【p2p、分布式，区块链笔记 UPNP】: 简单服务发现协议 SSDP

在设备加入网络，UPnP发现协议允许设备向控制点广告它的服务。它使用向一个标准地址和端口多址传送发现消息来实现。控制点在此端口上侦听是否有新服务加入系统。为了通知所有设备，一个设备为每个其上的嵌入设备和服务发送一系列相应的发现消息。每个消息也包含它表征设备或服务的特定信息。

SSDP的数据内容格式

SSDP (Simple Service Discovery Protocol) 的数据内容格式与HTTP协议格式十分类似。SSDP是一种基于 HTTPU (HTTP over UDP) 的协议，通常用于 UPnP 设备发现。
注：HTTP（HyperText Transfer Protocol）属于计算机网络中的应用层协议。而TCP/UDP是传输层协议。HTTP只是定义了一种信息的描述格式，并不一定要使用TCP进行传输。
SSDP是一种基于 UDP 的协议，所以它并不涉及到TCP协议中的三次握手（three-way handshake）来建立连接或者四次挥手（four-segment handshake）来关闭连接。
SSDP的操作主要包括发送发现请求（M-SEARCH）、响应发现请求（NOTIFY）以及注册服务（NOTIFY + LOCATION）等操作。它的工作机制主要是基于广播和多播消息，用于通告服务的存在以及查询网络上的服务。

特性	广播 (Broadcast)	多播 (Multicast)
目标主机	网络中的所有主机	特定的一组主机
地址范围	`255.255.255.255` (IPv4)	`224.0.0.0` 到 `239.255.255.255` (IPv4)
传输范围	局域网 (LAN)	局域网 (LAN) 和广域网 (WAN)
网络负载	高，因为所有设备都会接收	低，因为只有需要的设备接收
使用场景	ARP、DHCP 等简单网络服务	视频流、股票行情、在线游戏等
跨网络传输	不能跨路由器传播	可以跨路由器传播（需配置）
带宽效率	低，所有主机都接收	高，只有订阅的主机接收

在IPv4环境，当需要使用多播方式传送相关消息的时候，SSDP一般使用多播地址239.255.255.250和UDP端口号1900。

设备和控制点在SSDP中的角色

设备（Device） ：
- 被发现的设备，通常是嵌入式设备或网络设备。设备会周期性地发送NOTIFY消息来广播自己的存在。
- 当收到M-SEARCH请求时，也会响应NOTIFY消息。
控制点（Control Point） ：
- 发起服务发现的客户端，通常是PC、手机等。
- 控制点通过发送M-SEARCH请求来寻找特定的服务。
- 接收到NOTIFY消息后，控制点就可以对设备进行控制或获取信息。

NOTIFY报文

当设备通过DHCP或其他方式获取IP并加入网络后，会同构239.255.255.250:1900进行多播通告，控制点监听此端口以发现新的服务。

/*!
- \brief Sends SSDP advertisements, replies and shutdown messages.
- \return UPNP_E_SUCCESS if successful else appropriate error.
  /
  int AdvertiseAndReply(
  / [in] -1 = Send shutdown, 0 = send reply, 1 = Send Advertisement. /
  int AdFlag,
  / [in] Device handle. int value return by UpnpRegisterRootDevice、 UpnpRegisterRootDevice2、UpnpRegisterRootDevice3 or UpnpRegisterRootDevice4*/
  UpnpDevice_Handle Hnd,
  /* [in] Search type for sending replies. /
  enum SsdpSearchType SearchType,
  / [in] Destination address. */
  struct sockaddr DestAddr,
  / [in] Device type. */
  char DeviceType,
  / [in] Device UDN. <UDN>uuid:UUID</UDN> */
  char DeviceUDN,
  / [in] Service type. */
  char ServiceType,
  / [in] Advertisement age. */
  int Exp);

ssdp:alive

2024-10-05 19:39:29 UPNP-SSDP-2: Thread:0x7F5331C176C0 [.upnp/src/ssdp/ssdp_server.c:878]: Start of received response ----------------------------------------------------
NOTIFY * HTTP/1.1
HOST: 239.255.255.250:1900
CACHE-CONTROL: max-age=100
LOCATION: http://192.168.19.70:49152/tvdevicedesc.xml
OPT: "http://schemas.upnp.org/upnp/1/0/"; ns=01
01-NLS: 3f8c3c84-830e-11ef-b9c9-a0de7ba280b6
NT: urn:schemas-upnp-org:service:tvpicture:1 # 服务类型    
NTS: ssdp:alive  #表示通知消息的子类型
SERVER: Linux/5.15.153.1-microsoft-standard-WSL2, UPnP/1.0, Portable SDK for UPnP devices/17.2.0
X-User-Agent: redsonic
USN: uuid:Upnp-TVEmulator-1_0-1234567890001::urn:schemas-upnp-org:service:tvpicture:1


End of received response ------------------------------------------------------
From host 192.168.19.70

各字段描述见UPnP-arch-DeviceArchitecture-v1.0.pdf的16页。

ssdp:byebye

NOTIFY * HTTP/1.1
   Host: 239.255.255.250:reservedSSDPport
   NT: someunique:idscheme3
   NTS: ssdp:byebye
   USN: someunique:idscheme3

SEARCH报文

控制点向网络广播一个M-SEARCH请求(ssdp:discover)。请求中包含了目标的服务类型。

ssdp:discover

M-SEARCH * HTTP/1.1
   S: uuid:ijklmnop-7dec-11d0-a765-00a0c91e6bf6
   Host: 239.255.255.250:reservedSSDPport
   Man: "ssdp:discover"
   ST: ssdp:all  # 查询的目标
   MX: 3
   HTTP/1.1 200 OK
   S: uuid:ijklmnop-7dec-11d0-a765-00a0c91e6bf6
   Ext:
   Cache-Control: no-cache="Ext", max-age = 5000
   ST: ge:fridge
   USN: uuid:abcdefgh-7dec-11d0-a765-00a0c91e6bf6
   AL: <blender:ixl><http://foo/bar>

响应消息 (Response)

当设备接收到 M-SEARCH 消息时，如果匹配，会发送一个响应消息来通知请求者设备或服务的存在。控制点接收到NOTIFY消息后，就可以根据设备提供的详细信息，与设备建立连接。

HTTP/1.1 200 OK # 表示成功响应
CACHE-CONTROL: max-age=1800 # 指定响应的有效时间，以秒为单位
DATE: Tue, 20 Oct 2024 10:24:00 GMT # 响应生成的时间戳
EXT: # 扩展字段，保持空白
LOCATION: http://192.168.1.100:80/upnp/device.xml # 设备的 UPnP 描述文件的 URL
SERVER: Linux/2.6 UPnP/1.0 MediaTomb/0.12 # 包含设备的操作系统、UPnP 版本以及产品信息
ST: urn:schemas-upnp-org:device:MediaServer:1 # 搜索目标，响应请求中指定的设备或服务类型。
USN: uuid:abcd1234-5678-90ab-cdef-1234567890ab::urn:schemas-upnp-org:device:MediaServer:1 # 唯一服务名称，通常由设备的 UUID 和服务类型组成

代码实现

ST SsdpSearchType

// upnp\src\inc\ssdplib.h#L66-L75
/*! Enumeration to define all different types of ssdp searches */
typedef enum SsdpSearchType
{
	/*! Unknown search command. */
	SSDP_SERROR = -1,
	SSDP_ALL,
	SSDP_ROOTDEVICE,
	SSDP_DEVICEUDN,
	SSDP_DEVICETYPE,
	SSDP_SERVICE
} SType;

// upnp\src\inc\ssdplib.h#L77-L84
#define BUFSIZE (size_t)2500
#define SSDP_IP "239.255.255.250"
#define SSDP_IPV6_LINKLOCAL "FF02::C"
#define SSDP_IPV6_SITELOCAL "FF05::C"
#define SSDP_PORT 1900
#define NUM_TRY 3
#define THREAD_LIMIT 50
#define COMMAND_LEN 300

AdvertiseAndReply函数

c 复制代码

// pupnp-branch-1.14.x\upnp\src\ssdp\ssdp_server.c
/*!
 * \brief 发送 SSDP 广告、回复和关闭消息。
 *
 * \return 如果成功返回 UPNP_E_SUCCESS，否则返回适当的错误码。
 */
int AdvertiseAndReply(
	int AdFlag,           /* [in] -1 = 发送关闭消息，0 = 发送回复，1 = 发送广告。 */
	UpnpDevice_Handle Hnd,/* [in] 设备句柄。 */
	enum SsdpSearchType SearchType, /* [in] 发送回复的搜索类型。 */
	struct sockaddr *DestAddr, /* [in] 目标地址。 */
	char *DeviceType,    /* [in] 设备类型。 */
	char *DeviceUDN,     /* [in] 设备 UDN。 */
	char *ServiceType,   /* [in] 服务类型。 */
	int Exp              /* [in] 广告有效期。 */
)
{
    // 初始化了一些变量
	int retVal = UPNP_E_SUCCESS; long unsigned int i; long unsigned int j;	int defaultExp = DEFAULT_MAXAGE;	struct Handle_Info *SInfo = NULL;	char UDNstr[100];	char devType[100];	char servType[100];	IXML_NodeList *nodeList = NULL;	IXML_NodeList *tmpNodeList = NULL;	IXML_Node *tmpNode = NULL;	IXML_Node *tmpNode2 = NULL;	IXML_Node *textNode = NULL;	const DOMString tmpStr;	const DOMString dbgStr;	int NumCopy = 0;
	memset(UDNstr, 0, sizeof(UDNstr));	memset(devType, 0, sizeof(devType));	memset(servType, 0, sizeof(servType));

	UpnpPrintf(UPNP_ALL,API,__FILE__,__LINE__,"Inside AdvertiseAndReply with AdFlag = %d\n",AdFlag);

	/* Use a read lock */
	HandleReadLock(); // 检查设备句柄的有效性。如果句柄无效，则返回错误。
	if (GetHandleInfo(Hnd, &SInfo) != HND_DEVICE) {retVal = UPNP_E_INVALID_HANDLE;		goto end_function;	}
	defaultExp = SInfo->MaxAge;
	
	/* parse the device list and send advertisements/replies */
	while (NumCopy == 0 || (AdFlag && NumCopy < NUM_SSDP_COPY)) {
		// 资源解析，一般如果发生错误，continue跳过后续步骤，进入下一次循环过程
		if (NumCopy != 0)
			imillisleep(SSDP_PAUSE);
		NumCopy++;
		for (i = 0lu;; i++) {
			UpnpPrintf(UPNP_ALL,API,__FILE__,__LINE__,"Entering new device list with i = %lu\n\n",	i);
			tmpNode = ixmlNodeList_item(SInfo->DeviceList, i);
			if (!tmpNode) {UpnpPrintf(UPNP_ALL,API,__FILE__,__LINE__,"Exiting new device list with i = "       "%lu\n\n",i);
				break;
			}
			dbgStr = ixmlNode_getNodeName(tmpNode);
			UpnpPrintf(UPNP_INFO,API,__FILE__,	__LINE__,"Extracting device type once for %s\n",dbgStr);
			ixmlNodeList_free(nodeList);
			nodeList = ixmlElement_getElementsByTagName((IXML_Element *)tmpNode, "deviceType");
			if (!nodeList) continue;
			UpnpPrintf(UPNP_ALL,API,__FILE__,__LINE__,"Extracting UDN for %s\n",dbgStr);
			UpnpPrintf(UPNP_ALL,API,__FILE__,__LINE__,"Extracting device type\n");
			tmpNode2 = ixmlNodeList_item(nodeList, 0lu);
			if (!tmpNode2) continue;
			textNode = ixmlNode_getFirstChild(tmpNode2);
			if (!textNode) continue;
			UpnpPrintf(UPNP_ALL,API,__FILE__,__LINE__,"Extracting device type \n");
			tmpStr = ixmlNode_getNodeValue(textNode);
			if (!tmpStr) continue;
			strncpy(devType, tmpStr, sizeof(devType) - 1);
			UpnpPrintf(UPNP_ALL,API,__FILE__,__LINE__,"Extracting device type = %s\n",				devType);
			if (!tmpNode) { UpnpPrintf(UPNP_ALL,	API,__FILE__,	__LINE__,"TempNode is NULL\n");	}
			dbgStr = ixmlNode_getNodeName(tmpNode);
			UpnpPrintf(UPNP_ALL,API,__FILE__,__LINE__,"Extracting UDN for %s\n",dbgStr);
			ixmlNodeList_free(nodeList);
			nodeList = ixmlElement_getElementsByTagName((IXML_Element *)tmpNode, "UDN");
			if (!nodeList) {UpnpPrintf(UPNP_CRITICAL,API,__FILE__,	__LINE__,"UDN not found!\n");continue;}
			tmpNode2 = ixmlNodeList_item(nodeList, 0lu);
			if (!tmpNode2) {UpnpPrintf(UPNP_CRITICAL,API,__FILE__,	__LINE__,"UDN not found!\n");continue;}
			textNode = ixmlNode_getFirstChild(tmpNode2);
			if (!textNode) {UpnpPrintf(UPNP_CRITICAL,API,__FILE__,__LINE__,"UDN not found!\n");continue;}
			tmpStr = ixmlNode_getNodeValue(textNode);
			if (!tmpStr) {UpnpPrintf(UPNP_CRITICAL,API,__FILE__,__LINE__,"UDN not found!\n");	continue;}
			strncpy(UDNstr, tmpStr, sizeof(UDNstr) - 1);
			UpnpPrintf(UPNP_INFO,API,__FILE__,__LINE__,"Sending UDNStr = %s \n",UDNstr);
		
		
			if (AdFlag) {
				/* send the device advertisement */
				if (AdFlag == 1) {
					DeviceAdvertisement(devType,i == 0lu,UDNstr,SInfo->DescURL,	Exp,SInfo->DeviceAf,SInfo->PowerState,SInfo->SleepPeriod,SInfo->RegistrationState);
				} else {
					/* AdFlag == -1 */
					DeviceShutdown(devType,	i == 0lu,UDNstr,	SInfo->DescURL,	Exp,SInfo->DeviceAf,SInfo->PowerState,SInfo->SleepPeriod,SInfo->RegistrationState);
				}
			} else {
				switch (SearchType) {
				case SSDP_ALL:
					DeviceReply(DestAddr,devType,i == 0lu,UDNstr,SInfo->DescURL,defaultExp,SInfo->PowerState,SInfo->SleepPeriod,SInfo->RegistrationState);
					break;
				case SSDP_ROOTDEVICE:
					if (i == 0lu) {SendReply(DestAddr,devType,1,UDNstr,SInfo->DescURL,defaultExp,0,SInfo->PowerState,SInfo->SleepPeriod,SInfo->RegistrationState);}
					break;
				case SSDP_DEVICEUDN: {/* clang-format off */
					if (DeviceUDN && strlen(DeviceUDN) != (size_t)0) {
						if (strcasecmp(DeviceUDN, UDNstr)) {UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,"DeviceUDN=%s and search UDN=%s DID NOT match\n",UDNstr, DeviceUDN);} else {UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,"DeviceUDN=%s and search UDN=%s MATCH\n",UDNstr, DeviceUDN);SendReply(DestAddr, devType, 0, UDNstr, SInfo->DescURL, defaultExp, 0,SInfo->PowerState,SInfo->SleepPeriod,SInfo->RegistrationState);}   
					}/* clang-format on */ break;
				}
				case SSDP_DEVICETYPE: {
					/* clang-format off */
					if (!strncasecmp(DeviceType, devType, strlen(DeviceType) - (size_t)2)) {
						if (atoi(strrchr(DeviceType, ':') + 1) < atoi(&devType[strlen(devType) - (size_t)1])) {// /*请求的版本低于设备版本。设备版本必须使用较低的版本号和较低的描述URL进行回复*/
							/*UpnpPrintf+SendReply*/UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,"DeviceType=%s and search devType=%s MATCH\n",devType, DeviceType);SendReply(DestAddr, DeviceType, 0, UDNstr, SInfo->LowerDescURL,defaultExp, 1,SInfo->PowerState,SInfo->SleepPeriod,SInfo->RegistrationState);
						} else if (atoi(strrchr(DeviceType, ':') + 1)== atoi(&devType[strlen(devType) - (size_t)1])) {
							/*UpnpPrintf+SendReply*/UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,"DeviceType=%s and search devType=%s MATCH\n",devType, DeviceType);SendReply(DestAddr, DeviceType, 0, UDNstr, SInfo->DescURL,defaultExp, 1,SInfo->PowerState,SInfo->SleepPeriod,SInfo->RegistrationState);
						} else {UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,"DeviceType=%s and search devType=%s DID NOT MATCH\n",devType, DeviceType);
						}
					} else { UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,"DeviceType=%s and search devType=%s DID NOT MATCH\n",devType, DeviceType);
					}
					/* clang-format on */break;
				}
				default:
					break;
				}
			}


			/* send service advertisements for services
			 * corresponding to the same device */
			UpnpPrintf(UPNP_INFO,
				API,
				__FILE__,
				__LINE__,
				"Sending service Advertisement\n");
			/* Correct service traversal such that each device's
			 * serviceList is directly traversed as a child of its
			 * parent device. This ensures that the service's alive
			 * message uses the UDN of the parent device. */
			tmpNode = ixmlNode_getFirstChild(tmpNode);
			while (tmpNode) {
				dbgStr = ixmlNode_getNodeName(tmpNode);
				if (!strncmp(dbgStr,
					    SERVICELIST_STR,
					    sizeof SERVICELIST_STR)) {
					break;
				}
				tmpNode = ixmlNode_getNextSibling(tmpNode);
			}
			ixmlNodeList_free(nodeList);
			if (!tmpNode) {
				nodeList = NULL;
				continue;
			}
			nodeList = ixmlElement_getElementsByTagName(
				(IXML_Element *)tmpNode, "service");
			if (!nodeList) {
				UpnpPrintf(UPNP_INFO,
					API,
					__FILE__,
					__LINE__,
					"Service not found 3\n");
				continue;
			}
			for (j = 0lu;; j++) {
				tmpNode = ixmlNodeList_item(nodeList, j);
				if (!tmpNode) {
					break;
				}
				ixmlNodeList_free(tmpNodeList);
				tmpNodeList = ixmlElement_getElementsByTagName(
					(IXML_Element *)tmpNode, "serviceType");
				if (!tmpNodeList) {
					UpnpPrintf(UPNP_CRITICAL,
						API,
						__FILE__,
						__LINE__,
						"ServiceType not found \n");
					continue;
				}
				tmpNode2 = ixmlNodeList_item(tmpNodeList, 0lu);
				if (!tmpNode2)
					continue;
				textNode = ixmlNode_getFirstChild(tmpNode2);
				if (!textNode)
					continue;
				/* servType is of format
				 * Servicetype:ServiceVersion */
				tmpStr = ixmlNode_getNodeValue(textNode);
				if (!tmpStr)
					continue;
				strncpy(servType, tmpStr, sizeof(servType) - 1);
				UpnpPrintf(UPNP_INFO,
					API,
					__FILE__,
					__LINE__,
					"ServiceType = %s\n",
					servType);
				if (AdFlag) {
					if (AdFlag == 1) {
						ServiceAdvertisement(UDNstr,
							servType,
							SInfo->DescURL,
							Exp,
							SInfo->DeviceAf,
							SInfo->PowerState,
							SInfo->SleepPeriod,
							SInfo->RegistrationState);
					} else {
						/* AdFlag == -1 */
						ServiceShutdown(UDNstr,
							servType,
							SInfo->DescURL,
							Exp,
							SInfo->DeviceAf,
							SInfo->PowerState,
							SInfo->SleepPeriod,
							SInfo->RegistrationState);
					}
				} else {
					switch (SearchType) {
					case SSDP_ALL:
						ServiceReply(DestAddr,
							servType,
							UDNstr,
							SInfo->DescURL,
							defaultExp,
							SInfo->PowerState,
							SInfo->SleepPeriod,
							SInfo->RegistrationState);
						break;
					case SSDP_SERVICE:
						/* clang-format off */
						if (ServiceType) {
							if (!strncasecmp(ServiceType, servType, strlen(ServiceType) - (size_t)2)) {
								if (atoi(strrchr(ServiceType, ':') + 1) <
								    atoi(&servType[strlen(servType) - (size_t)1])) {
									/* the requested version is lower than the service version
									 * must reply with the lower version number and the lower
									 * description URL */
									UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,
										   "ServiceType=%s and search servType=%s MATCH\n",
										   ServiceType, servType);
									SendReply(DestAddr, ServiceType, 0, UDNstr, SInfo->LowerDescURL,
										  defaultExp, 1,
										  SInfo->PowerState,
										  SInfo->SleepPeriod,
										  SInfo->RegistrationState);
								} else if (atoi(strrchr (ServiceType, ':') + 1) ==
									   atoi(&servType[strlen(servType) - (size_t)1])) {
									UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,
										   "ServiceType=%s and search servType=%s MATCH\n",
										   ServiceType, servType);
									SendReply(DestAddr, ServiceType, 0, UDNstr, SInfo->DescURL,
										  defaultExp, 1,
										  SInfo->PowerState,
										  SInfo->SleepPeriod,
										  SInfo->RegistrationState);
								} else {
									UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,
									   "ServiceType=%s and search servType=%s DID NOT MATCH\n",
									   ServiceType, servType);
								}
							} else {
								UpnpPrintf(UPNP_INFO, API, __FILE__, __LINE__,
									   "ServiceType=%s and search servType=%s DID NOT MATCH\n",
									   ServiceType, servType);
							}
						}
						/* clang-format on */
						break;
					default:
						break;
					}
				}
			}
			ixmlNodeList_free(tmpNodeList);
			tmpNodeList = NULL;
			ixmlNodeList_free(nodeList);
			nodeList = NULL;
		}
	}

end_function:
	ixmlNodeList_free(tmpNodeList);
	ixmlNodeList_free(nodeList);
	UpnpPrintf(UPNP_ALL,
		API,
		__FILE__,
		__LINE__,
		"Exiting AdvertiseAndReply.\n");
	HandleUnlock();

	return retVal;
}

DeviceAdvertisement 根据输入参数创建设备广告请求

c 复制代码

/*!
 * \brief 根据输入参数创建设备广告请求，并将其发送到多播通道。
 * \return 如果成功返回 UPNP_E_SUCCESS，否则返回适当的错误码。
 */
int DeviceAdvertisement(
	char *DevType,/* [in] 设备的类型。 */
	int RootDev,/* [in] 标志，指示设备是否为根设备。 */
	char *Udn, /* [in] UDN（唯一设备名）。 */
	char *Location, /* [in] 位置 URL。 */
	int Duration,/* [in] 服务持续时间（秒）。 */
	int AddressFamily,/* [in] 设备地址族。 */
	int PowerState,/* [in] 根据 UPnP 低功耗标准定义的电源状态。 */
	int SleepPeriod,/* [in] 根据 UPnP 低功耗标准定义的睡眠周期。 */
	int RegistrationState /* [in] 根据 UPnP 低功耗标准定义的注册状态。 */
	);
{
	struct sockaddr_storage __ss;struct sockaddr_in *DestAddr4 = (struct sockaddr_in *)&__ss;struct sockaddr_in6 *DestAddr6 = (struct sockaddr_in6 *)&__ss;
	/* char Mil_Nt[LINE_SIZE] */
	char Mil_Usn[LINE_SIZE];char *msgs[3]; int ret_code = UPNP_E_OUTOF_MEMORY;	int rc = 0;

	UpnpPrintf(UPNP_INFO,SSDP,__FILE__,__LINE__,"In function DeviceAdvertisement\n");
	memset(&__ss, 0, sizeof(__ss));
	switch (AddressFamily) {
	case AF_INET:
		DestAddr4->sin_family = (sa_family_t)AF_INET;inet_pton(AF_INET, SSDP_IP, &DestAddr4->sin_addr);DestAddr4->sin_port = htons(SSDP_PORT);
		break;
	case AF_INET6:
		DestAddr6->sin6_family = (sa_family_t)AF_INET6;	inet_pton(AF_INET6,	 (isUrlV6UlaGua(Location)) ? SSDP_IPV6_SITELOCAL : SSDP_IPV6_LINKLOCAL, 	&DestAddr6->sin6_addr);
		DestAddr6->sin6_port = htons(SSDP_PORT); DestAddr6->sin6_scope_id = gIF_INDEX;
		break;
	default:
		UpnpPrintf(UPNP_CRITICAL,SSDP,__FILE__,__LINE__,"Invalid device address family.\n");
	}
	msgs[0] = NULL;	msgs[1] = NULL;	msgs[2] = NULL;
	/* If deviceis a root device , here we need to send 3 advertisement or reply */
	if (RootDev) {// 构建 USN 字符串：如果是根设备 (RootDev 为真)，则构建一个特殊的 USN（Unique Service Name），格式为 uuid::upnp:rootdevice。
		rc = snprintf(Mil_Usn, sizeof(Mil_Usn), "%s::upnp:rootdevice", Udn);
		if (rc < 0 || (unsigned int)rc >= sizeof(Mil_Usn))
			goto error_handler; //如果是根设备，那么会发送三条消息。
		CreateServicePacket(MSGTYPE_ADVERTISEMENT,"upnp:rootdevice",Mil_Usn,Location,Duration,&msgs[0],AddressFamily,PowerState,SleepPeriod,RegistrationState);
	}
	/* 创建消息  ： both root and sub-devices need to send these two messages 如果是子设备，那么会发送两条消息。*/
	CreateServicePacket(MSGTYPE_ADVERTISEMENT,Udn,Udn,Location,Duration,&msgs[1],AddressFamily,PowerState,SleepPeriod,RegistrationState);
	rc = snprintf(Mil_Usn, sizeof(Mil_Usn), "%s::%s", Udn, DevType);
	if (rc < 0 || (unsigned int)rc >= sizeof(Mil_Usn))
		goto error_handler;
	CreateServicePacket(MSGTYPE_ADVERTISEMENT,DevType,Mil_Usn,Location,Duration,&msgs[2],AddressFamily,PowerState,SleepPeriod,RegistrationState);
	/* check error */
	if ((RootDev && msgs[0] == NULL) || msgs[1] == NULL ||msgs[2] == NULL) {
		goto error_handler;
	}
	/* send packets */
	if (RootDev) { /* send 3 msg types */
		ret_code = NewRequestHandler((struct sockaddr *)&__ss, 3, &msgs[0]);
	} else { /* sub-device *//* send 2 msg types */
		ret_code = NewRequestHandler((struct sockaddr *)&__ss, 2, &msgs[1]);
	}
error_handler:
	/* free msgs */
	free(msgs[0]);free(msgs[1]);free(msgs[2]);
	return ret_code;
}

CreateServicePacket

/*!
 * \brief 创建一个 HTTP 请求包。根据输入参数，创建服务广告请求或服务关闭请求等。  静态函数，只能在此源文件内被调用。
 */
static void CreateServicePacket(
    int msg_type,          /*!< [in] 消息类型 (回复、广告或关闭) */
    const char *nt,        /*!< [in] SSDP 类型 */
    char *usn,             /*!< [in] 唯一服务名称 (进入 HTTP 头部) */
    char *location,        /*!< [in] 位置 URL */
    int duration,          /*!< [in] 服务持续时间 (秒) */
    char **packet,         /*!< [out] 输出缓冲区填充 HTTP 语句 */
    int AddressFamily,     /*!< [in] HTTP 请求的地址族 */
    int PowerState,        /*!< [in] 根据 UPnP 低功耗标准定义的电源状态 */
    int SleepPeriod,       /*!< [in] 根据 UPnP 低功耗标准定义的睡眠周期 */
    int RegistrationState  /*!< [in] 根据 UPnP 低功耗标准定义的注册状态 */
) {
    // 主要调用 http_MakeMessage 函数创建
}

NewRequestHandler：HTTP 请求发送到一多播通道

主要调用socket创建套接字，setsockopt配置套接字， sendto函数发送数据包。

c 复制代码

/*!
 * \brief Works as a request handler which passes the HTTP request string
 * to multicast channel.
 *
 * \return UPNP_E_SUCCESS if successful else appropriate error.
 */
static int NewRequestHandler(
	/*! [in] Ip address, to send the reply. */
	struct sockaddr *DestAddr,
	/*! [in] Number of packet to be sent. */
	int NumPacket,
	/*! [in] . */
	char **RqPacket)
{
	char errorBuffer[ERROR_BUFFER_LEN];
	SOCKET ReplySock;
	socklen_t socklen = sizeof(struct sockaddr_storage);
	int Index;
	struct in_addr replyAddr;
	/* a/c to UPNP Spec */
	int ttl = 4;
		#ifdef UPNP_ENABLE_IPV6
	int hops = 1;
		#endif
	char buf_ntop[INET6_ADDRSTRLEN];
	int ret = UPNP_E_SUCCESS;

	if (strlen(gIF_IPV4) > (size_t)0 &&
		!inet_pton(AF_INET, gIF_IPV4, &replyAddr)) {
		return UPNP_E_INVALID_PARAM;
	}

	ReplySock = socket((int)DestAddr->sa_family, SOCK_DGRAM, 0);
	if (ReplySock == INVALID_SOCKET) {
		strerror_r(errno, errorBuffer, ERROR_BUFFER_LEN);
		UpnpPrintf(UPNP_INFO,SSDP,__FILE__,__LINE__,"SSDP_LIB: New Request Handler:" "Error in socket(): %s\n",errorBuffer);
		return UPNP_E_OUTOF_SOCKET;
	}

	switch (DestAddr->sa_family) {
	case AF_INET:
		inet_ntop(AF_INET,&((struct sockaddr_in *)DestAddr)->sin_addr,buf_ntop,sizeof(buf_ntop));
		setsockopt(ReplySock,IPPROTO_IP,	IP_MULTICAST_IF,(char *)&replyAddr,	sizeof(replyAddr));
		setsockopt(ReplySock,IPPROTO_IP,IP_MULTICAST_TTL,(char *)&ttl,sizeof(int));
		socklen = sizeof(struct sockaddr_in);
		break;
		#ifdef UPNP_ENABLE_IPV6
	case AF_INET6:
		inet_ntop(AF_INET6,	&((struct sockaddr_in6 *)DestAddr)->sin6_addr,buf_ntop,sizeof(buf_ntop));
		setsockopt(ReplySock,IPPROTO_IPV6,IPV6_MULTICAST_IF,(char *)&gIF_INDEX,	sizeof(gIF_INDEX));
		setsockopt(ReplySock,IPPROTO_IPV6,IPV6_MULTICAST_HOPS,(char *)&hops,sizeof(hops));
		break;
		#endif
	default:
		UpnpPrintf(UPNP_CRITICAL,
			SSDP,
			__FILE__,
			__LINE__,
			"Invalid destination address specified.");
		ret = UPNP_E_NETWORK_ERROR;
		goto end_NewRequestHandler;
	}
	//  发送数据包
	for (Index = 0; Index < NumPacket; Index++) {
		ssize_t rc;
		UpnpPrintf(UPNP_INFO,
			SSDP,
			__FILE__,
			__LINE__,
			">>> SSDP SEND to %s >>>\n%s\n",
			buf_ntop,
			*(RqPacket + Index));
		rc = sendto(ReplySock,
			*(RqPacket + Index),
			strlen(*(RqPacket + Index)),
			0,
			DestAddr,
			socklen);
		if (rc == -1) {
			strerror_r(errno, errorBuffer, ERROR_BUFFER_LEN);
			UpnpPrintf(UPNP_INFO,
				SSDP,
				__FILE__,
				__LINE__,
				"SSDP_LIB: New Request Handler:"
				"Error in socket(): %s\n",
				errorBuffer);
			ret = UPNP_E_SOCKET_WRITE;
			goto end_NewRequestHandler;
		}
	}

end_NewRequestHandler:
	UpnpCloseSocket(ReplySock);

	return ret;
}

【p2p、分布式，区块链笔记 UPNP】: 简单服务发现协议 SSDP

SSDP的数据内容格式

设备和控制点在SSDP中的角色

NOTIFY报文

ssdp:alive

ssdp:byebye

SEARCH报文

ssdp:discover

响应消息 (Response)

代码实现

ST SsdpSearchType

AdvertiseAndReply函数

DeviceAdvertisement 根据输入参数创建设备广告请求

CreateServicePacket

NewRequestHandler：HTTP 请求发送到一多播通道

CG