[Libguestfs] [PATCH nbdkit] python: Turn python exceptions into nbdkit errors properly.

[Eric Blake]

On 04/05/2018 07:47 AM, Richard W.M. Jones wrote:
> ---
>  configure.ac                   |  8 +++++++
>  plugins/python/python.c        | 51 +++++++++++++++++++++++++++++++++++++++---
>  tests/Makefile.am              |  1 +
>  tests/python-exception.py      | 45 +++++++++++++++++++++++++++++++++++++
>  tests/test-python-exception.sh | 42 ++++++++++++++++++++++++++++++++++
>  5 files changed, 144 insertions(+), 3 deletions(-)
> 

> +/* Convert bytes/str/unicode into a string.  Caller must free. */
> +static char *
> +python_to_string (PyObject *str)
> +{
> +  char *r;
> +
> +  if (str) {
> +#ifdef HAVE_PYUNICODE_ASUTF8
> +    if (PyUnicode_Check (str)) {
> +      r = PyUnicode_AsUTF8 (str);
> +      r = strdup (r);
> +      return r;

Any simpler to just write:
return strdup (PyUnicode_AsUTF8 (str));

instead of using the temporary variable r?


>  static int
>  check_python_failure (const char *callback)
>  {
>    if (PyErr_Occurred ()) {
> -    nbdkit_error ("%s: callback failed: %s", script, callback);
> -    /* How to turn this into a string? XXX */
> -    PyErr_Print ();
> +    PyObject *type, *error, *traceback, *error_str;
> +    char *error_cstr;
> +
> +    /* Convert the Python exception to a string.
> +     * https://stackoverflow.com/a/1418703
> +     * But forget about the traceback, it's very hard to print.
> +     * https://stackoverflow.com/q/1796510
> +     */
> +    PyErr_Fetch (&type, &error, &traceback);
> +    PyErr_NormalizeException (&type, &error, &traceback);
> +    error_str = PyObject_Str (error);
> +    error_cstr = python_to_string (error_str);
> +    nbdkit_error ("%s: %s: error: %s",
> +                  script, callback, error_cstr ? : "<unknown>");

Okay, not the first use of that gcc extension.

Looks reasonable to me.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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