From 74ca850366e8012549cfdd34814a5e8596f642a9 Mon Sep 17 00:00:00 2001
From: Robert Vasek <robert.vasek@cern.ch>
Date: Thu, 10 Feb 2022 18:09:55 +0100
Subject: [PATCH] cutil: added BufferGroup

BufferGroup is a helper structure that holds Go-allocated slices of
C-allocated strings and their respective lengths. Useful for C functions
that consume byte buffers with explicit length instead of null-terminated
strings.
---
 internal/cutil/buffergroup.go      | 89 ++++++++++++++++++++++++++++++
 internal/cutil/buffergroup_test.go | 53 ++++++++++++++++++
 2 files changed, 142 insertions(+)
 create mode 100644 internal/cutil/buffergroup.go
 create mode 100644 internal/cutil/buffergroup_test.go

diff --git a/internal/cutil/buffergroup.go b/internal/cutil/buffergroup.go
new file mode 100644
index 0000000..447ec11
--- /dev/null
+++ b/internal/cutil/buffergroup.go
@@ -0,0 +1,89 @@
+package cutil
+
+// #include <stdlib.h>
+import "C"
+
+import (
+	"unsafe"
+)
+
+// BufferGroup is a helper structure that holds Go-allocated slices of
+// C-allocated strings and their respective lengths. Useful for C functions
+// that consume byte buffers with explicit length instead of null-terminated
+// strings. When used as input arguments in C functions, caller must make sure
+// the C code will not hold any pointers to either of the struct's attributes
+// after that C function returns.
+type BufferGroup struct {
+	// C-allocated buffers.
+	Buffers []CharPtr
+	// Lengths of C buffers, where Lengths[i] = length(Buffers[i]).
+	Lengths []SizeT
+}
+
+// TODO: should BufferGroup implementation change and the slices would contain
+//       nested Go pointers, they must be pinned with PtrGuard.
+
+// NewBufferGroupStrings returns new BufferGroup constructed from strings.
+func NewBufferGroupStrings(strs []string) *BufferGroup {
+	s := &BufferGroup{
+		Buffers: make([]CharPtr, len(strs)),
+		Lengths: make([]SizeT, len(strs)),
+	}
+
+	for i, str := range strs {
+		bs := []byte(str)
+		s.Buffers[i] = CharPtr(C.CBytes(bs))
+		s.Lengths[i] = SizeT(len(bs))
+	}
+
+	return s
+}
+
+// NewBufferGroupBytes returns new BufferGroup constructed
+// from slice of byte slices.
+func NewBufferGroupBytes(bss [][]byte) *BufferGroup {
+	s := &BufferGroup{
+		Buffers: make([]CharPtr, len(bss)),
+		Lengths: make([]SizeT, len(bss)),
+	}
+
+	for i, bs := range bss {
+		s.Buffers[i] = CharPtr(C.CBytes(bs))
+		s.Lengths[i] = SizeT(len(bs))
+	}
+
+	return s
+}
+
+// Free free()s the C-allocated memory.
+func (s *BufferGroup) Free() {
+	for _, ptr := range s.Buffers {
+		C.free(unsafe.Pointer(ptr))
+	}
+
+	s.Buffers = nil
+	s.Lengths = nil
+}
+
+// BuffersPtr returns a pointer to the beginning of the Buffers slice.
+func (s *BufferGroup) BuffersPtr() CharPtrPtr {
+	if len(s.Buffers) == 0 {
+		return nil
+	}
+
+	return CharPtrPtr(&s.Buffers[0])
+}
+
+// LengthsPtr returns a pointer to the beginning of the Lengths slice.
+func (s *BufferGroup) LengthsPtr() SizeTPtr {
+	if len(s.Lengths) == 0 {
+		return nil
+	}
+
+	return SizeTPtr(&s.Lengths[0])
+}
+
+func testBufferGroupGet(s *BufferGroup, index int) (str string, length int) {
+	bs := C.GoBytes(unsafe.Pointer(s.Buffers[index]), C.int(s.Lengths[index]))
+	return string(bs), int(s.Lengths[index])
+}
diff --git a/internal/cutil/buffergroup_test.go b/internal/cutil/buffergroup_test.go
new file mode 100644
index 0000000..9a0eccd
--- /dev/null
+++ b/internal/cutil/buffergroup_test.go
@@ -0,0 +1,53 @@
+package cutil
+
+import (
+	"testing"
+	"unsafe"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBufferGroup(t *testing.T) {
+	t.Run("Empty", func(t *testing.T) {
+		s := NewBufferGroupStrings(nil)
+		assert.NotPanics(t, func() { s.Free() })
+	})
+	t.Run("NotEmpty", func(t *testing.T) {
+		s := NewBufferGroupStrings([]string{"hello"})
+		assert.NotPanics(t, func() { s.Free() })
+	})
+	t.Run("FreeSetsNil", func(t *testing.T) {
+		s := NewBufferGroupStrings([]string{"hello"})
+		s.Free()
+		assert.Nil(t, s.Buffers)
+		assert.Nil(t, s.Lengths)
+	})
+	t.Run("DoubleFree", func(t *testing.T) {
+		s := NewBufferGroupStrings([]string{"hello"})
+		assert.NotPanics(t, func() { s.Free() })
+		assert.NotPanics(t, func() { s.Free() })
+	})
+	t.Run("ValidPtrs", func(t *testing.T) {
+		s := NewBufferGroupStrings([]string{"hello"})
+		defer s.Free()
+		assert.Equal(t, unsafe.Pointer(&s.Buffers[0]), unsafe.Pointer(s.BuffersPtr()))
+		assert.Equal(t, unsafe.Pointer(&s.Lengths[0]), unsafe.Pointer(s.LengthsPtr()))
+	})
+	t.Run("ValidContents", func(t *testing.T) {
+		values := []string{
+			"1", "12", "123", "世界", "abc\x00", "ab\x00c",
+		}
+
+		s := NewBufferGroupStrings(values)
+		defer s.Free()
+
+		assert.Equal(t, len(values), len(s.Buffers))
+		assert.Equal(t, len(values), len(s.Lengths))
+
+		for i := range values {
+			actualStr, actualLen := testBufferGroupGet(s, i)
+			assert.Equal(t, values[i], actualStr)
+			assert.Equal(t, len(values[i]), actualLen)
+		}
+	})
+}