Merge pull request #4450 from libgit2/ethomson/odb_loose_readstream

Streaming read support for the loose ODB backend

8 files changed, 555 insertions, 225 deletions

diff --git a/include/git2/odb.h b/include/git2/odb.h
index b7dc0c5f3..006a75b7a 100644
--- a/include/git2/odb.h
+++ b/include/git2/odb.h
@@ -357,11 +357,18 @@ GIT_EXTERN(void) git_odb_stream_free(git_odb_stream *stream);
  * @see git_odb_stream
  *
  * @param out pointer where to store the stream
+ * @param len pointer where to store the length of the object
+ * @param type pointer where to store the type of the object
  * @param db object database where the stream will read from
  * @param oid oid of the object the stream will read from
  * @return 0 if the stream was created; error code otherwise
  */
-GIT_EXTERN(int) git_odb_open_rstream(git_odb_stream **out, git_odb *db, const git_oid *oid);
+GIT_EXTERN(int) git_odb_open_rstream(
+	git_odb_stream **out,
+	size_t *len,
+	git_otype *type,
+	git_odb *db,
+	const git_oid *oid);
 
 /**
  * Open a stream for writing a pack file to the ODB.
diff --git a/include/git2/sys/odb_backend.h b/include/git2/sys/odb_backend.h
index 9bcc50ddd..792f103fe 100644
--- a/include/git2/sys/odb_backend.h
+++ b/include/git2/sys/odb_backend.h
@@ -56,7 +56,8 @@ struct git_odb_backend {
 		git_odb_stream **, git_odb_backend *, git_off_t, git_otype);
 
 	int (* readstream)(
-		git_odb_stream **, git_odb_backend *, const git_oid *);
+		git_odb_stream **, size_t *, git_otype *,
+		git_odb_backend *, const git_oid *);
 
 	int (* exists)(
 		git_odb_backend *, const git_oid *);
diff --git a/src/odb.c b/src/odb.c
index c2b17fade..775cf90de 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -1396,7 +1396,12 @@ void git_odb_stream_free(git_odb_stream *stream)
 	stream->free(stream);
 }
 
-int git_odb_open_rstream(git_odb_stream **stream, git_odb *db, const git_oid *oid)
+int git_odb_open_rstream(
+	git_odb_stream **stream,
+	size_t *len,
+	git_otype *type,
+	git_odb *db,
+	const git_oid *oid)
 {
 	size_t i, reads = 0;
 	int error = GIT_ERROR;
@@ -1409,7 +1414,7 @@ int git_odb_open_rstream(git_odb_stream **stream, git_odb *db, const git_oid *oi
 
 		if (b->readstream != NULL) {
 			++reads;
-			error = b->readstream(stream, b, oid);
+			error = b->readstream(stream, len, type, b, oid);
 		}
 	}
 
diff --git a/src/odb_loose.c b/src/odb_loose.c
index 9900aae2a..7d77eed38 100644
--- a/src/odb_loose.c
+++ b/src/odb_loose.c
@@ -21,6 +21,9 @@
 #include "git2/odb_backend.h"
 #include "git2/types.h"
 
+/* maximum possible header length */
+#define MAX_HEADER_LEN 64
+
 typedef struct { /* object header data */
 	git_otype type; /* object type */
 	size_t	size; /* object size */
@@ -31,6 +34,15 @@ typedef struct {
 	git_filebuf fbuf;
 } loose_writestream;
 
+typedef struct {
+	git_odb_stream stream;
+	git_map map;
+	char start[MAX_HEADER_LEN];
+	size_t start_len;
+	size_t start_read;
+	git_zstream zstream;
+} loose_readstream;
+
 typedef struct loose_backend {
 	git_odb_backend parent;
 
@@ -92,32 +104,42 @@ static int object_mkdir(const git_buf *name, const loose_backend *be)
 		GIT_MKDIR_PATH | GIT_MKDIR_SKIP_LAST | GIT_MKDIR_VERIFY_DIR, NULL);
 }
 
-static size_t get_binary_object_header(obj_hdr *hdr, git_buf *obj)
+static int parse_header_packlike(
+	obj_hdr *out, size_t *out_len, const unsigned char *data, size_t len)
 {
 	unsigned long c;
-	unsigned char *data = (unsigned char *)obj->ptr;
 	size_t shift, size, used = 0;
 
-	if (git_buf_len(obj) == 0)
-		return 0;
+	if (len == 0)
+		goto on_error;
 
 	c = data[used++];
-	hdr->type = (c >> 4) & 7;
+	out->type = (c >> 4) & 7;
 
 	size = c & 15;
 	shift = 4;
 	while (c & 0x80) {
-		if (git_buf_len(obj) <= used)
-			return 0;
+		if (len <= used)
+			goto on_error;
+
 		if (sizeof(size_t) * 8 <= shift)
-			return 0;
+			goto on_error;
+
 		c = data[used++];
 		size += (c & 0x7f) << shift;
 		shift += 7;
 	}
-	hdr->size = size;
 
-	return used;
+	out->size = size;
+
+	if (out_len)
+		*out_len = used;
+
+	return 0;
+
+on_error:
+	giterr_set(GITERR_OBJECT, "failed to parse loose object: invalid header");
+	return -1;
 }
 
 static int parse_header(
@@ -173,107 +195,26 @@ on_error:
 	return -1;
 }
 
-/***********************************************************
- *
- * ZLIB RELATED FUNCTIONS
- *
- ***********************************************************/
-
-static void init_stream(z_stream *s, void *out, size_t len)
-{
-	memset(s, 0, sizeof(*s));
-	s->next_out = out;
-	s->avail_out = (uInt)len;
-}
-
-static void set_stream_input(z_stream *s, void *in, size_t len)
-{
-	s->next_in = in;
-	s->avail_in = (uInt)len;
-}
-
-static void set_stream_output(z_stream *s, void *out, size_t len)
-{
-	s->next_out = out;
-	s->avail_out = (uInt)len;
-}
-
-
-static int start_inflate(z_stream *s, git_buf *obj, void *out, size_t len)
-{
-	int status;
-
-	init_stream(s, out, len);
-	set_stream_input(s, obj->ptr, git_buf_len(obj));
-
-	if ((status = inflateInit(s)) < Z_OK)
-		return status;
-
-	return inflate(s, 0);
-}
-
-static void abort_inflate(z_stream *s)
-{
-	inflateEnd(s);
-}
-
-static int finish_inflate(z_stream *s)
-{
-	int status = Z_OK;
-
-	while (status == Z_OK)
-		status = inflate(s, Z_FINISH);
-
-	inflateEnd(s);
-
-	if ((status != Z_STREAM_END) || (s->avail_in != 0)) {
-		giterr_set(GITERR_ZLIB, "failed to finish zlib inflation; stream aborted prematurely");
-		return -1;
-	}
-
-	return 0;
-}
-
-static int is_zlib_compressed_data(unsigned char *data)
+static int is_zlib_compressed_data(unsigned char *data, size_t data_len)
 {
 	unsigned int w;
 
+	if (data_len < 2)
+		return 0;
+
 	w = ((unsigned int)(data[0]) << 8) + data[1];
 	return (data[0] & 0x8F) == 0x08 && !(w % 31);
 }
 
-static int inflate_buffer(void *in, size_t inlen, void *out, size_t outlen)
-{
-	z_stream zs;
-	int status = Z_OK;
-
-	memset(&zs, 0x0, sizeof(zs));
-
-	zs.next_out = out;
-	zs.avail_out = (uInt)outlen;
-
-	zs.next_in = in;
-	zs.avail_in = (uInt)inlen;
-
-	if (inflateInit(&zs) < Z_OK) {
-		giterr_set(GITERR_ZLIB, "failed to inflate buffer");
-		return -1;
-	}
-
-	while (status == Z_OK)
-		status = inflate(&zs, Z_FINISH);
-
-	inflateEnd(&zs);
-
-	if (status != Z_STREAM_END /* || zs.avail_in != 0 */ ||
-		zs.total_out != outlen)
-	{
-		giterr_set(GITERR_ZLIB, "failed to inflate buffer; stream aborted prematurely");
-		return -1;
-	}
+/***********************************************************
+ *
+ * ODB OBJECT READING & WRITING
+ *
+ * Backend for the public API; read headers and full objects
+ * from the ODB. Write raw data to the ODB.
+ *
+ ***********************************************************/
 
-	return 0;
-}
 
 /*
  * At one point, there was a loose object format that was intended to
@@ -281,56 +222,62 @@ static int inflate_buffer(void *in, size_t inlen, void *out, size_t outlen)
  * of loose object data into packs. This format is no longer used, but
  * we must still read it.
  */
-static int inflate_packlike_loose_disk_obj(git_rawobj *out, git_buf *obj)
+static int read_loose_packlike(git_rawobj *out, git_buf *obj)
 {
-	unsigned char *in, *buf;
+	git_buf body = GIT_BUF_INIT;
+	const unsigned char *obj_data;
 	obj_hdr hdr;
-	size_t len, used, alloclen;
+	size_t obj_len, head_len, alloc_size;
+	int error;
+
+	obj_data = (unsigned char *)obj->ptr;
+	obj_len = obj->size;
 
 	/*
 	 * read the object header, which is an (uncompressed)
 	 * binary encoding of the object type and size.
 	 */
-	if ((used = get_binary_object_header(&hdr, obj)) == 0 ||
-		!git_object_typeisloose(hdr.type)) {
+	if ((error = parse_header_packlike(&hdr, &head_len, obj_data, obj_len)) < 0)
+		goto done;
+
+	if (!git_object_typeisloose(hdr.type) || head_len > obj_len) {
 		giterr_set(GITERR_ODB, "failed to inflate loose object");
-		return -1;
+		error = -1;
+		goto done;
 	}
 
+	obj_data += head_len;
+	obj_len -= head_len;
+
 	/*
 	 * allocate a buffer and inflate the data into it
 	 */
-	GITERR_CHECK_ALLOC_ADD(&alloclen, hdr.size, 1);
-	buf = git__malloc(alloclen);
-	GITERR_CHECK_ALLOC(buf);
-
-	in = ((unsigned char *)obj->ptr) + used;
-	len = obj->size - used;
-	if (inflate_buffer(in, len, buf, hdr.size) < 0) {
-		git__free(buf);
-		return -1;
+	if (GIT_ADD_SIZET_OVERFLOW(&alloc_size, hdr.size, 1) ||
+		git_buf_init(&body, alloc_size) < 0) {
+		error = -1;
+		goto done;
 	}
-	buf[hdr.size] = '\0';
 
-	out->data = buf;
+	if ((error = git_zstream_inflatebuf(&body, obj_data, obj_len)) < 0)
+		goto done;
+
 	out->len = hdr.size;
 	out->type = hdr.type;
+	out->data = git_buf_detach(&body);
 
-	return 0;
+done:
+	git_buf_free(&body);
+	return error;
 }
 
-static int inflate_disk_obj(git_rawobj *out, git_buf *obj)
+static int read_loose_standard(git_rawobj *out, git_buf *obj)
 {
 	git_zstream zstream = GIT_ZSTREAM_INIT;
-	unsigned char head[64], *body = NULL;
+	unsigned char head[MAX_HEADER_LEN], *body = NULL;
 	size_t decompressed, head_len, body_len, alloc_size;
 	obj_hdr hdr;
 	int error;
 
-	/* check for a pack-like loose object */
-	if (!is_zlib_compressed_data((unsigned char *)obj->ptr))
-		return inflate_packlike_loose_disk_obj(out, obj);
-
 	if ((error = git_zstream_init(&zstream, GIT_ZSTREAM_INFLATE)) < 0 ||
 		(error = git_zstream_set_input(&zstream, git_buf_cstr(obj), git_buf_len(obj))) < 0)
 		goto done;
@@ -338,9 +285,10 @@ static int inflate_disk_obj(git_rawobj *out, git_buf *obj)
 	decompressed = sizeof(head);
 
 	/*
-	* inflate the initial part of the compressed buffer in order to parse the
-	* header; read the largest header possible, then push back the remainder.
-	*/
+	 * inflate the initial part of the compressed buffer in order to
+	 * parse the header; read the largest header possible, then push the
+	 * remainder into the body buffer.
+	 */
 	if ((error = git_zstream_get_output(head, &decompressed, &zstream)) < 0 ||
 		(error = parse_header(&hdr, &head_len, head, decompressed)) < 0)
 		goto done;
@@ -391,20 +339,6 @@ done:
 	return error;
 }
 
-
-
-
-
-
-/***********************************************************
- *
- * ODB OBJECT READING & WRITING
- *
- * Backend for the public API; read headers and full objects
- * from the ODB. Write raw data to the ODB.
- *
- ***********************************************************/
-
 static int read_loose(git_rawobj *out, git_buf *loc)
 {
 	int error;
@@ -419,22 +353,62 @@ static int read_loose(git_rawobj *out, git_buf *loc)
 	out->len = 0;
 	out->type = GIT_OBJ_BAD;
 
-	if (!(error = git_futils_readbuffer(&obj, loc->ptr)))
-		error = inflate_disk_obj(out, &obj);
+	if ((error = git_futils_readbuffer(&obj, loc->ptr)) < 0)
+		goto done;
+
+	if (!is_zlib_compressed_data((unsigned char *)obj.ptr, obj.size))
+		error = read_loose_packlike(out, &obj);
+	else
+		error = read_loose_standard(out, &obj);
 
+done:
 	git_buf_free(&obj);
+	return error;
+}
+
+static int read_header_loose_packlike(
+	git_rawobj *out, const unsigned char *data, size_t len)
+{
+	obj_hdr hdr;
+	size_t header_len;
+	int error;
+
+	if ((error = parse_header_packlike(&hdr, &header_len, data, len)) < 0)
+		return error;
 
+	out->len = hdr.size;
+	out->type = hdr.type;
+
+	return error;
+}
+
+static int read_header_loose_standard(
+	git_rawobj *out, const unsigned char *data, size_t len)
+{
+	git_zstream zs = GIT_ZSTREAM_INIT;
+	obj_hdr hdr;
+	unsigned char inflated[MAX_HEADER_LEN];
+	size_t header_len, inflated_len = sizeof(inflated);
+	int error;
+
+	if ((error = git_zstream_init(&zs, GIT_ZSTREAM_INFLATE)) < 0 ||
+		(error = git_zstream_set_input(&zs, data, len)) < 0 ||
+		(error = git_zstream_get_output_chunk(inflated, &inflated_len, &zs)) < 0 ||
+		(error = parse_header(&hdr, &header_len, inflated, inflated_len)) < 0)
+		goto done;
+
+	out->len = hdr.size;
+	out->type = hdr.type;
+
+done:
+	git_zstream_free(&zs);
 	return error;
 }
 
 static int read_header_loose(git_rawobj *out, git_buf *loc)
 {
-	int error = 0, z_return = Z_ERRNO, read_bytes;
-	git_file fd;
-	z_stream zs;
-	obj_hdr header_obj;
-	size_t header_len;
-	unsigned char raw_buffer[16], inflated_buffer[64];
+	unsigned char obj[1024];
+	int fd, obj_len, error;
 
 	assert(out && loc);
 
@@ -443,35 +417,23 @@ static int read_header_loose(git_rawobj *out, git_buf *loc)
 
 	out->data = NULL;
 
-	if ((fd = git_futils_open_ro(loc->ptr)) < 0)
-		return fd;
-
-	init_stream(&zs, inflated_buffer, sizeof(inflated_buffer));
-
-	z_return = inflateInit(&zs);
+	if ((error = fd = git_futils_open_ro(loc->ptr)) < 0 ||
+		(error = obj_len = p_read(fd, obj, sizeof(obj))) < 0)
+		goto done;
 
-	while (z_return == Z_OK) {
-		if ((read_bytes = p_read(fd, raw_buffer, sizeof(raw_buffer))) > 0) {
-			set_stream_input(&zs, raw_buffer, read_bytes);
-			z_return = inflate(&zs, 0);
-		} else
-			z_return = Z_STREAM_END;
-	}
+	if (!is_zlib_compressed_data(obj, (size_t)obj_len))
+		error = read_header_loose_packlike(out, obj, (size_t)obj_len);
+	else
+		error = read_header_loose_standard(out, obj, (size_t)obj_len);
 
-	if ((z_return != Z_STREAM_END && z_return != Z_BUF_ERROR)
-		|| parse_header(&header_obj, &header_len, inflated_buffer, sizeof(inflated_buffer)) < 0
-		|| git_object_typeisloose(header_obj.type) == 0)
-	{
+	if (!error && !git_object_typeisloose(out->type)) {
 		giterr_set(GITERR_ZLIB, "failed to read loose object header");
 		error = -1;
-	} else {
-		out->len = header_obj.size;
-		out->type = header_obj.type;
+		goto done;
 	}
 
-	finish_inflate(&zs);
+done:
 	p_close(fd);
-
 	return error;
 }
 
@@ -812,7 +774,7 @@ static int loose_backend__foreach(git_odb_backend *_backend, git_odb_foreach_cb
 	return error;
 }
 
-static int loose_backend__stream_fwrite(git_odb_stream *_stream, const git_oid *oid)
+static int loose_backend__writestream_finalize(git_odb_stream *_stream, const git_oid *oid)
 {
 	loose_writestream *stream = (loose_writestream *)_stream;
 	loose_backend *backend = (loose_backend *)_stream->backend;
@@ -831,13 +793,13 @@ static int loose_backend__stream_fwrite(git_odb_stream *_stream, const git_oid *
 	return error;
 }
 
-static int loose_backend__stream_write(git_odb_stream *_stream, const char *data, size_t len)
+static int loose_backend__writestream_write(git_odb_stream *_stream, const char *data, size_t len)
 {
 	loose_writestream *stream = (loose_writestream *)_stream;
 	return git_filebuf_write(&stream->fbuf, data, len);
 }
 
-static void loose_backend__stream_free(git_odb_stream *_stream)
+static void loose_backend__writestream_free(git_odb_stream *_stream)
 {
 	loose_writestream *stream = (loose_writestream *)_stream;
 
@@ -856,11 +818,11 @@ static int filebuf_flags(loose_backend *backend)
 	return flags;
 }
 
-static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_backend, git_off_t length, git_otype type)
+static int loose_backend__writestream(git_odb_stream **stream_out, git_odb_backend *_backend, git_off_t length, git_otype type)
 {
 	loose_backend *backend;
 	loose_writestream *stream = NULL;
-	char hdr[64];
+	char hdr[MAX_HEADER_LEN];
 	git_buf tmp_path = GIT_BUF_INIT;
 	int hdrlen;
 
@@ -876,9 +838,9 @@ static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_
 
 	stream->stream.backend = _backend;
 	stream->stream.read = NULL; /* read only */
-	stream->stream.write = &loose_backend__stream_write;
-	stream->stream.finalize_write = &loose_backend__stream_fwrite;
-	stream->stream.free = &loose_backend__stream_free;
+	stream->stream.write = &loose_backend__writestream_write;
+	stream->stream.finalize_write = &loose_backend__writestream_finalize;
+	stream->stream.free = &loose_backend__writestream_free;
 	stream->stream.mode = GIT_STREAM_WRONLY;
 
 	if (git_buf_joinpath(&tmp_path, backend->objects_dir, "tmp_object") < 0 ||
@@ -896,11 +858,187 @@ static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_
 	return !stream ? -1 : 0;
 }
 
+static int loose_backend__readstream_read(
+	git_odb_stream *_stream,
+	char *buffer,
+	size_t buffer_len)
+{
+	loose_readstream *stream = (loose_readstream *)_stream;
+	size_t start_remain = stream->start_len - stream->start_read;
+	int total = 0, error;
+
+	/*
+	 * if we read more than just the header in the initial read, play
+	 * that back for the caller.
+	 */
+	if (start_remain && buffer_len) {
+		size_t chunk = min(start_remain, buffer_len);
+		memcpy(buffer, stream->start + stream->start_read, chunk);
+
+		buffer += chunk;
+		stream->start_read += chunk;
+
+		total += chunk;
+		buffer_len -= chunk;
+	}
+
+	if (buffer_len) {
+		size_t chunk = min(buffer_len, INT_MAX);
+
+		if ((error = git_zstream_get_output(buffer, &chunk, &stream->zstream)) < 0)
+			return error;
+
+		total += chunk;
+	}
+
+	return total;
+}
+
+static void loose_backend__readstream_free(git_odb_stream *_stream)
+{
+	loose_readstream *stream = (loose_readstream *)_stream;
+
+	git_futils_mmap_free(&stream->map);
+	git_zstream_free(&stream->zstream);
+	git__free(stream);
+}
+
+static int loose_backend__readstream_packlike(
+	obj_hdr *hdr,
+	loose_readstream *stream)
+{
+	const unsigned char *data;
+	size_t data_len, head_len;
+	int error;
+
+	data = stream->map.data;
+	data_len = stream->map.len;
+
+	/*
+	 * read the object header, which is an (uncompressed)
+	 * binary encoding of the object type and size.
+	 */
+	if ((error = parse_header_packlike(hdr, &head_len, data, data_len)) < 0)
+		return error;
+
+	if (!git_object_typeisloose(hdr->type)) {
+		giterr_set(GITERR_ODB, "failed to inflate loose object");
+		return -1;
+	}
+
+	return git_zstream_set_input(&stream->zstream,
+		data + head_len, data_len - head_len);
+}
+
+static int loose_backend__readstream_standard(
+	obj_hdr *hdr,
+	loose_readstream *stream)
+{
+	unsigned char head[MAX_HEADER_LEN];
+	size_t init, head_len;
+	int error;
+
+	if ((error = git_zstream_set_input(&stream->zstream,
+			stream->map.data, stream->map.len)) < 0)
+		return error;
+
+	init = sizeof(head);
+
+	/*
+	 * inflate the initial part of the compressed buffer in order to
+	 * parse the header; read the largest header possible, then store
+	 * it in the `start` field of the stream object.
+	 */
+	if ((error = git_zstream_get_output(head, &init, &stream->zstream)) < 0 ||
+		(error = parse_header(hdr, &head_len, head, init)) < 0)
+		return error;
+
+	if (!git_object_typeisloose(hdr->type)) {
+		giterr_set(GITERR_ODB, "failed to inflate disk object");
+		return -1;
+	}
+
+	if (init > head_len) {
+		stream->start_len = init - head_len;
+		memcpy(stream->start, head + head_len, init - head_len);
+	}
+
+	return 0;
+}
+
+static int loose_backend__readstream(
+	git_odb_stream **stream_out,
+	size_t *len_out,
+	git_otype *type_out,
+	git_odb_backend *_backend,
+	const git_oid *oid)
+{
+	loose_backend *backend;
+	loose_readstream *stream = NULL;
+	git_hash_ctx *hash_ctx = NULL;
+	git_buf object_path = GIT_BUF_INIT;
+	obj_hdr hdr;
+	int error = 0;
+
+	assert(stream_out && len_out && type_out && _backend && oid);
+
+	backend = (loose_backend *)_backend;
+	*stream_out = NULL;
+	*len_out = 0;
+	*type_out = GIT_OBJ_BAD;
+
+	if (locate_object(&object_path, backend, oid) < 0) {
+		error = git_odb__error_notfound("no matching loose object",
+			oid, GIT_OID_HEXSZ);
+		goto done;
+	}
+
+	stream = git__calloc(1, sizeof(loose_readstream));
+	GITERR_CHECK_ALLOC(stream);
+
+	hash_ctx = git__malloc(sizeof(git_hash_ctx));
+	GITERR_CHECK_ALLOC(hash_ctx);
+
+	if ((error = git_hash_ctx_init(hash_ctx)) < 0 ||
+		(error = git_futils_mmap_ro_file(&stream->map, object_path.ptr)) < 0 ||
+		(error = git_zstream_init(&stream->zstream, GIT_ZSTREAM_INFLATE)) < 0)
+		goto done;
+
+	/* check for a packlike loose object */
+	if (!is_zlib_compressed_data(stream->map.data, stream->map.len))
+		error = loose_backend__readstream_packlike(&hdr, stream);
+	else
+		error = loose_backend__readstream_standard(&hdr, stream);
+
+	if (error < 0)
+		goto done;
+
+	stream->stream.backend = _backend;
+	stream->stream.hash_ctx = hash_ctx;
+	stream->stream.read = &loose_backend__readstream_read;
+	stream->stream.free = &loose_backend__readstream_free;
+
+	*stream_out = (git_odb_stream *)stream;
+	*len_out = hdr.size;
+	*type_out = hdr.type;
+
+done:
+	if (error < 0) {
+		git_futils_mmap_free(&stream->map);
+		git_zstream_free(&stream->zstream);
+		git_hash_ctx_cleanup(hash_ctx);
+		git__free(stream);
+	}
+
+	git_buf_free(&object_path);
+	return error;
+}
+
 static int loose_backend__write(git_odb_backend *_backend, const git_oid *oid, const void *data, size_t len, git_otype type)
 {
 	int error = 0, header_len;
 	git_buf final_path = GIT_BUF_INIT;
-	char header[64];
+	char header[MAX_HEADER_LEN];
 	git_filebuf fbuf = GIT_FILEBUF_INIT;
 	loose_backend *backend;
 
@@ -1002,7 +1140,8 @@ int git_odb_backend_loose(
 	backend->parent.write = &loose_backend__write;
 	backend->parent.read_prefix = &loose_backend__read_prefix;
 	backend->parent.read_header = &loose_backend__read_header;
-	backend->parent.writestream = &loose_backend__stream;
+	backend->parent.writestream = &loose_backend__writestream;
+	backend->parent.readstream = &loose_backend__readstream;
 	backend->parent.exists = &loose_backend__exists;
 	backend->parent.exists_prefix = &loose_backend__exists_prefix;
 	backend->parent.foreach = &loose_backend__foreach;
diff --git a/src/zstream.c b/src/zstream.c
index 963c9a344..affa55653 100644
--- a/src/zstream.c
+++ b/src/zstream.c
@@ -87,9 +87,52 @@ size_t git_zstream_suggest_output_len(git_zstream *zstream)
 		return ZSTREAM_BUFFER_MIN_EXTRA;
 }
 
+int git_zstream_get_output_chunk(
+	void *out, size_t *out_len, git_zstream *zstream)
+{
+	size_t in_queued, in_used, out_queued;
+
+	/* set up input data */
+	zstream->z.next_in = (Bytef *)zstream->in;
+
+	/* feed as much data to zlib as it can consume, at most UINT_MAX */
+	if (zstream->in_len > UINT_MAX) {
+		zstream->z.avail_in = UINT_MAX;
+		zstream->flush = Z_NO_FLUSH;
+	} else {
+		zstream->z.avail_in = (uInt)zstream->in_len;
+		zstream->flush = Z_FINISH;
+	}
+	in_queued = (size_t)zstream->z.avail_in;
+
+	/* set up output data */
+	zstream->z.next_out = out;
+	zstream->z.avail_out = (uInt)*out_len;
+
+	if ((size_t)zstream->z.avail_out != *out_len)
+		zstream->z.avail_out = UINT_MAX;
+	out_queued = (size_t)zstream->z.avail_out;
+
+	/* compress next chunk */
+	if (zstream->type == GIT_ZSTREAM_INFLATE)
+		zstream->zerr = inflate(&zstream->z, zstream->flush);
+	else
+		zstream->zerr = deflate(&zstream->z, zstream->flush);
+
+	if (zstream_seterr(zstream))
+		return -1;
+
+	in_used = (in_queued - zstream->z.avail_in);
+	zstream->in_len -= in_used;
+	zstream->in += in_used;
+
+	*out_len = (out_queued - zstream->z.avail_out);
+
+	return 0;
+}
+
 int git_zstream_get_output(void *out, size_t *out_len, git_zstream *zstream)
 {
-	int zflush = Z_FINISH;
 	size_t out_remain = *out_len;
 
 	if (zstream->in_len && zstream->zerr == Z_STREAM_END) {
@@ -98,47 +141,17 @@ int git_zstream_get_output(void *out, size_t *out_len, git_zstream *zstream)
 	}
 
 	while (out_remain > 0 && zstream->zerr != Z_STREAM_END) {
-		size_t out_queued, in_queued, out_used, in_used;
+		size_t out_written = out_remain;
 
-		/* set up in data */
-		zstream->z.next_in  = (Bytef *)zstream->in;
-		zstream->z.avail_in = (uInt)zstream->in_len;
-
-		if ((size_t)zstream->z.avail_in != zstream->in_len) {
-			zstream->z.avail_in = UINT_MAX;
-			zflush = Z_NO_FLUSH;
-		} else {
-			zflush = Z_FINISH;
-		}
-		in_queued = (size_t)zstream->z.avail_in;
-
-		/* set up out data */
-		zstream->z.next_out = out;
-		zstream->z.avail_out = (uInt)out_remain;
-		if ((size_t)zstream->z.avail_out != out_remain)
-			zstream->z.avail_out = UINT_MAX;
-		out_queued = (size_t)zstream->z.avail_out;
-
-		/* compress next chunk */
-		if (zstream->type == GIT_ZSTREAM_INFLATE)
-			zstream->zerr = inflate(&zstream->z, zflush);
-		else
-			zstream->zerr = deflate(&zstream->z, zflush);
-
-		if (zstream_seterr(zstream))
+		if (git_zstream_get_output_chunk(out, &out_written, zstream) < 0)
 			return -1;
 
-		out_used = (out_queued - zstream->z.avail_out);
-		out_remain -= out_used;
-		out = ((char *)out) + out_used;
-
-		in_used = (in_queued - zstream->z.avail_in);
-		zstream->in_len -= in_used;
-		zstream->in += in_used;
+		out_remain -= out_written;
+		out = ((char *)out) + out_written;
 	}
 
 	/* either we finished the input or we did not flush the data */
-	assert(zstream->in_len > 0 || zflush == Z_FINISH);
+	assert(zstream->in_len > 0 || zstream->flush == Z_FINISH);
 
 	/* set out_size to number of bytes actually written to output */
 	*out_len = *out_len - out_remain;
diff --git a/src/zstream.h b/src/zstream.h
index c2404f328..47ecc1322 100644
--- a/src/zstream.h
+++ b/src/zstream.h
@@ -23,6 +23,7 @@ typedef struct {
 	git_zstream_t type;
 	const char *in;
 	size_t in_len;
+	int flush;
 	int zerr;
 } git_zstream;
 
@@ -35,6 +36,11 @@ int git_zstream_set_input(git_zstream *zstream, const void *in, size_t in_len);
 
 size_t git_zstream_suggest_output_len(git_zstream *zstream);
 
+/* get as much output as is available in the input buffer */
+int git_zstream_get_output_chunk(
+	void *out, size_t *out_len, git_zstream *zstream);
+
+/* get all the output from the entire input buffer */
 int git_zstream_get_output(void *out, size_t *out_len, git_zstream *zstream);
 
 bool git_zstream_done(git_zstream *zstream);
diff --git a/tests/odb/largefiles.c b/tests/odb/largefiles.c
index 22f136df5..cd3651b4a 100644
--- a/tests/odb/largefiles.c
+++ b/tests/odb/largefiles.c
@@ -1,5 +1,9 @@
 #include "clar_libgit2.h"
 #include "git2/odb_backend.h"
+#include "hash.h"
+#include "odb.h"
+
+#define LARGEFILE_SIZE 5368709122
 
 static git_repository *repo;
 static git_odb *odb;
@@ -25,7 +29,7 @@ static void writefile(git_oid *oid)
 	for (i = 0; i < 3041; i++)
 		cl_git_pass(git_buf_puts(&buf, "Hello, world.\n"));
 
-	cl_git_pass(git_odb_open_wstream(&stream, odb, 5368709122, GIT_OBJ_BLOB));
+	cl_git_pass(git_odb_open_wstream(&stream, odb, LARGEFILE_SIZE, GIT_OBJ_BLOB));
 	for (i = 0; i < 126103; i++)
 		cl_git_pass(git_odb_stream_write(stream, buf.ptr, buf.size));
 
@@ -63,6 +67,10 @@ void test_odb_largefiles__streamwrite(void)
 {
 	git_oid expected, oid;
 
+#ifndef GIT_ARCH_64
+	cl_skip();
+#endif
+
 	if (!cl_is_env_set("GITTEST_INVASIVE_FS_SIZE") ||
 		!cl_is_env_set("GITTEST_SLOW"))
 		cl_skip();
@@ -73,6 +81,52 @@ void test_odb_largefiles__streamwrite(void)
 	cl_assert_equal_oid(&expected, &oid);
 }
 
+void test_odb_largefiles__streamread(void)
+{
+	git_oid oid, read_oid;
+	git_odb_stream *stream;
+	char buf[10240];
+	char hdr[64];
+	size_t len, total = 0;
+	git_hash_ctx hash;
+	git_otype type;
+	int hdr_len, ret;
+
+#ifndef GIT_ARCH_64
+	cl_skip();
+#endif
+
+	if (!cl_is_env_set("GITTEST_INVASIVE_FS_SIZE") ||
+		!cl_is_env_set("GITTEST_SLOW"))
+		cl_skip();
+
+	writefile(&oid);
+
+	cl_git_pass(git_odb_open_rstream(&stream, &len, &type, odb, &oid));
+
+	cl_assert_equal_sz(LARGEFILE_SIZE, len);
+	cl_assert_equal_i(GIT_OBJ_BLOB, type);
+
+	cl_git_pass(git_hash_ctx_init(&hash));
+	hdr_len = git_odb__format_object_header(hdr, sizeof(hdr), len, type);
+
+	cl_git_pass(git_hash_update(&hash, hdr, hdr_len));
+
+	while ((ret = git_odb_stream_read(stream, buf, 10240)) > 0) {
+		cl_git_pass(git_hash_update(&hash, buf, ret));
+		total += ret;
+	}
+
+	cl_assert_equal_sz(LARGEFILE_SIZE, total);
+
+	git_hash_final(&read_oid, &hash);
+
+	cl_assert_equal_oid(&oid, &read_oid);
+
+	git_hash_ctx_cleanup(&hash);
+	git_odb_stream_free(stream);
+}
+
 void test_odb_largefiles__read_into_memory(void)
 {
 	git_oid oid;
@@ -112,3 +166,24 @@ void test_odb_largefiles__read_into_memory_rejected_on_32bit(void)
 
 	git_odb_object_free(obj);
 }
+
+void test_odb_largefiles__read_header(void)
+{
+	git_oid oid;
+	size_t len;
+	git_otype type;
+
+#ifndef GIT_ARCH_64
+	cl_skip();
+#endif
+
+	if (!cl_is_env_set("GITTEST_INVASIVE_FS_SIZE") ||
+		!cl_is_env_set("GITTEST_SLOW"))
+		cl_skip();
+
+	writefile(&oid);
+	cl_git_pass(git_odb_read_header(&len, &type, odb, &oid));
+
+	cl_assert_equal_sz(LARGEFILE_SIZE, len);
+	cl_assert_equal_i(GIT_OBJ_BLOB, type);
+}
diff --git a/tests/odb/loose.c b/tests/odb/loose.c
index 2e24d6723..83d080729 100644
--- a/tests/odb/loose.c
+++ b/tests/odb/loose.c
@@ -55,6 +55,63 @@ static void test_read_object(object_data *data)
 	git_odb_free(odb);
 }
 
+static void test_read_header(object_data *data)
+{
+	git_oid id;
+	git_odb *odb;
+	size_t len;
+	git_otype type;
+
+	write_object_files(data);
+
+	cl_git_pass(git_odb_open(&odb, "test-objects"));
+	cl_git_pass(git_oid_fromstr(&id, data->id));
+	cl_git_pass(git_odb_read_header(&len, &type, odb, &id));
+
+	cl_assert_equal_sz(data->dlen, len);
+	cl_assert_equal_i(git_object_string2type(data->type), type);
+
+	git_odb_free(odb);
+}
+
+static void test_readstream_object(object_data *data, size_t blocksize)
+{
+	git_oid id;
+	git_odb *odb;
+	git_odb_stream *stream;
+	git_rawobj tmp;
+	char buf[2048], *ptr = buf;
+	size_t remain;
+	int ret;
+
+	write_object_files(data);
+
+	cl_git_pass(git_odb_open(&odb, "test-objects"));
+	cl_git_pass(git_oid_fromstr(&id, data->id));
+	cl_git_pass(git_odb_open_rstream(&stream, &tmp.len, &tmp.type, odb, &id));
+
+	remain = tmp.len;
+
+	while (remain) {
+		cl_assert((ret = git_odb_stream_read(stream, ptr, blocksize)) >= 0);
+		if (ret == 0)
+			break;
+
+		cl_assert(remain >= (size_t)ret);
+		remain -= ret;
+		ptr += ret;
+	}
+
+	cl_assert(remain == 0);
+
+	tmp.data = buf;
+
+	cmp_objects(&tmp, data);
+
+	git_odb_stream_free(stream);
+	git_odb_free(odb);
+}
+
 void test_odb_loose__initialize(void)
 {
 	p_fsync__cnt = 0;
@@ -103,6 +160,33 @@ void test_odb_loose__simple_reads(void)
 	test_read_object(&some);
 }
 
+void test_odb_loose__streaming_reads(void)
+{
+	size_t blocksizes[] = { 1, 2, 4, 16, 99, 1024, 123456789 };
+	size_t i;
+
+	for (i = 0; i < ARRAY_SIZE(blocksizes); i++) {
+		test_readstream_object(&commit, blocksizes[i]);
+		test_readstream_object(&tree, blocksizes[i]);
+		test_readstream_object(&tag, blocksizes[i]);
+		test_readstream_object(&zero, blocksizes[i]);
+		test_readstream_object(&one, blocksizes[i]);
+		test_readstream_object(&two, blocksizes[i]);
+		test_readstream_object(&some, blocksizes[i]);
+	}
+}
+
+void test_odb_loose__read_header(void)
+{
+	test_read_header(&commit);
+	test_read_header(&tree);
+	test_read_header(&tag);
+	test_read_header(&zero);
+	test_read_header(&one);
+	test_read_header(&two);
+	test_read_header(&some);
+}
+
 void test_write_object_permission(
 	mode_t dir_mode, mode_t file_mode,
 	mode_t expected_dir_mode, mode_t expected_file_mode)