1 files changed, 142 insertions, 0 deletions
diff --git a/pkg/ext/compression.go b/pkg/ext/compression.go
new file mode 100644
index 0000000..92144b8
--- /dev/null
+++ b/pkg/ext/compression.go
@@ -0,0 +1,142 @@
+package ext
+
+import (
+	"compress/gzip"
+	"compress/lzw"
+	"errors"
+	"io"
+	"log/slog"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"git.gabrielgio.me/cerrado/pkg/u"
+	"github.com/andybalholm/brotli"
+	"github.com/klauspost/compress/zstd"
+)
+
+var (
+	invalidParamErr = errors.New("Invalid weighted param")
+)
+
+type CompressionResponseWriter struct {
+	innerWriter    http.ResponseWriter
+	compressWriter io.Writer
+}
+
+func Compress(next func(w http.ResponseWriter, r *http.Request)) func(w http.ResponseWriter, r *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if accept, ok := r.Header["Accept-Encoding"]; ok {
+			if compress, algo := GetCompressionWriter(u.FirstOrZero(accept), w); algo != "" {
+				defer compress.Close()
+				w.Header().Add("Content-Encoding", algo)
+				w = &CompressionResponseWriter{
+					innerWriter:    w,
+					compressWriter: compress,
+				}
+			}
+		}
+		next(w, r)
+	}
+}
+
+func GetCompressionWriter(header string, inner io.Writer) (io.WriteCloser, string) {
+	c := GetCompression(header)
+	switch c {
+	case "br":
+		return GetBrotliWriter(inner), c
+	case "gzip":
+		return GetGZIPWriter(inner), c
+	case "compress":
+		return GetLZWWriter(inner), c
+	case "zstd":
+		return GetZSTDWriter(inner), c
+	default:
+		return nil, ""
+	}
+
+}
+
+func (c *CompressionResponseWriter) Header() http.Header {
+	return c.innerWriter.Header()
+}
+func (c *CompressionResponseWriter) Write(b []byte) (int, error) {
+	return c.compressWriter.Write(b)
+}
+
+func (c *CompressionResponseWriter) WriteHeader(statusCode int) {
+	c.innerWriter.WriteHeader(statusCode)
+}
+
+func GetCompression(header string) string {
+	c := "*"
+	q := 0.0
+
+	if header == "" {
+		return c
+	}
+
+	// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Encoding
+	for _, e := range strings.Split(header, ",") {
+		ps := strings.Split(e, ";")
+		if len(ps) == 2 {
+			w, err := getWeighedValue(ps[1])
+			if err != nil {
+				slog.Error(
+					"Error parsing weighting from Accept-Encoding",
+					"error", err,
+				)
+				continue
+			}
+			// gettting weighting value
+			if w > q {
+				q = w
+				c = strings.Trim(ps[0], " ")
+			}
+		} else {
+			if 1 > q {
+				q = 1
+				c = strings.Trim(ps[0], " ")
+			}
+		}
+	}
+
+	return c
+}
+
+func GetGZIPWriter(w io.Writer) io.WriteCloser {
+	// error can be ignored here since it will only err when compression level
+	// is not valid
+	r, _ := gzip.NewWriterLevel(w, gzip.BestCompression)
+	return r
+}
+
+func GetBrotliWriter(w io.Writer) io.WriteCloser {
+	return brotli.NewWriterLevel(w, brotli.BestCompression)
+}
+
+func GetZSTDWriter(w io.Writer) io.WriteCloser {
+	// error can be ignored here since it will only opts are given
+	r, _ := zstd.NewWriter(w)
+	return r
+}
+
+func GetLZWWriter(w io.Writer) io.WriteCloser {
+	return lzw.NewWriter(w, lzw.LSB, 8)
+}
+
+func getWeighedValue(part string) (float64, error) {
+	ps := strings.SplitN(part, "=", 2)
+	if len(ps) != 2 {
+		return 0, invalidParamErr
+	}
+	if name := strings.TrimSpace(ps[0]); name == "q" {
+		w, err := strconv.ParseFloat(ps[1], 64)
+		if err != nil {
+			return 0, err
+		}
+		return w, nil
+	}
+
+	return 0, invalidParamErr
+}