From dd07c4aa3b6f308bac42b04c999c691de8ec2ac8 Mon Sep 17 00:00:00 2001
From: Maxime Mouial <maxime.mouial@gmail.com>
Date: Thu, 6 Dec 2018 17:05:44 -0700
Subject: [PATCH] Update error API for high level to expose Go error

---
 README.md           | 27 +++++++++++++++++++++++++++
 high_level_layer.go | 18 ++++++++++--------
 2 files changed, 37 insertions(+), 8 deletions(-)
 create mode 100644 README.md

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..4c454cb
--- /dev/null
+++ b/README.md
@@ -0,0 +1,27 @@
+go-python3
+==========
+
+Golang bindings for the C-API of CPython-3.
+
+This package provides a ``go`` package named "python" under which most of the
+``PyXYZ`` functions and macros of the public C-API of CPython have been
+exposed. Theoretically, you should be able use https://docs.python.org/3/c-api
+and know what to type in your ``go`` program.
+
+API
+---
+
+Some functions mix go code and call to Python function. Those functions will
+return and `int` and `error` type. The `int` represent the Python result code
+and the `error` represent any issue from the Go layer.
+
+Example:
+
+`func PyRun_AnyFile(filename string)` open `filename` and then call CPython API
+function `int PyRun_AnyFile(FILE *fp, const char *filename)`.
+
+Therefore its signature is `func PyRun_AnyFile(filename string) (int, error)`,
+the `int` represent the error code from the CPython `PyRun_AnyFile` function
+and error will be set if we failed to open `filename`.
+
+If an error is raise before calling th CPython function `int` default to `-1`.
diff --git a/high_level_layer.go b/high_level_layer.go
index 1df3e41..a27220e 100644
--- a/high_level_layer.go
+++ b/high_level_layer.go
@@ -10,7 +10,8 @@ import (
 )
 
 //Py_Main : https://docs.python.org/3/c-api/veryhigh.html?highlight=pycompilerflags#c.Py_Main
-func Py_Main(args []string) int {
+// "error" will be set if we fail to call "Py_DecodeLocale" on every "args".
+func Py_Main(args []string) (int, error) {
 	argc := C.int(len(args))
 	argv := make([]*C.wchar_t, argc, argc)
 	for i, arg := range args {
@@ -19,32 +20,33 @@ func Py_Main(args []string) int {
 
 		warg := C.Py_DecodeLocale(carg, nil)
 		if warg == nil {
-			return -1
+			return -1, fmt.Errorf("fail to call Py_DecodeLocale on '%s'", arg)
 		}
 		// Py_DecodeLocale requires a call to PyMem_RawFree to free the memory
 		defer C.PyMem_RawFree(unsafe.Pointer(warg))
 		argv[i] = warg
 	}
 
-	return int(C.Py_Main(argc, (**C.wchar_t)(unsafe.Pointer(&argv[0]))))
+	return int(C.Py_Main(argc, (**C.wchar_t)(unsafe.Pointer(&argv[0])))), nil
 }
 
 //PyRun_AnyFile : https://docs.python.org/3/c-api/veryhigh.html?highlight=pycompilerflags#c.PyRun_AnyFile
-func PyRun_AnyFile(filename string) int {
+// "error" will be set if we fail to open "filename".
+func PyRun_AnyFile(filename string) (int, error) {
 	cfilename := C.CString(filename)
 	defer C.free(unsafe.Pointer(cfilename))
 
 	mode := C.CString("r")
 	defer C.free(unsafe.Pointer(mode))
 
-	cfile := C.fopen(cfilename, mode)
-	if cfile == nil {
-		return 1
+	cfile, err := C.fopen(cfilename, mode)
+	if err != nil {
+		return -1, fmt.Errorf("fail to open '%s': %s", filename, err)
 	}
 	defer C.fclose(cfile)
 
 	// C.PyRun_AnyFile is a macro, using C.PyRun_AnyFileFlags instead
-	return int(C.PyRun_AnyFileFlags(cfile, cfilename, nil))
+	return int(C.PyRun_AnyFileFlags(cfile, cfilename, nil)), nil
 }
 
 //PyRun_SimpleString : https://docs.python.org/3/c-api/veryhigh.html?highlight=pycompilerflags#c.PyRun_SimpleString