使用 AWS SDK 并指定 If-Modified-Since 标头以从 Amazon S3 存储桶获取对象 - Amazon Simple Storage Service

使用 AWS SDK 并指定 If-Modified-Since 标头以从 Amazon S3 存储桶获取对象

下面的代码示例显示如何从 S3 存储桶中的对象读取数据,但前提是该桶自上次检索以来未被修改。

操作示例是大型程序的代码摘录,必须在上下文中运行。您可以在以下代码示例中查看此操作的上下文:

Rust
适用于 Rust 的 SDK
注意

在 GitHub 上查看更多内容。查找完整示例,学习如何在 AWS 代码示例存储库中进行设置和运行。

use aws_sdk_s3::{ error::SdkError, operation::head_object::HeadObjectError, primitives::{ByteStream, DateTime, DateTimeFormat}, Client, Error, }; use tracing::{error, warn}; const KEY: &str = "key"; const BODY: &str = "Hello, world!"; /// Demonstrate how `if-modified-since` reports that matching objects haven't /// changed. /// /// # Steps /// - Create a bucket. /// - Put an object in the bucket. /// - Get the bucket headers. /// - Get the bucket headers again but only if modified. /// - Delete the bucket. #[tokio::main] async fn main() -> Result<(), Error> { tracing_subscriber::fmt::init(); // Get a new UUID to use when creating a unique bucket name. let uuid = uuid::Uuid::new_v4(); // Load the AWS configuration from the environment. let client = Client::new(&aws_config::load_from_env().await); // Generate a unique bucket name using the previously generated UUID. // Then create a new bucket with that name. let bucket_name = format!("if-modified-since-{uuid}"); client .create_bucket() .bucket(bucket_name.clone()) .send() .await?; // Create a new object in the bucket whose name is `KEY` and whose // contents are `BODY`. let put_object_output = client .put_object() .bucket(bucket_name.as_str()) .key(KEY) .body(ByteStream::from_static(BODY.as_bytes())) .send() .await; // If the `PutObject` succeeded, get the eTag string from it. Otherwise, // report an error and return an empty string. let e_tag_1 = match put_object_output { Ok(put_object) => put_object.e_tag.unwrap(), Err(err) => { error!("{err:?}"); String::new() } }; // Request the object's headers. let head_object_output = client .head_object() .bucket(bucket_name.as_str()) .key(KEY) .send() .await; // If the `HeadObject` request succeeded, create a tuple containing the // values of the headers `last-modified` and `etag`. If the request // failed, return the error in a tuple instead. let (last_modified, e_tag_2) = match head_object_output { Ok(head_object) => ( Ok(head_object.last_modified().cloned().unwrap()), head_object.e_tag.unwrap(), ), Err(err) => (Err(err), String::new()), }; warn!("last modified: {last_modified:?}"); assert_eq!( e_tag_1, e_tag_2, "PutObject and first GetObject had differing eTags" ); println!("First value of last_modified: {last_modified:?}"); println!("First tag: {}\n", e_tag_1); // Send a second `HeadObject` request. This time, the `if_modified_since` // option is specified, giving the `last_modified` value returned by the // first call to `HeadObject`. // // Since the object hasn't been changed, and there are no other objects in // the bucket, there should be no matching objects. let head_object_output = client .head_object() .bucket(bucket_name.as_str()) .key(KEY) .if_modified_since(last_modified.unwrap()) .send() .await; // If the `HeadObject` request succeeded, the result is a typle containing // the `last_modified` and `e_tag_1` properties. This is _not_ the expected // result. // // The _expected_ result of the second call to `HeadObject` is an // `SdkError::ServiceError` containing the HTTP error response. If that's // the case and the HTTP status is 304 (not modified), the output is a // tuple containing the values of the HTTP `last-modified` and `etag` // headers. // // If any other HTTP error occurred, the error is returned as an // `SdkError::ServiceError`. let (last_modified, e_tag_2): (Result<DateTime, SdkError<HeadObjectError>>, String) = match head_object_output { Ok(head_object) => ( Ok(head_object.last_modified().cloned().unwrap()), head_object.e_tag.unwrap(), ), Err(err) => match err { SdkError::ServiceError(err) => { // Get the raw HTTP response. If its status is 304, the // object has not changed. This is the expected code path. let http = err.raw(); match http.status().as_u16() { // If the HTTP status is 304: Not Modified, return a // tuple containing the values of the HTTP // `last-modified` and `etag` headers. 304 => ( Ok(DateTime::from_str( http.headers().get("last-modified").unwrap(), DateTimeFormat::HttpDate, ) .unwrap()), http.headers().get("etag").map(|t| t.into()).unwrap(), ), // Any other HTTP status code is returned as an // `SdkError::ServiceError`. _ => (Err(SdkError::ServiceError(err)), String::new()), } } // Any other kind of error is returned in a tuple containing the // error and an empty string. _ => (Err(err), String::new()), }, }; warn!("last modified: {last_modified:?}"); assert_eq!( e_tag_1, e_tag_2, "PutObject and second HeadObject had different eTags" ); println!("Second value of last modified: {last_modified:?}"); println!("Second tag: {}", e_tag_2); // Clean up by deleting the object and the bucket. client .delete_object() .bucket(bucket_name.as_str()) .key(KEY) .send() .await?; client .delete_bucket() .bucket(bucket_name.as_str()) .send() .await?; Ok(()) }
  • 有关 API 详细信息,请参阅《AWS SDK for Rust API 参考》中的 GetObject

有关 AWS SDK 开发人员指南和代码示例的完整列表,请参阅 将此服务与 AWS SDK 结合使用。本主题还包括有关入门的信息以及有关先前的 SDK 版本的详细信息。