DeepStream之kafka開發

1. kafka的安裝與配置

不多贅述，參考敲代碼的椰子和@tsota兩位博主的文章。

2. .sh文件編寫

開啓kafka服務要開至少三個終端，我寫了一個.sh文件進行批處理，且將這些放在一個終端的多個標籤下。參考deepstream開發小結第3節

3. 發送數據改寫

本文繼上篇文章deepstream開發小結進行了補充，重點介紹發送數據的改寫。
首先參考DeepStream配置文件修改msg-conv-payload-type和 msg-conv-msg2p-lib（好吧，我懶了，感覺看英文更直觀準確，後面就沒翻譯了）
其中msg-conv-payload-type=0表示發送最全的信息，即每個object一個信息。msg-conv-payload-type=1表示發送mini版信息，即一幀一個信息，包含所有objects。msg-conv-payload-type=256是自定義的信息，需要用戶自己實現nvds_msg2p_*接口。參考官方論壇how to customize the json message sent to kafka server?
其中mini類似下面格式（其他格式可以自己跑一下test4和test5，這裏不貼圖了）

{
  "version" : "4.0",
  "id" : 33,
  "#timestamp" : "2020-04-09T21:20:48.851Z",
  "sensorId" : "sensor1",
  "objects" : [
    "68|429|472|465|580|person",
    "12|462|463|516|598|person",
    "13|258|466|414|832|person",
    "69|57|457|195|785|person"
  ]
}

本人是更改了/home/username/Downloads/deepstream_sdk_v4.0.2_x86_64/sources/libs/nvmsgconv目錄下的nvmsgconv.cpp文件mini函數。源碼見下：

static gchar *
generate_deepstream_message_minimal(NvDsMsg2pCtx *ctx, NvDsEvent *events, guint size)
{
    /*
  The JSON structure of the frame
  {
   "version": "4.0",
   "id": "frame-id",
   "@timestamp": "2018-04-11T04:59:59.828Z",
   "sensorId": "sensor-id",
   "objects": [
      ".......object-1 attributes...........",
      ".......object-2 attributes...........",
      ".......object-3 attributes..........."
    ]
  }
  */

    /*
  An example object with Vehicle object-type
  {
    "version": "4.0",
    "id": "frame-id",
    "@timestamp": "2018-04-11T04:59:59.828Z",
    "sensorId": "sensor-id",
    "objects": [
        "957|1834|150|1918|215|Vehicle|#|sedan|Bugatti|M|blue|CA 444|California|0.8",
        "..........."
    ]
  }
   */

    JsonNode *rootNode;
    JsonObject *jobject;
    JsonArray *jArray;
    guint i;
    stringstream ss;
    gchar *message = NULL;

    jArray = json_array_new();
    for (i = 0; i < size; i++)
    {
        ss.str("");
        ss.clear();

        NvDsEventMsgMeta *meta = events[i].metadata;
        ss << meta->trackingId << "|" << meta->bbox.left << "|" << meta->bbox.top
           << "|" << meta->bbox.left + meta->bbox.width << "|" << meta->bbox.top + meta->bbox.height
           << "|" << object_enum_to_str(meta->objType, meta->objectId);

        if (meta->extMsg && meta->extMsgSize)
        {
            // Attach secondary inference attributes.
            switch (meta->objType)
            {
            case NVDS_OBJECT_TYPE_VEHICLE:
            {
                NvDsVehicleObject *dsObj = (NvDsVehicleObject *)meta->extMsg;
                if (dsObj)
                {
                    ss << "|#|" << to_str(dsObj->type) << "|" << to_str(dsObj->make) << "|"
                       << to_str(dsObj->model) << "|" << to_str(dsObj->color) << "|" << to_str(dsObj->license)
                       << "|" << to_str(dsObj->region) << "|" << meta->confidence;
                }
            }
            break;
            case NVDS_OBJECT_TYPE_PERSON:
            {
                NvDsPersonObject *dsObj = (NvDsPersonObject *)meta->extMsg;
                if (dsObj)
                {
                    ss << "|#|" << to_str(dsObj->gender) << "|" << dsObj->age << "|"
                       << to_str(dsObj->hair) << "|" << to_str(dsObj->cap) << "|" << to_str(dsObj->apparel)
                       << "|" << meta->confidence;
                }
            }
            break;
            case NVDS_OBJECT_TYPE_FACE:
            {
                NvDsFaceObject *dsObj = (NvDsFaceObject *)meta->extMsg;
                if (dsObj)
                {
                    ss << "|#|" << to_str(dsObj->gender) << "|" << dsObj->age << "|"
                       << to_str(dsObj->hair) << "|" << to_str(dsObj->cap) << "|" << to_str(dsObj->glasses)
                       << "|" << to_str(dsObj->facialhair) << "|" << to_str(dsObj->name) << "|"
                       << "|" << to_str(dsObj->eyecolor) << "|" << meta->confidence;
                }
            }
            break;
            default:
                cout << "Object type (" << meta->objType << ") not implemented" << endl;
                break;
            }
        }

        json_array_add_string_element(jArray, ss.str().c_str());
    }

    // It is assumed that all events / objects are associated with same frame.
    // Therefore ts / sensorId / frameId of first object can be used.

    jobject = json_object_new();
    json_object_set_string_member(jobject, "version", "4.0");
    json_object_set_int_member(jobject, "id", events[0].metadata->frameId);
    json_object_set_string_member(jobject, "#timestamp", events[0].metadata->ts);
    if (events[0].metadata->sensorStr)
    {
        json_object_set_string_member(jobject, "sensorId", events[0].metadata->sensorStr);
    }
    else if (ctx->privData)
    {
        json_object_set_string_member(jobject, "sensorId",
                                      to_str((gchar *)sensor_id_to_str(ctx, events[0].metadata->sensorId)));
    }
    else
    {
        json_object_set_string_member(jobject, "sensorId", "0");
    }

    json_object_set_array_member(jobject, "objects", jArray);

    rootNode = json_node_new(JSON_NODE_OBJECT);
    json_node_set_object(rootNode, jobject);

    message = json_to_string(rootNode, TRUE);
    json_node_free(rootNode);
    json_object_unref(jobject);

    return message;
}

利用類似json_object_set_array_member()函數（不一定是array，也可以是string或int）可以改寫發送json數據的格式。代碼理解比較簡單，改寫也很簡單，就不贅述了。

4. 補充

這裏補充一些對於源碼的理解。
NvDsMsg2pCtx *ctx是配置文件, NvDsEvent *events是包含了NvDsEventMsgMeta的數組，guint size指一幀中object數量，幾個object就在主文件中存幾次eventmeta。

    typedef struct NvDsEventMsgMeta
    {
        /** type of event */
        NvDsEventType type;
        /** type of object */
        NvDsObjectType objType;
        /** bounding box of object */
        NvDsRect bbox;
        /** Geo-location of object */
        NvDsGeoLocation location;
        /** coordinate of object */
        NvDsCoordinate coordinate;
        /** signature of object */
        NvDsObjectSignature objSignature;
        /** class id of object */
        gint objClassId;
        /** id of sensor that generated the event */
        gint sensorId;
        /** id of analytics module that generated the event */
        gint moduleId;
        /** id of place related to the object */
        gint placeId;
        /** id of component that generated this event */
        gint componentId;
        /** video frame id of this event */
        gint frameId;
        /** confidence of inference */
        gdouble confidence;
        /** tracking id of object */
        gint trackingId;
        /** time stamp of generated event */
        gchar *ts;
        /** label of detected / inferred object */
        gchar *objectId;
        /** Identity string of sensor */
        gchar *sensorStr;
        /** other attributes associated with the object */
        gchar *otherAttrs;
        /** name of video file */
        gchar *videoPath;
        /**
   * To extend the event message meta data.
   * This can be used for custom values that can't be accommodated
   * in the existing fields OR if object(vehicle, person, face etc.) specific
   * values needs to be attached.
   */
        gpointer extMsg;
        /** size of custom object */
        guint extMsgSize;

    } NvDsEventMsgMeta;

還有一個坑，就是char *必須用strdup()進行拷貝，如果是string轉char *，不能直接str.c_str()，需要strdup(str.c_str())。否則你會發現要麼亂碼，要麼就是設成常量或靜態，字符串一幀中不會改變。

如有其他問題可以評論，我再補充。總的來說kafka這裏比較簡單。

DeepStream之kafka開發

1. kafka的安裝與配置

2. .sh文件編寫

3. 發送數據改寫

4. 補充

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