javaV2NIMStorageScene addCustomStorageScene(String sceneName, long expireTime);

objective-c- (void)addCustomStorageScene:(NSString *)sceneName expireTime:(NSUInteger)expireTime;

cppvirtual void addCustomStorageScene(nstd::string sceneName, uint64_t expireTime) = 0;

typescriptaddCustomStorageScene(sceneName: string, expireTime: number): V2NIMStorageScene

typescriptaddCustomStorageScene(sceneName: string, expireTime: number): V2NIMStorageScen

javaV2NIMStorageService v2StorageService = NIMClient.getService(V2NIMStorageService.class);
v2StorageService.addCustomStorageScene(sceneName, expireTime);

objective-c[[[NIMSDK sharedSDK] v2StorageService] addCustomStorageScene:@"scene_name" expireTime:1000];

cppstorageService.addCustomStorageScene("customScene", 0); // never expire

typescriptnim.V2NIMStorageService.addCustomStorageScene("nim", 86400)

typescriptnim.storageService.addCustomStorageScene("nim", 86400)

V2NIMStorageScene

无

javaList<V2NIMStorageScene> getStorageSceneList();

objective-c- (NSArray<V2NIMStorageScene *> *)getStorageSceneList;

cppvirtual nstd::vector<V2NIMStorageScene> getStorageSceneList() = 0;

typescriptgetStorageSceneList(): V2NIMStorageScene[]

typescriptgetStorageSceneList(): V2NIMStorageScene[]

javaV2NIMStorageService v2StorageService = NIMClient.getService(V2NIMStorageService.class);
List<V2NIMStorageScene> storageSceneList = v2StorageService.getStorageSceneList();

objective-c[[[NIMSDK sharedSDK] v2StorageService] getStorageSceneList];

cppauto sceneList = storageService.getStorageSceneList();

typescriptconst sceneList = nim.V2NIMStorageService.getStorageSceneList()

typescriptconst sceneList = nim.storageService.getStorageSceneList()

javaV2NIMUploadFileTask createUploadFileTask(V2NIMUploadFileParams params);

objective-c- (V2NIMUploadFileTask *)createUploadFileTask:(V2NIMUploadFileParams *)fileParams;

cppvirtual V2NIMUploadFileTask createUploadFileTask(V2NIMUploadFileParams fileParams) = 0;

typescriptcreateUploadFileTask(fileParams: V2NIMUploadFileParams): V2NIMUploadFileTask

typescriptcreateUploadFileTask(fileParams: V2NIMUploadFileParams): V2NIMUploadFileTask

javaV2NIMStorageService v2StorageService = NIMClient.getService(V2NIMStorageService.class);
V2NIMUploadFileParams params = new V2NIMUploadFileParams("filePath")
V2NIMUploadFileTask uploadFileTask = v2StorageService.createUploadFileTask(params);

objective-cV2NIMUploadFileParams *fileParams = [[V2NIMUploadFileParams alloc] init];
fileParams.filePath = @"filePath";
[[[NIMSDK sharedSDK] v2StorageService] createUploadFileTask:fileParams];

cppV2NIMUploadFileParams fileParams;
fileParams.filePath = "~/test.txt";
fileParams.name = "hello.txt";
fileParams.scene = "customScene";
auto uploadTask = storageService.createUploadFileTask(fileParams);

typescriptconst task = nim.V2NIMStorageService.createUploadFileTask({
    fileObj: document.getElementById('input-id').files[0]
}})

typescriptconst params:V2NIMUploadFileParams = {
    filePath: '文件沙盒路径',
    sceneName: '场景名'
} as V2NIMUploadFileParams

const task = nim.storageService.createUploadFileTask(params)

javavoid uploadFile(V2NIMUploadFileTask fileTask, V2NIMSuccessCallback<String> success,
    V2NIMFailureCallback failure,
    V2NIMProgressCallback progress);

objective-c- (void)uploadFile:(V2NIMUploadFileTask *)fileTask
           success:(V2NIMFileUploadSuccess)success
           failure:(V2NIMFileUploadFailure)failure
          progress:(V2NIMFileUploadProgress)progress;

cppvirtual void uploadFile(V2NIMUploadFileTask fileTask,
    V2NIMSuccessCallback<nstd::string> success,
    V2NIMFailureCallback failure,
    V2NIMProgressCallback progress) = 0;

typescriptuploadFile(fileTask: V2NIMUploadFileTask, progress: V2NIMProgressCallback): Promise<string>

typescriptuploadFile(fileTask: V2NIMUploadFileTask, progress: V2NIMProgressCallback): Promise<string>

javaV2NIMStorageService v2StorageService = NIMClient.getService(V2NIMStorageService.class);
v2StorageService.uploadFile(task, (V2NIMSuccessCallback<String>) s -> {
    // 上传成功
}, (V2NIMFailureCallback) error -> {
    // 上传失败
}, (V2NIMProgressCallback) progress -> {
    // 上传进度
});

objective-c[[[NIMSDK sharedSDK] v2StorageService] uploadFile:fileTask success:^(NSString * _Nonnull urlString) {
        // 上传成功
    } failure:^(V2NIMError * _Nonnull error) {
        // 上传失败
    } progress:^(float progress) {
         // 上传进度
    }];

cppV2NIMUploadFileParams fileParams;
fileParams.filePath = "~/test.txt";
fileParams.name = "hello.txt";
fileParams.scene = "customScene";
auto uploadTask = storageService.createUploadFileTask(fileParams);
storageService.uploadFile(
    uploadTask,
    [](nstd::string url) {
        // upload file succeeded
    },
    [](V2NIMError error) {
        // upload file failed, handle error
    },
    [](uint32_t progress) {
        // upload progress
    });

typescriptnim.V2NIMStorageService.uploadFile(task, function onProgress(progress) {
 console.log('uploadFile progress: ', progress)   
})

typescriptnim.storageService.uploadFile(task, function onProgress(progress) {
 console.log('uploadFile progress: ', progress)   
})

无返回值

Promise<string> 文件 URL 地址

• 请求成功，返回 V2NIMSuccessCallback 回调，包含文件 URL 地址。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储相关错误码。

• 请求成功，返回 V2NIMFileUploadSuccess 回调，可自定义设置。
• 请求失败，返回 V2NIMFileUploadFailure 回调，可自定义设置。

无

javavoid cancelUploadFile(V2NIMUploadFileTask fileTask, V2NIMSuccessCallback<Void> success,
    V2NIMFailureCallback failure);

objective-c- (void)cancelUploadFile:(V2NIMUploadFileTask *)fileTask
                 success:(V2NIMSuccessCallback)success
                 failure:(V2NIMFailureCallback)failure;

cppvirtual void cancelUploadFile(V2NIMUploadFileTask fileTask, V2NIMSuccessCallback<void> success, V2NIMFailureCallback failure) = 0;

typescriptcancelUploadFile(fileTask: V2NIMUploadFileTask): Promise<void>

typescriptcancelUploadFile(fileTask: V2NIMUploadFileTask): Promise<void>

javaV2NIMStorageService v2StorageService = NIMClient.getService(V2NIMStorageService.class);
v2StorageService.cancelUploadFile(task, (V2NIMSuccessCallback<Void>) s -> {
    // 取消成功
}, (V2NIMFailureCallback) error -> {
    // 取消失败
});

objective-c[[[NIMSDK sharedSDK] v2StorageService] cancelUploadFile:fileTask success:^{
        //取消成功
    } failure:^(V2NIMError * _Nonnull error) {
        //取消失败
    }];

cppV2NIMUploadFileTask fileTask;
// uploadFile
// ...
storageService.cancelUploadFile(
    fileTask,
    []() {
        // cancel upload file succeeded
    },
    [](V2NIMError error) {
        // cancel upload file failed, handle error
    });

typescriptnim.V2NIMStorageService.cancelUploadFile(task)

typescriptnim.storageService.cancelUploadFile(task)

无返回值

Promise<void>

• 请求成功，返回 V2NIMSuccessCallback 回调。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储相关错误码。

无

javavoid downloadFile(String url, String filePath, V2NIMSuccessCallback<String> success,
    V2NIMFailureCallback failure, V2NIMProgressCallback progress);

objective-c- (void)downloadFile:(NSString *)url
            filePath:(NSString *)filePath
             success:(V2NIMSuccessCallback)success
             failure:(V2NIMFailureCallback)failure
            progress:(nullable V2NIMProgressCallback)progress;

cppvirtual void v2::V2NIMStorageService::downloadFile	(	const nstd::string & 	url,
                                                        const nstd::string & 	savePath,
                                                        V2NIMSuccessCallback< nstd::string > 	success,
                                                        V2NIMFailureCallback 	failure,
                                                        V2NIMProgressCallback 	progress )	

javaString url = "https://www.abc.com/ttt.txt";
// 设置文件存储位置
String filePath = "xxx/ttt.txt";
NIMClient.getService(V2NIMStorageService.class).downloadFile(url, filePath, new V2NIMSuccessCallback<String>() {
    @Override
    public void onSuccess(String filePath) {
        // 下载成功
    }
}, new V2NIMFailureCallback() {
    @Override
    public void onFailure(V2NIMError error) {
        // 下载失败
    }
}, new V2NIMProgressCallback() {
    @Override
    public void onProgress(int progress) {
        // 下载进度
    }
});

objective-c// 按需配置远程目录
NSString *url = @"https://www.abc.com/ttt.txt";
// 按需配置存储目录
NSString *filePath = @"Document/ttt.txt";
[[NIMSDK sharedSDK].v2StorageService downloadFile:url filePath:filePath success:^() {
    // 成功回调
} failure:^(V2NIMError *error) {
    // 失败回调
} progress:^(NSUInteger progress) {
    // 进度回调
}]; 

cppstorageService.downloadFile(
    "https://example.com/test.txt",
    "~/test.txt",
    [](const nstd::string& url) {
        // download file succeeded
    },
    [](V2NIMError error) {
        // download file failed, handle error
    },
    [](uint32_t progress) {
        // download progress
    });

javavoid shortUrlToLong(String url, V2NIMSuccessCallback<String> success,
    V2NIMFailureCallback failure);

objective-c- (void)shortUrlToLong:(NSString *)url
               success:(V2NIMShortUrlToLongSuccess)success
               failure:(V2NIMFailureCallback)failure;

cppvirtual void v2::V2NIMStorageService::shortUrlToLong	(	const nstd::string & 	url,
                                                            V2NIMSuccessCallback< nstd::string > 	success,
                                                            V2NIMFailureCallback 	failure )	

typescriptshortUrlToLong(url: string): Promise<string>

javaString shortUrl = "https://s.netease.im/safe/AAAAAAAAAAAAAAAAAAAAAAAAAAA?_im_url=1";
NIMClient.getService(V2NIMStorageService.class).shortUrlToLong(shortUrl, new V2NIMSuccessCallback<String>() {
    @Override
    public void onSuccess(String longUrl) {
        // 转换成功
    }
}, new V2NIMFailureCallback() {
    @Override
    public void onFailure(V2NIMError error) {
        // 转换失败
    }
});

objective-c// 按需传入短链
NSString *shortUrl = @"https://s.netease.im/safe/AAAAAAAAAAAAAAAAAAAAAAAAAAA?_im_url=1";
[[NIMSDK sharedSDK].v2StorageService shortUrlToLong:shortUrl success:^(NSString *url) {
    // 成功回调
} failure:^(V2NIMError *error) {
    // 失败回调
}];

cppstorageService.shortUrlToLong("https://example.com/short?_im_url=1", [](nstd::string url) {
    // short url to long succeeded
}, [](V2NIMError error) {
    // short url to long failed, handle error
});

typescriptvar shortUrl = "https://s.netease.im/safe/AAAAAAAAAAAAAAAAAAAAAAAAAAA?_im_url=1";
var originUrl = await nim.V2NIMStorageService.shortUrlToLong(shortUrl)

无

Promise<string>

• 请求成功，返回 V2NIMSuccessCallback 回调。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储相关错误码。

• 请求成功，返回 V2NIMShortUrlToLongSuccess 回调，可自定义设置。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储相关错误码。

无

javapublic static String imageThumbUrl(String url,int thumbSize)

objective-c+ (NSString *)imageThumbUrl:(NSString *)url
                  thumbSize:(NSInteger)thumbSize;

cppnstd::string v2::V2NIMStorageUtil::imageThumbUrl	(	const nstd::string & 	url,
                                                        int32_t 	thumbSize )	

typescriptimageThumbUrl(url: string, thumbSize: number): string

typescriptimageThumbUrl(url: string, thumbSize: number): string

javaString url = "http://xxx.com/xxx.jpg";
int thumbSize = 100;
String imageThumbUrl = V2NIMStorageUtil.imageThumbUrl(url, thumbSize);

objective-c- (void)imageThumbUrl
{
    V2NIMMessage *message = nil; // message
    V2NIMMessageImageAttachment *attachment = nil; // image attachment
    if ([message.attachment isKindOfClass:V2NIMMessageImageAttachment.class]) {
        attachment = (V2NIMMessageImageAttachment *)(message.attachment);
    }
    if (attachment) {
        NSInteger size = 100; // screen size
        size *= UIScreen.mainScreen.scale;
        // keep aspect ratio and width or height > size
        NSString *thumbUrl = [V2NIMStorageUtil imageThumbUrl:attachment.url thumbSize:size];
    }
}

cppauto thumbURL= V2NIMStorageUtil::imageThumbUrl("image_url", 100);

typescriptconst url = nim.V2NIMStorageUtil.imageThumbUrl("https://host/path", 80)

typescriptconst url = nim.storageUtil.imageThumbUrl("https://host/path", 80)

javavoid getImageThumbUrl(V2NIMMessageAttachment attachment, 
                    V2NIMSize thumbSize, 
                    V2NIMSuccessCallback<V2NIMGetMediaResourceInfoResult> success,
                    V2NIMFailureCallback failure);

objective-c- (void)getImageThumbUrl:(V2NIMMessageAttachment *)attachment
               thumbSize:(V2NIMSize *)thumbSize
                 success:(V2NIMGetImageThumbUrlSuccess)success
                 failure:(V2NIMFailureCallback)failure;

c++virtual void v2::V2NIMStorageService::getImageThumbUrl	(
                const nstd::shared_ptr< V2NIMMessageAttachment > & 	attachment,
                const nstd::optional< V2NIMSize > & thumbSize,
                const V2NIMSuccessCallback< const V2NIMGetMediaResourceInfoResult & > & success,
                const V2NIMFailureCallback & 	failure 
)	

typescriptgetImageThumbUrl(attachment: V2NIMMessageAttachment, thumbSize: V2NIMSize): Promise<V2NIMGetMediaResourceInfoResult>

java// 从消息中获取附件，只能使用V2NIMMessageImageAttachment
V2NIMMessageAttachment attachment = message.getAttachment();
// 指定图片大小。0表示该维度不限制
V2NIMSize thumbSize = new V2NIMSize();
thumbSize.setWidth(100);
thumbSize.setHeight(0);

NIMClient.getService(V2NIMStorageService.class).getImageThumbUrl(attachment, thumbSize, s -> {
    // 获取成功
}, f -> {
    // 获取失败
});

objective-c// 从消息中获取附件，只能使用V2NIMMessageImageAttachment
V2NIMMessageAttachment *attachment = message.attachment;
// 指定图片大小。0表示该维度不限制
V2NIMSize *thumbSize = [[V2NIMSize alloc] initWithWidth:100 height:0];

[[NIMSDK sharedSDK].v2StorageService getImageThumbUrl:attachment thumbSize:thumbSize success:^(V2NIMGetMediaResourceInfoResult *result) {
    // 获取成功
} failure:^(V2NIMError *error) {
    // 获取失败
}];

c++storageService.getImageThumbUrl(attachment, V2NIMSize(150, 150), [](const V2NIMGetMediaResourceInfoResult& result) {
        // get image thumb url succeeded
    }, [](V2NIMError error) {
        // get image thumb url failed, handle error
    });

typescript/**
   * 生成图片缩略链接
   *
   * ESM 模式时，需要动态引入 V2NIMStorageUtil 后使用:
   * NIM.registerService(V2NIMStorageUtil, 'V2NIMStorageUtil')
   *
   * 使用示例: nim.V2NIMStorageService.getImageThumbUrl(attachment, { width: 100, height: 100 })
   */
  getImageThumbUrl(attachment: V2NIMMessageAttachment, thumbSize: V2NIMSize): Promise<V2NIMGetMediaResourceInfoResult>

无

Promise<V2NIMGetMediaResourceInfoResult>

• 请求成功，返回 V2NIMSuccessCallback<V2NIMGetMediaResourceInfoResult> 回调，包含附件下载路径。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储服务相关错误码。

• 请求成功，返回 V2NIMGetImageThumbUrlSuccess 回调，包含附件下载路径。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储服务相关错误码。

无

javapublic static String videoCoverUrl(String url,int offset)

objective-c+ (NSString *)videoCoverUrl:(NSString *)url
                     offset:(NSInteger)offset;

cppnstd::string v2::V2NIMStorageUtil::videoCoverUrl	(	const nstd::string & 	url,
                                                        int32_t 	offset,
                                                        int32_t 	thumbSize,
                                                        const nstd::string & 	type )	

typescriptvideoCoverUrl(url: string, offset: number): string

typescriptvideoCoverUrl(url: string, offset: number): string

javaString url = "http://xxx.com/xxx.jpg";
int offset = 0;
String videoCoverUrl = V2NIMStorageUtil.videoCoverUrl(url, offset);

objective-c- (void)videoCoverUrl
{
    V2NIMMessage *message = nil; // message
    V2NIMMessageVideoAttachment *attachment = nil; // video attachment
    if ([message.attachment isKindOfClass:V2NIMMessageVideoAttachment.class]) {
        attachment = (V2NIMMessageVideoAttachment *)(message.attachment);
    }
    if (attachment) {
        NSInteger offset = 0; // start of video
        NSString *coverUrl = [V2NIMStorageUtil videoCoverUrl:attachment.url offset:offset];
    }
}

cppauto coverURL = V2NIMStorageUtil::videoCoverUrl("video_url", 0, 150, "png");

typescriptconst url = nim.V2NIMStorageUtil.videoCoverUrl("https://host/path", 0)

typescriptconst url = nim.storageUtil.videoCoverUrl("https://host/path", 0)

javavoid getVideoCoverUrl(V2NIMMessageAttachment attachment, 
                      V2NIMSize thumbSize, 
                      V2NIMSuccessCallback<V2NIMGetMediaResourceInfoResult> success,
                      V2NIMFailureCallback failure);

objective-c- (void)getVideoCoverUrl:(V2NIMMessageAttachment *)attachment
               thumbSize:(V2NIMSize *)thumbSize
                 success:(V2NIMGetVideoCoverUrlSuccess)success
                 failure:(V2NIMFailureCallback)failure;

c++virtual void v2::V2NIMStorageService::getVideoCoverUrl	(	const nstd::shared_ptr< V2NIMMessageAttachment > & 	attachment,
const nstd::optional< V2NIMSize > & 	thumbSize,
const V2NIMSuccessCallback< const V2NIMGetMediaResourceInfoResult & > & 	success,
const V2NIMFailureCallback & 	failure 
)	

typescriptgetVideoCoverUrl(attachment: V2NIMMessageAttachment, thumbSize: V2NIMSize): Promise<V2NIMGetMediaResourceInfoResult>

java// 从消息中获取附件，只能使用V2NIMMessageVideoAttachment
V2NIMMessageAttachment attachment = message.getAttachment();
// 指定图片大小。0表示该维度不限制
V2NIMSize thumbSize = new V2NIMSize();
thumbSize.setWidth(100);
thumbSize.setHeight(0);

NIMClient.getService(V2NIMStorageService.class).getVideoCoverUrl(attachment, thumbSize, s -> {
    // 获取成功
}, f -> {
    // 获取失败
});

objective-c// 从消息中获取附件，只能使用V2NIMMessageVideoAttachment
V2NIMMessageAttachment *attachment = message.attachment;
// 指定图片大小。0表示该维度不限制
V2NIMSize *thumbSize = [[V2NIMSize alloc] initWithWidth:100 height:0];

[[NIMSDK sharedSDK].v2StorageService getVideoCoverUrl:attachment thumbSize:thumbSize success:^(V2NIMGetMediaResourceInfoResult *result) {
    // 获取成功
} failure:^(V2NIMError *error) {
    // 获取失败
}];

c++storageService.getVideoCoverUrl(attachment, V2NIMSize(150, 150), [](const V2NIMGetMediaResourceInfoResult& result) {
       // get video cover url succeeded
   }, [](V2NIMError error) {
       // get video cover url failed, handle error
   });

typescript /**
   * 生成视频封面图链接
   *
   * ESM 模式时，需要动态引入 V2NIMStorageUtil 后使用:
   * NIM.registerService(V2NIMStorageUtil, 'V2NIMStorageUtil')
   *
   * 使用示例: nim.V2NIMStorageService.getVideoCoverUrl(attachment, { width: 100, height: 100 })
   */
  getVideoCoverUrl(attachment: V2NIMMessageAttachment, thumbSize: V2NIMSize): Promise<V2NIMGetMediaResourceInfoResult>

无

Promise<V2NIMGetMediaResourceInfoResult>

• 请求成功，返回 V2NIMSuccessCallback<V2NIMGetMediaResourceInfoResult> 回调，包含附件下载路径。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储服务相关错误码。

• 请求成功，返回 V2NIMGetVideoCoverUrlSuccess 回调，包含附件下载路径。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储服务相关错误码。

无

java/**
 * 下载消息附件
 *
 * @param downloadParam 下载参数
 * @param success       下载消息附件成功回调
 * @param failure       下载消息附件失败回调
 * @param progress      下载消息附件进度回调
 */
void downloadAttachment(V2NIMDownloadMessageAttachmentParams downloadParam,                       
                        V2NIMSuccessCallback<String> success,
                        V2NIMFailureCallback failure, 
                        V2NIMProgressCallback progress);

objective-c- (void) downloadAttachment:	(V2NIMDownloadMessageAttachmentParams *) 	downloadParam
                    success:		(V2NIMDownloadAttachmentSuccess) 	success
                    failure:		(V2NIMFailureCallback) 	failure
                   progress:		(nullable V2NIMProgressCallback) 	progress 

c++virtual void v2::V2NIMStorageService::downloadAttachment(const V2NIMDownloadMessageAttachmentParams & 	downloadParam,
                                                         const V2NIMSuccessCallback< const nstd::string & > & 	success,
                                                         const V2NIMFailureCallback & 	failure,
                                                         const V2NIMProgressCallback & 	progress 
)	

java// 从消息中获取附件
// 只有V2NIMMessageFileAttachment及其子类可以用于下载原始资源
// 只有V2NIMMessageImageAttachment可以用于下载缩略图
// 只有V2NIMMessageVideoAttachment可以用于下载视频封面
V2NIMMessageAttachment attachment = message.getAttachment();
// 下载缩略图。
// 下载原始资源使用V2NIM_DOWNLOAD_ATTACHMENT_TYPE_SOURCE、下载视频封面使用V2NIM_DOWNLOAD_ATTACHMENT_TYPE_VIDEO_COVER
V2NIMDownloadAttachmentType type = V2NIMDownloadAttachmentType.V2NIM_DOWNLOAD_ATTACHMENT_TYPE_THUMBNAIL;
// 下载缩略图或者视频封面时，指定图片大小。0表示该维度不限制
V2NIMSize thumbSize = new V2NIMSize();
thumbSize.setWidth(100);
thumbSize.setHeight(0);
// 填写对应消息的端侧ID，使得下载完成后替换附件中的路径
String messageClientId = message.getMessageClientId();
// 指定文件的存储路径
String saveAs = "path/to/save";

V2NIMDownloadMessageAttachmentParams downloadParam = new V2NIMDownloadMessageAttachmentParams.V2NIMDownloadMessageAttachmentParamsBuilder(attachment)
        .type(type)
        .thumbSize(thumbSize)
        .messageClientId(messageClientId)
        .saveAs(saveAs).build();
NIMClient.getService(V2NIMStorageService.class).downloadAttachment(downloadParam, s -> {
    // 下载成功
}, f -> {
    // 下载失败
}, progress -> {
    // 下载进度变更
});

objective-c// 从消息中获取附件
// 只有V2NIMMessageFileAttachment及其子类可以用于下载原始资源
// 只有V2NIMMessageImageAttachment可以用于下载缩略图
// 只有V2NIMMessageVideoAttachment可以用于下载视频封面
V2NIMMessageAttachment *attachment = message.attachment;
V2NIMDownloadMessageAttachmentParams *downloadParams = [[V2NIMDownloadMessageAttachmentParams alloc] initWithAttachment:attachment];
// 下载缩略图。
// 下载原始资源使用V2NIM_DOWNLOAD_ATTACHMENT_TYPE_SOURCE、下载视频封面使用V2NIM_DOWNLOAD_ATTACHMENT_TYPE_VIDEO_COVER
downloadParams.type = V2NIM_DOWNLOAD_ATTACHMENT_TYPE_THUMBNAIL;
// 下载缩略图或者视频封面时，指定图片大小。0表示该维度不限制
downloadParams.thumbSize = [[V2NIMSize alloc] initWithWidth:100 height:0];
// 填写对应消息的端侧ID，使得下载完成后替换附件中的路径
downloadParams.messageClientId = message.messageClientId;
// 指定文件的存储路径
downloadParams.saveAs = @"path/to/save";

[[NIMSDK sharedSDK].v2StorageService downloadAttachment:attachment success:^(NSString *filePath) {
    // 下载成功
} failure:^(V2NIMError *error) {
    // 下载失败
} progress:^(NSUInteger progress) {
    // 下载进度变更
}];

c++V2NIMDownloadMessageAttachmentParams downloadParam;
downloadParam.attachment = attachment;
downloadParam.type = V2NIM_DOWNLOAD_ATTACHMENT_TYPE_SOURCE;
storageService.downloadAttachment(
    downloadParam,
    [](const nstd::string& path) {
        // download attachment succeeded
    },
    [](V2NIMError error) {
        // download attachment failed, handle error
    },
    [](uint32_t progress) {
        // download progress
    });

• 请求成功，返回 V2NIMSuccessCallback 回调，包含附件下载路径。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储服务相关错误码。
• 返回 V2NIMProgressCallback 回调，包含附件下载进度。

• 请求成功，返回 V2NIMDownloadAttachmentSuccess 回调，包含附件下载路径。
• 请求失败，返回 V2NIMFailureCallback 回调，包含存储服务相关错误码。
• 返回 V2NIMProgressCallback 回调，包含附件下载进度。