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Browse 自动分页 (上层封装)

C# 提供 BrowseWithPaging + BrowseNext 的自动循环, C SDK 没有现成 API, 需要业务自己封装. 本页给出一个推荐模板.

前置阅读

推荐封装​

把 Browse + 循环 BrowseNext 包装成一个 helper 函数, 业务直接拿一个完整的 (NodeId, BrowseName, NodeClass) 列表:

/* browse_all.h */
#include <darra_opcua/darra_opcua.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    char  node_id[128];
    char  browse_name[128];
    int32_t node_class;
} BrowsedRef;

typedef struct {
    BrowsedRef* items;
    uint32_t    count;
    uint32_t    capacity;
} BrowsedList;

void BrowsedList_Init(BrowsedList* l) {
    l->items = NULL; l->count = 0; l->capacity = 0;
}

void BrowsedList_Free(BrowsedList* l) {
    free(l->items); l->items = NULL; l->count = 0; l->capacity = 0;
}

static int append_one(BrowsedList* l, const DarraUa_ReferenceDescription* rd)
{
    if (l->count == l->capacity) {
        uint32_t cap = l->capacity ? l->capacity * 2 : 16;
        BrowsedRef* p = (BrowsedRef*)realloc(l->items, cap * sizeof(BrowsedRef));
        if (!p) return 0;
        l->items = p; l->capacity = cap;
    }
    BrowsedRef* item = &l->items[l->count++];
    DarraUa_Ref_GetNodeIdString(rd, item->node_id, (int32_t)sizeof(item->node_id));
    const char* bn = DarraUa_Ref_GetBrowseName(rd);
    snprintf(item->browse_name, sizeof(item->browse_name), "%s", bn ? bn : "");
    item->node_class = DarraUa_Ref_GetNodeClass(rd);
    return 1;
}

DarraUa_Status BrowseAll(DarraUa_SessionHandle h,
                         const char* node_id,
                         DarraUa_NodeClass filter,
                         BrowsedList* out)
{
    BrowsedList_Init(out);

    DarraUa_BrowseResult* page = NULL;
    DarraUa_Status st = DarraUa_Session_BrowseNode(h, node_id, filter, &page);
    if (!DARRA_UA_STATUS_IS_GOOD(st) || !page) return st;

    while (page) {
        uint32_t n = DarraUa_BrowseResult_GetCount(page);
        for (uint32_t i = 0; i < n; ++i) {
            append_one(out, DarraUa_BrowseResult_GetReference(page, i));
        }

        int32_t cp_len = 0;
        const uint8_t* cp = DarraUa_BrowseResult_GetContinuationPoint(page, &cp_len);
        if (!cp || cp_len <= 0) {
            DarraUa_BrowseResult_Delete(page);
            break;
        }
        uint8_t cp_copy[256];
        if (cp_len > (int32_t)sizeof(cp_copy)) {
            DarraUa_BrowseResult_Delete(page);
            break;
        }
        memcpy(cp_copy, cp, (size_t)cp_len);
        DarraUa_BrowseResult_Delete(page);
        page = NULL;
        DarraUa_Session_BrowseNext(h, 0, cp_copy, cp_len, &page);
    }

    return DARRA_UA_STATUS_GOOD;
}

用法​

BrowsedList list;
DarraUa_Status st = BrowseAll(h, "ns=2;s=BigFolder",
                              DARRA_UA_NODE_CLASS_VARIABLE, &list);

if (DARRA_UA_STATUS_IS_GOOD(st)) {
    printf("Got %u children\n", list.count);
    for (uint32_t i = 0; i < list.count; ++i) {
        printf("  %s -> %s\n", list.items[i].browse_name,
                                list.items[i].node_id);
    }
}
BrowsedList_Free(&list);

何时用 BrowseNode 直接 vs BrowseAll 封装​

场景API
已知子数 ≤ 50, 不关心分页DarraUa_Session_BrowseNode 直接用
不确定子数, 安全起见BrowseAll 封装
100+ 子节点的大节点BrowseAll 必选
一次浏览多个节点DarraUa_Session_BrowseNodes (注意当前 BrowseNodes 不返回 ContinuationPoint)

ContinuationPoint 是否会过期​

服务端 ContinuationPoint 通常 5 分钟超时. 客户端逻辑在 5 分钟内完成翻页就行, 否则需要从头 Browse 重新拿 CP.

下一步​