[GitHub] [beam] robertwb commented on a diff in pull request #26370: Ensure FnApi bag appends are not batched if it would exceed 10MB limit

["robertwb (via GitHub)" <gi...@apache.org>]

robertwb commented on code in PR #26370:
URL: https://github.com/apache/beam/pull/26370#discussion_r1181805751


##########
sdks/java/core/src/main/java/org/apache/beam/sdk/util/ByteStringOutputStream.java:
##########
@@ -153,6 +157,47 @@ public ByteString toByteStringAndReset() {
     return rval;
   }
 
+  /**
+   * Creates a byte string with the given size containing the prefix of the contents of this output
+   * stream.
+   */
+  public ByteString consumePrefixToByteString(int prefixSize) {
+    ByteString rval;
+    Preconditions.checkArgument(prefixSize <= size());
+    if (prefixSize == size()) {
+      return toByteStringAndReset();
+    }
+    int bytesFromBuffer = prefixSize - result.size();
+    if (bytesFromBuffer == 0) {
+      rval = result;
+      result = ByteString.EMPTY;
+      return rval;
+    }
+    if (bytesFromBuffer < 0) {
+      rval = result.substring(0, prefixSize);
+      result = result.substring(prefixSize);
+      return rval;
+    }
+    // Copy or reference the kept bytes for the rval.
+    if (shouldCopy(buffer.length, bytesFromBuffer)) {
+      byte[] bufferCopy = new byte[bytesFromBuffer];
+      System.arraycopy(buffer, 0, bufferCopy, 0, bytesFromBuffer);
+      rval = result.concat(UnsafeByteOperations.unsafeWrap(bufferCopy));

Review Comment:
   Any reason not to us ByteString.copyFrom here? 



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