refactor(custom): extract generic helper for FFmpeg iterator functions

- Add iterateFFmpeg[T any] helper to consolidate duplicate iteration
  pattern across six functions
- Refactor AVMuxerIterate, AVDemuxerIterate, AVParserIterate,
  AVCodecIterate, AVFilterIterate, AVBSFIterate to use the helper
- Centralise nil-check and type wrapping logic for easier maintenance

Author: flexiondotorg

custom.go

@@ -32,6 +32,17 @@ import (
 	"unsafe"
 )
 
+// iterateFFmpeg is a generic helper for FFmpeg iterator functions.
+// It handles the common pattern of calling a C iterator, checking for nil,
+// and wrapping the result in a Go type.
+func iterateFFmpeg[T any](opaque *unsafe.Pointer, iterate func(*unsafe.Pointer) unsafe.Pointer, wrap func(unsafe.Pointer) *T) *T {
+	ret := iterate(opaque)
+	if ret == nil {
+		return nil
+	}
+	return wrap(ret)
+}
+
 // AVMuxerIterate iterates over all registered muxers.
 //
 // @param opaque a pointer where libavformat will store the iteration state. Must
@@ -40,11 +51,13 @@ import (
 //
 // @return the next registered muxer or NULL when the iteration is finished
 func AVMuxerIterate(opaque *unsafe.Pointer) *AVOutputFormat {
-	ret := C.av_muxer_iterate((*unsafe.Pointer)(unsafe.Pointer(opaque)))
-	if ret == nil {
-		return nil
-	}
-	return &AVOutputFormat{ptr: ret}
+	return iterateFFmpeg(opaque,
+		func(op *unsafe.Pointer) unsafe.Pointer {
+			return unsafe.Pointer(C.av_muxer_iterate((*unsafe.Pointer)(unsafe.Pointer(op))))
+		},
+		func(p unsafe.Pointer) *AVOutputFormat {
+			return &AVOutputFormat{ptr: (*C.AVOutputFormat)(p)}
+		})
 }
 
 // AVDemuxerIterate iterates over all registered demuxers.
@@ -55,11 +68,13 @@ func AVMuxerIterate(opaque *unsafe.Pointer) *AVOutputFormat {
 //
 // @return the next registered demuxer or NULL when the iteration is finished
 func AVDemuxerIterate(opaque *unsafe.Pointer) *AVInputFormat {
-	ret := C.av_demuxer_iterate((*unsafe.Pointer)(unsafe.Pointer(opaque)))
-	if ret == nil {
-		return nil
-	}
-	return &AVInputFormat{ptr: ret}
+	return iterateFFmpeg(opaque,
+		func(op *unsafe.Pointer) unsafe.Pointer {
+			return unsafe.Pointer(C.av_demuxer_iterate((*unsafe.Pointer)(unsafe.Pointer(op))))
+		},
+		func(p unsafe.Pointer) *AVInputFormat {
+			return &AVInputFormat{ptr: (*C.AVInputFormat)(p)}
+		})
 }
 
 // AVParserIterate iterates over all registered codec parsers.
@@ -70,11 +85,13 @@ func AVDemuxerIterate(opaque *unsafe.Pointer) *AVInputFormat {
 //
 // @return the next registered parser or NULL when the iteration is finished
 func AVParserIterate(opaque *unsafe.Pointer) *AVCodecParser {
-	ret := (*C.AVCodecParser)(C.av_parser_iterate((*unsafe.Pointer)(unsafe.Pointer(opaque))))
-	if ret == nil {
-		return nil
-	}
-	return &AVCodecParser{ptr: ret}
+	return iterateFFmpeg(opaque,
+		func(op *unsafe.Pointer) unsafe.Pointer {
+			return unsafe.Pointer(C.av_parser_iterate((*unsafe.Pointer)(unsafe.Pointer(op))))
+		},
+		func(p unsafe.Pointer) *AVCodecParser {
+			return &AVCodecParser{ptr: (*C.AVCodecParser)(p)}
+		})
 }
 
 // AVCodecIterate iterates over all registered codecs.
@@ -85,11 +102,13 @@ func AVParserIterate(opaque *unsafe.Pointer) *AVCodecParser {
 //
 // @return the next registered codec or NULL when the iteration is finished
 func AVCodecIterate(opaque *unsafe.Pointer) *AVCodec {
-	ret := C.av_codec_iterate((*unsafe.Pointer)(unsafe.Pointer(opaque)))
-	if ret == nil {
-		return nil
-	}
-	return &AVCodec{ptr: ret}
+	return iterateFFmpeg(opaque,
+		func(op *unsafe.Pointer) unsafe.Pointer {
+			return unsafe.Pointer(C.av_codec_iterate((*unsafe.Pointer)(unsafe.Pointer(op))))
+		},
+		func(p unsafe.Pointer) *AVCodec {
+			return &AVCodec{ptr: (*C.AVCodec)(p)}
+		})
 }
 
 // AVFilterIterate iterates over all registered filters.
@@ -100,11 +119,13 @@ func AVCodecIterate(opaque *unsafe.Pointer) *AVCodec {
 //
 // @return the next registered filter or NULL when the iteration is finished
 func AVFilterIterate(opaque *unsafe.Pointer) *AVFilter {
-	ret := C.av_filter_iterate((*unsafe.Pointer)(unsafe.Pointer(opaque)))
-	if ret == nil {
-		return nil
-	}
-	return &AVFilter{ptr: ret}
+	return iterateFFmpeg(opaque,
+		func(op *unsafe.Pointer) unsafe.Pointer {
+			return unsafe.Pointer(C.av_filter_iterate((*unsafe.Pointer)(unsafe.Pointer(op))))
+		},
+		func(p unsafe.Pointer) *AVFilter {
+			return &AVFilter{ptr: (*C.AVFilter)(p)}
+		})
 }
 
 // AVBSFIterate iterates over all registered bitstream filters.
@@ -115,11 +136,13 @@ func AVFilterIterate(opaque *unsafe.Pointer) *AVFilter {
 //
 // @return the next registered bitstream filter or NULL when the iteration is finished
 func AVBSFIterate(opaque *unsafe.Pointer) *AVBitStreamFilter {
-	ret := C.av_bsf_iterate((*unsafe.Pointer)(unsafe.Pointer(opaque)))
-	if ret == nil {
-		return nil
-	}
-	return &AVBitStreamFilter{ptr: ret}
+	return iterateFFmpeg(opaque,
+		func(op *unsafe.Pointer) unsafe.Pointer {
+			return unsafe.Pointer(C.av_bsf_iterate((*unsafe.Pointer)(unsafe.Pointer(op))))
+		},
+		func(p unsafe.Pointer) *AVBitStreamFilter {
+			return &AVBitStreamFilter{ptr: (*C.AVBitStreamFilter)(p)}
+		})
 }
 
 // AVIOEnumProtocols iterates through names of available protocols.