diff --git a/cache.h b/cache.h
index a50a61a19787de..ed458957060466 100644
--- a/cache.h
+++ b/cache.h
@@ -1139,6 +1139,19 @@ extern int finalize_object_file(const char *tmpfile, const char *filename);
 
 extern int has_sha1_pack(const unsigned char *sha1);
 
+/*
+ * Open the loose object at path, check its sha1, and return the contents,
+ * type, and size. If the object is a blob, then "contents" may return NULL,
+ * to allow streaming of large blobs.
+ *
+ * Returns 0 on success, negative on error (details may be written to stderr).
+ */
+int read_loose_object(const char *path,
+		      const unsigned char *expected_sha1,
+		      enum object_type *type,
+		      unsigned long *size,
+		      void **contents);
+
 /*
  * Return true iff we have an object named sha1, whether local or in
  * an alternate object database, and whether packed or loose.  This
diff --git a/sha1_file.c b/sha1_file.c
index 6c8e4b43dd1ead..ca1c90e5d33785 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1670,13 +1670,21 @@ static int open_sha1_file(const unsigned char *sha1, const char **path)
 	return -1;
 }
 
-void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
+/*
+ * Map the loose object at "path" if it is not NULL, or the path found by
+ * searching for a loose object named "sha1".
+ */
+static void *map_sha1_file_1(const char *path,
+			     const unsigned char *sha1,
+			     unsigned long *size)
 {
-	const char *path;
 	void *map;
 	int fd;
 
-	fd = open_sha1_file(sha1, &path);
+	if (path)
+		fd = git_open(path);
+	else
+		fd = open_sha1_file(sha1, &path);
 	map = NULL;
 	if (fd >= 0) {
 		struct stat st;
@@ -1695,6 +1703,11 @@ void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 	return map;
 }
 
+void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
+{
+	return map_sha1_file_1(NULL, sha1, size);
+}
+
 unsigned long unpack_object_header_buffer(const unsigned char *buf,
 		unsigned long len, enum object_type *type, unsigned long *sizep)
 {
@@ -3792,3 +3805,117 @@ int for_each_packed_object(each_packed_object_fn cb, void *data, unsigned flags)
 	}
 	return r ? r : pack_errors;
 }
+
+static int check_stream_sha1(git_zstream *stream,
+			     const char *hdr,
+			     unsigned long size,
+			     const char *path,
+			     const unsigned char *expected_sha1)
+{
+	git_SHA_CTX c;
+	unsigned char real_sha1[GIT_SHA1_RAWSZ];
+	unsigned char buf[4096];
+	unsigned long total_read;
+	int status = Z_OK;
+
+	git_SHA1_Init(&c);
+	git_SHA1_Update(&c, hdr, stream->total_out);
+
+	/*
+	 * We already read some bytes into hdr, but the ones up to the NUL
+	 * do not count against the object's content size.
+	 */
+	total_read = stream->total_out - strlen(hdr) - 1;
+
+	/*
+	 * This size comparison must be "<=" to read the final zlib packets;
+	 * see the comment in unpack_sha1_rest for details.
+	 */
+	while (total_read <= size &&
+	       (status == Z_OK || status == Z_BUF_ERROR)) {
+		stream->next_out = buf;
+		stream->avail_out = sizeof(buf);
+		if (size - total_read < stream->avail_out)
+			stream->avail_out = size - total_read;
+		status = git_inflate(stream, Z_FINISH);
+		git_SHA1_Update(&c, buf, stream->next_out - buf);
+		total_read += stream->next_out - buf;
+	}
+	git_inflate_end(stream);
+
+	if (status != Z_STREAM_END) {
+		error("corrupt loose object '%s'", sha1_to_hex(expected_sha1));
+		return -1;
+	}
+
+	git_SHA1_Final(real_sha1, &c);
+	if (hashcmp(expected_sha1, real_sha1)) {
+		error("sha1 mismatch for %s (expected %s)", path,
+		      sha1_to_hex(expected_sha1));
+		return -1;
+	}
+
+	return 0;
+}
+
+int read_loose_object(const char *path,
+		      const unsigned char *expected_sha1,
+		      enum object_type *type,
+		      unsigned long *size,
+		      void **contents)
+{
+	int ret = -1;
+	int fd = -1;
+	void *map = NULL;
+	unsigned long mapsize;
+	git_zstream stream;
+	char hdr[32];
+
+	*contents = NULL;
+
+	map = map_sha1_file_1(path, NULL, &mapsize);
+	if (!map) {
+		error_errno("unable to mmap %s", path);
+		goto out;
+	}
+
+	if (unpack_sha1_header(&stream, map, mapsize, hdr, sizeof(hdr)) < 0) {
+		error("unable to unpack header of %s", path);
+		goto out;
+	}
+
+	*type = parse_sha1_header(hdr, size);
+	if (*type < 0) {
+		error("unable to parse header of %s", path);
+		git_inflate_end(&stream);
+		goto out;
+	}
+
+	if (*type == OBJ_BLOB) {
+		if (check_stream_sha1(&stream, hdr, *size, path, expected_sha1) < 0)
+			goto out;
+	} else {
+		*contents = unpack_sha1_rest(&stream, hdr, *size, expected_sha1);
+		if (!*contents) {
+			error("unable to unpack contents of %s", path);
+			git_inflate_end(&stream);
+			goto out;
+		}
+		if (check_sha1_signature(expected_sha1, *contents,
+					 *size, typename(*type))) {
+			error("sha1 mismatch for %s (expected %s)", path,
+			      sha1_to_hex(expected_sha1));
+			free(*contents);
+			goto out;
+		}
+	}
+
+	ret = 0; /* everything checks out */
+
+out:
+	if (map)
+		munmap(map, mapsize);
+	if (fd >= 0)
+		close(fd);
+	return ret;
+}