[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

2 files changed, 19 insertions, 7 deletions

diff --git a/internal/transport/derefmedia.go b/internal/transport/derefmedia.go
index 265a9e77e..873032f39 100644
--- a/internal/transport/derefmedia.go
+++ b/internal/transport/derefmedia.go
@@ -23,30 +23,42 @@ import (
 	"net/http"
 	"net/url"
 
+	"codeberg.org/gruf/go-bytesize"
+	"codeberg.org/gruf/go-iotools"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 )
 
-func (t *transport) DereferenceMedia(ctx context.Context, iri *url.URL) (io.ReadCloser, int64, error) {
+func (t *transport) DereferenceMedia(ctx context.Context, iri *url.URL, maxsz int64) (io.ReadCloser, error) {
 	// Build IRI just once
 	iriStr := iri.String()
 
 	// Prepare HTTP request to this media's IRI
 	req, err := http.NewRequestWithContext(ctx, "GET", iriStr, nil)
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 	req.Header.Add("Accept", "*/*") // we don't know what kind of media we're going to get here
 
 	// Perform the HTTP request
 	rsp, err := t.GET(req)
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 
 	// Check for an expected status code
 	if rsp.StatusCode != http.StatusOK {
-		return nil, 0, gtserror.NewFromResponse(rsp)
+		return nil, gtserror.NewFromResponse(rsp)
 	}
 
-	return rsp.Body, rsp.ContentLength, nil
+	// Check media within size limit.
+	if rsp.ContentLength > maxsz {
+		_ = rsp.Body.Close()       // close early.
+		sz := bytesize.Size(maxsz) // nicer log format
+		return nil, gtserror.Newf("media body exceeds max size %s", sz)
+	}
+
+	// Update response body with maximum supported media size.
+	rsp.Body, _, _ = iotools.UpdateReadCloserLimit(rsp.Body, maxsz)
+
+	return rsp.Body, nil
 }
diff --git a/internal/transport/transport.go b/internal/transport/transport.go
index 110c19b3d..2971ca603 100644
--- a/internal/transport/transport.go
+++ b/internal/transport/transport.go
@@ -67,8 +67,8 @@ type Transport interface {
 	// Dereference fetches the ActivityStreams object located at this IRI with a GET request.
 	Dereference(ctx context.Context, iri *url.URL) (*http.Response, error)
 
-	// DereferenceMedia fetches the given media attachment IRI, returning the reader and filesize.
-	DereferenceMedia(ctx context.Context, iri *url.URL) (io.ReadCloser, int64, error)
+	// DereferenceMedia fetches the given media attachment IRI, returning the reader limited to given max.
+	DereferenceMedia(ctx context.Context, iri *url.URL, maxsz int64) (io.ReadCloser, error)
 
 	// DereferenceInstance dereferences remote instance information, first by checking /api/v1/instance, and then by checking /.well-known/nodeinfo.
 	DereferenceInstance(ctx context.Context, iri *url.URL) (*gtsmodel.Instance, error)