application-dev/napi/rawfile-guidelines.md

# RawFile Development

## When to Use

This document describes how to use Native Rawfile APIs to manage the directories and files in the **rawfile** directory in OpenHarmony. You can use the APIs to perform operations, such as traversing a directory and opening, searching for, reading, and closing a file in the the **rawfile** directory.

## Available APIs

| API                                                          | Description                                                  |
| :----------------------------------------------------------- | :----------------------------------------------------------- |
| NativeResourceManager *OH_ResourceManager_InitNativeResourceManager(napi_env env, napi_value jsResMgr) | Initializes a Native resource manager instance.              |
| RawDir *OH_ResourceManager_OpenRawDir(const NativeResourceManager *mgr, const char *dirName) | Opens a directory in the **rawfile** directory.              |
| int OH_ResourceManager_GetRawFileCount(RawDir *rawDir)       | Obtains the number of files in the specified directory.      |
| const char *OH_ResourceManager_GetRawFileName(RawDir *rawDir, int index) | Obtains the name of a file in the **rawfile** directory.     |
| RawFile *OH_ResourceManager_OpenRawFile(const NativeResourceManager *mgr, const char *fileName) | Opens a file in the **rawfile** directory.                   |
| long OH_ResourceManager_GetRawFileSize(RawFile *rawFile)     | Obtains the size of a file in the **rawfile** directory.     |
| int OH_ResourceManager_SeekRawFile(const RawFile *rawFile, long offset, int whence) | Seeks for the read/write position in a file in the **rawfile** directory based on the specified offset. |
| long OH_ResourceManager_GetRawFileOffset(const RawFile *rawFile) | Obtains the offset of a file.                                |
| int OH_ResourceManager_ReadRawFile(const RawFile *rawFile, void *buf, size_t length) | Reads data from a file in the **rawfile** directory.         |
| void OH_ResourceManager_CloseRawFile(RawFile *rawFile)       | Closes a file in the **rawfile** directory to release resources. |
| void OH_ResourceManager_CloseRawDir(RawDir *rawDir)          | Closes a directory in the **rawfile** directory to release resources. |
| bool OH_ResourceManager_GetRawFileDescriptor(const RawFile *rawFile, RawFileDescriptor &descriptor) | Obtains the file descriptor (FD) of a file in the **rawfile** directory. |
| bool OH_ResourceManager_ReleaseRawFileDescriptor(const RawFileDescriptor &descriptor) | Releases the FD of a file in the **rawfile** directory.      |
| void OH_ResourceManager_ReleaseNativeResourceManager(NativeResourceManager *resMgr) | Releases a Native resource manager instance.                 |

## Functions

1. Call **OH_ResourceManager_OpenRawDir** to obtain a **RawDir** instance based on the **NativeResourceManager** instance.

    ```c++
    RawDir* rawDir = OH_ResourceManager_OpenRawDir(nativeResourceManager, path.c_str());
    ```

2. Call **OH_ResourceManager_GetRawFileCount** to obtain the total number of files in the directory based on the **RawDir** instance.

    ```c++
    int count = OH_ResourceManager_GetRawFileCount(rawDir);
    ```

3. Call **OH_ResourceManager_GetRawFileName** to obtain the name of a file based on the specified index.

    ```c++
    for (int index = 0; index < count; index++) {
        std::string fileName = OH_ResourceManager_GetRawFileName(rawDir, index);
    }
    ```

4. Call **OH_ResourceManager_OpenRawFile** to open a **RawFile** instance with the specified file name.

    ```c++
    RawFile* rawFile = OH_ResourceManager_OpenRawFile(nativeResourceManager, fileName.c_str());
    ```

5. Call **OH_ResourceManager_GetRawFileSize** to obtain the size of the file.

    ```c++
    long rawFileSize = OH_ResourceManager_GetRawFileSize(rawFile);
    ```

6. Call **OH_ResourceManager_SeekRawFile** to seek for the read/write position in the file based on the specified offset.

    ```c++
    int position = OH_ResourceManager_SeekRawFile(rawFile, 10, 0);
    int position = OH_ResourceManager_SeekRawFile(rawFile, 0 , 1);
    int position = OH_ResourceManager_SeekRawFile(rawFile, -10, 2);
    ```

7. Call **OH_ResourceManager_GetRawFileOffset** to obtain the file offset.

    ```c++
    long rawFileOffset = OH_ResourceManager_GetRawFileOffset(rawFile)
    ```

8. Call **OH_ResourceManager_ReadRawFile** to read a file.

    ```c++
    std::unique_ptr<char[]> mediaData = std::make_unique<char[]>(rawFileSize);
    long rawFileOffset = OH_ResourceManager_ReadRawFile(rawFile, mediaData.get(), rawFileSize);
    ```

9. Call **OH_ResourceManager_CloseRawFile** to close the file to release resources.

    ```c++
    OH_ResourceManager_CloseRawFile(rawFile);
    ```

10. Call **OH_ResourceManager_CloseRawDir** to close the file directory.

    ```c++
    OH_ResourceManager_CloseRawDir(rawDir);
    ```

11. Call **OH_ResourceManager_GetRawFileDescriptor** to obtain the FD of the file.

    ```c++
    RawFileDescriptor descriptor;
    bool result = OH_ResourceManager_GetRawFileDescriptor(rawFile, descriptor);
    ```

12. Call **OH_ResourceManager_ReleaseRawFileDescriptor** to release the FD of the file.

    ```c++
    OH_ResourceManager_ReleaseRawFileDescriptor(descriptor);
    ```

13. Call **OH_ResourceManager_ReleaseNativeResourceManager** to release the Native resource manager.

    ```c++
    OH_ResourceManager_ReleaseNativeResourceManager(nativeResourceManager);
    ```

## How to Develop

The following describes how to obtain the file list in the **rawfile** directory, file content, and FD {fd, offset, length} on the JavaScript side as an example.

1. Create a project.

   ![Creating a C++ application](figures/rawfile1.png)

2. Add dependencies.

   After the project is created, the **cpp** directory is created under the project. The directory contains files such as **libentry/index.d.ts**, **hello.cpp**, and **CMakeLists.txt**.

   1. Open the **src/main/cpp/CMakeLists.txt** file, and add **librawfile.z.so** and **libhilog_ndk.z.so** to **target_link_libraries**.

      ```
      target_link_libraries(entry PUBLIC libace_napi.z.so libhilog_ndk.z.so librawfile.z.so)
      ```


   2. Open the **src/main/cpp/types/libentry/index.d.ts** file, and declare the application functions **getFileList**, **getRawFileContent**, and **getRawFileDescriptor**.

      ```c++
      import resourceManager from '@ohos.resourceManager';
      export const getFileList: (resmgr: resourceManager.ResourceManager, path: string) => Array<String>;
      export const getRawFileContent: (resmgr: resourceManager.ResourceManager, path: string) => Uint8Array;
      export const getRawFileDescriptor: (resmgr: resourceManager.ResourceManager, path: string) => resourceManager.RawFileDescriptor;
      ```


3. Modify the source file.

   1. Open the **src/main/cpp/hello.cpp** file. During initialization, the file maps the external JavaScript APIs **getFileList**, **getRawFileContent**, and **getRawFileDescriptor** to C++ native APIs **GetFileList**, **GetRawFileContent**, and **GetRawFileDescriptor**.

      ```c++
      EXTERN_C_START
      static napi_value Init(napi_env env, napi_value exports)
      {
          napi_property_descriptor desc[] = {
              { "getFileList", nullptr, GetFileList, nullptr, nullptr, nullptr, napi_default, nullptr },
              { "getRawFileContent", nullptr, GetRawFileContent, nullptr, nullptr, nullptr, napi_default, nullptr },
              { "getRawFileDescriptor", nullptr, GetRawFileDescriptor, nullptr, nullptr, nullptr, napi_default, nullptr }
          };

          napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc);
          return exports;
      }
      EXTERN_C_END
      ```


   2. Add the three functions to the **src/main/cpp/hello.cpp** file.

      ```c++
      static napi_value GetFileList(napi_env env, napi_callback_info info)
      static napi_value GetRawFileContent(napi_env env, napi_callback_info info)
      static napi_value GetRawFileDescriptor(napi_env env, napi_callback_info info)
      ```


   3. Obtain JavaScript resource objects from the **hello.cpp** file, and convert them to Native resource objects. Then, call the Native APIs to obtain the file list, file content, and FD {fd, offset, length}.

      The sample code is as follows:

      ```c++
      // Example 1: Use GetFileList to obtain the raw file list.
      static napi_value GetFileList(napi_env env, napi_callback_info info)
      {
          OH_LOG_Print(LOG_APP, LOG_ERROR, GLOBAL_RESMGR, tag, "NDKTest Begin");
          size_t requireArgc = 3;
          size_t argc = 2;
          napi_value argv[2] = { nullptr };
          // Obtain arguments of the native API.
          napi_get_cb_info(env, info, &argc, argv, nullptr, nullptr);

          // Obtain argv[0], which specifies conversion of the JavaScript resource object (that is, OH_ResourceManager_InitNativeResourceManager) to a native object.
          NativeResourceManager *mNativeResMgr = OH_ResourceManager_InitNativeResourceManager(env, argv[0]);

          // Obtain argv[1], which specifies the relative path of the raw file.
          size_t strSize;
          char strBuf[256];
          napi_get_value_string_utf8(env, argv[1], strBuf, sizeof(strBuf), &strSize);
          std::string dirName(strBuf, strSize);

          // Obtain the corresponding rawDir pointer object.
          RawDir* rawDir = OH_ResourceManager_OpenRawDir(mNativeResMgr, dirName.c_str());

          // Obtain the number of files and folders in rawDir.
          int count = OH_ResourceManager_GetRawFileCount(rawDir);

          // Traverse rawDir to obtain the list of file names and save it.
          std::vector<std::string> tempArray;
          for(int i = 0; i < count; i++) {
              std::string filename = OH_ResourceManager_GetRawFileName(rawDir, i);
              tempArray.emplace_back(filename);
          }

          napi_value fileList;
          napi_create_array(env, &fileList);
          for (size_t i = 0; i < tempArray.size(); i++) {
              napi_value jsString;
              napi_create_string_utf8(env, tempArray[i].c_str(), NAPI_AUTO_LENGTH, &jsString);
              napi_set_element(env, fileList, i, jsString);
          }

          // Close the rawDir pointer object.
          OH_ResourceManager_CloseRawDir(rawDir);
          OH_ResourceManager_ReleaseNativeResourceManager(mNativeResMgr);
          return fileList;
      }

      // Example 2: Use rawDir pointer object to obtain the content of the raw file.
      napi_value CreateJsArrayValue(napi_env env, std::unique_ptr<uint8_t[]> &data, long length)
      {
          napi_value buffer;
          napi_status status = napi_create_external_arraybuffer(env, data.get(), length,
                  [](napi_env env, void *data, void *hint) {
                      delete[] static_cast<char*>(data);
                  }, nullptr, &buffer);
          if (status != napi_ok) {
              OH_LOG_Print(LOG_APP, LOG_ERROR, GLOBAL_RESMGR, tag, "Failed to create external array buffer");
              return nullptr;
          }
          napi_value result = nullptr;
          status = napi_create_typedarray(env, napi_uint8_array, length, buffer, 0, &result);
          if (status != napi_ok) {
              OH_LOG_Print(LOG_APP, LOG_ERROR, GLOBAL_RESMGR, tag, "Failed to create media typed array");
              return nullptr;
          }
          data.release();
          return result;
      }
      static napi_value GetRawFileContent(napi_env env, napi_callback_info info)
      {
          OH_LOG_Print(LOG_APP, LOG_ERROR, GLOBAL_RESMGR, tag, "GetFileContent Begin");
          size_t requireArgc = 3;
          size_t argc = 2;
          napi_value argv[2] = { nullptr };
          // Obtain arguments of the native API.
          napi_get_cb_info(env, info, &argc, argv, nullptr, nullptr);

          // Obtain argv[0], which specifies conversion of the JavaScript resource object (that is, OH_ResourceManager_InitNativeResourceManager) to a native object.
          NativeResourceManager *mNativeResMgr = OH_ResourceManager_InitNativeResourceManager(env, argv[0]);
          size_t strSize;
          char strBuf[256];
          napi_get_value_string_utf8(env, argv[1], strBuf, sizeof(strBuf), &strSize);
          std::string filename(strBuf, strSize);

          // Obtain the raw file pointer object.
          RawFile *rawFile = OH_ResourceManager_OpenRawFile(mNativeResMgr, filename.c_str());
          if (rawFile != nullptr) {
              OH_LOG_Print(LOG_APP, LOG_ERROR, GLOBAL_RESMGR, tag, "OH_ResourceManager_OpenRawFile success");
          }
          // Obtain the size of the raw file and apply for memory.
          long len = OH_ResourceManager_GetRawFileSize(rawFile);
          std::unique_ptr<uint8_t[]> data= std::make_unique<uint8_t[]>(len);
          // Read the raw file.
          int res = OH_ResourceManager_ReadRawFile(rawFile, data.get(), len);
          // Close the rawDir pointer object.
          OH_ResourceManager_CloseRawFile(rawFile);
          OH_ResourceManager_ReleaseNativeResourceManager(mNativeResMgr);
          // Convert the native object to a JavaScript object.
          return CreateJsArrayValue(env, data, len);
      }

      // Example 3: Use GetRawFileDescriptor to obtain the FD of the raw file.
      napi_value createJsFileDescriptor(napi_env env, RawFileDescriptor &descriptor)
      {
          napi_value result;
          napi_status status = napi_create_object(env, &result);
          if (status != napi_ok) {
              return result;
          }

          napi_value fd;
          status = napi_create_int32(env, descriptor.fd, &fd);
          if (status != napi_ok) {
              return result;
          }
          status = napi_set_named_property(env, result, "fd", fd);
          if (status != napi_ok) {
              return result;
          }

          napi_value offset;
          status = napi_create_int64(env, descriptor.start, &offset);
          if (status != napi_ok) {
              return result;
          }
          status = napi_set_named_property(env, result, "offset", offset);
          if (status != napi_ok) {
              return result;
          }

          napi_value length;
          status = napi_create_int64(env, descriptor.length, &length);
          if (status != napi_ok) {
              return result;
          }
          status = napi_set_named_property(env, result, "length", length);
          if (status != napi_ok) {
              return result;
          }
          return result;
      }
      static napi_value GetRawFileDescriptor(napi_env env, napi_callback_info info)
      {
          OH_LOG_Print(LOG_APP, LOG_ERROR, GLOBAL_RESMGR, tag, "NDKTest GetRawFileDescriptor Begin");
          size_t requireArgc = 3;
          size_t argc = 2;
          napi_value argv[2] = { nullptr };
          // Obtain arguments of the native API.
          napi_get_cb_info(env, info, &argc, argv, nullptr, nullptr);

          napi_valuetype valueType;
          napi_typeof(env, argv[0], &valueType);
          // Obtain the native resourceManager object.
          NativeResourceManager *mNativeResMgr = OH_ResourceManager_InitNativeResourceManager(env, argv[0]);
          size_t strSize;
          char strBuf[256];
          napi_get_value_string_utf8(env, argv[1], strBuf, sizeof(strBuf), &strSize);
          std::string filename(strBuf, strSize);
          // Obtain the raw file pointer object.
          RawFile *rawFile = OH_ResourceManager_OpenRawFile(mNativeResMgr, filename.c_str());
          if (rawFile != nullptr) {
              OH_LOG_Print(LOG_APP, LOG_ERROR, GLOBAL_RESMGR, tag, "OH_ResourceManager_OpenRawFile success");
          }
          // Obtain the FD of the raw file, that is, RawFileDescriptor {fd, offset, length}.
          RawFileDescriptor descriptor;
          OH_ResourceManager_GetRawFileDescriptor(rawFile, descriptor);
          // Close the rawDir pointer object.
          OH_ResourceManager_CloseRawFile(rawFile);
          OH_ResourceManager_ReleaseNativeResourceManager(mNativeResMgr);
          // Convert the native object to a JavaScript object.
          return createJsFileDescriptor(env,descriptor);
      }
      ```


4. Call JavaScript APIs.

   1. Open **src\main\ets\pages\index.ets**, and import **libentry.so**.

   2. Obtain the JavaScript resource object, that is, **resourceManager**.

   3. Call **getFileList**, that is, the Native API declared in **src/main/cpp/types/libentry/index.d.ts**. When calling the API, pass in the JavaScript resource object and the relative path of the file.

      The sample code is as follows:

      ```js
      import hilog from '@ohos.hilog';
      import testNapi from 'libentry.so'  // Import the libentry.so file.
      @Entry
      @Component
      struct Index {
          @State message: string = 'Hello World'
          private resmgr = getContext().resourceManager;  // Obtain the JavaScript resource object.
          build() {
              Row() {
              Column() {
                  Text(this.message)
                  .fontSize(50)
                  .fontWeight(FontWeight.Bold)
                  .onClick(() => {
                      hilog.isLoggable(0x0000, 'testTag', hilog.LogLevel.INFO);
                      let rawfilelist = testNapi.getFileList(this.resmgr, ""); // Pass the JavaScript resource object and the relative path of the raw file.
                      console.log("rawfilelist" + rawfilelist);
                      let rawfileContet = testNapi.getRawFileContent(this.resmgr, "rawfile1.txt");
                      console.log("rawfileContet" + rawfileContet);
                      let rawfileDescriptor = testNapi.getRawFileDescriptor(this.resmgr, "rawfile1.txt");
                      console.log("getRawFileDescriptor" + rawfileDescriptor.fd, rawfileDescriptor.offset, rawfileDescriptor.length);
                  })
              }
              .width('100%')
              }
              .height('100%')
          }
      }
      ```