From e6a14f8cacd5da0c8495e666ec5514bcd2dfe802 Mon Sep 17 00:00:00 2001
From: Noam Kleinburd <noamk@chain-reaction.io>
Date: Sun, 19 Nov 2023 14:04:23 +0200
Subject: [PATCH] Implement efficient copies of bytes.

---
 _examples/gobytes/gobytes.go | 33 ++++++++++++++++++++++++++
 _examples/gobytes/test.py    | 18 ++++++++++++++
 bind/gen_slice.go            | 46 ++++++++++++++++++++++++++++++++++++
 main_test.go                 | 20 ++++++++++++++++
 4 files changed, 117 insertions(+)
 create mode 100644 _examples/gobytes/gobytes.go
 create mode 100644 _examples/gobytes/test.py

diff --git a/_examples/gobytes/gobytes.go b/_examples/gobytes/gobytes.go
new file mode 100644
index 0000000..f7721e8
--- /dev/null
+++ b/_examples/gobytes/gobytes.go
@@ -0,0 +1,33 @@
+// Copyright 2017 The go-python Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gobytes
+
+func HashBytes(b []byte) [4]byte {
+	result := [4]byte{0, 0, 0, 0}
+	full_blocks := len(b) / 4
+	for i := 0; i < full_blocks; i++ {
+		for j := 0; j < 4; j++ {
+			result[j] ^= b[4*i+j]
+		}
+	}
+	if full_blocks*4 < len(b) {
+		for j := 0; j < 4; j++ {
+			if full_blocks*4+j < len(b) {
+				result[j] ^= b[full_blocks*4+j]
+			} else {
+				result[j] ^= 0x55
+			}
+		}
+	}
+	return result
+}
+
+func CreateBytes(len byte) []byte {
+	res := make([]byte, len)
+	for i := (byte)(0); i < len; i++ {
+		res[i] = i
+	}
+	return res
+}
diff --git a/_examples/gobytes/test.py b/_examples/gobytes/test.py
new file mode 100644
index 0000000..09887bc
--- /dev/null
+++ b/_examples/gobytes/test.py
@@ -0,0 +1,18 @@
+# Copyright 2017 The go-python Authors.  All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+from __future__ import print_function
+import gobytes, go
+
+a = bytes([0, 1, 2, 3])
+b = gobytes.CreateBytes(10)
+print ("Python bytes:", a)
+print ("Go slice: ", b)
+
+print ("gobytes.HashBytes from Go bytes:", gobytes.HashBytes(b))
+
+print("Python bytes to Go: ", go.Slice_byte.from_bytes(a))
+print("Go bytes to Python: ", bytes(go.Slice_byte([3, 4, 5])))
+
+print("OK")
diff --git a/bind/gen_slice.go b/bind/gen_slice.go
index bb33214..4ef47e4 100644
--- a/bind/gen_slice.go
+++ b/bind/gen_slice.go
@@ -277,6 +277,25 @@ otherwise parameter is a python list that we copy from
 			g.pywrap.Outdent()
 			g.pywrap.Outdent()
 		}
+
+		if slNm == "Slice_byte" {
+			g.pywrap.Printf("@staticmethod\n")
+			g.pywrap.Printf("def from_bytes(value):\n")
+			g.pywrap.Indent()
+			g.pywrap.Printf(`"""Create a Go []byte object from a Python bytes object"""
+`)
+			g.pywrap.Printf("handle = _%s_from_bytes(value)\n", qNm)
+			g.pywrap.Printf("return Slice_byte(handle=handle)\n")
+			g.pywrap.Outdent()
+			g.pywrap.Printf("def __bytes__(self):\n")
+			g.pywrap.Indent()
+			g.pywrap.Printf(`"""Convert the slice to a bytes object."""
+`)
+			g.pywrap.Printf("return _%s_to_bytes(self.handle)\n", qNm)
+			g.pywrap.Outdent()
+			g.pywrap.Outdent()
+
+		}
 	}
 
 	if !extTypes || !pyWrapOnly {
@@ -367,6 +386,33 @@ otherwise parameter is a python list that we copy from
 
 			g.pybuild.Printf("mod.add_function('%s_append', None, [param('%s', 'handle'), param('%s', 'value'%s)])\n", slNm, PyHandle, esym.cpyname, transfer_ownership)
 		}
+
+		if slNm == "Slice_byte" {
+			g.gofile.Printf("//export Slice_byte_from_bytes\n")
+			g.gofile.Printf("func Slice_byte_from_bytes(o *C.PyObject) CGoHandle {\n")
+			g.gofile.Indent()
+			g.gofile.Printf("size := C.PyBytes_Size(o)\n")
+			g.gofile.Printf("ptr := unsafe.Pointer(C.PyBytes_AsString(o))\n")
+			g.gofile.Printf("data := make([]byte, size)\n")
+			g.gofile.Printf("tmp := unsafe.Slice((*byte)(ptr), size)\n")
+			g.gofile.Printf("copy(data, tmp)\n")
+			g.gofile.Printf("return handleFromPtr_Slice_byte(&data)\n")
+			g.gofile.Outdent()
+			g.gofile.Printf("}\n\n")
+
+			g.gofile.Printf("//export Slice_byte_to_bytes\n")
+			g.gofile.Printf("func Slice_byte_to_bytes(handle CGoHandle) *C.PyObject {\n")
+			g.gofile.Indent()
+			g.gofile.Printf("s := deptrFromHandle_Slice_byte(handle)\n")
+			g.gofile.Printf("ptr := unsafe.Pointer(&s[0])\n")
+			g.gofile.Printf("size := len(s)\n")
+			g.gofile.Printf("return C.PyBytes_FromStringAndSize((*C.char)(ptr), C.long(size))\n")
+			g.gofile.Outdent()
+			g.gofile.Printf("}\n\n")
+
+			g.pybuild.Printf("mod.add_function('Slice_byte_from_bytes', retval('%s'%s), [param('PyObject*', 'o', transfer_ownership=False)])\n", PyHandle, caller_owns_ret)
+			g.pybuild.Printf("mod.add_function('Slice_byte_to_bytes', retval('PyObject*', caller_owns_return=True), [param('%s', 'handle')])\n", PyHandle)
+		}
 	}
 }
 
diff --git a/main_test.go b/main_test.go
index 38c03e3..5592072 100644
--- a/main_test.go
+++ b/main_test.go
@@ -23,6 +23,7 @@ var (
 	testBackends = map[string]string{}
 	features     = map[string][]string{
 		"_examples/hi":          []string{"py3"},
+		"_examples/gobytes":     []string{"py3"},
 		"_examples/funcs":       []string{"py3"},
 		"_examples/sliceptr":    []string{"py3"},
 		"_examples/simple":      []string{"py3"},
@@ -267,6 +268,25 @@ OK
 
 }
 
+func TestBytes(t *testing.T) {
+	// t.Parallel()
+	path := "_examples/gobytes"
+	testPkg(t, pkg{
+		path:   path,
+		lang:   features[path],
+		cmd:    "build",
+		extras: nil,
+		want: []byte(`Python bytes: b'\x00\x01\x02\x03'
+Go slice:  go.Slice_byte len: 10 handle: 1 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+gobytes.HashBytes from Go bytes: gobytes.Array_4_byte len: 4 handle: 2 [12, 13, 81, 81]
+Python bytes to Go:  go.Slice_byte len: 4 handle: 3 [0, 1, 2, 3]
+Go bytes to Python:  b'\x03\x04\x05'
+OK
+`),
+	})
+
+}
+
 func TestBindFuncs(t *testing.T) {
 	// t.Parallel()
 	path := "_examples/funcs"