3 files changed, 131 insertions, 0 deletions
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..ecfef6d
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module gziphandler
+
+go 1.15
diff --git a/handler.go b/handler.go
new file mode 100644
index 0000000..ab21180
--- /dev/null
+++ b/handler.go
@@ -0,0 +1,53 @@
+package gziphandler
+
+import (
+	"compress/gzip"
+	"net/http"
+	"strings"
+)
+
+type gw struct {
+	http.ResponseWriter
+	w *gzip.Writer
+}
+
+func (w *gw) Write(d []byte) (int, error) {
+	return w.w.Write(d)
+}
+
+func (w *gw) Close() error {
+	return w.w.Close()
+}
+
+func acceptsGzip(r *http.Request) bool {
+	ae := r.Header.Get("Accept-Encoding")
+	for _, e := range strings.Split(ae, ",") {
+		vals := strings.Split(e, ";")
+		if len(vals) < 1 {
+			continue
+		}
+		if strings.TrimSpace(vals[0]) == "gzip" {
+			return true
+		}
+	}
+	return false
+}
+
+// Handler returns an http.Handler that compresses the response data written
+// by an existing handler h, using the compress/gzip.Writer with default
+// compression level.
+func Handler(h http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !acceptsGzip(r) {
+			h.ServeHTTP(w, r)
+			return
+		}
+		w.Header().Set("Content-Encoding", "gzip")
+		gw := &gw{
+			ResponseWriter: w,
+			w:              gzip.NewWriter(w),
+		}
+		h.ServeHTTP(gw, r)
+		gw.Close()
+	})
+}
diff --git a/handler_test.go b/handler_test.go
new file mode 100644
index 0000000..f1a034e
--- /dev/null
+++ b/handler_test.go
@@ -0,0 +1,75 @@
+package gziphandler
+
+import (
+	"compress/gzip"
+	"io"
+	"net"
+	"net/http"
+	"strings"
+	"testing"
+)
+
+type d struct {
+	data string
+	gzip bool
+}
+
+func TestHandler(t *testing.T) {
+	data := []d{
+		{"abc", true},
+		{"qweqweqwe", false},
+		{"lkajwdlajwdlkajwdlkjawl", true},
+	}
+	http.HandleFunc("/test", func(w http.ResponseWriter, r *http.Request) {
+		_, err := io.Copy(w, r.Body)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+	})
+	handler := Handler(http.DefaultServeMux)
+	l, err := net.Listen("tcp", "127.0.0.1:8080")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer l.Close()
+	go http.Serve(l, handler)
+	for _, d := range data {
+		doReq(t, d)
+	}
+}
+
+func doReq(t *testing.T, d d) {
+	req, err := http.NewRequest(http.MethodPost, "http://127.0.0.1:8080/test", strings.NewReader(d.data))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if d.gzip {
+		req.Header.Set("Accept-Encoding", "gzip")
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	var sb strings.Builder
+	r := resp.Body
+	if d.gzip {
+		ce := resp.Header.Get("Content-Encoding")
+		if ce != "gzip" {
+			t.Errorf("expected content encoding %s, got %s", "gzip", ce)
+		}
+		r, err = gzip.NewReader(resp.Body)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+	_, err = io.Copy(&sb, r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	s := sb.String()
+	if d.data != s {
+		t.Errorf("expected response %s, got %s", d.data, s)
+	}
+}