Subject: [PATCH 6/6] odb/transaction: make `write_object_stream()` pluggable

From: Justin Tobler <[email-masked]>
Date: Mon, 30 Mar 2026 22:38:35 -0500

How an ODB transaction handles writing objects is expected to vary
between implementations. Introduce a new `write_object_stream()`
callback in `struct odb_transaction` to make this function pluggable.
Wire up `index_blob_packfile_transaction()` for use with `struct
odb_transaction_files` accordingly.

Signed-off-by: Justin Tobler <[email-masked]>
---
 object-file.c     |  9 +++++----
 odb/transaction.c |  7 +++++++
 odb/transaction.h | 25 ++++++++++++++++++++++---
 3 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/object-file.c b/object-file.c
index 4c797d6498..b1c97faef3 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1680,10 +1680,10 @@ int index_fd(struct index_state *istate, struct object_id *oid,
 				.data = &data,
 			};
 
-			ret = index_blob_packfile_transaction(odb->transaction,
-							      &in_stream,
-							      xsize_t(st->st_size),
-							      oid);
+			ret = odb_transaction_write_object_stream(odb->transaction,
+								  &in_stream,
+								  xsize_t(st->st_size),
+								  oid);
 			odb_transaction_commit(transaction);
 		} else {
 			if (hash_blob_stream(the_repository->hash_algo, oid, fd,
@@ -2146,6 +2146,7 @@ struct odb_transaction *odb_transaction_files_begin(struct odb_source *source)
 	transaction = xcalloc(1, sizeof(*transaction));
 	transaction->base.source = source;
 	transaction->base.commit = odb_transaction_files_commit;
+	transaction->base.write_object_stream = index_blob_packfile_transaction;
 
 	return &transaction->base;
 }
diff --git a/odb/transaction.c b/odb/transaction.c
index 592ac84075..b16e07aebf 100644
--- a/odb/transaction.c
+++ b/odb/transaction.c
@@ -26,3 +26,10 @@ void odb_transaction_commit(struct odb_transaction *transaction)
 	transaction->source->odb->transaction = NULL;
 	free(transaction);
 }
+
+int odb_transaction_write_object_stream(struct odb_transaction *transaction,
+					struct odb_write_stream *stream,
+					size_t len, struct object_id *oid)
+{
+	return transaction->write_object_stream(transaction, stream, len, oid);
+}
diff --git a/odb/transaction.h b/odb/transaction.h
index a56e392f21..584e8de36e 100644
--- a/odb/transaction.h
+++ b/odb/transaction.h
@@ -12,14 +12,24 @@
  *
  * Each ODB source is expected to implement its own transaction handling.
  */
-struct odb_transaction;
-typedef void (*odb_transaction_commit_fn)(struct odb_transaction *transaction);
 struct odb_transaction {
 	/* The ODB source the transaction is opened against. */
 	struct odb_source *source;
 
 	/* The ODB source specific callback invoked to commit a transaction. */
-	odb_transaction_commit_fn commit;
+	void (*commit)(struct odb_transaction *transaction);
+
+	/*
+	 * This callback is expected to write the given object stream into
+	 * the ODB transaction.
+	 *
+	 * The resulting object ID shall be written into the out pointer. The
+	 * callback is expected to return 0 on success, a negative error code
+	 * otherwise.
+	 */
+	int (*write_object_stream)(struct odb_transaction *transaction,
+				   struct odb_write_stream *stream, size_t len,
+				   struct object_id *oid);
 };
 
 /*
@@ -35,4 +45,13 @@ struct odb_transaction *odb_transaction_begin(struct object_database *odb);
  */
 void odb_transaction_commit(struct odb_transaction *transaction);
 
+/*
+ * Writes the object in the provided stream into the transaction. The resulting
+ * object ID is written into the out pointer. Returns 0 on success, a negative
+ * error code otherwise.
+ */
+int odb_transaction_write_object_stream(struct odb_transaction *transaction,
+					struct odb_write_stream *stream,
+					size_t len, struct object_id *oid);
+
 #endif
-- 
2.53.0.381.g628a66ccf6