net-snmp 5.5学习笔记 client部分

net-snmp 5.5学习笔记snmpget动作的学习net-snmp的两个头文件#include #include 以及snmpv3使用的头文件#include "net-snmp/transform_oids.h"包含以上头文件后请无视下文中函数上面的头文件。net-snmp中几个重要的结构体：  结构体名                             用处-------------------------------------------------------------netsnmp_session                在snmp会话中会用到的结构体netsnmp_pdu                    snmp协议数据单元netsnmp_variable_list          用于组织snmp协议返回的数据使用net-snmp基本的流程:/** 变量定义以及初始化*/struct snmp_session session, *ss;struct snmp_pdu *pdu;struct snmp_pdu *response;           oid anOID[MAX_OID_LEN];size_t anOID_len = MAX_OID_LEN;   struct variable_list *vars;int status;/** 初始化snmp库*/init_snmp("snmpapp");/** 初始化session*/snmp_sess_init( &session );                   /* set up defaults *//* 设置get操作的snmp版本为snmpv1 */session.version = SNMP_VERSION_1;   /* 设置snmp的团体名 */session.community = "demopublic";session.community_len = strlen(session.community);/* 初始化win32的socket，在unix上是空操作 */SOCK_STARTUP;/** 打开session*/ss = snmp_open(&session);                     /* 建立会话 *//** 创建请求的协议数据单元*   1) 用于取得system.sysDescr.0的值*/pdu = snmp_pdu_create(SNMP_MSG_GET);read_objid(".1.3.6.1.2.1.1.1.0", anOID, &anOID_len);   #if OTHER_METHODSget_node("sysDescr.0", anOID, &anOID_len);read_objid("system.sysDescr.0", anOID, &anOID_len);#endifsnmp_add_null_var(pdu, anOID, anOID_len);/** 发送请求并接收响应*/status = snmp_synch_response(ss, pdu, &response);/** 处理响应*/if (status == STAT_SUCCESS && response->errstat == SNMP_ERR_NOERROR) {     /*      * SUCCESS: 打印结果      */     for(vars = response->variables; vars; vars = vars->next_variable)       print_variable(vars->name, vars->name_length, vars);   } else {     /*      * FAILURE: 打印错误信息      */     if (status == STAT_SUCCESS)       fprintf(stderr, "Error in packet\nReason: %s\n",               snmp_errstring(response->errstat));     else       snmp_sess_perror("snmpget", ss);    }/** 清理工作:*  1) 释放响应结构体*  2) 关闭session.*/if (response)   snmp_free_pdu(response);snmp_close(ss);/* 清理win32的socket,unix上为空操作 */SOCK_CLEANUP;以上用到的函数有：初始化snmp库：#include void init_snmp(const char *);                   用于初始化snmp库关于session的操作：#include void snmp_sess_init(netsnmp_session *);         用于初始化sessionnetsnmp_session *snmp_open(netsnmp_session *);  打开socket并绑定响应的udp端口，如果返回空,则设置snmp_errno为错误代码int snmp_close(netsnmp_session *);              关闭输入的session，释放session中申请的内存，抛弃所有未处理的请求，关闭所有socket，返回值为1是表示成功，否则返回0int snmp_close_sessions(void);                  关闭所有打开的session关于pdu的操作：#include #include netsnmp_pdu    *snmp_pdu_create(int type);     根据type创建snmp的pdu,一下为type可选值/* * PDU types in SNMPv1, SNMPsec, SNMPv2p, SNMPv2c, SNMPv2u, SNMPv2*, and SNMPv3  */#define SNMP_MSG_GET        (ASN_CONTEXT | ASN_CONSTRUCTOR | 0x0) /* a0=160 */#define SNMP_MSG_GETNEXT    (ASN_CONTEXT | ASN_CONSTRUCTOR | 0x1) /* a1=161 */#define SNMP_MSG_RESPONSE   (ASN_CONTEXT | ASN_CONSTRUCTOR | 0x2) /* a2=162 */#define SNMP_MSG_SET        (ASN_CONTEXT | ASN_CONSTRUCTOR | 0x3) /* a3=163 *//* * PDU types in SNMPv1 and SNMPsec  */#define SNMP_MSG_TRAP       (ASN_CONTEXT | ASN_CONSTRUCTOR | 0x4) /* a4=164 *//* * PDU types in SNMPv2p, SNMPv2c, SNMPv2u, SNMPv2*, and SNMPv3  */#define SNMP_MSG_GETBULK    (ASN_CONTEXT | ASN_CONSTRUCTOR | 0x5) /* a5=165 */#define SNMP_MSG_INFORM     (ASN_CONTEXT | ASN_CONSTRUCTOR | 0x6) /* a6=166 */#define SNMP_MSG_TRAP2      (ASN_CONTEXT | ASN_CONSTRUCTOR | 0x7) /* a7=167 *//* * PDU types in SNMPv2u, SNMPv2*, and SNMPv3  */#define SNMP_MSG_REPORT     (ASN_CONTEXT | ASN_CONSTRUCTOR | 0x8) /* a8=168 *//* * internal modes that should never be used by the protocol for the * pdu type. * * All modes  */#define SNMP_MSG_INTERNAL_SET_BEGIN        -1#define SNMP_MSG_INTERNAL_SET_RESERVE1     0    /* these should match snmp.h */#define SNMP_MSG_INTERNAL_SET_RESERVE2     1#define SNMP_MSG_INTERNAL_SET_ACTION       2#define SNMP_MSG_INTERNAL_SET_COMMIT       3#define SNMP_MSG_INTERNAL_SET_FREE         4#define SNMP_MSG_INTERNAL_SET_UNDO         5#define SNMP_MSG_INTERNAL_SET_MAX          6#define SNMP_MSG_INTERNAL_CHECK_VALUE           17#define SNMP_MSG_INTERNAL_ROW_CREATE            18#define SNMP_MSG_INTERNAL_UNDO_SETUP            19#define SNMP_MSG_INTERNAL_SET_VALUE             20#define SNMP_MSG_INTERNAL_CHECK_CONSISTENCY     21#define SNMP_MSG_INTERNAL_UNDO_SET              22#define SNMP_MSG_INTERNAL_COMMIT                23#define SNMP_MSG_INTERNAL_UNDO_COMMIT           24#define SNMP_MSG_INTERNAL_IRREVERSIBLE_COMMIT   25#define SNMP_MSG_INTERNAL_UNDO_CLEANUP          26/* * modes > 128 for non sets. * Note that 160-168 overlap with SNMP ASN1 pdu types */#define SNMP_MSG_INTERNAL_PRE_REQUEST           128#define SNMP_MSG_INTERNAL_OBJECT_LOOKUP         129#define SNMP_MSG_INTERNAL_POST_REQUEST          130#define SNMP_MSG_INTERNAL_GET_STASH             131netsnmp_pdu *snmp_clone_pdu(netsnmp_pdu *pdu);                                                克隆一份pdunetsnmp_pdu *snmp_fix_pdu(netsnmp_pdu *pdu, int idx);                                                修复一个接收到的pdu，idx使用创建pdu时的type，修复后需要释放响应pduvoid snmp_free_pdu(netsnmp_pdu *pdu);           释放pdu设置pud中值的操作：#include #include netsnmp_variable_list *   snmp_pdu_add_variable(netsnmp_pdu *pdu,                             const oid * name, size_t name_length,                             u_char type,                             const void * value, size_t len);                                                向pdu中添加一个oid和这个oid的值netsnmp_variable_list *   snmp_varlist_add_variable(netsnmp_variable_list ** varlist,                             const oid * name, size_t name_length,                             u_char type,                             const void * value, size_t len);                                                向netsnmp_variable_list中添加一个oid和这个oid的值netsnmp_variable_list *   snmp_add_null_var(netsnmp_pdu *pdu,                             const oid * name, size_t name_length);                                                向pdu中添加一个没有值的oidnetsnmp_variable_list *   snmp_clone_varbind(netsnmp_variable_list * varlist);                                                克隆结构体接收和发送snmp的pud有两种方式：同步和异步。同步方式如下：#include #include int snmp_synch_response(netsnmp_session *, netsnmp_pdu *,netsnmp_pdu **);                                                同步发送请求和接收相应。异步方式如下：请参考http://www.net-snmp.org/wiki/index.php/TUT:Simple_Async_Application异步和同步不同之处在于：/* 异步session中需要设置callback */session.callback = asynch_response;            /* default callback */session.callback_magic = hs;#include int snmp_send(netsnmp_session *, netsnmp_pdu *);                                                发送异步请求。成功返回1，错误返回0int snmp_async_send(netsnmp_session *, netsnmp_pdu *,                                netsnmp_callback, void *);                                                发送异步请求。成功返回1，错误返回0。使用参数的callback和data传送到回调函数int snmp_select_info(int *numfds, fd_set *fdset, struct timeval *timeout,                     int *block);                                                返回session打开的fd的fdset。int snmp_select_info2(int *, netsnmp_large_fd_set *,                      struct timeval *, int *);void snmp_read(fd_set *fdset);                  检查fdset是否可读，如果可读就调用callbackvoid snmp_read2(netsnmp_large_fd_set *);void snmp_timeout(void);                        select超时返回后可以调用该函数，用于提示用户超时。其他辅助函数：/* Output */void print_variable(const oid * objid, size_t objidlen,                    const netsnmp_variable_list * variable);void fprint_variable(FILE * fp,                     const oid * objid, size_t objidlen,                     const netsnmp_variable_list * variable);int snprint_variable(char *buf, size_t buf_len,                     const oid * objid, size_t objidlen,                     const netsnmp_variable_list * variable);void print_value(const oid * objid, size_t objidlen,                 const netsnmp_variable_list * variable);void fprint_value(FILE * fp,                  const oid * objid, size_t objidlen,                  const netsnmp_variable_list * variable);int snprint_value(char *buf, size_t buf_len,                  const oid * objid, size_t objidlen,                  const netsnmp_variable_list * variable);/* * provided for backwards compatability.  Don't use these functions. * See snmp_debug.h and snmp_debug.c instead. */void snmp_set_do_debugging(int);int  snmp_get_do_debugging(void);void snmp_sess_error(void *, int *, int *, char **);void netsnmp_sess_log_error(int priority,                            const char *prog_string,                            netsnmp_session * ss);void snmp_sess_perror(const char *prog_string,                                 netsnmp_session * ss);const char *snmp_pdu_type(int type);/* Searching the MIB Tree */oid *snmp_parse_oid(const char *, oid *, size_t *);int read_objid(const char *, oid *, size_t *);int get_module_node(const char *, const char *, oid *, size_t *);