many shared libraries |
| 83 = Cannot exec a shared library directly |
| 84 = Invalid or incomplete multibyte or wide character |
| 85 = Interrupted system call should be restarted |
| 86 = Streams pipe error |
| 87 = Too many users |
| 88 = Socket operation on non-socket |
| 89 = Destination address required |
| 90 = Message too long |
| 91 = Protocol wrong type for socket |
| 92 = Protocol not available |
| 93 = Protocol not supported |
| 94 = Socket type not supported |
| 95 = Operation not supported |
| 96 = Protocol family not supported |
| 97 = Address family not supported by protocol |
| 98 = Address already in use |
| 99 = Cannot assign requested address |
| 100 = Network is down |
| 101 = Network is unreachable |
| 102 = Network dropped connection on reset |
| 103 = Software caused connection abort |
| 104 = Connection reset by peer |
| 105 = No buffer space available |
| 106 = Transport endpoint is already connected |
| 107 = Transport endpoint is not connected |
| 108 = Cannot send after transport endpoint shutdown |
| 109 = Too many references: cannot splice |
| 110 = Connection timed out |
| 111 = Connection refused |
| 112 = Host is down |
| 113 = No route to host |
| 114 = Operation already in progress |
| 115 = Operation now in progress |
| 116 = Stale NFS file handle |
| 117 = Structure needs cleaning |
| 118 = Not a XENIX named type file |
| 119 = No XENIX semaphores available |
| 120 = Is a named type file |
| 121 = Remote I/O error |
| 122 = Disk quota exceeded |
| 123 = No medium found |
| 124 = Wrong medium type |