对象存储是云的基础组件之一，各大云厂商都有相关产品。这里跟大家介绍一下rust与对象存储交到的基本套路和其中的一些技巧。

基本连接

我们以 [S3 sdk](https://github.com/awslabs/aws-sdk-rust)为例来说说基本的连接与操作，作者验证过aws、京东云、阿里云。主要的增删改查功能没有什么差别。

基本依赖  Cargo.toml

  # oss  aws-config = { git = "https://github.com/awslabs/aws-sdk-rust", branch = "main" }  aws-sdk-s3 = { git = "https://github.com/awslabs/aws-sdk-rust", branch = "main" }  aws-types = { git = "https://github.com/awslabs/aws-sdk-rust", branch = "main",  feature = ["hardcoded-credentials"] }  aws-credential-types = { git = "https://github.com/awslabs/aws-sdk-rust", branch = "main" }  aws-smithy-types = { git = "https://github.com/awslabs/aws-sdk-rust", branch = "main" }

建立客户端

let shared_config = SdkConfig::builder()         .credentials_provider(SharedCredentialsProvider::new(Credentials::new(            "LTAI5t7NPuPKsXm6UeSa1",            "DGHuK03ESXQYqQ83buKMHs9NAwz",             None,             None,             "Static",         )))         .endpoint_url("http://oss-cn-beijing.aliyuncs.com")         .region(Region::new("oss-cn-beijing"))         .build();     let s3_config_builder = aws_sdk_s3::config::Builder::from(&shared_config);     let client = aws_sdk_s3::Client::from_conf(s3_config_builder.build());

建立Client所需要的参数主要有你需要访问的oss的AK、SK，endpoint url 以及服务所在的区域。以上信息都可以在服务商的帮助文档查询到。

对象列表

let mut obj_list = client     .list_objects_v2()     .bucket(bucket)     .max_keys(max_keys)     .prefix(prefix_str)     .continuation_token(token_str);
let list = obj_list.send().await.unwrap();println!("{:?}",list.contents());println!("{:?}",list.next_continuation_token());

使用list_objects_v2函数返回对象列表，相比list_objects函数，list_objects_v2可以通过continuation_token和max_keys控制返回列表的长度。list.contents()返回对象列表数组，list.next_continuation_token()返回继续查询的token。

上传文件

let content = ByteStream::from("content in file".as_bytes()); let exp = aws_smithy_types::DateTime::from_secs(100);let upload = client    .put_object()    .bucket("bucket")    .key("/test/key")    .expires(exp)    .body(content);upload.send().await.unwrap();

指定bucket及对象路径，body接受ByteStream类型作为文件内容，最后设置过期时间expires，无过期时间时不指定该配置即可。

下载文件

let key = "/tmp/test/key".to_string();let resp = client    .get_object()    .bucket("bucket")    .key(&key)    .send()    .await.unwrap();let data = resp.body.collect().await.unwrap();let bytes = data.into_bytes();
let path = std::path::Path::new("/tmp/key")if let Some(p) = path.parent() {    std::fs::create_dir_all(p).unwrap();}let mut file = OpenOptions::new()    .write(true)    .truncate(true)    .create(true)    .open(path).unwrap();let _ = file.write(&*bytes);file.flush().unwrap();

通过get_object()函数获取GetObjectOutput。返回值的body 就是文件内容，将 body 转换为 bytes，最后打开文件写入即可。

删除文件

let mut keys = vec![];let key1 = ObjectIdentifier::builder()    .set_key(Some("/tmp/key1".to_string()))    .build();let key2 = ObjectIdentifier::builder()    .set_key(Some("/tmp/key2".to_string()))    .build()keys.push(key1);keys.push(key2)client    .delete_objects()    .bucket(bucket)    .delete(Delete::builder().set_objects(Some(keys)).build())    .send()    .await    .unwrap();

delete_objects 批量删除对象。首先构建keys vector，定义要删除的对象，然后通过Delete::builder()，构建 Delete model。

大文件上传

let mut file = fs::File::open("/tmp/file_name").unwrap();let chunk_size = 1024*1024;let mut part_number = 0;let mut upload_parts: Vec = Vec::new();
//获取上传idlet multipart_upload_res: CreateMultipartUploadOutput = self    .client    .create_multipart_upload()    .bucket("bucket")    .key("/tmp/key")    .send()    .await.unwrap();let upload_id = match multipart_upload_res.upload_id() {    Some(id) => id,    None => {        return Err(anyhow!("upload id is None"));    }};
//分段上传文件并记录completer_partloop {    let mut buf = vec![0; chuck_size];    let read_count = file.read(&mut buf)?;    part_number += 1;
    if read_count == 0 {        break;    }
    let body = &buf[..read_count];    let stream = ByteStream::from(body.to_vec());
    let upload_part_res = self        .client        .upload_part()        .key(key)        .bucket(bucket)        .upload_id(upload_id)        .body(stream)        .part_number(part_number)        .send()        .await.unwrap();
    let completer_part = CompletedPart::builder()        .e_tag(upload_part_res.e_tag.unwrap_or_default())        .part_number(part_number)        .build();
    upload_parts.push(completer_part);
    if read_count != chuck_size {        break;    }}// 完成上传文件合并let completed_multipart_upload: CompletedMultipartUpload =    CompletedMultipartUpload::builder()        .set_parts(Some(upload_parts))        .build();
let _complete_multipart_upload_res = self    .client    .complete_multipart_upload()    .bucket("bucket")    .key(key)    .multipart_upload(completed_multipart_upload)    .upload_id(upload_id)    .send()    .await.unwrap();

有时候面对大文件，比如几百兆甚至几个G的文件，为了节约带宽和内存，我才采取分段上传的方案，然后在对象存储的服务端做合并。基本流程是：指定bucket和key，获取一个上传id；按流读取文件，分段上传字节流，并记录CompletedPart;通知服务器按照CompletedPart 集合来合并文件。具体过程代码已加注释，这里不再累述。

大文件下载

let mut file = match OpenOptions::new()            .truncate(true)            .create(true)            .write(true)            .open("/tmp/target_file");let key = "/tmp/test/key".to_string();let resp = client    .get_object()    .bucket("bucket")    .key(&key)    .send()    .await.unwrap();
let content_len = resp.content_length();let mut byte_stream_async_reader = resp.body.into_async_read();let mut content_len_usize: usize = content_len.try_into().unwrap();loop {    if content_len_usize > chunk_size {        let mut buffer = vec![0; chunk_size];        let _ = byte_stream_async_reader.read_exact(&mut buffer).await.unwrap();        file.write_all(&buffer).unwrap();        content_len_usize -= chunk_size;        continue;    } else {        let mut buffer = vec![0; content_len_usize];        let _ = byte_stream_async_reader.read_exact(&mut buffer).await.unwrap();        file.write_all(&buffer).unwrap();        break;    }}file.flush().unwrap();

在从对象存储服务端下载文件的过程中也会遇到大文件问题。为了节约带宽和内存，我们采取读取字节流的方式分段写入文件。首先get_object()函数获取ByteStream，通过async_reader流式读取对象字节，分段写入文件。

对象存储的相关话题今天先聊到这儿，下期见。

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