In my case, I was checking logs for a system that crawls pages and hence attempts to resolve and connect to thousands of hosts. This system logs the exceptions, but unfortunately did not provide a customized message when doing so. Analyzing the logs showed that the two most common error messages were: 1) a failure to resolve the hostname and 2) failing to connect to an HTTP server on the host. An example error message for the first case is
java.net.UnknownHostException: some-host-that-does-not-exist. This message is quite useful as the exception name explains the problem and the message tells me the name of the host that could not be resolved. An example message for the second case is java.net.SocketTimeoutException: connect timed out. This message is explains the problem, but doesn't given me the crucial information of what it was trying to connect to. Though this can easily be fixed in the application code, it is disappointing that the default message is so bad. I have noticed that my opinion of a programming language or technology seems to go down steadily the longer I am forced to use it at work. Is the grass greener on one of the other sides? How do other languages, or rather the networking libraries they provide, fair for this use case? I looked at 13 options to see how many would give a decent error message for both use cases. The results were not very encouraging. Only one option, Go, had reasonable messages for both. For the host not found case 4 options included the hostname. Only two options provided the host and port in the failed to connect case. The results are summarized in the table below the fold with links to the source code and raw error messages.
| Language - Library | Host not found | Unable to connect |
|---|---|---|
| Bash - nc | No | Yes |
| C - sys/socket.h | No | No |
| C++ - boost::asio | No | No |
| C# - System.Net.Sockets | No | No |
| D - std.socket | Yes | No |
| Erlang - gen_tcp | No | No |
| Go - net.Dial | Yes | Yes |
| Haskell - Network.Socket | No | No |
| Java - java.net.Socket | Yes | No |
| Perl - IO::Socket::INET | Yes | No |
| Python - socket | No | No |
| Ruby - socket | No | No |
| TCL - socket | No | No |
Bash - NC command
#!/bin/bash if [ "$1" == "" ] || [ "$2" == "" ]; then echo "Usage: $0 <host> <port>" exit 1 fi nc -v -w1 $1 $2
$ ./connect.sh some-host-that-does-not-exist 12345 nc: getaddrinfo: nodename nor servname provided, or not known
$ ./connect.sh 1.2.3.4 12345 nc: connect to 1.2.3.4 port 12345 (tcp) failed: Operation timed out
C - sys/socket.h
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/socket.h> #include <netdb.h> void die(void (*f)(const char *), const char *label) { f(label); exit(EXIT_FAILURE); } int main(int argc, char **argv) { if (argc < 3) { printf("Usage: %s <host> <port>\n", argv[0]); return EXIT_FAILURE; } int s = socket(PF_INET, SOCK_STREAM, 0); if (s < 0) { die(perror, "socket"); } struct hostent *host = gethostbyname(argv[1]); if (host == NULL) { die(herror, "gethostbyname"); } struct sockaddr_in addr; memset(&addr, 0, sizeof(addr)); addr.sin_family = AF_INET; addr.sin_port = htons(atoi(argv[2])); addr.sin_addr = *(struct in_addr *) host->h_addr; if (connect(s, (struct sockaddr *) &addr, sizeof(addr)) < 0) { die(perror, "connect"); } if (close(s) < 0) { die(perror, "close"); } return EXIT_SUCCESS; }
$ ./connect some-host-that-does-not-exist 12345 gethostbyname: Unknown host
$ ./connect 1.2.3.4 12345 connect: Connection timed out
C++ - boost::asio
#include <iostream> #include <cstdlib> #include <boost/asio.hpp> #include <boost/system/error_code.hpp> using namespace boost::asio; using namespace boost::asio::ip; int main(int argc, char **argv) { if (argc < 3) { std::cout << "Usage: " << argv[0] << " <host> <port>" << std::endl; return EXIT_FAILURE; } io_service service; boost::system::error_code error; tcp::resolver resolver(service); tcp::resolver::query query(argv[1], argv[2]); tcp::resolver::iterator iter = resolver.resolve(query, error); tcp::resolver::iterator end; if (iter == end) { throw boost::system::system_error(error); } tcp::socket socket(service); socket.connect(*iter); socket.close(); return EXIT_SUCCESS; }
$ ./connect some-host-that-does-not-exist 12345 terminate called after throwing an instance of 'boost::system::system_error' what(): Host not found (authoritative) Abort trap
$ ./connect 1.2.3.4 12345 terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::system::system_error> >' what(): Operation timed out Abort trap
C# - System.Net.Sockets
Note I tested this using Mono, not the implementation from Microsoft. I don't know if the error message would be exactly the same or not.using System; using System.Net.Sockets; public class Connect { static public void Main(String[] args) { if (args.Length < 2) { Console.WriteLine("Usage: connect.exe <host> <port>"); Environment.Exit(1); } TcpClient s = new TcpClient(args[0], int.Parse(args[1])); s.Close(); } }
$ mono ./connect.exe some-host-that-does-not-exist 12345 Unhandled Exception: System.Net.Sockets.SocketException: No such host is known at System.Net.Dns.hostent_to_IPHostEntry (System.String h_name, System.String[] h_aliases, System.String[] h_addrlist) [0x00000] in <filename unknown>:0 at System.Net.Dns.GetHostByName (System.String hostName) [0x00000] in <filename unknown>:0 at System.Net.Dns.GetHostEntry (System.String hostNameOrAddress) [0x00000] in <filename unknown>:0 at System.Net.Dns.GetHostAddresses (System.String hostNameOrAddress) [0x00000] in <filename unknown>:0 at System.Net.Sockets.TcpClient.Connect (System.String hostname, Int32 port) [0x00000] in <filename unknown>:0 at System.Net.Sockets.TcpClient..ctor (System.String hostname, Int32 port) [0x00000] in <filename unknown>:0 at Connect.Main (System.String[] args) [0x00000] in <filename unknown>:0
$ mono ./connect.exe 1.2.3.4 12345 Unhandled Exception: System.Net.Sockets.SocketException: Connection timed out at System.Net.Sockets.Socket.Connect (System.Net.EndPoint remoteEP) [0x00000] in <filename unknown>:0 at System.Net.Sockets.TcpClient.Connect (System.Net.IPEndPoint remote_end_point) [0x00000] in <filename unknown>:0 at System.Net.Sockets.TcpClient.Connect (System.Net.IPAddress[] ipAddresses, Int32 port) [0x00000] in <filename unknown>:0
D - std.socket
This is the first, and so far only, program I have written in D. I was pleasantly surprised by how easy it was to get it working. Overall I spent about thirty minutes including the time to download and install the compiler and then learn enough about the language to cobble together this simple example. Definitely a language I will look into more.import std.conv; import std.stdio; import std.socket; int main(string[] args) { if (args.length < 3) { writefln("Usage: %s <host> <port>", args[0]); return 1; } Socket s = new Socket( AddressFamily.INET, SocketType.STREAM, ProtocolType.TCP); s.connect(new InternetAddress(args[1], to!ushort(args[2]))); s.close(); return 0; }
$ ./connect some-host-that-does-not-exist 12345 std.socket.AddressException: Unable to resolve host 'some-host-that-does-not-exist' ---------------- 5 connect 0x00023c5e std std.socket.InternetAddress.__ctor(immutable(char)[], ushort) + 166 6 connect 0x00001a9e _Dmain + 246 7 connect 0x00013043 extern (C) int rt.dmain2.main(int, char**) + 23 8 connect 0x00012f7a extern (C) int rt.dmain2.main(int, char**) + 42 9 connect 0x0001308b extern (C) int rt.dmain2.main(int, char**) + 59 10 connect 0x00012f7a extern (C) int rt.dmain2.main(int, char**) + 42 11 connect 0x00012f07 main + 179 12 connect 0x0000199d start + 53 13 ??? 0x00000003 0x0 + 3
$ ./connect 1.2.3.4 12345 std.socket.SocketException: Unable to connect socket: Operation timed out ---------------- 5 connect 0x00024301 D3std6socket6Socket7connectMFC3std6socket7AddressZv + 129 6 connect 0x00001aaa _Dmain + 258 7 connect 0x00013043 extern (C) int rt.dmain2.main(int, char**) + 23 8 connect 0x00012f7a extern (C) int rt.dmain2.main(int, char**) + 42 9 connect 0x0001308b extern (C) int rt.dmain2.main(int, char**) + 59 10 connect 0x00012f7a extern (C) int rt.dmain2.main(int, char**) + 42 11 connect 0x00012f07 main + 179 12 connect 0x0000199d start + 53 13 ??? 0x00000003 0x0 + 3
Erlang - gen_tcp
-module(connect). -export([doConnect/2]). doConnect(Host, Port) -> case gen_tcp:connect(Host, Port, [binary, {packet, 0}]) of {ok, Socket} -> gen_tcp:close(Socket); {error, Reason} -> io:format("error: ~p~n", [Reason]) end.
12> connect:doConnect("some-host-that-does-not-exist", 12345). error: nxdomain
13> connect:doConnect("1.2.3.4", 12345). error: etimedout
Go - net.Dial
package main import ( "fmt" "log" "net" "os" ) func main() { if len(os.Args) < 3 { fmt.Printf("Usage: %s <host> <port>\n", os.Args[0]) os.Exit(1) } client, err := net.Dial("tcp", "", os.Args[1] + ":" + os.Args[2]) if err != nil { log.Exit("connect error:", err) } client.Close() }
$ ./connect some-host-that-does-not-exist 12345 2010/10/08 12:13:32 connect error: dial tcp some-host-that-does-not-exist:12345: lookup some-host-that-does-not-exist.: no such host
$ ./connect 1.2.3.4 12345 2010/10/08 12:15:04 connect error: dial tcp 1.2.3.4:12345: operation timed out
Haskell - Network.Socket
import Data.Maybe import Network.Socket import System doConnect :: [String] -> IO () doConnect [host, port] = do addrs <- getAddrInfo (Just defaultHints) (Just host) (Just port) let addr = head addrs s <- socket (addrFamily addr) Stream 0 connect s (addrAddress addr) sClose s doConnect _ = do name <- getProgName putStrLn $ "Usage: " ++ name ++ " <host> <port>" exitFailure main = do args <- getArgs doConnect args
$ ./connect some-host-that-does-not-exist 12345 connect: getAddrInfo: does not exist (nodename nor servname provided, or not known)
$ ./connect 1.2.3.4 12345 connect: connect: does not exist (Network is unreachable)
Java - java.net.Socket
import java.net.*; public class Connect { public static void main(String[] args) throws Exception { if (args.length < 2) { System.out.println("Usage: java Connect <host> <port>"); System.exit(1); } InetSocketAddress addr = new InetSocketAddress( args[0], Integer.valueOf(args[1])); Socket s = new Socket(); s.connect(addr, 1000); } }
$ java Connect some-host-that-does-not-exist 12345 Exception in thread "main" java.net.UnknownHostException: some-host-that-does-not-exist at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:177) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366) at java.net.Socket.connect(Socket.java:529) at Connect.main(Connect.java:12)
$ java Connect 1.2.3.4 12345 Exception in thread "main" java.net.SocketTimeoutException: connect timed out at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366) at java.net.Socket.connect(Socket.java:529) at Connect.main(Connect.java:12)
Perl - IO::Socket::INET
#!/usr/bin/perl use strict; use warnings; use IO::Socket::INET; if (scalar @ARGV < 2) { print "Usage: $0 <host> <port>\n"; exit 1; } my $s = IO::Socket::INET->new(PeerAddr => $ARGV[0], PeerPort => $ARGV[1]); die $@ unless $s; $s->close;
$ ./connect.pl some-host-that-does-not-exist 12345 IO::Socket::INET: Bad hostname 'some-host-that-does-not-exist' at ./connect.pl line 13.
$ ./connect.pl 1.2.3.4 12345 IO::Socket::INET: connect: Connection timed out at ./connect.pl line 13.
Python - socket
#!/usr/bin/python import socket import sys if len(sys.argv) < 3: print "Usage: %s <host> <port>" % sys.argv[0] sys.exit(1) s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((sys.argv[1], int(sys.argv[2]))) s.close()
$ ./connect.py some-host-that-does-not-exist 12345 Traceback (most recent call last): File "./connect.py", line 11, in ? s.connect((sys.argv[1], int(sys.argv[2]))) File "<string>", line 1, in connect socket.gaierror: (-2, 'Name or service not known')
$ ./connect.py 1.2.3.4 12345 Traceback (most recent call last): File "./connect.py", line 11, in ? s.connect((sys.argv[1], int(sys.argv[2]))) File "<string>", line 1, in connect socket.error: (110, 'Connection timed out')
Ruby - socket
#!/usr/bin/ruby require 'socket' if ARGV.length < 2 print "Usage: #{$0} <host> <port>\n" exit(1) end s = TCPSocket.open(ARGV[0], ARGV[1]) s.close
$ ./connect.rb some-host-that-does-not-exist 12345 ./connect.rb:10:in `initialize': getaddrinfo: Name or service not known (SocketError) from ./connect.rb:10:in `open' from ./connect.rb:10
$ ./connect.rb 1.2.3.4 12345 ./connect.rb:10:in `initialize': Connection timed out - connect(2) (Errno::ETIMEDOUT) from ./connect.rb:10:in `open' from ./connect.rb:10
TCL - socket
#!/usr/bin/tclsh if {$argc < 2} { puts "Usage: $argv0 <host> <port>" exit 1 } set s [socket [lindex $argv 0] [lindex $argv 1]] close s
$ ./connect.tcl some-host-that-does-not-exist 12345 couldn't open socket: host is unreachable (nodename nor servname provided, or not known) while executing "socket [lindex $argv 0] [lindex $argv 1]" invoked from within "set s [socket [lindex $argv 0] [lindex $argv 1]]" (file "./connect.tcl" line 8)
$ ./connect.tcl 1.2.3.4 12345 couldn't open socket: connection timed out while executing "socket [lindex $argv 0] [lindex $argv 1]" invoked from within "set s [socket [lindex $argv 0] [lindex $argv 1]]" (file "./connect.tcl" line 8)
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