[PATCH 15/30] packed-backend: create abstraction for writing refs

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <derrickstolee@github.com>

The packed-refs file is a plaintext file format that starts with a
header line, then each ref is given as one or two lines (two if there is
a peeled value). These lines are written as part of a sequence of
updates which are merged with the existing ref iterator in
merge_iterator_and_updates(). That method is currently tied directly to
write_packed_entry_v1().

When creating a new version of the packed-file format, it would be
valuable to use this merging logic in an identical way. Create a new
function pointer type, write_ref_fn, and use that type in
merge_iterator_and_updates().

Notably, the function pointer type no longer depends on a FILE pointer,
but instead takes an arbitrary "void *write_data" parameter. This
flexibility will be critical in the future, since the planned v2 format
will use the chunk-format API and need a more complicated structure than
the output FILE.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 refs/packed-backend.c   | 26 +++++++++++++++-----------
 refs/packed-backend.h   | 16 ++++++++++++++--
 refs/packed-format-v1.c |  7 +++++--
 3 files changed, 34 insertions(+), 15 deletions(-)

diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 0dff78f02c8..7ed9475812c 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -535,10 +535,11 @@ static void add_write_error(struct packed_ref_store *refs, struct strbuf *err)
 		    get_tempfile_path(refs->tempfile), strerror(errno));
 }
 
-static int merge_iterator_and_updates(struct packed_ref_store *refs,
-				      struct string_list *updates,
-				      struct strbuf *err,
-				      FILE *out)
+int merge_iterator_and_updates(struct packed_ref_store *refs,
+			       struct string_list *updates,
+			       struct strbuf *err,
+			       write_ref_fn write_fn,
+			       void *write_data)
 {
 	struct ref_iterator *iter = NULL;
 	int ok, i;
@@ -634,9 +635,10 @@ static int merge_iterator_and_updates(struct packed_ref_store *refs,
 			struct object_id peeled;
 			int peel_error = ref_iterator_peel(iter, &peeled);
 
-			if (write_packed_entry_v1(out, iter->refname,
-						  iter->oid,
-						  peel_error ? NULL : &peeled)) {
+			if (write_fn(iter->refname,
+				     iter->oid,
+				     peel_error ? NULL : &peeled,
+				     write_data)) {
 				add_write_error(refs, err);
 				goto error;
 			}
@@ -657,9 +659,10 @@ static int merge_iterator_and_updates(struct packed_ref_store *refs,
 			int peel_error = peel_object(&update->new_oid,
 						     &peeled);
 
-			if (write_packed_entry_v1(out, update->refname,
-						  &update->new_oid,
-						  peel_error ? NULL : &peeled)) {
+			if (write_fn(update->refname,
+				     &update->new_oid,
+				     peel_error ? NULL : &peeled,
+				     write_data)) {
 				add_write_error(refs, err);
 				goto error;
 			}
@@ -725,7 +728,8 @@ static int write_with_updates(struct packed_ref_store *refs,
 		goto error;
 	}
 
-	ok = merge_iterator_and_updates(refs, updates, err, out);
+	ok = merge_iterator_and_updates(refs, updates, err,
+					write_packed_entry_v1, out);
 
 	if (ok != ITER_DONE) {
 		strbuf_addstr(err, "unable to write packed-refs file: "
diff --git a/refs/packed-backend.h b/refs/packed-backend.h
index 143ed6d4f6c..b6908bb002c 100644
--- a/refs/packed-backend.h
+++ b/refs/packed-backend.h
@@ -192,6 +192,17 @@ struct packed_ref_iterator {
 	unsigned int flags;
 };
 
+typedef int (*write_ref_fn)(const char *refname,
+			    const struct object_id *oid,
+			    const struct object_id *peeled,
+			    void *write_data);
+
+int merge_iterator_and_updates(struct packed_ref_store *refs,
+			       struct string_list *updates,
+			       struct strbuf *err,
+			       write_ref_fn write_fn,
+			       void *write_data);
+
 /**
  * Parse the buffer at the given snapshot to verify that it is a
  * packed-refs file in version 1 format. Update the snapshot->peeled
@@ -227,8 +238,9 @@ void verify_buffer_safe_v1(struct snapshot *snapshot);
 void sort_snapshot_v1(struct snapshot *snapshot);
 int write_packed_file_header_v1(FILE *out);
 int next_record_v1(struct packed_ref_iterator *iter);
-int write_packed_entry_v1(FILE *fh, const char *refname,
+int write_packed_entry_v1(const char *refname,
 			  const struct object_id *oid,
-			  const struct object_id *peeled);
+			  const struct object_id *peeled,
+			  void *write_data);
 
 #endif /* REFS_PACKED_BACKEND_H */
diff --git a/refs/packed-format-v1.c b/refs/packed-format-v1.c
index ef9e6618c89..2d071567c02 100644
--- a/refs/packed-format-v1.c
+++ b/refs/packed-format-v1.c
@@ -441,10 +441,13 @@ int write_packed_file_header_v1(FILE *out)
  * error, return a nonzero value and leave errno set at the value left
  * by the failing call to `fprintf()`.
  */
-int write_packed_entry_v1(FILE *fh, const char *refname,
+int write_packed_entry_v1(const char *refname,
 			  const struct object_id *oid,
-			  const struct object_id *peeled)
+			  const struct object_id *peeled,
+			  void *write_data)
 {
+	FILE *fh = write_data;
+
 	if (fprintf(fh, "%s %s\n", oid_to_hex(oid), refname) < 0 ||
 	    (peeled && fprintf(fh, "^%s\n", oid_to_hex(peeled)) < 0))
 		return -1;
-- 
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