From b09a8517059a74499c1fdfe37f9c2842a7cbb229 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Arpad=20M=C3=BCller?= <arpad-m@users.noreply.github.com>
Date: Mon, 6 Nov 2023 16:16:55 +0100
Subject: [PATCH] Make azure blob storage not do extra metadata requests
 (#5777)

Load the metadata from the returned `GetBlobResponse` and avoid
downloading it via a separate request.
As it turns out, the SDK does return the metadata:
https://github.com/Azure/azure-sdk-for-rust/issues/1439 .

This PR will reduce the number of requests to Azure caused by downloads.

Fixes #5571
---
 libs/remote_storage/src/azure_blob.rs | 43 +++++++--------------------
 1 file changed, 10 insertions(+), 33 deletions(-)

diff --git a/libs/remote_storage/src/azure_blob.rs b/libs/remote_storage/src/azure_blob.rs
index f0521d27c5..ae08e9b171 100644
--- a/libs/remote_storage/src/azure_blob.rs
+++ b/libs/remote_storage/src/azure_blob.rs
@@ -1,21 +1,18 @@
 //! Azure Blob Storage wrapper
 
+use std::collections::HashMap;
 use std::env;
 use std::num::NonZeroU32;
 use std::sync::Arc;
-use std::{borrow::Cow, collections::HashMap, io::Cursor};
+use std::{borrow::Cow, io::Cursor};
 
 use super::REMOTE_STORAGE_PREFIX_SEPARATOR;
 use anyhow::Result;
 use azure_core::request_options::{MaxResults, Metadata, Range};
-use azure_core::Header;
 use azure_identity::DefaultAzureCredential;
 use azure_storage::StorageCredentials;
 use azure_storage_blobs::prelude::ClientBuilder;
-use azure_storage_blobs::{
-    blob::operations::GetBlobBuilder,
-    prelude::{BlobClient, ContainerClient},
-};
+use azure_storage_blobs::{blob::operations::GetBlobBuilder, prelude::ContainerClient};
 use futures_util::StreamExt;
 use http_types::StatusCode;
 use tokio::io::AsyncRead;
@@ -112,16 +109,19 @@ impl AzureBlobStorage {
 
     async fn download_for_builder(
         &self,
-        metadata: StorageMetadata,
         builder: GetBlobBuilder,
     ) -> Result<Download, DownloadError> {
         let mut response = builder.into_stream();
 
+        let mut metadata = HashMap::new();
         // TODO give proper streaming response instead of buffering into RAM
         // https://github.com/neondatabase/neon/issues/5563
         let mut buf = Vec::new();
         while let Some(part) = response.next().await {
             let part = part.map_err(to_download_error)?;
+            if let Some(blob_meta) = part.blob.metadata {
+                metadata.extend(blob_meta.iter().map(|(k, v)| (k.to_owned(), v.to_owned())));
+            }
             let data = part
                 .data
                 .collect()
@@ -131,28 +131,9 @@ impl AzureBlobStorage {
         }
         Ok(Download {
             download_stream: Box::pin(Cursor::new(buf)),
-            metadata: Some(metadata),
+            metadata: Some(StorageMetadata(metadata)),
         })
     }
-    // TODO get rid of this function once we have metadata included in the response
-    // https://github.com/Azure/azure-sdk-for-rust/issues/1439
-    async fn get_metadata(
-        &self,
-        blob_client: &BlobClient,
-    ) -> Result<StorageMetadata, DownloadError> {
-        let builder = blob_client.get_metadata();
-
-        let response = builder.into_future().await.map_err(to_download_error)?;
-        let mut map = HashMap::new();
-
-        for md in response.metadata.iter() {
-            map.insert(
-                md.name().as_str().to_string(),
-                md.value().as_str().to_string(),
-            );
-        }
-        Ok(StorageMetadata(map))
-    }
 
     async fn permit(&self, kind: RequestKind) -> tokio::sync::SemaphorePermit<'_> {
         self.concurrency_limiter
@@ -269,11 +250,9 @@ impl RemoteStorage for AzureBlobStorage {
         let _permit = self.permit(RequestKind::Get).await;
         let blob_client = self.client.blob_client(self.relative_path_to_name(from));
 
-        let metadata = self.get_metadata(&blob_client).await?;
-
         let builder = blob_client.get();
 
-        self.download_for_builder(metadata, builder).await
+        self.download_for_builder(builder).await
     }
 
     async fn download_byte_range(
@@ -285,8 +264,6 @@ impl RemoteStorage for AzureBlobStorage {
         let _permit = self.permit(RequestKind::Get).await;
         let blob_client = self.client.blob_client(self.relative_path_to_name(from));
 
-        let metadata = self.get_metadata(&blob_client).await?;
-
         let mut builder = blob_client.get();
 
         if let Some(end_exclusive) = end_exclusive {
@@ -301,7 +278,7 @@ impl RemoteStorage for AzureBlobStorage {
             builder = builder.range(Range::new(start_inclusive, end_exclusive));
         }
 
-        self.download_for_builder(metadata, builder).await
+        self.download_for_builder(builder).await
     }
 
     async fn delete(&self, path: &RemotePath) -> anyhow::Result<()> {