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title	author	copyright	version
Mini-XML 4.0 Programming Manual	Michael R Sweet	Copyright © 2003-2024, All Rights Reserved.	4

Mini-XML was initially developed for the Gutenprint project to replace the rather large and unwieldy libxml2 library with something substantially smaller and easier-to-use. It all began one morning in June of 2003 when Robert posted the following sentence to the developer's list:

It's bad enough that we require libxml2, but rolling our own XML parser is a bit more than we can handle.

I then replied with:

Given the limited scope of what you use in XML, it should be trivial to code a mini-XML API in a few hundred lines of code.

I took my own challenge and coded furiously for two days to produce the initial public release of Mini-XML, total lines of code: 696. Robert promptly integrated Mini-XML into Gutenprint and removed libxml2.

Thanks to lots of feedback and support from various developers, Mini-XML has evolved since then to provide a more complete XML implementation and now stands at a whopping 3,875 lines of code, compared to 175,808 lines of code for libxml2 version 2.11.7.

Resources

The Mini-XML home page can be found at https://www.msweet.org/mxml. From there you can download the current version of Mini-XML, access the issue tracker, and find other resources.

Mini-XML v4 has a slightly different API than prior releases. See the Migrating from Mini-XML v3.x chapter for details.

Legal Stuff

The Mini-XML library is copyright © 2003-2024 by Michael R Sweet and is provided under the Apache License Version 2.0 with an (optional) exception to allow linking against GPL2/LGPL2-only software. See the files "LICENSE" and "NOTICE" for more information.

Using Mini-XML

Mini-XML provides a single header file which you include:

#include <mxml.h>

The Mini-XML library is included with your program using the -lmxml4 option:

gcc -o myprogram myprogram.c -lmxml4

If you have the pkg-config software installed, you can use it to determine the proper compiler and linker options for your installation:

gcc `pkg-config --cflags mxml4` -o myprogram myprogram.c `pkg-config --libs mxml4`

Note: The library name "mxml4" is a configure-time option. If you use the --disable-libmxml4-prefix configure option the library is named "mxml".

Loading an XML File

You load an XML file using the mxmlLoadFile function:

mxml_node_t *
mxmlLoadFilename(mxml_node_t *top, const char *filename,
                 mxml_load_cb_t load_cb, void *load_cbdata,
                 mxml_sax_cb_t sax_cb, void *sax_cbdata);

The load_cb argument specifies a function that assigns child (value) node types for each element in the document. The default callback (NULL) supports passing a pointer to an mxml_type_t variable containing the type of value nodes. For example, to load the XML file "filename.xml" containing literal strings you can use:

mxml_node_t *tree;
mxml_type_t type = MXML_TYPE_OPAQUE;

tree = mxmlLoadFilename(/*top*/NULL, "filename.xml",
                        /*load_cb*/NULL, /*load_cbdata*/&type,
                        /*sax_cb*/NULL, /*sax_cbdata*/NULL);

Mini-XML also provides functions to load from a FILE pointer, a file descriptor, or string:

mxml_node_t *
mxmlLoadFd(mxml_node_t *top, int fd,
           mxml_load_cb_t load_cb, void *load_cbdata,
           mxml_sax_cb_t sax_cb, void *sax_cbdata);

mxml_node_t *
mxmlLoadFile(mxml_node_t *top, FILE *fp,
             mxml_load_cb_t load_cb, void *load_cbdata,
             mxml_sax_cb_t sax_cb, void *sax_cbdata);

mxml_node_t *
mxmlLoadString(mxml_node_t *top, const char *s,
           mxml_load_cb_t load_cb, void *load_cbdata,
           mxml_sax_cb_t sax_cb, void *sax_cbdata);

Load Callbacks

The load_xxx arguments to the mxmlLoadXxx functions are a callback function and a data pointer which are used to determine the value type of each data node in an XML document. The default (NULL) callback expects the load_cbdata argument to be a pointer to a mxml_type_t variable that contains the desired value node type - if NULL, it uses the MXML_TYPE_TEXT (whitespace-separated text) type.

You can provide your own callback function for more complex XML documents. Your callback function will receive a pointer to the current element node and must return the value type of the immediate children for that element node: MXML_TYPE_CUSTOM, MXML_TYPE_INTEGER, MXML_TYPE_OPAQUE, MXML_TYPE_REAL, or MXML_TYPE_TEXT. The function is called after the element and its attributes have been read so you can look at the element name, attributes, and attribute values to determine the proper value type to return.

The following callback function looks for an attribute named "type" or the element name to determine the value type for its child nodes:

mxml_type_t
my_load_cb(void *cbdata, mxml_node_t *node)
{
  const char *type;

 /*
  * You can lookup attributes and/or use the element name,
  * hierarchy, etc...
  */

  type = mxmlElementGetAttr(node, "type");
  if (type == NULL)
    type = mxmlGetElement(node);
  if (type == NULL)
    type = "text";

  if (!strcmp(type, "integer"))
    return (MXML_TYPE_INTEGER);
  else if (!strcmp(type, "opaque"))
    return (MXML_TYPE_OPAQUE);
  else if (!strcmp(type, "real"))
    return (MXML_TYPE_REAL);
  else
    return (MXML_TYPE_TEXT);
}

To use this callback function, simply specify it when you call any of the load functions:

mxml_node_t *tree;

tree = mxmlLoadFilename(/*top*/NULL, "filename.xml",
                        my_load_cb, /*load_cbdata*/NULL,
                        /*sax_cb*/NULL, /*sax_cbdata*/NULL);

Nodes

Every piece of information in an XML file is stored in memory in "nodes". Nodes are defined by the mxml_node_t structure. Each node has a typed value, optional user data, a parent node, sibling nodes (previous and next), and potentially child nodes.

For example, if you have an XML file like the following:

<?xml version="1.0" encoding="utf-8"?>
<data>
    <node>val1</node>
    <node>val2</node>
    <node>val3</node>
    <group>
        <node>val4</node>
        <node>val5</node>
        <node>val6</node>
    </group>
    <node>val7</node>
    <node>val8</node>
</data>

the node tree for the file would look like the following in memory:

?xml version="1.0" encoding="utf-8"?
  |
data
  |
node - node - node - group - node - node
  |      |      |      |       |      |
val1   val2   val3     |     val7   val8
                       |
                     node - node - node
                       |      |      |
                     val4   val5   val6

where "-" is a pointer to the sibling node and "|" is a pointer to the first child or parent node.

The mxmlGetType function gets the type of a node:

mxml_type_t
mxmlGetType(mxml_node_t *node);

MXML_TYPE_CDATA : CDATA,
MXML_TYPE_COMMENT : A comment,
MXML_TYPE_CUSTOM : A custom value defined by your application,
MXML_TYPE_DECLARATION : A declaration such as <!DOCTYPE html>,
MXML_TYPE_DIRECTIVE : A processing instruction such as <?xml version="1.0"?>,
MXML_TYPE_ELEMENT : An XML element,
MXML_TYPE_INTEGER : A whitespace-delimited integer value,
MXML_TYPE_OPAQUE : An opaque string value that preserves all whitespace,
MXML_TYPE_REAL : A whitespace-delimited floating point value, or
MXML_TYPE_TEXT : A whitespace-delimited text (fragment) value.

The parent and sibling nodes are accessed using the mxmlGetParent, mxmlGetNextSibling, and mxmlGetPreviousSibling functions, while the children of an element node are accessed using the mxmlGetFirstChild or mxmlGetLastChild functions:

mxml_node_t *
mxmlGetFirstChild(mxml_node_t *node);

mxml_node_t *
mxmlGetLastChild(mxml_node_t *node);

mxml_node_t *
mxmlGetNextSibling(mxml_node_t *node);

mxml_node_t *
mxmlGetParent(mxml_node_t *node);

mxml_node_t *
mxmlGetPrevSibling(mxml_node_t *node);

The mxmlGetUserData function gets any user (application) data associated with the node:

void *
mxmlGetUserData(mxml_node_t *node);

Creating XML Documents

You can create and update XML documents in memory using the various mxmlNewXxx functions. The following code will create the XML document described in the previous section:

mxml_node_t *xml;    /* <?xml version="1.0"?> */
mxml_node_t *data;   /* <data> */
mxml_node_t *node;   /* <node> */
mxml_node_t *group;  /* <group> */

xml = mxmlNewXML("1.0");

data = mxmlNewElement(xml, "data");

    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val1");
    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val2");
    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val3");

    group = mxmlNewElement(data, "group");

        node = mxmlNewElement(group, "node");
        mxmlNewText(node, false, "val4");
        node = mxmlNewElement(group, "node");
        mxmlNewText(node, false, "val5");
        node = mxmlNewElement(group, "node");
        mxmlNewText(node, false, "val6");

    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val7");
    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val8");

We start by creating the declaration node common to all XML files using the mxmlNewXML function:

xml = mxmlNewXML("1.0");

We then create the <data> node used for this document using the mxmlNewElement function. The first argument specifies the parent node (xml) while the second specifies the element name (data):

data = mxmlNewElement(xml, "data");

Each <node>...</node> in the file is created using the mxmlNewElement and mxmlNewText functions. The first argument of mxmlNewText specifies the parent node (node). The second argument specifies whether whitespace appears before the text - false in this case. The last argument specifies the actual text to add:

node = mxmlNewElement(data, "node");
mxmlNewText(node, false, "val1");

The resulting in-memory XML document can then be saved or processed just like one loaded from disk or a string.

Saving an XML File

You save an XML file using the mxmlSaveFilename function:

bool
mxmlSaveFilename(mxml_node_t *node, const char *filename,
                 mxml_save_cb_t cb, void *cbdata);

The cb and cbdata arguments specify a function and data pointer that is called to determine what whitespace (if any) is inserted before and after each element node. A NULL value tells Mini-XML to not include any extra whitespace. For example, so save an XML file to the file "filename.xml" with no extra whitespace:

mxmlSaveFile(xml, "filename.xml", /*cb*/NULL, /*cbdata*/NULL);

Mini-XML also provides functions to save to a file descriptor, FILE pointer, or strings:

char *
mxmlSaveAllocString(mxml_node_t *node, mxml_save_cb_t cb,
                    void *cbdata);

bool
mxmlSaveFd(mxml_node_t *node, int fd, mxml_save_cb_t cb,
           void *cbdata);

bool
mxmlSaveFile(mxml_node_t *node, FILE *fp, mxml_save_cb_t cb,
             void *cbdata);

size_t
mxmlSaveString(mxml_node_t *node, char *buffer, size_t bufsize,
               mxml_save_cb_t cb, void *cbdata);

Controlling Line Wrapping

When saving XML documents, Mini-XML normally wraps output lines at column 75 so that the text is readable in terminal windows. The mxmlSetWrapMargin function overrides the default wrap margin for the current thread:

void mxmlSetWrapMargin(int column);

For example, the following code sets the margin to 132 columns:

mxmlSetWrapMargin(132);

while the following code disables wrapping by setting the margin to 0:

mxmlSetWrapMargin(0);

Save Callbacks

The last arguments to the mxmlSaveXxx functions are a callback function and data pointer which is used to automatically insert whitespace in an XML document. Your callback function will be called up to four times for each element node with a pointer to the node and a where value of MXML_WS_BEFORE_OPEN, MXML_WS_AFTER_OPEN, MXML_WS_BEFORE_CLOSE, or MXML_WS_AFTER_CLOSE. The callback function should return NULL if no whitespace should be added or the string to insert (spaces, tabs, carriage returns, and newlines) otherwise.

The following whitespace callback can be used to add whitespace to XHTML output to make it more readable in a standard text editor:

const char *
whitespace_cb(void *cbdata, mxml_node_t *node, mxml_ws_t where)
{
  const char *element;

 /*
  * We can conditionally break to a new line before or after
  * any element.  These are just common HTML elements...
  */

  element = mxmlGetElement(node);

  if (!strcmp(element, "html") ||
      !strcmp(element, "head") ||
      !strcmp(element, "body") ||
      !strcmp(element, "pre") ||
      !strcmp(element, "p") ||
      !strcmp(element, "h1") ||
      !strcmp(element, "h2") ||
      !strcmp(element, "h3") ||
      !strcmp(element, "h4") ||
      !strcmp(element, "h5") ||
      !strcmp(element, "h6"))
  {
   /*
    * Newlines before open and after close...
    */

    if (where == MXML_WS_BEFORE_OPEN ||
        where == MXML_WS_AFTER_CLOSE)
      return ("\n");
  }
  else if (!strcmp(element, "dl") ||
           !strcmp(element, "ol") ||
           !strcmp(element, "ul"))
  {
   /*
    * Put a newline before and after list elements...
    */

    return ("\n");
  }
  else if (!strcmp(element, "dd") ||
           !strcmp(element, "dt") ||
           !strcmp(element, "li"))
  {
   /*
    * Put a tab before <li>'s, <dd>'s, and <dt>'s, and a
    * newline after them...
    */

    if (where == MXML_WS_BEFORE_OPEN)
      return ("\t");
    else if (where == MXML_WS_AFTER_CLOSE)
      return ("\n");
  }

 /*
  * Otherwise return NULL for no added whitespace...
  */

  return (NULL);
}

To use this callback function, simply use the name when you call any of the save functions:

FILE *fp;
mxml_node_t *tree;

fp = fopen("filename.xml", "w");
mxmlSaveFile(tree, fp, whitespace_cb, /*cbdata*/NULL);
fclose(fp);

Memory Management

Once you are done with the XML data, use the mxmlDelete function to free the memory that is used for a particular node and its children:

void
mxmlDelete(mxml_node_t *tree);

You can also use reference counting to manage memory usage. The mxmlRetain and mxmlRelease functions increment and decrement a node's use count, respectively. When the use count goes to zero, mxmlRelease calls mxmlDelete to actually free the memory used by the node tree. New nodes start with a use count of 1.

More About Nodes

Element Nodes

Element (MXML_TYPE_ELEMENT) nodes are created using the mxmlNewElement function. Element attributes are set using the mxmlElementSetAttr and mxmlElementSetAttrf functions and cleared using the mxmlElementClearAttr function:

mxml_node_t *
mxmlNewElement(mxml_node_t *parent, const char *name);

void
mxmlElementClearAttr(mxml_node_t *node, const char *name);

void
mxmlElementSetAttr(mxml_node_t *node, const char *name,
                   const char *value);

void
mxmlElementSetAttrf(mxml_node_t *node, const char *name,
                    const char *format, ...);

The mxmlGetElement function retrieves the element name while the mxmlElementGetAttr function retrieves the value string for a named attribute associated with the element. The mxmlElementGetAttrByIndex and mxmlElementGetAttrCount functions retrieve attributes by index:

const char *
mxmlGetElement(mxml_node_t *node);

const char *
mxmlElementGetAttr(mxml_node_t *node, const char *name);

const char *
mxmlElementGetAttrByIndex(mxml_node_t *node, size_t idx,
                          const char **name);

size_t
mxmlElementGetAttrCount(mxml_node_t *node);

CDATA Nodes

CDATA (MXML_TYPE_CDATA) nodes are created using the mxmlNewCDATA and mxmlNewCDATAf functions:

mxml_node_t *
mxmlNewCDATA(mxml_node_t *parent, const char *string);

mxml_node_t *
mxmlNewCDATAf(mxml_node_t *parent, const char *format, ...);

The mxmlGetCDATA function retrieves the CDATA string pointer for a node:

const char *
mxmlGetCDATA(mxml_node_t *node);

Comment Nodes

Comment (MXML_TYPE_COMMENT) nodes are created using the mxmlNewComment and mxmlNewCommentf functions, for example:

mxml_node_t *node = mxmlNewComment(" This is a comment ");

mxml_node_t *node = mxmlNewCommentf(" This is comment %d ", 42);

Similarly, the mxmlGetComment function retrieves the comment string pointer for a node:

const char *comment = mxmlGetComment(node);
/* returns " This is a comment " */

Processing Instruction Nodes

Processing instruction (MXML_TYPE_DIRECTIVE) nodes are created using the mxmlNewDirective and mxmlNewDirectivef functions:

mxml_node_t *node = mxmlNewDirective("xml-stylesheet type=\"text/css\" href=\"style.css\"");

mxml_node_t *node = mxmlNewDirectivef("xml version=\"%s\"", version);

The mxmlGetDirective function retrieves the processing instruction string for a node:

const char *instr = mxmlGetElement(node);
/* returns "xml-stylesheet type=\"text/css\" href=\"style.css\"" */

The mxmlNewXML function can be used to create the top-level "xml" processing instruction with an associated version number:

mxml_node_t *
mxmlNewXML(const char *version);

Integer Nodes

Integer (MXML_TYPE_INTEGER) nodes are created using the mxmlNewInteger function:

mxml_node_t *
mxmlNewInteger(mxml_node_t *parent, long integer);

The mxmlGetInteger function retrieves the integer value for a node:

long
mxmlGetInteger(mxml_node_t *node);

Opaque String Nodes

Opaque string (MXML_TYPE_OPAQUE) nodes are created using the mxmlNewOpaque and mxmlNewOpaquef functions:

mxml_node_t *
mxmlNewOpaque(mxml_node_t *parent, const char *opaque);

mxml_node_t *
mxmlNewOpaquef(mxml_node_t *parent, const char *format, ...);

The mxmlGetOpaque function retrieves the opaque string pointer for a node:

const char *
mxmlGetOpaque(mxml_node_t *node);

Text Nodes

Whitespace-delimited text string (MXML_TYPE_TEXT) nodes are created using the mxmlNewText and mxmlNewTextf functions. Each text node consists of a text string and (leading) whitespace boolean value.

mxml_node_t *
mxmlNewText(mxml_node_t *parent, bool whitespace,
            const char *string);

mxml_node_t *
mxmlNewTextf(mxml_node_t *parent, bool whitespace,
             const char *format, ...);

The mxmlGetText function retrieves the text string pointer and whitespace boolean value for a node:

const char *
mxmlGetText(mxml_node_t *node, bool *whitespace);

Real Number Nodes

Real number (MXML_TYPE_REAL) nodes are created using the mxmlNewReal function:

mxml_node_t *
mxmlNewReal(mxml_node_t *parent, double real);

The mxmlGetReal function retrieves the real number for a node:

double
mxmlGetReal(mxml_node_t *node);

Locating Data in an XML Document

Mini-XML provides many functions for enumerating, searching, and indexing XML documents.

Finding Nodes

The mxmlFindPath function finds the (first) value node under a specific element using a "path":

mxml_node_t *
mxmlFindPath(mxml_node_t *node, const char *path);

The path string can contain the "*" wildcard to match a single element node in the hierarchy. For example, the following code will find the first "node" element under the "group" element, first using an explicit path and then using a wildcard:

mxml_node_t *value = mxmlFindPath(xml, "data/group/node");

mxml_node_t *value = mxmlFindPath(xml, "data/*/node");

The mxmlFindElement function can be used to find a named element, optionally matching an attribute and value:

mxml_node_t *
mxmlFindElement(mxml_node_t *node, mxml_node_t *top,
                const char *element, const char *attr,
                const char *value, int descend);

The "element", "attr", and "value" arguments can be passed as NULL to act as wildcards, e.g.:

/* Find the first "a" element */
node = mxmlFindElement(tree, tree, "a", NULL, NULL,
                       MXML_DESCEND_ALL);

/* Find the first "a" element with "href" attribute */
node = mxmlFindElement(tree, tree, "a", "href", NULL,
                       MXML_DESCEND_ALL);

/* Find the first "a" element with "href" to a URL */
node = mxmlFindElement(tree, tree, "a", "href",
                       "http://msweet.org/",
                       MXML_DESCEND_ALL);

/* Find the first element with a "src" attribute*/
node = mxmlFindElement(tree, tree, NULL, "src", NULL,
                       MXML_DESCEND_ALL);

/* Find the first element with a "src" = "foo.jpg" */
node = mxmlFindElement(tree, tree, NULL, "src", "foo.jpg",
                       MXML_DESCEND_ALL);

You can also iterate with the same function:

mxml_node_t *node;

for (node = mxmlFindElement(tree, tree, "element", NULL,
                            NULL, MXML_DESCEND_ALL);
     node != NULL;
     node = mxmlFindElement(node, tree, "element", NULL,
                            NULL, MXML_DESCEND_ALL))
{
  ... do something ...
}

The descend argument (MXML_DESCEND_ALL in the examples above) can be one of three constants:

MXML_DESCEND_NONE: ignore child nodes in the element hierarchy, instead using siblings (same level) or parent nodes (above) until the top (root) node is reached.
MXML_DESCEND_FIRST: start the search with the first child of the node, and then search siblings. You'll normally use this when iterating through direct children of a parent node, e.g. all of the "node" and "group" elements under the "?xml" parent node in the previous example.
MXML_DESCEND_ALL: search child nodes first, then sibling nodes, and then parent nodes.

Iterating Nodes

While the mxmlFindNode and mxmlFindPath functions will find a particular element node, sometimes you need to iterate over all nodes. The mxmlWalkNext and mxmlWalkPrev functions can be used to iterate through the XML node tree:

mxml_node_t *
mxmlWalkNext(mxml_node_t *node, mxml_node_t *top,
             int descend);

mxml_node_t *
mxmlWalkPrev(mxml_node_t *node, mxml_node_t *top,
             int descend);

Depending on the value of the descend argument, these functions will automatically traverse child, sibling, and parent nodes until the top node is reached. For example, the following code will iterate over all of the nodes in the sample XML document in the previous section:

mxml_node_t *node;

for (node = xml;
     node != NULL;
     node = mxmlWalkNext(node, xml, MXML_DESCEND_ALL))
{
  ... do something ...
}

The nodes will be returned in the following order:

<?xml version="1.0" encoding="utf-8"?>
<data>
<node>
val1
<node>
val2
<node>
val3
<group>
<node>
val4
<node>
val5
<node>
val6
<node>
val7
<node>
val8

Indexing

The mxmlIndexNew function allows you to create an index of nodes for faster searching and enumeration:

mxml_index_t *
mxmlIndexNew(mxml_node_t *node, const char *element,
             const char *attr);

The element and attr arguments control which elements are included in the index. If element is not NULL then only elements with the specified name are added to the index. Similarly, if attr is not NULL then only elements containing the specified attribute are added to the index. The nodes are sorted in the index.

For example, the following code creates an index of all "id" values in an XML document:

mxml_index_t *ind = mxmlIndexNew(xml, NULL, "id");

Once the index is created, the mxmlIndexFind function can be used to find a matching node:

mxml_node_t *
mxmlIndexFind(mxml_index_t *ind, const char *element,
              const char *value);

For example, the following code will find the element whose "id" string is "42":

mxml_node_t *node = mxmlIndexFind(ind, NULL, "42");

Alternately, the mxmlIndexReset and mxmlIndexEnum functions can be used to enumerate the nodes in the index:

mxml_node_t *
mxmlIndexReset(mxml_index_t *ind);

mxml_node_t *
mxmlIndexEnum(mxml_index_t *ind);

Typically these functions will be used in a for loop:

mxml_node_t *node;

for (node = mxmlIndexReset(ind);
     node != NULL;
     node = mxmlIndexEnum(ind))
{
  ... do something ...
}

The mxmlIndexCount function returns the number of nodes in the index:

size_t
mxmlIndexGetCount(mxml_index_t *ind);

Finally, the mxmlIndexDelete function frees all memory associated with the index:

void
mxmlIndexDelete(mxml_index_t *ind);

Custom Data Types

Mini-XML supports custom data types via per-thread load and save callbacks. Only a single set of callbacks can be active at any time for the current thread, however your callbacks can store additional information in order to support multiple custom data types as needed. The MXML_TYPE_CUSTOM node type identifies custom data nodes.

The mxmlGetCustom function retrieves the custom value pointer for a node.

const void *
mxmlGetCustom(mxml_node_t *node);

Custom (MXML_TYPE_CUSTOM) nodes are created using the mxmlNewCustom function or using a custom per-thread load callbacks specified using the mxmlSetCustomHandlers function:

typedef void (*mxml_custom_destroy_cb_t)(void *);
typedef bool (*mxml_custom_load_cb_t)(mxml_node_t *, const char *);
typedef char *(*mxml_custom_save_cb_t)(mxml_node_t *);

mxml_node_t *
mxmlNewCustom(mxml_node_t *parent, void *data,
              mxml_custom_destroy_cb_t destroy);

int
mxmlSetCustom(mxml_node_t *node, void *data,
              mxml_custom_destroy_cb_t destroy);

void
mxmlSetCustomHandlers(mxml_custom_load_cb_t load,
                      mxml_custom_save_cb_t save);

The load callback receives a pointer to the current data node and a string of opaque character data from the XML source with character entities converted to the corresponding UTF-8 characters. For example, if we wanted to support a custom date/time type whose value is encoded as "yyyy-mm-ddThh:mm:ssZ" (ISO format), the load callback would look like the following:

typedef struct
{
  unsigned year,    /* Year */
           month,   /* Month */
           day,     /* Day */
           hour,    /* Hour */
           minute,  /* Minute */
           second;  /* Second */
  time_t   unix;    /* UNIX time */
} iso_date_time_t;

bool
load_custom(mxml_node_t *node, const char *data)
{
  iso_date_time_t *dt;
  struct tm tmdata;

 /*
  * Allocate data structure...
  */

  dt = calloc(1, sizeof(iso_date_time_t));

 /*
  * Try reading 6 unsigned integers from the data string...
  */

  if (sscanf(data, "%u-%u-%uT%u:%u:%uZ", &(dt->year),
             &(dt->month), &(dt->day), &(dt->hour),
             &(dt->minute), &(dt->second)) != 6)
  {
   /*
    * Unable to read numbers, free the data structure and
    * return an error...
    */

    free(dt);

    return (false);
  }

 /*
  * Range check values...
  */

  if (dt->month < 1 || dt->month > 12 ||
      dt->day < 1 || dt->day > 31 ||
      dt->hour < 0 || dt->hour > 23 ||
      dt->minute < 0 || dt->minute > 59 ||
      dt->second < 0 || dt->second > 60)
  {
   /*
    * Date information is out of range...
    */

    free(dt);

    return (false);
  }

 /*
  * Convert ISO time to UNIX time in seconds...
  */

  tmdata.tm_year = dt->year - 1900;
  tmdata.tm_mon  = dt->month - 1;
  tmdata.tm_day  = dt->day;
  tmdata.tm_hour = dt->hour;
  tmdata.tm_min  = dt->minute;
  tmdata.tm_sec  = dt->second;

  dt->unix = gmtime(&tmdata);

 /*
  * Assign custom node data and destroy (free) function
  * pointers...
  */

  mxmlSetCustom(node, data, free);

 /*
  * Return with no errors...
  */

  return (true);
}

The function itself can return true on success or false if it is unable to decode the custom data or the data contains an error. Custom data nodes contain a void pointer to the allocated custom data for the node and a pointer to a destructor function which will free the custom data when the node is deleted. In this example, we use the standard free function since everything is contained in a single calloc'd block.

The save callback receives the node pointer and returns an allocated string containing the custom data value. The following save callback could be used for our ISO date/time type:

char *
save_custom(mxml_node_t *node)
{
  char data[255];
  iso_date_time_t *dt;


  dt = (iso_date_time_t *)mxmlGetCustom(node);

  snprintf(data, sizeof(data),
           "%04u-%02u-%02uT%02u:%02u:%02uZ",
           dt->year, dt->month, dt->day, dt->hour,
           dt->minute, dt->second);

  return (strdup(data));
}

You register the callback functions using the mxmlSetCustomCallbacks function:

mxmlSetCustomCallbacks(load_custom, save_custom);

SAX (Stream) Loading of Documents

Mini-XML supports an implementation of the Simple API for XML (SAX) which allows you to load and process an XML document as a stream of nodes. Aside from allowing you to process XML documents of any size, the Mini-XML implementation also allows you to retain portions of the document in memory for later processing.

The mxmlLoadXxx functions support a SAX callback and associated data. The callback function receives the data pointer you supplied, the node, and an event code and returns true to continue processing or false to stop:

bool
sax_cb(void *cbdata, mxml_node_t *node,
       mxml_sax_event_t event)
{
  ... do something ...

  // Continue processing...
  return (true);
}

The event will be one of the following:

MXML_SAX_EVENT_CDATA: CDATA was just read.
MXML_SAX_EVENT_COMMENT: A comment was just read.
MXML_SAX_EVENT_DATA: Data (integer, opaque, real, or text) was just read.
MXML_SAX_EVENT_DECLARATION: A declaration was just read.
MXML_SAX_EVENT_DIRECTIVE: A processing directive/instruction was just read.
MXML_SAX_EVENT_ELEMENT_CLOSE - A close element was just read (</element>)
MXML_SAX_EVENT_ELEMENT_OPEN - An open element was just read (<element>)

Elements are released after the close element is processed. All other nodes are released after they are processed. The SAX callback can retain the node using the mxmlRetain function. For example, the following SAX callback will retain all nodes, effectively simulating a normal in-memory load:

bool
sax_cb(void *cbdata, mxml_node_t *node, mxml_sax_event_t event)
{
  if (event != MXML_SAX_ELEMENT_CLOSE)
    mxmlRetain(node);

  return (true);
}

More typically the SAX callback will only retain a small portion of the document that is needed for post-processing. For example, the following SAX callback will retain the title and headings in an XHTML file. It also retains the (parent) elements like <html>, <head>, and <body>, and processing directives like <?xml ... ?> and declarations like <!DOCTYPE ... >:

bool
sax_cb(void *cbdata, mxml_node_t *node,
       mxml_sax_event_t event)
{
  if (event == MXML_SAX_ELEMENT_OPEN)
  {
   /*
    * Retain headings and titles...
    */

    const char *element = mxmlGetElement(node);

    if (!strcmp(element, "html") ||
        !strcmp(element, "head") ||
        !strcmp(element, "title") ||
        !strcmp(element, "body") ||
        !strcmp(element, "h1") ||
        !strcmp(element, "h2") ||
        !strcmp(element, "h3") ||
        !strcmp(element, "h4") ||
        !strcmp(element, "h5") ||
        !strcmp(element, "h6"))
      mxmlRetain(node);
  }
  else if (event == MXML_SAX_DECLARATION)
    mxmlRetain(node);
  else if (event == MXML_SAX_DIRECTIVE)
    mxmlRetain(node);
  else if (event == MXML_SAX_DATA)
  {
    if (mxmlGetRefCount(mxmlGetParent(node)) > 1)
    {
     /*
      * If the parent was retained, then retain this data
      * node as well.
      */

      mxmlRetain(node);
    }
  }

  return (true);
}

The resulting skeleton document tree can then be searched just like one loaded without the SAX callback function. For example, a filter that reads an XHTML document from stdin and then shows the title and headings in the document would look like:

mxml_node_t *doc, *title, *body, *heading;

doc = mxmlLoadFd(/*top*/NULL, /*fd*/0,
                 /*load_cb*/NULL, /*load_cbdata*/NULL,
                 sax_cb, /*sax_cbdata*/NULL);

title = mxmlFindElement(doc, doc, "title", NULL, NULL,
                        MXML_DESCEND_ALL);

if (title)
  print_children(title);

body = mxmlFindElement(doc, doc, "body", NULL, NULL,
                       MXML_DESCEND_ALL);

if (body)
{
  for (heading = mxmlGetFirstChild(body);
       heading;
       heading = mxmlGetNextSibling(heading))
    print_children(heading);
}

The print_children function is:

void
print_children(mxml_node_t *parent)
{
  mxml_node_t *node;
  const char *text;
  bool whitespace;

  for (node = mxmlGetFirstChild(parent);
       node != NULL;
       node = mxmlGetNextSibling(node))
  {
    text = mxmlGetText(node, &whitespace);

    if (whitespace)
      putchar(' ');

    fputs(text, stdout);
  }

  putchar('\n');
}

Migrating from Mini-XML v3.x

The following incompatible API changes were made in Mini-XML v4.0:

SAX events are now named MXML_SAX_EVENT_foo instead of MXML_SAX_foo.
SAX callbacks now return a boolean value.
The mxmlSAXLoadXxx functions have been removed in favor of passing the SAX callback function and data pointers to the mxmlLoadXxx functions.
Node types are now named MXML_TYPE_foo instead of MXML_foo.
Descend values are now normalized to MXML_DESCEND_ALL, MXML_DESCEND_FIRST, and MXML_DESCEND_NONE.
Functions that returned 0 on success and -1 on error now return true on success and false on error.
CDATA nodes ("<![CDATA[...]]>") now have their own type (MXML_TYPE_CDATA).
Comment nodes ("") now have their own type (MXML_TYPE_COMMENT).
Custom node callbacks are now set using the mxmlSetCustomCallbacks function instead of mxmlSetCustomHandlers.
Declaration nodes ("<!...>") now have their own type (MXML_TYPE_DECLARATION).
Element attributes are now cleared with the mxmlElementClearAttr function instead of mxmlElementDeleteAttr.
Processing instruction/directive nodes ("<?...?>") now have their own type (MXML_TYPE_DIRECTIVE).
Integer nodes (MXML_TYPE_INTEGER) now use the long type.
Text nodes (MXML_TYPE_TEXT) now use the bool type for the whitespace value.

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