[performance] remove local copying of file for satisfying range headers

internal/api/fileserver/servefile.go

@@ -19,17 +19,17 @@
 package fileserver
 
 import (
-	"bytes"
 	"fmt"
 	"io"
 	"net/http"
 	"strconv"
+	"strings"
 
+	"codeberg.org/gruf/go-fastcopy"
 	"github.com/gin-gonic/gin"
 	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
 	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
-	"github.com/superseriousbusiness/gotosocial/internal/iotools"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
 	"github.com/superseriousbusiness/gotosocial/internal/oauth"
 )
@@ -87,20 +87,19 @@ func (m *Module) ServeFile(c *gin.Context) {
 		return
 	}
 
-	defer func() {
-		// close content when we're done
-		if content.Content != nil {
-			if err := content.Content.Close(); err != nil {
-				log.Errorf("ServeFile: error closing readcloser: %s", err)
-			}
-		}
-	}()
-
 	if content.URL != nil {
+		// This is a non-local S3 file we're proxying to.
 		c.Redirect(http.StatusFound, content.URL.String())
 		return
 	}
 
+	defer func() {
+		// Close content when we're done, catch errors.
+		if err := content.Content.Close(); err != nil {
+			log.Errorf("ServeFile: error closing readcloser: %s", err)
+		}
+	}()
+
 	// TODO: if the requester only accepts text/html we should try to serve them *something*.
 	// This is mostly needed because when sharing a link to a gts-hosted file on something like mastodon, the masto servers will
 	// attempt to look up the content to provide a preview of the link, and they ask for text/html.
@@ -118,45 +117,123 @@ func (m *Module) ServeFile(c *gin.Context) {
 		return
 	}
 
-	// create a "slurp" buffer ;)
-	b := make([]byte, 64)
-
-	// Try read the first 64 bytes into memory, to try return a more useful "not found" error.
-	if _, err := io.ReadFull(content.Content, b); err != nil &&
-		(err != io.ErrUnexpectedEOF && err != io.EOF) {
-		err = fmt.Errorf("ServeFile: error reading from content: %w", err)
-		apiutil.ErrorHandler(c, gtserror.NewErrorNotFound(err, err.Error()), m.processor.InstanceGetV1)
+	// Look for a provided range header.
+	rng := c.GetHeader("Range")
+	if rng == "" {
+		// This is a simple query for the whole file, so do a read from whole reader.
+		c.DataFromReader(http.StatusOK, content.ContentLength, format, content.Content, nil)
 		return
 	}
 
-	// reconstruct the original content reader
-	r := io.MultiReader(bytes.NewReader(b), content.Content)
+	// Set known content-type and serve this file range.
+	c.Header("Content-Type", format)
+	serveFileRange(c.Writer, content.Content, rng, content.ContentLength)
+}
+
+// serveFileRange serves the range of a file from a given source reader, without the
+// need for implementation of io.Seeker. Instead we read the first 'start' many bytes
+// into a discard reader. Code is adapted from https://codeberg.org/gruf/simplehttp.
+func serveFileRange(rw http.ResponseWriter, src io.Reader, rng string, size int64) {
+	var i int
 
-	// Check the Range header: if this is a simple query for the whole file, we can return it now.
-	if c.GetHeader("Range") == "" && c.GetHeader("If-Range") == "" {
-		c.DataFromReader(http.StatusOK, content.ContentLength, format, r, nil)
+	if i = strings.IndexByte(rng, '='); i < 0 {
+		// Range must include a separating '=' to indicate start
+		http.Error(rw, "Bad Range Header", http.StatusBadRequest)
 		return
 	}
 
-	// Range is set, so we need a ReadSeeker to pass to the ServeContent function.
-	tfs, err := iotools.TempFileSeeker(r)
-	if err != nil {
-		err = fmt.Errorf("ServeFile: error creating temp file seeker: %w", err)
-		apiutil.ErrorHandler(c, gtserror.NewErrorInternalError(err), m.processor.InstanceGetV1)
+	if rng[:i] != "bytes" {
+		// We only support byte ranges in our implementation
+		http.Error(rw, "Unsupported Range Unit", http.StatusBadRequest)
 		return
 	}
-	defer func() {
-		if err := tfs.Close(); err != nil {
-			log.Errorf("ServeFile: error closing temp file seeker: %s", err)
+
+	// Reslice past '='
+	rng = rng[i+1:]
+
+	if i = strings.IndexByte(rng, '-'); i < 0 {
+		// Range header must contain a beginning and end separated by '-'
+		http.Error(rw, "Bad Range Header", http.StatusBadRequest)
+		return
+	}
+
+	var (
+		err error
+
+		// default start + end ranges
+		start, end = int64(0), size - 1
+
+		// start + end range strings
+		startRng, endRng string
+	)
+
+	if startRng = rng[:i]; len(startRng) > 0 {
+		// Parse the start of this byte range
+		start, err = strconv.ParseInt(startRng, 10, 64)
+		if err != nil {
+			http.Error(rw, "Bad Range Header", http.StatusBadRequest)
+			return
 		}
-	}()
 
-	// to avoid ServeContent wasting time seeking for the
-	// mime type, set this header already since we know it
-	c.Header("Content-Type", format)
+		if start < 0 {
+			// This range starts *before* the file start, why did they send this lol
+			rw.Header().Set("Content-Range", "bytes *"+strconv.FormatInt(size, 10))
+			http.Error(rw, "Unsatisfiable Range", http.StatusRequestedRangeNotSatisfiable)
+			return
+		}
+	} else {
+		// No start supplied, implying file start
+		startRng = "0"
+	}
+
+	if endRng = rng[i+1:]; len(endRng) > 0 {
+		// Parse the end of this byte range
+		end, err = strconv.ParseInt(endRng, 10, 64)
+		if err != nil {
+			http.Error(rw, "Bad Range Header", http.StatusBadRequest)
+			return
+		}
 
-	// allow ServeContent to handle the rest of the request;
-	// it will handle Range as appropriate, and write correct
-	// response headers, http code, etc
-	http.ServeContent(c.Writer, c.Request, fileName, content.ContentUpdated, tfs)
+		if end > size {
+			// This range exceeds length of the file, therefore unsatisfiable
+			rw.Header().Set("Content-Range", "bytes *"+strconv.FormatInt(size, 10))
+			http.Error(rw, "Unsatisfiable Range", http.StatusRequestedRangeNotSatisfiable)
+			return
+		}
+	} else {
+		// No end supplied, implying file end
+		endRng = strconv.FormatInt(end, 10)
+	}
+
+	if start >= end {
+		// This range starts _after_ their range end, unsatisfiable and nonsense!
+		rw.Header().Set("Content-Range", "bytes *"+strconv.FormatInt(size, 10))
+		http.Error(rw, "Unsatisfiable Range", http.StatusRequestedRangeNotSatisfiable)
+		return
+	}
+
+	// Dump the first 'start' many bytes into the void...
+	if _, err := fastcopy.CopyN(io.Discard, src, start); err != nil {
+		log.Errorf("error reading from source: %v", err)
+		return
+	}
+
+	// Determine content len
+	length := end - start
+
+	if end < size-1 {
+		// Range end < file end, limit the reader
+		src = io.LimitReader(src, length)
+	}
+
+	// Write the necessary length and range headers
+	rw.Header().Set("Content-Range", "bytes "+startRng+"-"+endRng+"/"+strconv.FormatInt(size, 10))
+	rw.Header().Set("Content-Length", strconv.FormatInt(length, 10))
+	rw.WriteHeader(http.StatusPartialContent)
+
+	// Read the "seeked" source reader into destination writer.
+	if _, err := fastcopy.Copy(rw, src); err != nil {
+		log.Errorf("error reading from source: %v", err)
+		return
+	}
 }