[feature] support processing of (many) more media types (#3090)

* initial work replacing our media decoding / encoding pipeline with ffprobe + ffmpeg

* specify the video codec to use when generating static image from emoji

* update go-storage library (fixes incompatibility after updating go-iotools)

* maintain image aspect ratio when generating a thumbnail for it

* update readme to show go-ffmpreg

* fix a bunch of media tests, move filesize checking to callers of media manager for more flexibility

* remove extra debug from error message

* fix up incorrect function signatures

* update PutFile to just use regular file copy, as changes are file is on separate partition

* fix remaining tests, remove some unneeded tests now we're working with ffmpeg/ffprobe

* update more tests, add more code comments

* add utilities to generate processed emoji / media outputs

* fix remaining tests

* add test for opus media file, add license header to utility cmds

* limit the number of concurrently available ffmpeg / ffprobe instances

* reduce number of instances

* further reduce number of instances

* fix envparsing test with configuration variables

* update docs and configuration with new media-{local,remote}-max-size variables

vendor/codeberg.org/gruf/go-iotools/helpers.go

@@ -0,0 +1,85 @@
+package iotools
+
+import "io"
+
+// AtEOF returns true when reader at EOF,
+// this is checked with a 0 length read.
+func AtEOF(r io.Reader) bool {
+	_, err := r.Read(nil)
+	return (err == io.EOF)
+}
+
+// GetReadCloserLimit attempts to cast io.Reader to access its io.LimitedReader with limit.
+func GetReaderLimit(r io.Reader) (*io.LimitedReader, int64) {
+	lr, ok := r.(*io.LimitedReader)
+	if !ok {
+		return nil, -1
+	}
+	return lr, lr.N
+}
+
+// UpdateReaderLimit attempts to  update the limit of a reader for existing, newly wrapping if necessary.
+func UpdateReaderLimit(r io.Reader, limit int64) (*io.LimitedReader, int64) {
+	lr, ok := r.(*io.LimitedReader)
+	if !ok {
+		lr = &io.LimitedReader{r, limit}
+		return lr, limit
+	}
+
+	if limit < lr.N {
+		// Update existing.
+		lr.N = limit
+	}
+
+	return lr, lr.N
+}
+
+// GetReadCloserLimit attempts to unwrap io.ReadCloser to access its io.LimitedReader with limit.
+func GetReadCloserLimit(rc io.ReadCloser) (*io.LimitedReader, int64) {
+	rct, ok := rc.(*ReadCloserType)
+	if !ok {
+		return nil, -1
+	}
+	lr, ok := rct.Reader.(*io.LimitedReader)
+	if !ok {
+		return nil, -1
+	}
+	return lr, lr.N
+}
+
+// UpdateReadCloserLimit attempts to update the limit of a readcloser for existing, newly wrapping if necessary.
+func UpdateReadCloserLimit(rc io.ReadCloser, limit int64) (io.ReadCloser, *io.LimitedReader, int64) {
+
+	// Check for our wrapped ReadCloserType.
+	if rct, ok := rc.(*ReadCloserType); ok {
+
+		// Attempt to update existing wrapped limit reader.
+		if lr, ok := rct.Reader.(*io.LimitedReader); ok {
+
+			if limit < lr.N {
+				// Update existing.
+				lr.N = limit
+			}
+
+			return rct, lr, lr.N
+		}
+
+		// Wrap the reader type with new limit.
+		lr := &io.LimitedReader{rct.Reader, limit}
+		rct.Reader = lr
+
+		return rct, lr, lr.N
+	}
+
+	// Wrap separated types.
+	rct := &ReadCloserType{
+		Reader: rc,
+		Closer: rc,
+	}
+
+	// Wrap separated reader part with limit.
+	lr := &io.LimitedReader{rct.Reader, limit}
+	rct.Reader = lr
+
+	return rct, lr, lr.N
+}