panic: runtime error: index out of range

[xaionaro]

Got an error:

panic: runtime error: index out of range

goroutine 1 [running]:
github.com/timtadh/lexmachine/machines.DFALexerEngine.func1(0xda8, 0xc42000c018, 0x52a405, 0x1b, 0xc420051e50, 0x6)
        /root/go/src/github.com/timtadh/lexmachine/machines/dfa_machine.go:82 +0x7b6
github.com/timtadh/lexmachine.(*Scanner).Next(0xc4200b16e0, 0x1b, 0xc420051e50, 0x6, 0x6, 0x23)
        /root/go/src/github.com/timtadh/lexmachine/lexer.go:146 +0x50
github.com/xaionaro-go/isccfg.Parse(0x53e3e0, 0xc42001a0c0, 0x1000, 0xc42009c000, 0x1000)
        /root/go/src/github.com/xaionaro-go/isccfg/isccfg.go:72 +0x2f1
main.main()
        /root/go/src/github.com/xaionaro-go/isccfg/iscparser/main.go:27 +0x17e

Setup:

func NewLexer() *lexmachine.Lexer {
        literals := []string{
                "{",
                "}",
                ";",
                ",",
        }
        tokens := []string{
                "COMMENT",
                "ID",
        }
        tokens = append(tokens, literals...)
        tokenIds := map[string]int{}
        for i, tok := range tokens {
                tokenIds[tok] = i 
        }
        lex := lexmachine.NewLexer()

        skip := func(*lexmachine.Scanner, *lexmachines.Match) (interface{}, error) {
                return nil, nil 
        }
        token := func(name string) lexmachine.Action {
                return func(s *lexmachine.Scanner, m *lexmachines.Match) (interface{}, error) {
                        return s.Token(tokenIds[name], string(m.Bytes), m), nil 
                }
        }

        lex.Add([]byte(`#[^\n]*\n?`), token("COMMENT"))
        lex.Add([]byte(`([a-z]|[A-Z]|[0-9]|_|\-|\.)*`), token("ID"))
        lex.Add([]byte(`"([^\\"]|(\\.))*"`), token("ID"))
        lex.Add([]byte("[\n \t]"), skip)
        for _, lit := range literals {
                lex.Add([]byte(lit), token(lit))
        }

        err := lex.Compile()
        if err != nil {
                panic(err)
        }

        return lex 
}

func Parse(reader io.Reader) (cfg Config, err error) {
        var notParsedConfig []byte
        notParsedConfig, err = ioutil.ReadAll(reader)
        if err != nil {
                return
        }

        lex := NewLexer()

        var scanner *lexmachine.Scanner
        scanner, err = lex.Scanner(notParsedConfig)
        if err != nil {
                return
        }
        for tok, err, eof := scanner.Next(); !eof; tok, err, eof = scanner.Next() {
                if err != nil {
                        return Config{}, err 
                }
                token := tok.(*lexmachine.Token)
                fmt.Printf("%-7v | %-10v | %v:%v-%v:%v\n",
                        token.Type,
                        string(token.Lexeme),
                        token.StartLine,
                        token.StartColumn,
                        token.EndLine,
                        token.EndColumn)
        }

        return
}

The input text:

# dhcpd.conf
#
# Sample configuration file for ISC dhcpd
#

# option definitions common to all supported networks...
option domain-name "example.org";
option domain-name-servers ns1.example.org, ns2.example.org;

default-lease-time 600;
max-lease-time 7200;

# The ddns-updates-style parameter controls whether or not the server will
# attempt to do a DNS update when a lease is confirmed. We default to the
# behavior of the version 2 packages ('none', since DHCP v2 didn't
# have support for DDNS.)
ddns-update-style none;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
#authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
#log-facility local7;

# No service will be given on this subnet, but declaring it helps the 
# DHCP server to understand the network topology.

#subnet 10.152.187.0 netmask 255.255.255.0 {
#}

# This is a very basic subnet declaration.

#subnet 10.254.239.0 netmask 255.255.255.224 {
#  range 10.254.239.10 10.254.239.20;
#  option routers rtr-239-0-1.example.org, rtr-239-0-2.example.org;
#}

# This declaration allows BOOTP clients to get dynamic addresses,
# which we don't really recommend.

#subnet 10.254.239.32 netmask 255.255.255.224 {
#  range dynamic-bootp 10.254.239.40 10.254.239.60;
#  option broadcast-address 10.254.239.31;
#  option routers rtr-239-32-1.example.org;
#}

# A slightly different configuration for an internal subnet.
#subnet 10.5.5.0 netmask 255.255.255.224 {
#  range 10.5.5.26 10.5.5.30;
#  option domain-name-servers ns1.internal.example.org;
#  option domain-name "internal.example.org";
#  option routers 10.5.5.1;
#  option broadcast-address 10.5.5.31;
#  default-lease-time 600;
#  max-lease-time 7200;
#}

# Hosts which require special configuration options can be listed in
# host statements.   If no address is specified, the address will be
# allocated dynamically (if possible), but the host-specific information
# will still come from the host declaration.

#host passacaglia {
#  hardware ethernet 0:0:c0:5d:bd:95;
#  filename "vmunix.passacaglia";
#  server-name "toccata.example.com";
#}

# Fixed IP addresses can also be specified for hosts.   These addresses
# should not also be listed as being available for dynamic assignment.
# Hosts for which fixed IP addresses have been specified can boot using
# BOOTP or DHCP.   Hosts for which no fixed address is specified can only
# be booted with DHCP, unless there is an address range on the subnet
# to which a BOOTP client is connected which has the dynamic-bootp flag
# set.
#host fantasia {
#  hardware ethernet 08:00:07:26:c0:a5;
#  fixed-address fantasia.example.com;
#}

# You can declare a class of clients and then do address allocation
# based on that.   The example below shows a case where all clients
# in a certain class get addresses on the 10.17.224/24 subnet, and all
# other clients get addresses on the 10.0.29/24 subnet.

#class "foo" {
#  match if substring (option vendor-class-identifier, 0, 4) = "SUNW";
#}

#shared-network 224-29 {
#  subnet 10.17.224.0 netmask 255.255.255.0 {
#    option routers rtr-224.example.org;
#  }
#  subnet 10.0.29.0 netmask 255.255.255.0 {
#    option routers rtr-29.example.org;
#  }
#  pool {
#    allow members of "foo";
#    range 10.17.224.10 10.17.224.250;
#  }
#  pool {
#    deny members of "foo";
#    range 10.0.29.10 10.0.29.230;
#  }
#}

[timtadh]

@xaionaro taking a look now.

[xaionaro]

Re-tested from master. Works. Thanks.

[xaionaro]

Just FYI:

I got it into an infinite loop (returning the same empty token due to * instead of +). It seems to be wrong.
If it's interesting I can provide a setup where you can repeat the problem.

[timtadh]

@xaionaro why don't you open an issue for that? Maybe what I should do is check to see if the expression matches the empty string and issue a warning? An infinite loop is definitely the wrong behavior.

[xaionaro]

Opened an issue:
#22