Simple XML Subset Parser

Simple XML Subset Parser — parses a subset of XML.

Synopsis


#include <glib.h>


enum        GMarkupError;
#define     G_MARKUP_ERROR
enum        GMarkupParseFlags;
            GMarkupParseContext;
            GMarkupParser;
gchar*      g_markup_escape_text            (const gchar *text,
                                             gssize length);
gchar*      g_markup_printf_escaped         (const char *format,
                                             ...);
gchar*      g_markup_vprintf_escaped        (const char *format,
                                             va_list args);
gboolean    g_markup_parse_context_end_parse
                                            (GMarkupParseContext *context,
                                             GError **error);
void        g_markup_parse_context_free     (GMarkupParseContext *context);
void        g_markup_parse_context_get_position
                                            (GMarkupParseContext *context,
                                             gint *line_number,
                                             gint *char_number);
const gchar* g_markup_parse_context_get_element
                                            (GMarkupParseContext *context);
GMarkupParseContext* g_markup_parse_context_new
                                            (const GMarkupParser *parser,
                                             GMarkupParseFlags flags,
                                             gpointer user_data,
                                             GDestroyNotify user_data_dnotify);
gboolean    g_markup_parse_context_parse    (GMarkupParseContext *context,
                                             const gchar *text,
                                             gssize text_len,
                                             GError **error);

Description

The "GMarkup" parser is intended to parse a simple markup format that's a subset of XML. This is a small, efficient, easy-to-use parser. It should not be used if you expect to interoperate with other applications generating full-scale XML. However, it's very useful for application data files, config files, etc. where you know your application will be the only one writing the file. Full-scale XML parsers should be able to parse the subset used by GMarkup, so you can easily migrate to full-scale XML at a later time if the need arises.

GMarkup is not guaranteed to signal an error on all invalid XML; the parser may accept documents that an XML parser would not. However, invalid XML documents are not considered valid GMarkup documents.

Simplifications to XML include:

  • Only UTF-8 encoding is allowed.

  • No user-defined entities.

  • Processing instructions, comments and the doctype declaration are "passed through" but are not interpreted in any way.

  • No DTD or validation.

The markup format does support:

  • Elements

  • Attributes

  • 5 standard entities: &amp; &lt; &gt; &quot; &apos;

  • Character references

  • Sections marked as CDATA

Details

enum GMarkupError

typedef enum
{
  G_MARKUP_ERROR_BAD_UTF8,
  G_MARKUP_ERROR_EMPTY,
  G_MARKUP_ERROR_PARSE,
  /* These three are primarily intended for specific GMarkupParser
   * implementations to set.
   */
  G_MARKUP_ERROR_UNKNOWN_ELEMENT,
  G_MARKUP_ERROR_UNKNOWN_ATTRIBUTE,
  G_MARKUP_ERROR_INVALID_CONTENT
} GMarkupError;

Error codes returned by markup parsing.

G_MARKUP_ERROR_BAD_UTF8 text being parsed was not valid UTF-8
G_MARKUP_ERROR_EMPTY document contained nothing, or only whitespace
G_MARKUP_ERROR_PARSE document was ill-formed
G_MARKUP_ERROR_UNKNOWN_ELEMENT error should be set by GMarkupParser functions; element wasn't known
G_MARKUP_ERROR_UNKNOWN_ATTRIBUTE error should be set by GMarkupParser functions; attribute wasn't known
G_MARKUP_ERROR_INVALID_CONTENT error should be set by GMarkupParser functions; something was wrong with contents of the document, e.g. invalid attribute value

G_MARKUP_ERROR

#define G_MARKUP_ERROR g_markup_error_quark ()

Error domain for markup parsing. Errors in this domain will be from the GMarkupError enumeration. See GError for information on error domains.


enum GMarkupParseFlags

typedef enum
{
  /* Hmm, can't think of any at the moment */
  G_MARKUP_DO_NOT_USE_THIS_UNSUPPORTED_FLAG = 1 << 0
  
} GMarkupParseFlags;

There are no flags right now. Pass "0" for the flags argument to all functions.

G_MARKUP_DO_NOT_USE_THIS_UNSUPPORTED_FLAG flag you should not use.

GMarkupParseContext

typedef struct _GMarkupParseContext GMarkupParseContext;

A parse context is used to parse a stream of bytes that you expect to contain marked-up text. See g_markup_parse_context_new(), GMarkupParser, and so on for more details.


GMarkupParser

typedef struct {
  /* Called for open tags <foo bar="baz"> */
  void (*start_element)  (GMarkupParseContext *context,
                          const gchar         *element_name,
                          const gchar        **attribute_names,
                          const gchar        **attribute_values,
                          gpointer             user_data,
                          GError             **error);

  /* Called for close tags </foo> */
  void (*end_element)    (GMarkupParseContext *context,
                          const gchar         *element_name,
                          gpointer             user_data,
                          GError             **error);

  /* Called for character data */
  /* text is not nul-terminated */
  void (*text)           (GMarkupParseContext *context,
                          const gchar         *text,
                          gsize                text_len,  
                          gpointer             user_data,
                          GError             **error);

  /* Called for strings that should be re-saved verbatim in this same
   * position, but are not otherwise interpretable.  At the moment
   * this includes comments and processing instructions.
   */
  /* text is not nul-terminated. */
  void (*passthrough)    (GMarkupParseContext *context,
                          const gchar         *passthrough_text,
                          gsize                text_len,  
                          gpointer             user_data,
                          GError             **error);

  /* Called on error, including one set by other
   * methods in the vtable. The GError should not be freed.
   */
  void (*error)          (GMarkupParseContext *context,
                          GError              *error,
                          gpointer             user_data);
} GMarkupParser;

Any of the fields in GMarkupParser can be NULL, in which case they will be ignored. Except for the error function, any of these callbacks can set an error; in particular the G_MARKUP_ERROR_UNKNOWN_ELEMENT, G_MARKUP_ERROR_UNKNOWN_ATTRIBUTE, and G_MARKUP_ERROR_INVALID_CONTENT errors are intended to be set from these callbacks. If you set an error from a callback, g_markup_parse_context_parse() will report that error back to its caller.

start_element () Callback to invoke when the opening tag of an element is seen.
end_element () Callback to invoke when the closing tag of an element is seen
text () Callback to invoke when some text is seen (text is always inside an element)
passthrough () Callback to invoke for comments, processing instructions and doctype declarations; if you're re-writing the parsed document, write the passthrough text back out in the same position
error () Callback to invoke when an error occurs

g_markup_escape_text ()

gchar*      g_markup_escape_text            (const gchar *text,
                                             gssize length);

Escapes text so that the markup parser will parse it verbatim. Less than, greater than, ampersand, etc. are replaced with the corresponding entities. This function would typically be used when writing out a file to be parsed with the markup parser.

Note that this function doesn't protect whitespace and line endings from being processed according to the XML rules for normalization of line endings and attribute values.

text : some valid UTF-8 text
length : length of text in bytes
Returns : escaped text

g_markup_printf_escaped ()

gchar*      g_markup_printf_escaped         (const char *format,
                                             ...);

Formats arguments according to format, escaping all string and character arguments in the fashion of g_markup_escape_text(). This is useful when you want to insert literal strings into XML-style markup output, without having to worry that the strings might themselves contain markup.

const char *store = "Fortnum & Mason";
const char *item = "Tea";
char *output;
 
output = g_markup_printf_escaped ("<purchase>"
                                  "<store>%s</store>"
                                  "<item>%s</item>"
                                  "</purchase>",
                                  store, item);

format : printf() style format string
... : the arguments to insert in the format string
Returns : newly allocated result from formatting operation. Free with g_free().

Since 2.4


g_markup_vprintf_escaped ()

gchar*      g_markup_vprintf_escaped        (const char *format,
                                             va_list args);

Formats the data in args according to format, escaping all string and character arguments in the fashion of g_markup_escape_text(). See g_markup_printf_escaped().

format : printf() style format string
args : variable argument list, similar to vprintf()
Returns : newly allocated result from formatting operation. Free with g_free().

Since 2.4


g_markup_parse_context_end_parse ()

gboolean    g_markup_parse_context_end_parse
                                            (GMarkupParseContext *context,
                                             GError **error);

Signals to the GMarkupParseContext that all data has been fed into the parse context with g_markup_parse_context_parse(). This function reports an error if the document isn't complete, for example if elements are still open.

context : a GMarkupParseContext
error : return location for a GError
Returns : TRUE on success, FALSE if an error was set

g_markup_parse_context_free ()

void        g_markup_parse_context_free     (GMarkupParseContext *context);

Frees a GMarkupParseContext. Can't be called from inside one of the GMarkupParser functions.

context : a GMarkupParseContext

g_markup_parse_context_get_position ()

void        g_markup_parse_context_get_position
                                            (GMarkupParseContext *context,
                                             gint *line_number,
                                             gint *char_number);

Retrieves the current line number and the number of the character on that line. Intended for use in error messages; there are no strict semantics for what constitutes the "current" line number other than "the best number we could come up with for error messages."

context : a GMarkupParseContext
line_number : return location for a line number, or NULL
char_number : return location for a char-on-line number, or NULL

g_markup_parse_context_get_element ()

const gchar* g_markup_parse_context_get_element
                                            (GMarkupParseContext *context);

Retrieves the name of the currently open element.

context : a GMarkupParseContext
Returns : the name of the currently open element, or NULL

Since 2.2


g_markup_parse_context_new ()

GMarkupParseContext* g_markup_parse_context_new
                                            (const GMarkupParser *parser,
                                             GMarkupParseFlags flags,
                                             gpointer user_data,
                                             GDestroyNotify user_data_dnotify);

Creates a new parse context. A parse context is used to parse marked-up documents. You can feed any number of documents into a context, as long as no errors occur; once an error occurs, the parse context can't continue to parse text (you have to free it and create a new parse context).

parser : a GMarkupParser
flags : one or more GMarkupParseFlags
user_data : user data to pass to GMarkupParser functions
user_data_dnotify : user data destroy notifier called when the parse context is freed
Returns : a new GMarkupParseContext

g_markup_parse_context_parse ()

gboolean    g_markup_parse_context_parse    (GMarkupParseContext *context,
                                             const gchar *text,
                                             gssize text_len,
                                             GError **error);

Feed some data to the GMarkupParseContext. The data need not be valid UTF-8; an error will be signaled if it's invalid. The data need not be an entire document; you can feed a document into the parser incrementally, via multiple calls to this function. Typically, as you receive data from a network connection or file, you feed each received chunk of data into this function, aborting the process if an error occurs. Once an error is reported, no further data may be fed to the GMarkupParseContext; all errors are fatal.

context : a GMarkupParseContext
text : chunk of text to parse
text_len : length of text in bytes
error : return location for a GError
Returns : FALSE if an error occurred, TRUE on success