XML Parser for Libsvgtiny

发表于 2020-04-08 分类于系统与底层阅读时长 ≈ 4 分钟

这是我的硕士论文笔记系列第三篇，原文写于 2016 年五月。

Libxml2

Libxml2資料結構

/**
 * xmlNode:
 *
 * A node in an XML tree.
 */

typedef struct _xmlNode xmlNode;
typedef xmlNode *xmlNodePtr;                                                                                                                      
struct _xmlNode {
    void           *_private;	/* application data */
    xmlElementType   type;	/* type number, must be second ! */
    const xmlChar   *name;      /* the name of the node, or the entity */
    struct _xmlNode *children;  /* parent->childs link */
    struct _xmlNode *last;	/* last child link */
    struct _xmlNode *parent;	/* child->parent link */
    struct _xmlNode *next;	/* next sibling link  */
    struct _xmlNode *prev;	/* previous sibling link  */
    struct _xmlDoc  *doc;	/* the containing document */

    /* End of common part */
    xmlNs           *ns;	/* pointer to the associated namespace */
    xmlChar         *content;	/* the content */
    struct _xmlAttr *properties;/* properties list */
    xmlNs           *nsDef;	/* namespace definitions on this node */
    void            *psvi;	/* for type/PSVI informations */
    unsigned short   line;	/* line number */
    unsigned short   extra;	/* extra data for XPath/XSLT */
};


/**
 * xmlDoc:
 *                                                                                                                                                
 * An XML document.
 */
typedef struct _xmlDoc xmlDoc;
typedef xmlDoc *xmlDocPtr;
struct _xmlDoc {
    void           *_private;	/* application data */
    xmlElementType  type;	/* XML_DOCUMENT_NODE, must be second ! */
    char           *name;	/* name/filename/URI of the document */
    struct _xmlNode *children;	/* the document tree */
    struct _xmlNode *last;	/* last child link */
    struct _xmlNode *parent;	/* child->parent link */
    struct _xmlNode *next;	/* next sibling link  */
    struct _xmlNode *prev;	/* previous sibling link  */
    struct _xmlDoc  *doc;	/* autoreference to itself */

    /* End of common part */
    int compression;		/* level of zlib compression */
    int standalone;		/* standalone document (no external refs)
                		¦ 1 if standalone="yes"
                		¦ 0 if standalone="no"
                		¦ -1 if there is no XML declaration
                		¦ -2 if there is an XML declaration, but no
                    			standalone attribute was specified */
    struct _xmlDtd  *intSubset; /* the document internal subset */
    struct _xmlDtd  *extSubset; /* the document external subset */
    struct _xmlNs   *oldNs;	/* Global namespace, the old way */
    const xmlChar  *version;	/* the XML version string */
    const xmlChar  *encoding;	/* external initial encoding, if any */
    void           *ids;	/* Hash table for ID attributes if any */
    void           *refs;	/* Hash table for IDREFs attributes if any */
    const xmlChar  *URL;	/* The URI for that document */
    int             charset;	/* encoding of the in-memory contentactually an xmlCharEncoding */
    struct _xmlDict *dict;	/* dict used to allocate names or NULL */
    void           *psvi;	/* for type/PSVI informations */
    int             parseFlags;	/* set of xmlParserOption used to parse the document */
    int             properties; /* set of xmlDocProperties for this document set at the end of parsing */
};


/**
 * xmlAttribute:
 *
 * An Attribute declaration in a DTD.
 */

typedef struct _xmlAttribute xmlAttribute;
typedef xmlAttribute *xmlAttributePtr;
struct _xmlAttribute {
    void		*_private;	/* application data */
    xmlElementType	type;	/* XML_ATTRIBUTE_DECL, must be second ! */
    const xmlChar	*name;	/* Attribute name */
    struct _xmlNode	*children;	/* NULL */
    struct _xmlNode	*last;	/* NULL */
    struct _xmlDtd	*parent;	/* -> DTD */
    struct _xmlNode	*next;	/* next sibling link  */
    struct _xmlNode	*prev;	/* previous sibling link  */
    struct _xmlDoc	*doc;	/* the containing document */

    struct _xmlAttribute	*nexth;	/* next in hash table */
    xmlAttributeType		atype;	/* The attribute type */
    xmlAttributeDefault		def;	/* the default */
    const xmlChar		*defaultValue;	/* or the default value */
    xmlEnumerationPtr		tree;	/* or the enumeration tree if any */
    const xmlChar		*prefix;	/* the namespace prefix if any */
    const xmlChar		*elem;	/* Element holding the attribute */
};

Libxml2構建API

1	dom_xml_parser dom_xml_parser_create(void dontCare1, void dontCare2, MesgFuncPtr mesgFunc, void dontCare3, dom_document **outDocument);

呼叫xmlInitParser()初始化parser，然後使用calloc定義了dom_document和dom_xml_parser的指針各一個。

1	dom_xml_error dom_xml_parser_parse_chunk(dom_xml_parser parser, const uint8_t data, size_t len);

呼叫xmlReadMemory()函式解析。

1	dom_exception dom_document_get_document_element(dom_document document, dom_element *outNode);

用來尋找根<svg>，實作直接呼叫xmlDocGetRootElement()函式得到document→node，相當於默認是SVG檔案。

1	dom_exception dom_node_get_node_name(dom_node node, dom_string *outString);

自幹一個dom_string_create_interned()函式：

如果svg→node→ns和svg→node→ns→prefix存在，呼叫asprintf(&qname, "%s:%s", n->ns->prefix, n->name)先把字串寫進qname，然後再通過自幹的函式把qname給outString；
若不存在就直接呼叫自幹函式把svg→node→name的值給outString。

1	dom_exception dom_document_get_element_by_id(dom_node node, dom_string string, dom_element **outNode);

被svgtiny_gradient.c使用，先呼叫xmlHasProp()函式檢查document→node是否存在id這個屬性：

若id屬性存在则檢查裏面是否存在需要的ID字串，把gradient的指標指向這個document；
內部還實作了一個getElementById()函式，供這個API調用，也是類似呼叫xmlHasProp()和做strcasecmp()。

1	dom_exception dom_element_get_attribute(dom_node node, dom_string string, dom_string **outAttribute);

呼叫xmlHasProp()得到指定的屬性，例如讀svg的d屬性，也就是path。

1	dom_exception dom_element_get_elements_by_tag_name(dom_element element, dom_string string, dom_nodelist **outNodeList);

被svgtiny_gradient.c使用。遍歷element→node→children鏈表，只要節點的名字和tag名相同，就把其加入nodeList裏。

1	dom_exception dom_node_get_node_type(dom_node node, dom_node_type outType);

需要注意node type的種類要滿足。

dom_xml_error dom_xml_parser_completed(dom_xml_parser *parser);
dom_xml_error dom_xml_parser_destroy(dom_xml_parser *parser);
dom_exception dom_nodelist_get_length(dom_nodelist *nodeList, uint32_t *outLen);
dom_exception dom_nodelist_item(dom_nodelist *nodeList, uint32_t index, dom_node **outItemp);
void dom_node_unref(dom_node *node);
void dom_nodelist_unref(dom_nodelist *nodeList);
dom_exception dom_node_get_first_child(dom_element *element, dom_element **outChild);
int dom_string_caseless_isequal(dom_string *a, dom_string *b);
dom_exception dom_node_get_next_sibling(dom_element *element, dom_element **outChild);
dom_exception dom_text_get_whole_text(dom_element *element, dom_string **outString);
lwc_error lwc_intern_string(const char *data, size_t len, lwc_string **outString);
int dom_string_caseless_lwc_isequal(dom_string *str, lwc_string *lwcString);
void lwc_string_unref(lwc_string *lwcString);
uint32_t dom_string_byte_length(dom_string *str);                        
dom_exception dom_string_create_interned(const uint8_t *data, size_t len, dom_string **outString);
char *dom_string_data(dom_string *str);
int dom_string_isequal(dom_string *a, dom_string *b);                    
dom_string *dom_string_ref(dom_string *str);
void dom_string_unref(dom_string *str);