Linux 下C使用XML传递消息（字符串）

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在linux下经常要进行socket通信，而数据流多采用目前流行的xml格式，这就会有两个用的比较多的功能：
1、接收端将收到的字符串转换成xml格式的数据；
2、发送端将xml格式的数据转换成字符串发送。

运用libxml2组件进行上述操作实际上是xmlDocPtr和xmlChar两种类型之间的转换。

1. xmlDocPtr -> xmlChar
xmlDocPtr doc;
xmlChar *xmlbuff;
int buffersize;
xmlDocDumpFormatMemory(doc, &xmlbuff, &buffersize, 1);
2. xmlChar -> xmlDocPtr
xmlDocPtr doc;
char * cData;
doc = xmlParseMemory(docname, strlen(cData)+1);
怎样把xmlChar转换成char就无须多讲了，直接用（char*）强行转换也行。

(以上，转自http://hi.baidu.com/dante300/blog/item/b0962f51e472261d0cf3e3ad.html)

下面的例子，srv端等待6601端口的数据，并使用XML解析，取得其中的name和age项，并打印到终端

client端读取一个XML文件，并把读取的数据转换为字符串，向服务端的端口发送
[cpp] view plaincopy
/*srv.c By ksir in 2011-10-14*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <libxml/parser.h>
#include <libxml/xmlmemory.h>

#define MAXLINE 80
int port = 6601;        /*Port of socket*/

/*parse XML and show content of 'name','age'*/
int parseXML(xmlDocPtr tmpdoc)
{
    //printf("This is in parseXML\n");
    xmlNodePtr curNode; /*Keep node of the xml tree*/
    xmlChar *szKey;

    /*Get the root Node from tmpdoc*/
    curNode = xmlDocGetRootElement(tmpdoc);
    /*check the content of the document*/
    if (NULL == curNode)
    {
        xmlFreeDoc(tmpdoc);
        return -3;
    }

    /*Check the type of the root element*/
    if(xmlStrcmp(curNode->name,BAD_CAST"n"))
    {
        printf("Document of the wrong type");
        xmlFreeDoc(tmpdoc);
        return -4;
    }
    curNode = curNode->xmlChildrenNode;
    xmlNodePtr propNpdePtr =curNode;
    while (curNode != NULL)
    {
        /*compare element nodes,show the content*/
        if( !(xmlStrcmp(curNode->name,(const xmlChar *)"name")))
        {
            szKey = xmlNodeGetContent(curNode);
            printf("name:%s\n",szKey);
            xmlFree(szKey);
        }
        else if( !(xmlStrcmp(curNode->name,(const xmlChar *)"age")))
        {
            printf("Age:%s\n",xmlNodeGetContent(curNode));
        }
        /*traverse*/
        curNode = curNode->next;
    }
    xmlFreeDoc(tmpdoc);
    return 0;
}

int main(void)
{
    struct sockaddr_in sin;
    struct sockaddr_in rin;
    int sock_fd;
    int address_size;
    char buf[MAXLINE];
    char str[INET_ADDRSTRLEN];
    int len;
    int n;

    xmlDocPtr doc;

    bzero(&sin, sizeof(sin));
    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = INADDR_ANY;
    sin.sin_port = htons(port);


    sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
    if (-1 == sock_fd)
    {
        perror("call to socket");
        exit(1);
    }
    n = bind(sock_fd, (struct sockaddr *)&sin, sizeof(sin));
    if (-1 == n)
    {
        perror("call to bind");
        exit(1);
    }

    while(1)
    {
        address_size = sizeof(rin);
        n = recvfrom(sock_fd,buf,MAXLINE,0,(struct sockaddr *)&rin,
                &address_size);
        if (-1 == n)
        {
            perror("call to recvfrom.\n");
            exit(1);
        }
    //  printf("you ip is %s at port %d:%s\n",
    //          inet_ntop(AF_INET, &rin.sin_addr,str,sizeof(str)),
    //          ntohs(rin.sin_port),(char *)buf);

        /*transfer buf to xml*/
        doc = xmlParseMemory((char *)buf,strlen(buf)+1);
        if (NULL == doc)
        {
            printf("xmlParseMemory fail\n");
            return -2;
        }
        parseXML(doc);
    }
    return 0;
}

客户端代码：
[cpp] view plaincopy
/*Client.c by ksir in 2011-10-14*/

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<sys/types.h>
#include<unistd.h>
#include<sys/socket.h>
#include<linux/in.h>
#include <libxml/parser.h>
#include <libxml/xmlmemory.h>


int main(int argc,char *argv[])
{
    if(argc<2){
        printf("Please input a file !\n");
        exit(0);
    }
    int sock;
    struct sockaddr_in toAddr;
    struct sockaddr_in fromAddr;

    unsigned int fromLen;
    char recvBuffer[128];
    sock=socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);
    if(sock<0){
        printf("Sock failed!\n");
        exit(1);
    }

    memset(&toAddr,0,sizeof(toAddr));

    toAddr.sin_family=AF_INET;
    toAddr.sin_addr.s_addr=inet_addr("10.11.1.88");
    toAddr.sin_port=htons(6601);

    /*Get the xmlfile and parse into string*/
    xmlDocPtr doc;      /*file descriptor of the xml*/
    xmlChar *xmlbuf;
    char *szDocName;
    int buffersize;

    szDocName = argv[1];

    /*Open with GB2312*/
    doc = xmlReadFile(szDocName,"GB2312",XML_PARSE_RECOVER);
    xmlDocDumpFormatMemory(doc, &xmlbuf, &buffersize, 1);
    printf((char *) xmlbuf);

    while(1)
    {
        sleep(1);

        if(sendto(sock,xmlbuf,strlen(xmlbuf)+1,0,(struct sockaddr *)&toAddr,sizeof(toAddr)) == -1){
            printf("Sendto failed!\n");
            exit(2);
            }

    printf("OK!\n");
    }
    close(sock);
}
使用的XML文件：
[html] view plaincopy
<n>
    <name>
    ksir
    </name>
    <age>
    18
    </age>
</n>

使用libxml2库的.c文件的编译：
gcc -o srv ser.c -I /usr/include/libxml2/ -L /usr/local/lib -lxml2
LIBXML2的学习地址：http://www.xmlsoft.org/html/libxml-tree.html