From e5ae44fe8287c6a5f91c8f9dfced7cb661f0d79b Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Wed, 28 Apr 2021 10:50:08 +0200
Subject: [PATCH] Tidy up some error handling a little.

---
 src/lib/exceptions.h          |  8 ++++++++
 src/lib/ffmpeg.cc             |  7 ++++---
 src/lib/ffmpeg_image_proxy.cc | 20 ++++++++++++--------
 3 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/src/lib/exceptions.h b/src/lib/exceptions.h
index c64f561a8..8bce0c8ab 100644
--- a/src/lib/exceptions.h
+++ b/src/lib/exceptions.h
@@ -44,6 +44,14 @@ public:
 	explicit DecodeError (std::string s)
 		: std::runtime_error (s)
 	{}
+
+	explicit DecodeError (std::string function, std::string caller)
+		: std::runtime_error (String::compose("%1 failed in %2", function, caller))
+	{}
+
+	explicit DecodeError (std::string function, std::string caller, int error)
+		: std::runtime_error (String::compose("%1 failed in %2 (%3)", function, caller, error))
+	{}
 };
 
 class CryptoError : public std::runtime_error
diff --git a/src/lib/ffmpeg.cc b/src/lib/ffmpeg.cc
index 7bb17f9bf..3de5da275 100644
--- a/src/lib/ffmpeg.cc
+++ b/src/lib/ffmpeg.cc
@@ -192,7 +192,7 @@ FFmpeg::setup_general ()
 
 	_frame = av_frame_alloc ();
 	if (_frame == 0) {
-		throw DecodeError (N_("could not allocate frame"));
+		throw std::bad_alloc ();
 	}
 }
 
@@ -225,8 +225,9 @@ DCPOMATIC_DISABLE_WARNINGS
 			/* Enable following of links in files */
 			av_dict_set_int (&options, "enable_drefs", 1, 0);
 
-			if (avcodec_open2 (context, codec, &options) < 0) {
-				throw DecodeError (N_("could not open decoder"));
+			int r = avcodec_open2 (context, codec, &options);
+			if (r < 0) {
+				throw DecodeError (N_("avcodec_open2"), N_("FFmpeg::setup_decoders"), r);
 			}
 		} else {
 			dcpomatic_log->log (String::compose ("No codec found for stream %1", i), LogEntry::TYPE_WARNING);
diff --git a/src/lib/ffmpeg_image_proxy.cc b/src/lib/ffmpeg_image_proxy.cc
index d082a8ef7..5e3b725cf 100644
--- a/src/lib/ffmpeg_image_proxy.cc
+++ b/src/lib/ffmpeg_image_proxy.cc
@@ -124,6 +124,8 @@ DCPOMATIC_DISABLE_WARNINGS
 ImageProxy::Result
 FFmpegImageProxy::image (optional<dcp::Size>) const
 {
+	auto constexpr name_for_errors = "FFmpegImageProxy::image";
+
 	boost::mutex::scoped_lock lm (_mutex);
 
 	if (_image) {
@@ -162,34 +164,36 @@ FFmpegImageProxy::image (optional<dcp::Size>) const
 		}
 	}
 
-	if (avformat_find_stream_info(format_context, 0) < 0) {
-		throw DecodeError (_("could not find stream information"));
+	int r = avformat_find_stream_info(format_context, 0);
+	if (r < 0) {
+		throw DecodeError (N_("avcodec_find_stream_info"), name_for_errors, r);
 	}
 
 	DCPOMATIC_ASSERT (format_context->nb_streams == 1);
 
 	AVFrame* frame = av_frame_alloc ();
 	if (!frame) {
-		throw DecodeError (N_("could not allocate frame"));
+		std::bad_alloc ();
 	}
 
 	AVCodecContext* codec_context = format_context->streams[0]->codec;
 	AVCodec* codec = avcodec_find_decoder (codec_context->codec_id);
 	DCPOMATIC_ASSERT (codec);
 
-	if (avcodec_open2 (codec_context, codec, 0) < 0) {
-		throw DecodeError (N_("could not open decoder"));
+	r = avcodec_open2 (codec_context, codec, 0);
+	if (r < 0) {
+		throw DecodeError (N_("avcodec_open2"), name_for_errors, r);
 	}
 
 	AVPacket packet;
-	int r = av_read_frame (format_context, &packet);
+	r = av_read_frame (format_context, &packet);
 	if (r < 0) {
-		throw DecodeError (N_("could not read frame"));
+		throw DecodeError (N_("av_read_frame"), name_for_errors, r);
 	}
 
 	int frame_finished;
 	if (avcodec_decode_video2(codec_context, frame, &frame_finished, &packet) < 0 || !frame_finished) {
-		throw DecodeError (N_("could not decode video"));
+		throw DecodeError (N_("avcodec_decode_video2"), name_for_errors, r);
 	}
 
 	AVPixelFormat const pix_fmt = static_cast<AVPixelFormat>(frame->format);
-- 
2.30.2