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

From: Patrick Steinhardt <[email-masked]>
Date: Tue, 31 Mar 2026 09:48:53 +0200

On Mon, Mar 30, 2026 at 10:38:35PM -0500, Justin Tobler wrote:
> 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;
>  }

I was originally expecting the upcast to `odb_transaction_files` in
`index_blob_packfile_transaction()` to go away in this last step, but
that of course doesn't make much sense as it now _becomes_ the
implementation of `write_object_stream()`.

But should we rename to `odb_transaction_files_write_object_stream()`?

> 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.

Should we note that for now, the expectation is to always write a blob?

Patrick