fixed the problem. see #1. Just took this PR code and added a new endpiont so the difference could be seen.

Author: Monstera33

MsAzureBlobstorageLargeFileProblemApp.run.xml

@@ -3,7 +3,7 @@
     <module name="downloader" />
     <option name="SHORTEN_COMMAND_LINE" value="ARGS_FILE" />
     <option name="SPRING_BOOT_MAIN_CLASS" value="com.azureproblem.blob.application.MsAzureBlobstorageLargeFileProblemApp" />
-    <option name="VM_PARAMETERS" value="-Xmx5G -XX:+CrashOnOutOfMemoryError" />
+    <option name="VM_PARAMETERS" value="-Xmx500M -XX:+CrashOnOutOfMemoryError" />
     <extension name="coverage">
       <pattern>
         <option name="PATTERN" value="com.azureproblem.blob.application.*" />

MsAzureBlobstorageLargeFileProblemFileServerApp.run.xml

@@ -3,7 +3,7 @@
     <module name="fileserver" />
     <option name="SHORTEN_COMMAND_LINE" value="ARGS_FILE" />
     <option name="SPRING_BOOT_MAIN_CLASS" value="com.azureproblem.bug.application.MsAzureBlobstorageLargeFileProblemFileServerApp" />
-    <option name="VM_PARAMETERS" value="-Xmx5G -XX:+CrashOnOutOfMemoryError" />
+    <option name="VM_PARAMETERS" value="-Xmx20G -XX:+CrashOnOutOfMemoryError" />
     <extension name="coverage">
       <pattern>
         <option name="PATTERN" value="com.azureproblem.bug.application.*" />

README.md

@@ -45,10 +45,18 @@ please checkout the log of the app. You see that it only this msg and the app ha
 
 It is strange that the app can write (stream) any file to the file system. But we can not stream
 something bigger than 250MB to the blobstorage, although we use a Output stream the same as in
-the File case. 
+the File case.
 
 ## Generate Testdata on the client side and store it to the BlobStorage
 
-This calls generate test data on the client side and writes it directly to the Blob Storage. Not 
+This calls generate test data on the client side and writes it directly to the Blob Storage. Not
 Data is transmitted via REST.
-`localhost:8544/trigger-generation-of-random-data-to-blobstore/260`
+`localhost:8544/trigger-generation-of-random-data-to-blobstore/260`
+
+# Solution
+
+The Problem could be solved by using `BlobAsyncClient`. In the code I added a working version see
+`trigger-download-to-blob-working-ok`.
+
+See also https://github.com/git9999999/azure-blob-large-file-upload-problem/pull/1 Thansk a lot
+to alzimmermsft.

downloader/src/main/java/com/azureproblem/blob/controller/AzureBlobBugDownloaderController.java

@@ -2,7 +2,9 @@
 
 import static org.apache.commons.lang3.ObjectUtils.isEmpty;
 
+import com.azure.storage.blob.BlobContainerAsyncClient;
 import com.azure.storage.blob.BlobContainerClient;
+import com.azure.storage.blob.BlobServiceAsyncClient;
 import com.azure.storage.blob.BlobServiceClient;
 import com.azure.storage.blob.BlobServiceClientBuilder;
 import com.azure.storage.blob.models.ParallelTransferOptions;
@@ -11,6 +13,7 @@
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
+import java.nio.ByteBuffer;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.security.SecureRandom;
@@ -48,11 +51,14 @@ public class AzureBlobBugDownloaderController {
     private final WebClient webClient;
 
     private final ParallelTransferOptions parallelTransferOptions;
+    private final BlobContainerAsyncClient blobContainerAsyncClient;
 
 
     public AzureBlobBugDownloaderController(BlobServiceClientBuilder blobServiceClientBuilder) {
         this.blobServiceClient = blobServiceClientBuilder.buildClient();
         this.containerClient = this.blobServiceClient.getBlobContainerClient(BLOB_CONTAINER_NAME);
+        BlobServiceAsyncClient blobServiceAsyncClient = blobServiceClientBuilder.buildAsyncClient();
+        this.blobContainerAsyncClient = blobServiceAsyncClient.getBlobContainerAsyncClient(BLOB_CONTAINER_NAME);
         log.debug("technicalAppIp '{}' technicalAppPort '{}'", "8545", "8545");
         this.webClient = msCommonWebClientBuilder().baseUrl(createUrl("client", "localhost", "8545")).build();
 
@@ -156,6 +162,31 @@ public void triggerDownloadToBlob(@PathVariable int fileSizeInMb) {
     }
 
 
+    @GetMapping(path = "/trigger-download-to-blob-working-ok/{fileSizeInMb}")
+    public void triggerDownloadToBlobWorkingOk(@PathVariable int fileSizeInMb) {
+        log.info("triggerDownloadToBlob");
+
+        var flux = this.webClient
+            .get()
+            .uri("/serve-file/" + fileSizeInMb)
+            .accept(MediaType.APPLICATION_OCTET_STREAM)
+            .exchangeToFlux(clientResponse -> clientResponse.body(BodyExtractors.toDataBuffers()));
+
+        var destination = "TestDownloadToAzureBlobStorage" + System.currentTimeMillis() + ".pdf";
+
+        var blobClientTarget = this.blobContainerAsyncClient.getBlobAsyncClient(destination);
+
+        blobClientTarget.upload(flux.map(dataBuffer -> {
+            ByteBuffer buffer = ByteBuffer.allocate(dataBuffer.readableByteCount());
+            dataBuffer.toByteBuffer(buffer);
+            DataBufferUtils.release(dataBuffer);
+            return buffer;
+        }), this.parallelTransferOptions).block();
+
+        log.info("!!!!!!!!!!!!!!!!!!!!!!!!!!!!   end download of {}", destination);
+    }
+
+
     /**
      * https://stackoverflow.com/questions/76575117/can-not-transfer-more-than-250mb-with-databufferutils-write-to-azure-blob-storag/76580753#76580753
      */