(arrow) branch main updated: GH-47918: [Format] Clarify that empty compressed buffers can omit the length header (#48541)

[apitrou]

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The following commit(s) were added to refs/heads/main by this push:
     new d6cc592d6c GH-47918: [Format] Clarify that empty compressed buffers 
can omit the length header (#48541)
d6cc592d6c is described below

commit d6cc592d6ca9c5cb5ed5b8c38839742dc8372ec4
Author: Antoine Pitrou <anto...@python.org>
AuthorDate: Thu Dec 18 16:03:56 2025 +0100

    GH-47918: [Format] Clarify that empty compressed buffers can omit the 
length header (#48541)
    
    ### Rationale for this change
    
    The 8-byte length header is considered optional for empty compressed 
buffers in Arrow C++ and other implementations.
    
    ### Are these changes tested?
    
    Not applicable.
    
    ### Are there any user-facing changes?
    
    No.
    
    * GitHub Issue: #47918
    
    Authored-by: Antoine Pitrou <anto...@python.org>
    Signed-off-by: Antoine Pitrou <anto...@python.org>
---
 format/Message.fbs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/format/Message.fbs b/format/Message.fbs
index be57533d88..a03738040c 100644
--- a/format/Message.fbs
+++ b/format/Message.fbs
@@ -42,7 +42,7 @@ struct FieldNode {
   null_count: long;
 }
 
-enum CompressionType:byte {
+enum CompressionType: byte {
   // LZ4 frame format, for portability, as provided by lz4frame.h or wrappers
   // thereof. Not to be confused with "raw" (also called "block") format
   // provided by lz4.h
@@ -55,7 +55,7 @@ enum CompressionType:byte {
 /// Provided for forward compatibility in case we need to support different
 /// strategies for compressing the IPC message body (like whole-body
 /// compression rather than buffer-level) in the future
-enum BodyCompressionMethod:byte {
+enum BodyCompressionMethod: byte {
   /// Each constituent buffer is first compressed with the indicated
   /// compressor, and then written with the uncompressed length in the first 8
   /// bytes as a 64-bit little-endian signed integer followed by the compressed
@@ -63,6 +63,8 @@ enum BodyCompressionMethod:byte {
   /// uncompressed length may be set to -1 to indicate that the data that
   /// follows is not compressed, which can be useful for cases where
   /// compression does not yield appreciable savings.
+  /// Also, empty buffers can optionally be written out as 0-byte compressed
+  /// buffers, thereby omitting the 8-bytes length header.
   BUFFER
 }