-Configuration and command line parser
-=====================================
+Configuration parser
+====================
-Libucw contains a parser for configuration files described in
-<<config:>>.
+Libucw contains a parser for configuration files. The syntax of the
+configuration files is described in <<config:>>, here we explain the
+interface of the parser.
-The principle is you specify the structure of the configuration file,
-the section names, variable names and types and your C variables that
-are assigned to them. Then you run the parser and it fills your
-variables with the values from the configuration file.
+Basically, you write a description of the configuration file syntax,
+which maps configuration items to variables of your program. Then
+Then you run the parser and it fills your variables with the values
+from the configuration file.
-It is modular. It means you do not have to write all configuration at
-the same place, you just declare the parts you need locally and do not
-care about the other parts.
-
-The command line parser has the same interface as unix getopt_long,
-but handles setting of configuration files and configuration values
-from command line.
+The descriptions are modular. The configuration can be split to sections,
+each section declared at a separate place. You can also define your own
+data types.
- <<example,Example>>
* <<ex_structure,The structure>>
- * <<ex_load,Loading>>
+ * <<ex_load,Loading configuration>>
+- <<deep,Getting deeper>>
+ * <<conf_multi,Arrays and lists>>
+ * <<reload,Reloading configuration>>
+ * <<custom_parser,Creating custom parsers>>
+ * <<hooks,Hooks>>
- <<conf_h,ucw/conf.h>>
+ * <<conf_ctxt,Configuration contexts>>
+ * <<conf_load,Safe configuration loading>>
* <<conf_types,Data types>>
* <<conf_macros,Convenience macros>>
* <<alloc,Memory allocation>>
* <<journal,Undo journal>>
+ * <<declare,Section declaration>>
* <<bparser,Parsers for basic types>>
+ * <<conf_direct,Direct access>>
+ * <<conf_dump,Debug dumping>>
+- <<getopt_h,ucw/getopt.h>>
+ * <<conf_getopt,Loading configuration by cf_getopt()>> (obsolete)
+ * <<getopt_example,Example>> (obsolete)
[[example]]
Example
-------
+If you want to just load simple configuration, this is the part you
+want to read. This simple example should give you the overview. Look
+at the <<conf_macros,convenience macros>> section to see list of
+supported data types, sections, etc.
[[ex_cfile]]
-Let's say you have configuration file with this content and want to
-load it:
+Suppose you have configuration file with the following content and you
+want to load it:
HelloWorld {
Text "Hello planet"
}
The variables are used to store the loaded values. Their initial
-values work as default, if nothing else is loaded. The hw_config()
+values work as defaults, if nothing else is loaded. The hw_config()
structure assigns the variables to configuration names. The hw_init()
function (because of the `CONSTRUCTOR` macro) is run before main()
-is called and it plugs in the whole section to the parser.
+is called and it tells the parser that the section exists (alternatively,
+you can call @cf_declare_section() at the start of your main()).
You can plug in as many configuration sections as you like, from
various places across your code.
[[ex_load]]
-Loading of the values
+Loading configuration
~~~~~~~~~~~~~~~~~~~~~
-You need to parse the command line arguments and load the
-configuration. You can do it in a similar way to this example.
+You can load the configuration explicitly by calling @cf_load().
+That can be convenient when writing a library, but in normal programs,
+you can ask the <<opt:,option parser>> to handle it for you.
+
+A typical example follows, please see the <<opt:conf,interface between
+conf and opt>> for details.
+
+ #include <ucw/lib.h>
+ #include <ucw/opt.h>
+
+ static struct opt_section options = {
+ OPT_ITEMS {
+ // More options can be specified here
+ OPT_HELP("Configuration options:"),
+ OPT_CONF_OPTIONS,
+ OPT_END
+ }
+ };
+
+ int main(int argc, char **argv)
+ {
+ cf_def_file = "default.cf";
+ opt_parse(&options, argv+1);
+ // Configuration file is already loaded here
+ return 0;
+ }
+
+[[deep]]
+Getting deeper
+--------------
+
+Since the configuration system is somehow complicated, this part gives
+you a little overview of what you can find and where.
+
+[[conf_multi]]
+Arrays and lists
+~~~~~~~~~~~~~~~~
+
+It is sometime needed to have multiple items of the same type. There
+are three ways to do that:
+
+*Static arrays*::
+ An array with fixed maximum length. You provide
+ the length and already allocated array which is filled with items.
+ The configuration may contain less than the maximum length items.
++
+For example, you can have an static array of five unsigned integers:
++
+ static uns array[] = { 1, 2, 3, 4, 5 };
++
+ static struct cf_section section = {
+ CF_ITEMS {
+ CF_UNS_ARY("array", array, 5),
+ CF_END
+ }
+ };
+
+*Dynamic arrays*::
+ Similar to static array, but you provide pointer
+ to pointer to the given item (eg. if you want dynamic array of
+ integers, you give `**int`). The parser allocates a <<gary:,growing array>>
+ of the required size.
++
+If you want dynamic array of strings, you would use:
++
+ static char *array[];
++
+ static struct cf_section section = {
+ CF_ITEMS {
+ CF_STRING_DYN("array", &array, CF_ANY_NUM),
+ CF_END
+ }
+ };
+
+*Lists*::
+ Linked lists based on <<lists:clists,clists>>. You provide description
+ of single node and pointer to the
+ <<lists:struct_clist,`struct clist`>> variable. All the nodes will
+ be created dynamically and put there.
++
+First element of your structure must be <<lists:struct_cnode,`cnode`>>.
++
+The first example is list of strings and uses <<lists:simple_lists,simple
+lists>>:
++
+ static struct clist list;
++
+ static struct cf_section section = {
+ CF_ITEMS {
+ CF_LIST("list", &list, &cf_string_list_config),
+ CF_END
+ }
+ };
++
+Another example, describing how to create more complicated list node
+than just a string can be found at the <<def_CF_TYPE,`CF_TYPE`>> macro.
+
+[[reload]]
+Reloading configuration
+~~~~~~~~~~~~~~~~~~~~~~~
+
+The configuration system allows you to reload configuration at
+runtime. The new config changes the values against the default values.
+It means, if the default value for variable `A` is `10`, the currently
+loaded config sets it to `42` and the new config does not talk about
+this variable, `A` will have a value of `10` after a successful load.
+
+Furthermore, if the loading of a new configuration fails, the current
+configuration is preserved.
+
+All this is done with <<journal,config journalling>>. The load of the
+first config creates a journal entry. If you try to load some new
+configuration, it is partially rolled back to defaults (the rollback
+happens, but instead of removing the journal entry, another journal
+entry is added for the rollback). If the loading succeeds, the two
+journal entries are removed and a new one, for the new configuration,
+is added. If it fails, the first one is replayed and the rollback
+entry is removed.
+
+See <<cf_reload()>>.
+
+[[custom_parser]]
+Creating custom parsers
+~~~~~~~~~~~~~~~~~~~~~~~
+
+If you need to parse some data type the configuration system can't
+handle, you can write your own parser. But before you start, you
+should know a few things.
+
+The parser needs to support <<journal,journalling>>. To accomplish that,
+you have to use the <<alloc,configuration mempool>> for memory allocation.
+
+Now, you need a function with the same signature as
+<<type_cf_parser1,`cf_parser1`>>. Parse the first parameter (the
+string) and store the data in the second parameter. You may want to
+write a dumper function, with signature of
+<<type_cf_dumper1,`cf_dumper1`>> (needed for debug dumps).
+
+Fill in a structure <<struct_cf_user_type,cf_user_type>> and use the
+new data type in your configuration description with
+<<def_CF_USER,`CF_USER`>> macro as its @t parameter.
+
+You do not need to call @cf_journal_block() on the variable you store
+the result. It is true you change it, but it was stored to journal
+before your parser function was called.
+
+[[hooks]]
+Hooks
+~~~~~
+
+The configuration system supports hooks. They are used to initialize the
+configuration (if simple default value of variable is not enough) and
+to check the sanity of loaded data.
+
+Each hook is of type <<type_cf_hook,`cf_hook`>> and you can include
+them in configuration description using <<def_CF_INIT,`CF_INIT`>> and
+<<def_CF_COMMIT,`CF_COMMIT`>> macros.
+
+The hooks should follow similar guidelines as custom parsers (well,
+init hooks do not need to call @cf_journal_block()) to support
+journalling. If you change nothing in the commit hook, you do not need
+to care about the journalling either.
+
+You may use the return value to inform about errors. Just return the
+error message, or NULL if everything went well.
+
+Another similar function is a copy function. It is very similar to a
+hook and is used when the item is copied and is too complicated to use
+simple memcpy(). Its type is <<type_cf_copier,`cf_copier`>> and is
+specified by the <<def_CF_COPY,`CF_COPY`>> macro. It's return value is
+the same as the one of a hook.
+
+[[conf_h]]
+ucw/conf.h
+----------
+
+This header file contains the public interface of the configuration module.
+
+!!ucw/conf.h
+
+[[getopt_h]]
+ucw/getopt.h
+------------
+
+This header contains routines for parsing command line arguments and
+loading the default configuration.
+
+In new programs, please consider using the new <<opt:,option parser>>
+instead. The getopt interface is already considered obsolete and may
+be removed in the future.
+
+!!ucw/getopt.h
+
+Example
+~~~~~~~
+Typically, @cf_getopt() is used as follows: it works like
+the traditional @getopt_long() from the C library, but it also handles
+configuration files.
#include <ucw/lib.h>
#include <ucw/conf.h>
#include <ucw/getopt.h>
- static byte short_opts[] = CF_SHORT_OPTS "v";
+ static char short_opts[] = CF_SHORT_OPTS "v";
static struct option long_opts[] = {
CF_LONG_OPTS
{ "verbose", 0, 0, 'v' },
{ NULL, 0, 0, 0 }
};
- int verbose;
+ static int verbose;
int main(int argc, char *argv[]) {
cf_def_file = "default.cf";
case 'v': verbose = 1; break;
default: fprintf("Unknown option %c\n", opt); return 1;
}
+ }
The `short_opts` and `long_opts` variables describe the command line
arguments. Notice the `CF_SHORT_OPTS` and `CF_LONG_OPTS` macros. They
-add options for the configuration parser. These options are handled
-internally by @cf_getopt(). It loads the configuration before it starts
-giving you your program's options.
-
-See documentation of unix getopt_long() function.
-
-[[conf_h]]
-ucw/conf.h
-----------
+add the `-S` and `-C` options for the configuration parser as described
+in <<config:>>. These options are handled internally by @cf_getopt().
-Use this file if you want define a configuration section, request
-loading of some variables or create new item type.
-
-!!ucw/conf.h
+You can rely on the configuration files having been loaded before the
+first of your program's options is parsed.
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