Python: Restrict code to stable ABI subset

Limit usage of the Python C API to the stable ABI subset as defined
by PEP 384. This removes some type definitions and functions which
libsigrokdecode made use of. Convert all affected code to suitable
API alternatives. Also fix a few leaks that became apparent while
working on the code.

The most visible change is that PyTypeObject is now an opaque type.
Thus, the custom Decoder and srd_logic types are now created on the
heap via an alternative API. Unfortunately, since tp_name is now
inaccessible, type names had to be removed from the log output.

Stack traces after Python exceptions are now formatted by calling
into Python, since the trace object C API is no longer available.

1 files changed, 5 insertions, 6 deletions

diff --git a/decoder.c b/decoder.c
index 753a88a..e50345f 100644
--- a/decoder.c
+++ b/decoder.c
@@ -225,8 +225,7 @@ static int get_options(struct srd_decoder *d)
 				o->def = g_variant_new_double(dval);
 			} else {
 				srd_err("Protocol decoder %s option 'default' has "
-						"value of unsupported type '%s'.", d->name,
-						Py_TYPE(py_default)->tp_name);
+						"value of unsupported type.", d->name);
 				return SRD_ERR_PYTHON;
 			}
 			g_variant_ref_sink(o->def);
@@ -333,7 +332,7 @@ SRD_API int srd_decoder_load(const char *module_name)
 
 	/* Import the Python module. */
 	if (!(d->py_mod = PyImport_ImportModule(module_name))) {
-		srd_exception_catch("Import of '%s' failed.", module_name);
+		srd_exception_catch("Import of '%s' failed", module_name);
 		goto err_out;
 	}
 
@@ -376,7 +375,7 @@ SRD_API int srd_decoder_load(const char *module_name)
 		goto err_out;
 	}
 	py_method = PyObject_GetAttrString(d->py_dec, "start");
-	if (!PyFunction_Check(py_method)) {
+	if (!PyCallable_Check(py_method)) {
 		srd_err("Protocol decoder %s Decoder class attribute 'start' "
 			"is not a method.", module_name);
 		goto err_out;
@@ -390,7 +389,7 @@ SRD_API int srd_decoder_load(const char *module_name)
 		goto err_out;
 	}
 	py_method = PyObject_GetAttrString(d->py_dec, "decode");
-	if (!PyFunction_Check(py_method)) {
+	if (!PyCallable_Check(py_method)) {
 		srd_err("Protocol decoder %s Decoder class attribute 'decode' "
 			"is not a method.", module_name);
 		goto err_out;
@@ -588,7 +587,7 @@ SRD_API char *srd_decoder_doc_get(const struct srd_decoder *dec)
 		return NULL;
 
 	if (!(py_str = PyObject_GetAttrString(dec->py_mod, "__doc__"))) {
-		srd_exception_catch("");
+		srd_exception_catch("Failed to get docstring");
 		return NULL;
 	}