From b65528360f1153c2f912d272cce18abe56e25562 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?=
 <avarab@gmail.com>
Date: Wed, 5 May 2021 14:33:28 +0200
Subject: [PATCH 1/5] streaming.c: avoid forward declarations
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Change code added in 46bf043807c (streaming: a new API to read from
the object store, 2011-05-11) to avoid forward declarations of the
functions it uses. We can instead move this code to the bottom of the
file, and thus avoid the open_method_decl() calls.

Aside from the addition of the "static helpers[...]" comment being
added here, and the removal of the forward declarations this is a
move-only change.

The style of the added "static helpers[...]"  comment isn't in line
with our usual coding style, but is consistent with several other
comments used in this file, so let's use that style consistently here.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 streaming.c | 171 +++++++++++++++++++++++++---------------------------
 1 file changed, 83 insertions(+), 88 deletions(-)

diff --git a/streaming.c b/streaming.c
index 800f07a52c..b0d439e47a 100644
--- a/streaming.c
+++ b/streaming.c
@@ -42,20 +42,6 @@ struct stream_vtbl {
 	ssize_t read_istream_ ##name \
 	(struct git_istream *st, char *buf, size_t sz)
 
-/* forward declaration */
-static open_method_decl(incore);
-static open_method_decl(loose);
-static open_method_decl(pack_non_delta);
-static struct git_istream *attach_stream_filter(struct git_istream *st,
-						struct stream_filter *filter);
-
-
-static open_istream_fn open_istream_tbl[] = {
-	open_istream_incore,
-	open_istream_loose,
-	open_istream_pack_non_delta,
-};
-
 #define FILTER_BUFFER (1024*16)
 
 struct filtered_istream {
@@ -97,80 +83,6 @@ struct git_istream {
 	} u;
 };
 
-int close_istream(struct git_istream *st)
-{
-	int r = st->vtbl->close(st);
-	free(st);
-	return r;
-}
-
-ssize_t read_istream(struct git_istream *st, void *buf, size_t sz)
-{
-	return st->vtbl->read(st, buf, sz);
-}
-
-static enum input_source istream_source(struct repository *r,
-					const struct object_id *oid,
-					enum object_type *type,
-					struct object_info *oi)
-{
-	unsigned long size;
-	int status;
-
-	oi->typep = type;
-	oi->sizep = &size;
-	status = oid_object_info_extended(r, oid, oi, 0);
-	if (status < 0)
-		return stream_error;
-
-	switch (oi->whence) {
-	case OI_LOOSE:
-		return loose;
-	case OI_PACKED:
-		if (!oi->u.packed.is_delta && big_file_threshold < size)
-			return pack_non_delta;
-		/* fallthru */
-	default:
-		return incore;
-	}
-}
-
-struct git_istream *open_istream(struct repository *r,
-				 const struct object_id *oid,
-				 enum object_type *type,
-				 unsigned long *size,
-				 struct stream_filter *filter)
-{
-	struct git_istream *st;
-	struct object_info oi = OBJECT_INFO_INIT;
-	const struct object_id *real = lookup_replace_object(r, oid);
-	enum input_source src = istream_source(r, real, type, &oi);
-
-	if (src < 0)
-		return NULL;
-
-	st = xmalloc(sizeof(*st));
-	if (open_istream_tbl[src](st, r, &oi, real, type)) {
-		if (open_istream_incore(st, r, &oi, real, type)) {
-			free(st);
-			return NULL;
-		}
-	}
-	if (filter) {
-		/* Add "&& !is_null_stream_filter(filter)" for performance */
-		struct git_istream *nst = attach_stream_filter(st, filter);
-		if (!nst) {
-			close_istream(st);
-			return NULL;
-		}
-		st = nst;
-	}
-
-	*size = st->size;
-	return st;
-}
-
-
 /*****************************************************************
  *
  * Common helpers
@@ -508,11 +420,94 @@ static open_method_decl(incore)
 	return st->u.incore.buf ? 0 : -1;
 }
 
+/*****************************************************************************
+ * static helpers variables and functions for users of streaming interface
+ *****************************************************************************/
+
+static open_istream_fn open_istream_tbl[] = {
+	open_istream_incore,
+	open_istream_loose,
+	open_istream_pack_non_delta,
+};
+
+static enum input_source istream_source(struct repository *r,
+					const struct object_id *oid,
+					enum object_type *type,
+					struct object_info *oi)
+{
+	unsigned long size;
+	int status;
+
+	oi->typep = type;
+	oi->sizep = &size;
+	status = oid_object_info_extended(r, oid, oi, 0);
+	if (status < 0)
+		return stream_error;
+
+	switch (oi->whence) {
+	case OI_LOOSE:
+		return loose;
+	case OI_PACKED:
+		if (!oi->u.packed.is_delta && big_file_threshold < size)
+			return pack_non_delta;
+		/* fallthru */
+	default:
+		return incore;
+	}
+}
+
 
 /****************************************************************
  * Users of streaming interface
  ****************************************************************/
 
+int close_istream(struct git_istream *st)
+{
+	int r = st->vtbl->close(st);
+	free(st);
+	return r;
+}
+
+ssize_t read_istream(struct git_istream *st, void *buf, size_t sz)
+{
+	return st->vtbl->read(st, buf, sz);
+}
+
+struct git_istream *open_istream(struct repository *r,
+				 const struct object_id *oid,
+				 enum object_type *type,
+				 unsigned long *size,
+				 struct stream_filter *filter)
+{
+	struct git_istream *st;
+	struct object_info oi = OBJECT_INFO_INIT;
+	const struct object_id *real = lookup_replace_object(r, oid);
+	enum input_source src = istream_source(r, real, type, &oi);
+
+	if (src < 0)
+		return NULL;
+
+	st = xmalloc(sizeof(*st));
+	if (open_istream_tbl[src](st, r, &oi, real, type)) {
+		if (open_istream_incore(st, r, &oi, real, type)) {
+			free(st);
+			return NULL;
+		}
+	}
+	if (filter) {
+		/* Add "&& !is_null_stream_filter(filter)" for performance */
+		struct git_istream *nst = attach_stream_filter(st, filter);
+		if (!nst) {
+			close_istream(st);
+			return NULL;
+		}
+		st = nst;
+	}
+
+	*size = st->size;
+	return st;
+}
+
 int stream_blob_to_fd(int fd, const struct object_id *oid, struct stream_filter *filter,
 		      int can_seek)
 {

From 0d9af06e36d2e88e5e370c23e876a835fcf8b7ce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?=
 <avarab@gmail.com>
Date: Wed, 5 May 2021 14:33:29 +0200
Subject: [PATCH 2/5] streaming.c: remove enum/function/vtbl indirection
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Remove the indirection of discovering a function pointer to use via an
enum and virtual table. This refactors code added in
46bf043807c (streaming: a new API to read from the object store,
2011-05-11).

We can instead simply return an "open_istream_fn" for use from the
"istream_source()" selector function directly. This allows us to get
rid of the "incore", "loose" and "pack_non_delta" enum
variables. We'll return the functions instead.

The "stream_error" variable in that enum can likewise go in favor of
returning NULL, which is what the open_istream() was doing when it got
that value anyway.

We can thus remove the entire enum, and the "open_istream_tbl" virtual
table that (indirectly) referenced it.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 streaming.c | 36 +++++++++++-------------------------
 1 file changed, 11 insertions(+), 25 deletions(-)

diff --git a/streaming.c b/streaming.c
index b0d439e47a..628369519b 100644
--- a/streaming.c
+++ b/streaming.c
@@ -8,13 +8,6 @@
 #include "replace-object.h"
 #include "packfile.h"
 
-enum input_source {
-	stream_error = -1,
-	incore = 0,
-	loose = 1,
-	pack_non_delta = 2
-};
-
 typedef int (*open_istream_fn)(struct git_istream *,
 			       struct repository *,
 			       struct object_info *,
@@ -424,16 +417,10 @@ static open_method_decl(incore)
  * static helpers variables and functions for users of streaming interface
  *****************************************************************************/
 
-static open_istream_fn open_istream_tbl[] = {
-	open_istream_incore,
-	open_istream_loose,
-	open_istream_pack_non_delta,
-};
-
-static enum input_source istream_source(struct repository *r,
-					const struct object_id *oid,
-					enum object_type *type,
-					struct object_info *oi)
+static open_istream_fn istream_source(struct repository *r,
+				      const struct object_id *oid,
+				      enum object_type *type,
+				      struct object_info *oi)
 {
 	unsigned long size;
 	int status;
@@ -442,21 +429,20 @@ static enum input_source istream_source(struct repository *r,
 	oi->sizep = &size;
 	status = oid_object_info_extended(r, oid, oi, 0);
 	if (status < 0)
-		return stream_error;
+		return NULL;
 
 	switch (oi->whence) {
 	case OI_LOOSE:
-		return loose;
+		return open_istream_loose;
 	case OI_PACKED:
 		if (!oi->u.packed.is_delta && big_file_threshold < size)
-			return pack_non_delta;
+			return open_istream_pack_non_delta;
 		/* fallthru */
 	default:
-		return incore;
+		return open_istream_incore;
 	}
 }
 
-
 /****************************************************************
  * Users of streaming interface
  ****************************************************************/
@@ -482,13 +468,13 @@ struct git_istream *open_istream(struct repository *r,
 	struct git_istream *st;
 	struct object_info oi = OBJECT_INFO_INIT;
 	const struct object_id *real = lookup_replace_object(r, oid);
-	enum input_source src = istream_source(r, real, type, &oi);
+	open_istream_fn open_fn = istream_source(r, real, type, &oi);
 
-	if (src < 0)
+	if (!open_fn)
 		return NULL;
 
 	st = xmalloc(sizeof(*st));
-	if (open_istream_tbl[src](st, r, &oi, real, type)) {
+	if (open_fn(st, r, &oi, real, type)) {
 		if (open_istream_incore(st, r, &oi, real, type)) {
 			free(st);
 			return NULL;

From bc062ad001f31a466d9aa3987005e34b3d9bbff4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?=
 <avarab@gmail.com>
Date: Wed, 5 May 2021 14:33:30 +0200
Subject: [PATCH 3/5] streaming.c: remove {open,close,read}_method_decl()
 macros
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Remove the {open,close,read}_method_decl() macros added in
46bf043807c (streaming: a new API to read from the object store,
2011-05-11) in favor of inlining the definition of the arguments of
these functions.

Since we'll end up using them via the "{open,close,read}_istream_fn"
types we don't gain anything in the way of compiler checking by using
these macros, and as of preceding commits we no longer need to declare
these argument lists twice. So declaring them at a distance just
serves to make the code less readable.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 streaming.c | 47 ++++++++++++++++++++++-------------------------
 1 file changed, 22 insertions(+), 25 deletions(-)

diff --git a/streaming.c b/streaming.c
index 628369519b..7e039df388 100644
--- a/streaming.c
+++ b/streaming.c
@@ -21,20 +21,6 @@ struct stream_vtbl {
 	read_istream_fn read;
 };
 
-#define open_method_decl(name) \
-	int open_istream_ ##name \
-	(struct git_istream *st, struct repository *r, \
-	 struct object_info *oi, const struct object_id *oid, \
-	 enum object_type *type)
-
-#define close_method_decl(name) \
-	int close_istream_ ##name \
-	(struct git_istream *st)
-
-#define read_method_decl(name) \
-	ssize_t read_istream_ ##name \
-	(struct git_istream *st, char *buf, size_t sz)
-
 #define FILTER_BUFFER (1024*16)
 
 struct filtered_istream {
@@ -95,13 +81,14 @@ static void close_deflated_stream(struct git_istream *st)
  *
  *****************************************************************/
 
-static close_method_decl(filtered)
+static int close_istream_filtered(struct git_istream *st)
 {
 	free_stream_filter(st->u.filtered.filter);
 	return close_istream(st->u.filtered.upstream);
 }
 
-static read_method_decl(filtered)
+static ssize_t read_istream_filtered(struct git_istream *st, char *buf,
+				     size_t sz)
 {
 	struct filtered_istream *fs = &(st->u.filtered);
 	size_t filled = 0;
@@ -187,7 +174,7 @@ static struct git_istream *attach_stream_filter(struct git_istream *st,
  *
  *****************************************************************/
 
-static read_method_decl(loose)
+static ssize_t read_istream_loose(struct git_istream *st, char *buf, size_t sz)
 {
 	size_t total_read = 0;
 
@@ -232,7 +219,7 @@ static read_method_decl(loose)
 	return total_read;
 }
 
-static close_method_decl(loose)
+static int close_istream_loose(struct git_istream *st)
 {
 	close_deflated_stream(st);
 	munmap(st->u.loose.mapped, st->u.loose.mapsize);
@@ -244,7 +231,10 @@ static struct stream_vtbl loose_vtbl = {
 	read_istream_loose,
 };
 
-static open_method_decl(loose)
+static int open_istream_loose(struct git_istream *st, struct repository *r,
+			      struct object_info *oi,
+			      const struct object_id *oid,
+			      enum object_type *type)
 {
 	st->u.loose.mapped = map_loose_object(r, oid, &st->u.loose.mapsize);
 	if (!st->u.loose.mapped)
@@ -275,7 +265,8 @@ static open_method_decl(loose)
  *
  *****************************************************************/
 
-static read_method_decl(pack_non_delta)
+static ssize_t read_istream_pack_non_delta(struct git_istream *st, char *buf,
+					   size_t sz)
 {
 	size_t total_read = 0;
 
@@ -333,7 +324,7 @@ static read_method_decl(pack_non_delta)
 	return total_read;
 }
 
-static close_method_decl(pack_non_delta)
+static int close_istream_pack_non_delta(struct git_istream *st)
 {
 	close_deflated_stream(st);
 	return 0;
@@ -344,7 +335,11 @@ static struct stream_vtbl pack_non_delta_vtbl = {
 	read_istream_pack_non_delta,
 };
 
-static open_method_decl(pack_non_delta)
+static int open_istream_pack_non_delta(struct git_istream *st,
+				       struct repository *r,
+				       struct object_info *oi,
+				       const struct object_id *oid,
+				       enum object_type *type)
 {
 	struct pack_window *window;
 	enum object_type in_pack_type;
@@ -379,13 +374,13 @@ static open_method_decl(pack_non_delta)
  *
  *****************************************************************/
 
-static close_method_decl(incore)
+static int close_istream_incore(struct git_istream *st)
 {
 	free(st->u.incore.buf);
 	return 0;
 }
 
-static read_method_decl(incore)
+static ssize_t read_istream_incore(struct git_istream *st, char *buf, size_t sz)
 {
 	size_t read_size = sz;
 	size_t remainder = st->size - st->u.incore.read_ptr;
@@ -404,7 +399,9 @@ static struct stream_vtbl incore_vtbl = {
 	read_istream_incore,
 };
 
-static open_method_decl(incore)
+static int open_istream_incore(struct git_istream *st, struct repository *r,
+			   struct object_info *oi, const struct object_id *oid,
+			   enum object_type *type)
 {
 	st->u.incore.buf = read_object_file_extended(r, oid, type, &st->size, 0);
 	st->u.incore.read_ptr = 0;

From de94c0eace41c9d93f6c2c97e98797afabb5932e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?=
 <avarab@gmail.com>
Date: Wed, 5 May 2021 14:33:31 +0200
Subject: [PATCH 4/5] streaming.c: stop passing around "object_info *" to
 open()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Change the streaming interface to stop passing around the "struct
object_info" the open() functions.

As seen in 7ef2d9a2604 (streaming: read non-delta incrementally from a
pack, 2011-05-13) which introduced the "st->u.in_pack" assignments
being changed here only the open_istream_pack_non_delta() path need
these.

So let's instead do this when preparing the selected callback in the
istream_source() function. This might also allow the compiler to
reduce the lifetime of the "oi" variable, as we've moved it from
"git_istream()" to "istream_source()".

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 streaming.c | 42 ++++++++++++++++++++----------------------
 1 file changed, 20 insertions(+), 22 deletions(-)

diff --git a/streaming.c b/streaming.c
index 7e039df388..f6059ee828 100644
--- a/streaming.c
+++ b/streaming.c
@@ -10,7 +10,6 @@
 
 typedef int (*open_istream_fn)(struct git_istream *,
 			       struct repository *,
-			       struct object_info *,
 			       const struct object_id *,
 			       enum object_type *);
 typedef int (*close_istream_fn)(struct git_istream *);
@@ -232,7 +231,6 @@ static struct stream_vtbl loose_vtbl = {
 };
 
 static int open_istream_loose(struct git_istream *st, struct repository *r,
-			      struct object_info *oi,
 			      const struct object_id *oid,
 			      enum object_type *type)
 {
@@ -337,15 +335,12 @@ static struct stream_vtbl pack_non_delta_vtbl = {
 
 static int open_istream_pack_non_delta(struct git_istream *st,
 				       struct repository *r,
-				       struct object_info *oi,
 				       const struct object_id *oid,
 				       enum object_type *type)
 {
 	struct pack_window *window;
 	enum object_type in_pack_type;
 
-	st->u.in_pack.pack = oi->u.packed.pack;
-	st->u.in_pack.pos = oi->u.packed.offset;
 	window = NULL;
 
 	in_pack_type = unpack_object_header(st->u.in_pack.pack,
@@ -400,8 +395,7 @@ static struct stream_vtbl incore_vtbl = {
 };
 
 static int open_istream_incore(struct git_istream *st, struct repository *r,
-			   struct object_info *oi, const struct object_id *oid,
-			   enum object_type *type)
+			       const struct object_id *oid, enum object_type *type)
 {
 	st->u.incore.buf = read_object_file_extended(r, oid, type, &st->size, 0);
 	st->u.incore.read_ptr = 0;
@@ -414,26 +408,30 @@ static int open_istream_incore(struct git_istream *st, struct repository *r,
  * static helpers variables and functions for users of streaming interface
  *****************************************************************************/
 
-static open_istream_fn istream_source(struct repository *r,
+static open_istream_fn istream_source(struct git_istream *st,
+				      struct repository *r,
 				      const struct object_id *oid,
-				      enum object_type *type,
-				      struct object_info *oi)
+				      enum object_type *type)
 {
 	unsigned long size;
 	int status;
+	struct object_info oi = OBJECT_INFO_INIT;
 
-	oi->typep = type;
-	oi->sizep = &size;
-	status = oid_object_info_extended(r, oid, oi, 0);
+	oi.typep = type;
+	oi.sizep = &size;
+	status = oid_object_info_extended(r, oid, &oi, 0);
 	if (status < 0)
 		return NULL;
 
-	switch (oi->whence) {
+	switch (oi.whence) {
 	case OI_LOOSE:
 		return open_istream_loose;
 	case OI_PACKED:
-		if (!oi->u.packed.is_delta && big_file_threshold < size)
+		if (!oi.u.packed.is_delta && big_file_threshold < size) {
+			st->u.in_pack.pack = oi.u.packed.pack;
+			st->u.in_pack.pos = oi.u.packed.offset;
 			return open_istream_pack_non_delta;
+		}
 		/* fallthru */
 	default:
 		return open_istream_incore;
@@ -462,17 +460,17 @@ struct git_istream *open_istream(struct repository *r,
 				 unsigned long *size,
 				 struct stream_filter *filter)
 {
-	struct git_istream *st;
-	struct object_info oi = OBJECT_INFO_INIT;
+	struct git_istream *st = xmalloc(sizeof(*st));
 	const struct object_id *real = lookup_replace_object(r, oid);
-	open_istream_fn open_fn = istream_source(r, real, type, &oi);
+	open_istream_fn open_fn = istream_source(st, r, real, type);
 
-	if (!open_fn)
+	if (!open_fn) {
+		free(st);
 		return NULL;
+	}
 
-	st = xmalloc(sizeof(*st));
-	if (open_fn(st, r, &oi, real, type)) {
-		if (open_istream_incore(st, r, &oi, real, type)) {
+	if (open_fn(st, r, real, type)) {
+		if (open_istream_incore(st, r, real, type)) {
 			free(st);
 			return NULL;
 		}

From d4e2d15a8b028352df480e7be9f1864f59c16299 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?=
 <avarab@gmail.com>
Date: Wed, 5 May 2021 14:33:32 +0200
Subject: [PATCH 5/5] streaming.c: move {open,close,read} from vtable to
 "struct git_istream"
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Move the definition of the structure around the open/close/read
functions introduced in 46bf043807c (streaming: a new API to read from
the object store, 2011-05-11) to instead populate "close" and "read"
members in the "struct git_istream".

This gets us rid of an extra pointer deference, and I think makes more
sense. The "close" and "read" functions are the primary interface to
the stream itself.

Let's also populate a "open" callback in the same struct. That's now
used by open_istream() after istream_source() decides what "open"
function should be used. This isn't needed to get rid of the
"stream_vtbl" variables, but makes sense for consistency.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 streaming.c | 72 +++++++++++++++++++++--------------------------------
 1 file changed, 29 insertions(+), 43 deletions(-)

diff --git a/streaming.c b/streaming.c
index f6059ee828..5f480ad50c 100644
--- a/streaming.c
+++ b/streaming.c
@@ -15,11 +15,6 @@ typedef int (*open_istream_fn)(struct git_istream *,
 typedef int (*close_istream_fn)(struct git_istream *);
 typedef ssize_t (*read_istream_fn)(struct git_istream *, char *, size_t);
 
-struct stream_vtbl {
-	close_istream_fn close;
-	read_istream_fn read;
-};
-
 #define FILTER_BUFFER (1024*16)
 
 struct filtered_istream {
@@ -33,7 +28,10 @@ struct filtered_istream {
 };
 
 struct git_istream {
-	const struct stream_vtbl *vtbl;
+	open_istream_fn open;
+	close_istream_fn close;
+	read_istream_fn read;
+
 	unsigned long size; /* inflated size of full object */
 	git_zstream z;
 	enum { z_unused, z_used, z_done, z_error } z_state;
@@ -146,18 +144,14 @@ static ssize_t read_istream_filtered(struct git_istream *st, char *buf,
 	return filled;
 }
 
-static struct stream_vtbl filtered_vtbl = {
-	close_istream_filtered,
-	read_istream_filtered,
-};
-
 static struct git_istream *attach_stream_filter(struct git_istream *st,
 						struct stream_filter *filter)
 {
 	struct git_istream *ifs = xmalloc(sizeof(*ifs));
 	struct filtered_istream *fs = &(ifs->u.filtered);
 
-	ifs->vtbl = &filtered_vtbl;
+	ifs->close = close_istream_filtered;
+	ifs->read = read_istream_filtered;
 	fs->upstream = st;
 	fs->filter = filter;
 	fs->i_end = fs->i_ptr = 0;
@@ -225,11 +219,6 @@ static int close_istream_loose(struct git_istream *st)
 	return 0;
 }
 
-static struct stream_vtbl loose_vtbl = {
-	close_istream_loose,
-	read_istream_loose,
-};
-
 static int open_istream_loose(struct git_istream *st, struct repository *r,
 			      const struct object_id *oid,
 			      enum object_type *type)
@@ -251,8 +240,9 @@ static int open_istream_loose(struct git_istream *st, struct repository *r,
 	st->u.loose.hdr_used = strlen(st->u.loose.hdr) + 1;
 	st->u.loose.hdr_avail = st->z.total_out;
 	st->z_state = z_used;
+	st->close = close_istream_loose;
+	st->read = read_istream_loose;
 
-	st->vtbl = &loose_vtbl;
 	return 0;
 }
 
@@ -328,11 +318,6 @@ static int close_istream_pack_non_delta(struct git_istream *st)
 	return 0;
 }
 
-static struct stream_vtbl pack_non_delta_vtbl = {
-	close_istream_pack_non_delta,
-	read_istream_pack_non_delta,
-};
-
 static int open_istream_pack_non_delta(struct git_istream *st,
 				       struct repository *r,
 				       const struct object_id *oid,
@@ -358,7 +343,9 @@ static int open_istream_pack_non_delta(struct git_istream *st,
 		break;
 	}
 	st->z_state = z_unused;
-	st->vtbl = &pack_non_delta_vtbl;
+	st->close = close_istream_pack_non_delta;
+	st->read = read_istream_pack_non_delta;
+
 	return 0;
 }
 
@@ -389,17 +376,13 @@ static ssize_t read_istream_incore(struct git_istream *st, char *buf, size_t sz)
 	return read_size;
 }
 
-static struct stream_vtbl incore_vtbl = {
-	close_istream_incore,
-	read_istream_incore,
-};
-
 static int open_istream_incore(struct git_istream *st, struct repository *r,
 			       const struct object_id *oid, enum object_type *type)
 {
 	st->u.incore.buf = read_object_file_extended(r, oid, type, &st->size, 0);
 	st->u.incore.read_ptr = 0;
-	st->vtbl = &incore_vtbl;
+	st->close = close_istream_incore;
+	st->read = read_istream_incore;
 
 	return st->u.incore.buf ? 0 : -1;
 }
@@ -408,10 +391,10 @@ static int open_istream_incore(struct git_istream *st, struct repository *r,
  * static helpers variables and functions for users of streaming interface
  *****************************************************************************/
 
-static open_istream_fn istream_source(struct git_istream *st,
-				      struct repository *r,
-				      const struct object_id *oid,
-				      enum object_type *type)
+static int istream_source(struct git_istream *st,
+			  struct repository *r,
+			  const struct object_id *oid,
+			  enum object_type *type)
 {
 	unsigned long size;
 	int status;
@@ -421,20 +404,23 @@ static open_istream_fn istream_source(struct git_istream *st,
 	oi.sizep = &size;
 	status = oid_object_info_extended(r, oid, &oi, 0);
 	if (status < 0)
-		return NULL;
+		return status;
 
 	switch (oi.whence) {
 	case OI_LOOSE:
-		return open_istream_loose;
+		st->open = open_istream_loose;
+		return 0;
 	case OI_PACKED:
 		if (!oi.u.packed.is_delta && big_file_threshold < size) {
 			st->u.in_pack.pack = oi.u.packed.pack;
 			st->u.in_pack.pos = oi.u.packed.offset;
-			return open_istream_pack_non_delta;
+			st->open = open_istream_pack_non_delta;
+			return 0;
 		}
 		/* fallthru */
 	default:
-		return open_istream_incore;
+		st->open = open_istream_incore;
+		return 0;
 	}
 }
 
@@ -444,14 +430,14 @@ static open_istream_fn istream_source(struct git_istream *st,
 
 int close_istream(struct git_istream *st)
 {
-	int r = st->vtbl->close(st);
+	int r = st->close(st);
 	free(st);
 	return r;
 }
 
 ssize_t read_istream(struct git_istream *st, void *buf, size_t sz)
 {
-	return st->vtbl->read(st, buf, sz);
+	return st->read(st, buf, sz);
 }
 
 struct git_istream *open_istream(struct repository *r,
@@ -462,14 +448,14 @@ struct git_istream *open_istream(struct repository *r,
 {
 	struct git_istream *st = xmalloc(sizeof(*st));
 	const struct object_id *real = lookup_replace_object(r, oid);
-	open_istream_fn open_fn = istream_source(st, r, real, type);
+	int ret = istream_source(st, r, real, type);
 
-	if (!open_fn) {
+	if (ret) {
 		free(st);
 		return NULL;
 	}
 
-	if (open_fn(st, r, real, type)) {
+	if (st->open(st, r, real, type)) {
 		if (open_istream_incore(st, r, real, type)) {
 			free(st);
 			return NULL;