OdbBackend: implement subclassed read_header

src/odb_backend.c

@@ -41,7 +41,8 @@ struct py_odb_backend
     git_odb_backend backend;
     PyObject *self;
     PyObject *read_callable,
-             *read_prefix_callable;
+             *read_prefix_callable,
+             *read_header_callable;
 };
 
 static int
@@ -65,7 +66,7 @@ py_odb_backend_read(void **ptr, size_t *sz,
         return GIT_EUSER;
 
     const char *bytes;
-    if (!PyArg_ParseTuple(result, "iy#", type, &bytes, sz) || !bytes)
+    if (!PyArg_ParseTuple(result, "ny#", type, &bytes, sz) || !bytes)
         return GIT_EUSER;
 
     /* XXX: This assumes the default libgit2 allocator is in use and will
@@ -100,7 +101,7 @@ py_odb_backend_read_prefix(git_oid *oid_out, void **ptr, size_t *sz,
         return GIT_EUSER;
 
     const char *bytes;
-    if (!PyArg_ParseTuple(result, "Oiy#",
+    if (!PyArg_ParseTuple(result, "Ony#",
                 &py_oid_out, type, &bytes, sz) || !bytes)
         return GIT_EUSER;
 
@@ -115,6 +116,32 @@ py_odb_backend_read_prefix(git_oid *oid_out, void **ptr, size_t *sz,
     return 0;
 }
 
+static int
+py_odb_backend_read_header(size_t *len, git_object_t *type,
+        git_odb_backend *_be, const git_oid *oid)
+{
+    int err;
+    PyObject *args, *py_oid, *result;
+    struct py_odb_backend *be = (struct py_odb_backend *)_be;
+
+    py_oid = git_oid_to_python(oid);
+    args = Py_BuildValue("(O)", py_oid);
+    result = PyObject_CallObject(be->read_header_callable, args);
+    Py_DECREF(py_oid);
+
+    if ((err = git_error_for_exc()) != 0) {
+        return err;
+    }
+
+    if (result == NULL)
+        return GIT_EUSER;
+
+    if (!PyArg_ParseTuple(result, "nn", type, len))
+        return GIT_EUSER;
+
+    return 0;
+}
+
 int
 OdbBackend_init(OdbBackend *self, PyObject *args, PyObject *kwds)
 {
@@ -143,6 +170,11 @@ OdbBackend_init(OdbBackend *self, PyObject *args, PyObject *kwds)
     if (be->read_prefix_callable)
         be->backend.read_prefix = py_odb_backend_read_prefix;
 
+    be->read_header_callable = PyObject_GetAttrString(
+            (PyObject *)self, "read_header");
+    if (be->read_header_callable)
+        be->backend.read_header = py_odb_backend_read_header;
+
     self->odb_backend = &be->backend;
     return 0;
 }
@@ -267,9 +299,41 @@ OdbBackend_read_prefix(OdbBackend *self, PyObject *py_hex)
     return tuple;
 }
 
+PyDoc_STRVAR(OdbBackend_read_header__doc__,
+    "read_header(oid) -> (type, len)\n"
+    "\n"
+    "Read raw object header from this odb backend.\n");
+
+PyObject *
+OdbBackend_read_header(OdbBackend *self, PyObject *py_hex)
+{
+    int err;
+    size_t len;
+    git_object_t type;
+    git_oid oid;
+
+    if (self->odb_backend->read_header == NULL) {
+        Py_INCREF(Py_NotImplemented);
+        return Py_NotImplemented;
+    }
+
+    len = py_oid_to_git_oid(py_hex, &oid);
+    if (len == 0)
+        return NULL;
+
+    err = self->odb_backend->read_header(&len, &type, self->odb_backend, &oid);
+    if (err != 0) {
+        Error_set_oid(err, &oid, len);
+        return NULL;
+    }
+
+    return Py_BuildValue("(ni)", type, len);
+}
+
 PyMethodDef OdbBackend_methods[] = {
     METHOD(OdbBackend, read, METH_O),
     METHOD(OdbBackend, read_prefix, METH_O),
+    METHOD(OdbBackend, read_header, METH_O),
     {NULL}
 };