[PATCH v2 3/7] odb: update `struct odb_write_stream` read() callback

[Justin Tobler <jltobler@gmail.com>]

The `read()` callback used by `struct odb_write_stream` currently
returns a pointer to an internal buffer along with the number of bytes
read. This makes buffer ownership unclear and provides no way to report
errors.

Update the interface to instead require the caller to provide a buffer,
and have the callback return the number of bytes written to it or a
negative value on error. Call sites are updated accordingly.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
---
 builtin/unpack-objects.c | 19 +++++++------------
 object-file.c            | 13 ++++++++++---
 odb.h                    |  2 +-
 3 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index bc9b1e047e..420619e2cb 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -360,24 +360,21 @@ static void unpack_non_delta_entry(enum object_type type, unsigned long size,
 
 struct input_zstream_data {
 	git_zstream *zstream;
-	unsigned char buf[8192];
 	int status;
 };
 
-static const void *feed_input_zstream(struct odb_write_stream *in_stream,
-				      unsigned long *readlen)
+static ssize_t feed_input_zstream(struct odb_write_stream *in_stream,
+				  unsigned char *buf, size_t buf_len)
 {
 	struct input_zstream_data *data = in_stream->data;
 	git_zstream *zstream = data->zstream;
 	void *in = fill(1);
 
-	if (in_stream->is_finished) {
-		*readlen = 0;
-		return NULL;
-	}
+	if (in_stream->is_finished)
+		return 0;
 
-	zstream->next_out = data->buf;
-	zstream->avail_out = sizeof(data->buf);
+	zstream->next_out = buf;
+	zstream->avail_out = buf_len;
 	zstream->next_in = in;
 	zstream->avail_in = len;
 
@@ -385,9 +382,7 @@ static const void *feed_input_zstream(struct odb_write_stream *in_stream,
 
 	in_stream->is_finished = data->status != Z_OK;
 	use(len - zstream->avail_in);
-	*readlen = sizeof(data->buf) - zstream->avail_out;
-
-	return data->buf;
+	return buf_len - zstream->avail_out;
 }
 
 static void stream_blob(unsigned long size, unsigned nr)
diff --git a/object-file.c b/object-file.c
index bfbb632cf8..f3038756fc 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1066,6 +1066,7 @@ int odb_source_loose_write_stream(struct odb_source *source,
 	struct git_hash_ctx c, compat_c;
 	struct strbuf tmp_file = STRBUF_INIT;
 	struct strbuf filename = STRBUF_INIT;
+	unsigned char buf[8192];
 	int dirlen;
 	char hdr[MAX_HEADER_LEN];
 	int hdrlen;
@@ -1098,9 +1099,15 @@ int odb_source_loose_write_stream(struct odb_source *source,
 		unsigned char *in0 = stream.next_in;
 
 		if (!stream.avail_in && !in_stream->is_finished) {
-			const void *in = in_stream->read(in_stream, &stream.avail_in);
-			stream.next_in = (void *)in;
-			in0 = (unsigned char *)in;
+			ssize_t read_len = in_stream->read(in_stream, buf, sizeof(buf));
+			if (read_len < 0) {
+				err = -1;
+				goto cleanup;
+			}
+
+			stream.avail_in = read_len;
+			stream.next_in = buf;
+			in0 = buf;
 			/* All data has been read. */
 			if (in_stream->is_finished)
 				flush = 1;
diff --git a/odb.h b/odb.h
index ec5367b13e..91ec206eed 100644
--- a/odb.h
+++ b/odb.h
@@ -530,7 +530,7 @@ static inline int odb_write_object(struct object_database *odb,
 }
 
 struct odb_write_stream {
-	const void *(*read)(struct odb_write_stream *, unsigned long *len);
+	ssize_t (*read)(struct odb_write_stream *, unsigned char *, size_t len);
 	void *data;
 	int is_finished;
 };
-- 
2.53.0.381.g628a66ccf6