From baa096c4f4e6824189792c379aebb0d408aef4ec Mon Sep 17 00:00:00 2001
From: ltdk <usr@ltdk.xyz>
Date: Sun, 8 Sep 2024 23:31:23 -0400
Subject: [PATCH] Implement static serving of compressed files

---
 server/upstream/upstream.go | 93 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 92 insertions(+), 1 deletion(-)

diff --git a/server/upstream/upstream.go b/server/upstream/upstream.go
index d9c131e..f02e4c0 100644
--- a/server/upstream/upstream.go
+++ b/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 +57,73 @@ type Options struct {
 	ServeRaw bool
 }
 
+// allowed encodings
+var allowedEncodings = map[string]string{
+	"gzip":     ".gz",
+	"br":       ".br",
+	"zstd":     ".zstd",
+	"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, ",") {
+		splits := strings.SplitN(encoding, ";q=", 2)
+		name := splits[0]
+		quality := 1.0
+
+		if len(splits) > 1 {
+			var err error
+			quality, err = strconv.ParseFloat(splits[1], 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()
@@ -97,7 +169,26 @@ 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)
+	// pick first non-404 response for encoding
+	var reader io.ReadCloser
+	var header http.Header
+	var statusCode int
+	var err error
+	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)
+		if statusCode == 404 {
+			continue
+		}
+		log.Debug().Msgf("using %s encoding", encoding)
+		if encoding != "identity" {
+			header.Set(headerContentEncoding, encoding)
+		}
+	}
+
 	if reader != nil {
 		defer reader.Close()
 	}