跳到主要内容

FindServers (C)

前置 / 配套

API​

DARRA_OPCUA_API DarraUa_Status DARRA_OPCUA_CALL DarraUa_Discovery_FindServers(
    const char*                   endpoint_url,
    uint32_t                      timeout_ms,
    DarraUa_FindServersResult**   out_result);

DARRA_OPCUA_API uint32_t DARRA_OPCUA_CALL
DarraUa_FindServersResult_GetCount(const DarraUa_FindServersResult* r);

DARRA_OPCUA_API const DarraUa_ApplicationDescription* DARRA_OPCUA_CALL
DarraUa_FindServersResult_GetServer(
    const DarraUa_FindServersResult* r, uint32_t index);

DARRA_OPCUA_API void DARRA_OPCUA_CALL
DarraUa_FindServersResult_Delete(DarraUa_FindServersResult* r);

向 Local Discovery Server (LDS) 查询同域内注册的所有 OPC UA Server.

ApplicationDescription 字段​

typedef struct {
    char*    application_uri;
    char*    product_uri;
    char*    application_name;          /* LocalizedText.text */
    int32_t  application_type;          /* 0=Server 1=Client 2=ClientAndServer 3=DiscoveryServer */
    char*    gateway_server_uri;
    char*    discovery_profile_uri;
    int32_t  discovery_url_count;
    char**   discovery_urls;
} DarraUa_ApplicationDescription;

所有指针字段由 Stack 在 FindServers 内部分配, 由 DarraUa_FindServersResult_Delete 统一释放.

完整示例​

#include <darra_opcua/darra_opcua.h>
#include <stdio.h>

int main(int argc, char** argv)
{
    const char* lds = (argc >= 2) ? argv[1] : "opc.tcp://lds-host:4840";
    DarraUa_Initialize();

    DarraUa_FindServersResult* res = NULL;
    DarraUa_Status st = DarraUa_Discovery_FindServers(lds, 5000, &res);
    if (!DARRA_UA_STATUS_IS_GOOD(st)) {
        fprintf(stderr, "FindServers failed: 0x%08X (%s)\n",
                (unsigned)st, DarraUa_StatusName(st));
        DarraUa_Shutdown();
        return 1;
    }

    uint32_t n = DarraUa_FindServersResult_GetCount(res);
    printf("Domain has %u servers:\n", (unsigned)n);

    for (uint32_t i = 0; i < n; ++i) {
        const DarraUa_ApplicationDescription* a =
            DarraUa_FindServersResult_GetServer(res, i);
        if (!a) continue;
        printf("\n  App:    %s\n", a->application_name);
        printf("  AppUri: %s\n", a->application_uri);
        printf("  Type:   %d\n", (int)a->application_type);
        printf("  URLs:\n");
        for (int u = 0; u < a->discovery_url_count; ++u)
            printf("    - %s\n", a->discovery_urls[u]);
    }

    DarraUa_FindServersResult_Delete(res);
    DarraUa_Shutdown();
    return 0;
}

LDS​

LDS = Local Discovery Server, OPC Foundation 提供. 同子网内 Server 启动时可注册到 LDS, 客户端通过 FindServers 即发现全部.

LDS 默认监听 4840 (与普通 Server 同端口), 通常装在专门一台主机, 也可与 Server 共部署.

用例: 主备 Server 切换​

冗余场景下, 主备 Server 都注册到同一 LDS. 客户端定期 FindServers, 主 Server 失联时切到备:

const char* primary_uri = "urn:plant:server-primary";
const char* backup_uri  = "urn:plant:server-backup";

DarraUa_FindServersResult* res = NULL;
DarraUa_Discovery_FindServers("opc.tcp://lds:4840", 5000, &res);

const char* chosen_url = NULL;
uint32_t n = DarraUa_FindServersResult_GetCount(res);
for (uint32_t i = 0; i < n; ++i) {
    const DarraUa_ApplicationDescription* a =
        DarraUa_FindServersResult_GetServer(res, i);
    if (strcmp(a->application_uri, primary_uri) == 0 &&
        a->discovery_url_count > 0) {
        chosen_url = a->discovery_urls[0];
        break;
    }
}
if (!chosen_url) {
    /* 退到备 */
    for (uint32_t i = 0; i < n; ++i) {
        const DarraUa_ApplicationDescription* a =
            DarraUa_FindServersResult_GetServer(res, i);
        if (strcmp(a->application_uri, backup_uri) == 0 &&
            a->discovery_url_count > 0) {
            chosen_url = a->discovery_urls[0];
            break;
        }
    }
}
/* ... 用 chosen_url 配 cfg.endpoint_url 建会话 ... */
DarraUa_FindServersResult_Delete(res);

下一步​