The parser

Detailed Description

The console/config library defines a simple language used to interact with the console or to configure the application. The parser is not concerned about interpreting commands or arguments, checking that a command exists or managing directories. The parser just takes the input and parses it.

1. The Language

The config/console language is used in configuration files and interactively at the console. Some features of the language are more useful in config files, others at the interactive console but the language is the same in both cases.

Let's start with a sample of the config/console language. The following is written as a configuration file

# My someserver configuration file

/server/port 1234;

/logger/targets {
    console {
        accept senf::log::Debug IMPORTANT;
        accept server::ServerLog CRITICAL;
    }

    provide serverlog senf::log::FileTarget "/var/log/server.log";
    serverlog {
        reject senf::log::Debug senf::Console::Server NOTICE;
        accept senf::log::Debug NOTICE;
        accept server::ServerLog;
    }
}

/server/stuffing (UDPPacket x"01 02 03 04");
/server/allow_hosts 10.1.2.3               # our internal server
                    10.2.3.4 10.4.3.5      # client workstations
    ;

/help/infoUrl "http://senf.j32.de/src/doc";

The interactive syntax is the same with some notes:

  • All commands must be complete on a single line. This includes grouping constructs which must be closed on the same line they are opened.
  • The last ';' is optional. However, multiple commands may be entered on a single line when they are separated by ';'.
  • An empty line on the interactive console will repeat the last command.
The language consists of a small number of syntactic entities:

1.1. Special characters

These are characters, which have a special meaning. Some are used internally, others are just returned as punctuation tokens
# Comments are marked with '#' and continue to the end of the line
/ path component separator
( ) argument grouping
{ } directory grouping
; command terminator
, = punctuation tokens

1.2. Basic elements

A word is any sequence of consecutive characters which does not include any special character. Examples for words are thus 
12.34
jens@fit.fraunhofer.de
eth0
1>2

The following are not valid words:

a/b/c
a,b

A string literal is just that: A double-quoted string (C/C++ style) possibly with embedded escape chars:

"\"foo\""
"\x04test"

A hex-string literal is used to represent binary data. It looks like a string which has only hexadecimal bytes or whitespace as contents (comments and newlines are Ok when not read from the interactive console)

x"01 02 03 0405"
x"01 02   # ID header
  0405    # payload
  "

A token is a word, string or hex-string, or a single special character (that's true, any special character is allowed as a token). '(' and ')' must be properly nested.

A path is a sequence of words separated by '/' (and optional whitespace). A path may have an optional initial and/or a terminating '/'.

a/b/c
foo / bar /
/server

1.3. Statements

There are several types of statements:
  • The bulk of all statements are path statements
  • There are some built-in statements which are mostly useful at the interactive console
  • A special form of statement is the directory group
A path statement consists of a (possibly relative) path followed by any number of arguments and terminated with a ';' (or end-of-input) 
/path/to/command arg1 "arg2" (complex=(1 2) another) ;
Every argument is either
  • A single word, string or hex-string
  • or a parenthesized list of tokens.
So above command has three arguments: 'arg1', 'arg2' (a single token each) and one argument with the 7 tokens 'complex', '=', '(', '1', '2', ')', 'another'. The interpretation of the arguments is completely up to the command.

A built-in statement is one of

cd path Change current directory
ls [ path ] List contents of path or current directory
exit Exit interactive console
help [ path ] Show help for path or current directory

A directory group statement is a block of statements all executed relatively to a fixed directory.

/some/path {
    statement ;
    . . .
}
At the beginning of the block, the current directory is saved and the directory is changed to the given directory. All commands are executed and at the end of the block, the saved directory is restored.

2. The parser API

The senf::console::CommandParser is responsible for taking text input and turning it into a sequence of senf::console::ParseCommandInfo structures. The structures are returned by passing them successively to a callback function.

Every statement is returned as a senf::console::ParseCommandInfo instance. Directory groups are handled specially: They are divided into two special built-in commands called PUSHD and POPD.


3. Classes

class   senf::console::Token
  Single argument token. More...
class   senf::console::ParseCommandInfo
  Single parsed console command. More...
class   senf::console::CommandParser
  Parse commands. More...