Implement static serving of compressed files (#387)

This provides an option for #223 without fully resolving it. (I think.)

Essentially, it acts very similar to the `gzip_static` and similar options for nginx, where it will check for the existence of pre-compressed files and serve those instead if the client allows it. I couldn't find a pre-existing way to actually parse the Accept-Encoding header properly (admittedly didn't look very hard) and just implemented one on my own that should be fine.

This should hopefully not have the same DOS vulnerabilities as #302, since it relies on the existing caching system. Compressed versions of files will be cached just like any other files, and that includes cache for missing files as well.

The compressed files will also be accessible directly, and this won't automatically decompress them. So, if you have a `tar.gz` file that you access directly, it will still be downloaded as the gzipped version, although you will now gain the option to download the `.tar` directly and decompress it in transit. (Which doesn't affect the server at all, just the client's way of interpreting it.)

----

One key thing this change also adds is a short-circuit when accessing directories: these always return 404 via the API, although they'd try the cache anyway and go through that route, which was kind of slow. Adding in the additional encodings, it's going to try for .gz, .br, and .zst files in the worst case as well, which feels wrong. So, instead, it just always falls back to the index-check behaviour if the path ends in a slash or is empty. (Which is implicitly just a slash.)

----

For testing, I set up this repo: https://codeberg.org/clarfonthey/testrepo

I ended up realising that LFS wasn't supported by default with `just dev`, so, it ended up working until I made sure the files on the repo *didn't* use LFS.

Assuming you've run `just dev`, you can go directly to this page in the browser here: https://clarfonthey.localhost.mock.directory:4430/testrepo/
And also you can try a few cURL commands:

```shell
curl https://clarfonthey.localhost.mock.directory:4430/testrepo/ --verbose --insecure
curl -H 'Accept-Encoding: gz' https://clarfonthey.localhost.mock.directory:4430/testrepo/ --verbose --insecure | gunzip -
curl -H 'Accept-Encoding: br' https://clarfonthey.localhost.mock.directory:4430/testrepo/ --verbose --insecure | brotli --decompress -
curl -H 'Accept-Encoding: zst' https://clarfonthey.localhost.mock.directory:4430/testrepo/ --verbose --insecure | zstd --decompress -
```

Reviewed-on: https://codeberg.org/Codeberg/pages-server/pulls/387
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: ltdk <usr@ltdk.xyz>
Co-committed-by: ltdk <usr@ltdk.xyz>

server/certificates/certificates.go

@@ -196,7 +196,7 @@ func (c *AcmeClient) retrieveCertFromDB(sni, mainDomainSuffix string, useDnsProv
 		// renew certificates 7 days before they expire
 		if tlsCertificate.Leaf.NotAfter.Before(time.Now().Add(7 * 24 * time.Hour)) {
 			// TODO: use ValidTill of custom cert struct
-			if res.CSR != nil && len(res.CSR) > 0 {
+			if len(res.CSR) > 0 {
 				// CSR stores the time when the renewal shall be tried again
 				nextTryUnix, err := strconv.ParseInt(string(res.CSR), 10, 64)
 				if err == nil && time.Now().Before(time.Unix(nextTryUnix, 0)) {

server/gitea/cache.go

@@ -37,7 +37,12 @@ type FileResponse struct {
 	Exists    bool
 	IsSymlink bool
 	ETag      string
+
+	// uncompressed MIME type
 	MimeType string
+
+	// raw MIME type (if compressed, type of compression)
+	RawMime string
 	Body    []byte
 }
 
@@ -45,7 +50,7 @@ func (f FileResponse) IsEmpty() bool {
 	return len(f.Body) == 0
 }
 
-func (f FileResponse) createHttpResponse(cacheKey string) (header http.Header, statusCode int) {
+func (f FileResponse) createHttpResponse(cacheKey string, decompress bool) (header http.Header, statusCode int) {
 	header = make(http.Header)
 
 	if f.Exists {
@@ -58,7 +63,12 @@ func (f FileResponse) createHttpResponse(cacheKey string) (header http.Header, s
 		header.Set(giteaObjectTypeHeader, objTypeSymlink)
 	}
 	header.Set(ETagHeader, f.ETag)
+
+	if decompress {
 		header.Set(ContentTypeHeader, f.MimeType)
+	} else {
+		header.Set(ContentTypeHeader, f.RawMime)
+	}
 	header.Set(ContentLengthHeader, fmt.Sprintf("%d", len(f.Body)))
 	header.Set(PagesCacheIndicatorHeader, "true")
 

server/gitea/client.go

@@ -42,6 +42,7 @@ const (
 	ETagHeader            = "ETag"
 	ContentTypeHeader     = "Content-Type"
 	ContentLengthHeader   = "Content-Length"
+	ContentEncodingHeader = "Content-Encoding"
 )
 
 type Client struct {
@@ -103,7 +104,7 @@ func (client *Client) ContentWebLink(targetOwner, targetRepo, branch, resource s
 }
 
 func (client *Client) GiteaRawContent(targetOwner, targetRepo, ref, resource string) ([]byte, error) {
-	reader, _, _, err := client.ServeRawContent(targetOwner, targetRepo, ref, resource)
+	reader, _, _, err := client.ServeRawContent(targetOwner, targetRepo, ref, resource, false)
 	if err != nil {
 		return nil, err
 	}
@@ -111,21 +112,21 @@ func (client *Client) GiteaRawContent(targetOwner, targetRepo, ref, resource str
 	return io.ReadAll(reader)
 }
 
-func (client *Client) ServeRawContent(targetOwner, targetRepo, ref, resource string) (io.ReadCloser, http.Header, int, error) {
+func (client *Client) ServeRawContent(targetOwner, targetRepo, ref, resource string, decompress bool) (io.ReadCloser, http.Header, int, error) {
 	cacheKey := fmt.Sprintf("%s/%s/%s|%s|%s", rawContentCacheKeyPrefix, targetOwner, targetRepo, ref, resource)
 	log := log.With().Str("cache_key", cacheKey).Logger()
 	log.Trace().Msg("try file in cache")
 	// handle if cache entry exist
 	if cache, ok := client.responseCache.Get(cacheKey); ok {
 		cache := cache.(FileResponse)
-		cachedHeader, cachedStatusCode := cache.createHttpResponse(cacheKey)
+		cachedHeader, cachedStatusCode := cache.createHttpResponse(cacheKey, decompress)
 		// TODO: check against some timestamp mismatch?!?
 		if cache.Exists {
 			log.Debug().Msg("[cache] exists")
 			if cache.IsSymlink {
 				linkDest := string(cache.Body)
 				log.Debug().Msgf("[cache] follow symlink from %q to %q", resource, linkDest)
-				return client.ServeRawContent(targetOwner, targetRepo, ref, linkDest)
+				return client.ServeRawContent(targetOwner, targetRepo, ref, linkDest, decompress)
 			} else if !cache.IsEmpty() {
 				log.Debug().Msgf("[cache] return %d bytes", len(cache.Body))
 				return io.NopCloser(bytes.NewReader(cache.Body)), cachedHeader, cachedStatusCode, nil
@@ -170,13 +171,17 @@ func (client *Client) ServeRawContent(targetOwner, targetRepo, ref, resource str
 					}
 
 					log.Debug().Msgf("follow symlink from %q to %q", resource, linkDest)
-					return client.ServeRawContent(targetOwner, targetRepo, ref, linkDest)
+					return client.ServeRawContent(targetOwner, targetRepo, ref, linkDest, decompress)
 				}
 			}
 
 			// now we are sure it's content so set the MIME type
-			mimeType := client.getMimeTypeByExtension(resource)
+			mimeType, rawType := client.getMimeTypeByExtension(resource)
+			if decompress {
 				resp.Response.Header.Set(ContentTypeHeader, mimeType)
+			} else {
+				resp.Response.Header.Set(ContentTypeHeader, rawType)
+			}
 
 			if !shouldRespBeSavedToCache(resp.Response) {
 				return reader, resp.Response.Header, resp.StatusCode, err
@@ -187,6 +192,7 @@ func (client *Client) ServeRawContent(targetOwner, targetRepo, ref, resource str
 				Exists:   true,
 				ETag:     resp.Header.Get(ETagHeader),
 				MimeType: mimeType,
+				RawMime:  rawType,
 			}
 			return fileResp.CreateCacheReader(reader, client.responseCache, cacheKey), resp.Response.Header, resp.StatusCode, nil
 
@@ -300,16 +306,31 @@ func (client *Client) GiteaCheckIfOwnerExists(owner string) (bool, error) {
 	return false, nil
 }
 
-func (client *Client) getMimeTypeByExtension(resource string) string {
-	mimeType := mime.TypeByExtension(path.Ext(resource))
+func (client *Client) extToMime(ext string) string {
+	mimeType := mime.TypeByExtension(ext)
 	mimeTypeSplit := strings.SplitN(mimeType, ";", 2)
 	if client.forbiddenMimeTypes[mimeTypeSplit[0]] || mimeType == "" {
 		mimeType = client.defaultMimeType
 	}
-	log.Trace().Msgf("probe mime of %q is %q", resource, mimeType)
 	return mimeType
 }
 
+func (client *Client) getMimeTypeByExtension(resource string) (mimeType, rawType string) {
+	rawExt := path.Ext(resource)
+	innerExt := rawExt
+	switch rawExt {
+	case ".gz", ".br", ".zst":
+		innerExt = path.Ext(resource[:len(resource)-len(rawExt)])
+	}
+	rawType = client.extToMime(rawExt)
+	mimeType = rawType
+	if innerExt != rawExt {
+		mimeType = client.extToMime(innerExt)
+	}
+	log.Trace().Msgf("probe mime of %q is (%q / raw %q)", resource, mimeType, rawType)
+	return mimeType, rawType
+}
+
 func shouldRespBeSavedToCache(resp *http.Response) bool {
 	if resp == nil {
 		return false

server/upstream/header.go

@@ -24,5 +24,8 @@ func (o *Options) setHeader(ctx *context.Context, header http.Header) {
 	} else {
 		ctx.RespWriter.Header().Set(gitea.ContentTypeHeader, mime)
 	}
+	if encoding := header.Get(gitea.ContentEncodingHeader); encoding != "" && encoding != "identity" {
+		ctx.RespWriter.Header().Set(gitea.ContentEncodingHeader, encoding)
+	}
 	ctx.RespWriter.Header().Set(headerLastModified, o.BranchTimestamp.In(time.UTC).Format(http.TimeFormat))
 }

server/upstream/upstream.go

@@ -1,10 +1,13 @@
 package upstream
 
 import (
+	"cmp"
 	"errors"
 	"fmt"
 	"io"
 	"net/http"
+	"slices"
+	"strconv"
 	"strings"
 	"time"
 
@@ -19,6 +22,8 @@ import (
 const (
 	headerLastModified    = "Last-Modified"
 	headerIfModifiedSince = "If-Modified-Since"
+	headerAcceptEncoding  = "Accept-Encoding"
+	headerContentEncoding = "Content-Encoding"
 
 	rawMime = "text/plain; charset=utf-8"
 )
@@ -52,6 +57,72 @@ type Options struct {
 	ServeRaw bool
 }
 
+// allowed encodings
+var allowedEncodings = map[string]string{
+	"gzip":     ".gz",
+	"br":       ".br",
+	"zstd":     ".zst",
+	"identity": "",
+}
+
+// parses Accept-Encoding header into a list of acceptable encodings
+func AcceptEncodings(header string) []string {
+	log.Trace().Msgf("got accept-encoding: %s", header)
+	encodings := []string{}
+	globQuality := 0.0
+	qualities := make(map[string]float64)
+
+	for _, encoding := range strings.Split(header, ",") {
+		name, quality_str, has_quality := strings.Cut(encoding, ";q=")
+		quality := 1.0
+
+		if has_quality {
+			var err error
+			quality, err = strconv.ParseFloat(quality_str, 64)
+			if err != nil || quality < 0 {
+				continue
+			}
+		}
+
+		name = strings.TrimSpace(name)
+
+		if name == "*" {
+			globQuality = quality
+		} else {
+			_, allowed := allowedEncodings[name]
+			if allowed {
+				qualities[name] = quality
+				if quality > 0 {
+					encodings = append(encodings, name)
+				}
+			}
+		}
+	}
+
+	if globQuality > 0 {
+		for encoding := range allowedEncodings {
+			_, exists := qualities[encoding]
+			if !exists {
+				encodings = append(encodings, encoding)
+				qualities[encoding] = globQuality
+			}
+		}
+	} else {
+		_, exists := qualities["identity"]
+		if !exists {
+			encodings = append(encodings, "identity")
+			qualities["identity"] = -1
+		}
+	}
+
+	slices.SortStableFunc(encodings, func(x, y string) int {
+		// sort in reverse order; big quality comes first
+		return cmp.Compare(qualities[y], qualities[x])
+	})
+	log.Trace().Msgf("decided encoding order: %v", encodings)
+	return encodings
+}
+
 // Upstream requests a file from the Gitea API at GiteaRoot and writes it to the request context.
 func (o *Options) Upstream(ctx *context.Context, giteaClient *gitea.Client, redirectsCache cache.ICache) bool {
 	log := log.With().Strs("upstream", []string{o.TargetOwner, o.TargetRepo, o.TargetBranch, o.TargetPath}).Logger()
@@ -97,10 +168,34 @@ func (o *Options) Upstream(ctx *context.Context, giteaClient *gitea.Client, redi
 
 	log.Debug().Msg("Preparing")
 
-	reader, header, statusCode, err := giteaClient.ServeRawContent(o.TargetOwner, o.TargetRepo, o.TargetBranch, o.TargetPath)
+	var reader io.ReadCloser
+	var header http.Header
+	var statusCode int
+	var err error
+
+	// pick first non-404 response for encoding, *only* if not root
+	if o.TargetPath == "" || strings.HasSuffix(o.TargetPath, "/") {
+		err = gitea.ErrorNotFound
+	} else {
+		for _, encoding := range AcceptEncodings(ctx.Req.Header.Get(headerAcceptEncoding)) {
+			log.Trace().Msgf("try %s encoding", encoding)
+
+			// add extension for encoding
+			path := o.TargetPath + allowedEncodings[encoding]
+			reader, header, statusCode, err = giteaClient.ServeRawContent(o.TargetOwner, o.TargetRepo, o.TargetBranch, path, true)
+			if statusCode == 404 {
+				continue
+			}
+			log.Debug().Msgf("using %s encoding", encoding)
+			if encoding != "identity" {
+				header.Set(headerContentEncoding, encoding)
+			}
+			break
+		}
 		if reader != nil {
 			defer reader.Close()
 		}
+	}
 
 	log.Debug().Msg("Aquisting")