Add method to write file to io.Writer

context.go

@@ -20,14 +20,34 @@
 package libheif
 
 // #cgo pkg-config: libheif
-// #include <stdlib.h>
-// #include <string.h>
-// #include <libheif/heif.h>
+/*
+#include <stdlib.h>
+#include <string.h>
+#include <libheif/heif.h>
+
+extern struct heif_error writeGo(void* data, size_t size, void* userdata);
+
+struct heif_error writeCgo(struct heif_context* ctx, const void* data, size_t size, void* userdata) {
+	struct heif_error err = writeGo((char*)data, size, userdata);
+	if (!err.message) {
+		switch (err.code) {
+			case heif_error_Ok:
+				err.message = "Success";
+				break;
+			default:
+				err.message = "Error writing";
+				break;
+		}
+	}
+	return err;
+}
+*/
 import "C"
 
 import (
 	"errors"
 	"fmt"
+	"io"
 	"runtime"
 	"unsafe"
 )
@@ -112,6 +132,32 @@ func (c *Context) NewEncoder(compression CompressionFormat) (*Encoder, error) {
 	return c.convertEncoderDescriptor(descriptors[0])
 }
 
+// Write saves the current image.
+func (c *Context) Write(w io.Writer) error {
+	defer runtime.KeepAlive(c)
+
+	writer := &C.struct_heif_writer{
+		writer_api_version: 1,
+
+		write: (*[0]byte)(C.writeCgo),
+	}
+	writerData := &writerData{
+		w: w,
+	}
+
+	var p runtime.Pinner
+	p.Pin(w)
+	defer p.Unpin()
+
+	err := C.heif_context_write(c.context, writer, unsafe.Pointer(writerData))
+	if writerData.err != nil {
+		// Bubble up error returned by passed io.Writer
+		return writerData.err
+	}
+
+	return convertHeifError(err)
+}
+
 // WriteToFile saves the current image to the given file.
 func (c *Context) WriteToFile(filename string) error {
 	defer runtime.KeepAlive(c)

context_writer.go

@@ -0,0 +1,62 @@
+/*
+ * Go interface to libheif
+ *
+ * Copyright (c) 2018-2024 struktur AG, Joachim Bauch <[email protected]>
+ *
+ * libheif is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version.
+ *
+ * libheif is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with libheif.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package libheif
+
+// #cgo pkg-config: libheif
+/*
+#include <stdlib.h>
+#include <string.h>
+#include <libheif/heif.h>
+*/
+import "C"
+
+import (
+	"io"
+	"unsafe"
+)
+
+type writerData struct {
+	w   io.Writer
+	err error
+}
+
+//export writeGo
+func writeGo(data *C.void, size C.size_t, userdata *C.void) C.struct_heif_error {
+	writer := (*writerData)(unsafe.Pointer(userdata))
+	if writer.err != nil {
+		return C.struct_heif_error{
+			code:    C.heif_error_Ok,
+			subcode: C.heif_suberror_Unspecified,
+		}
+	}
+
+	_, err := writer.w.Write(C.GoBytes(unsafe.Pointer(data), C.int(size)))
+	if err != nil {
+		writer.err = err
+		return C.struct_heif_error{
+			code:    C.heif_error_Usage_error,
+			subcode: C.heif_suberror_Unspecified,
+		}
+	}
+
+	return C.struct_heif_error{
+		code:    C.heif_error_Ok,
+		subcode: C.heif_suberror_Unspecified,
+	}
+}