Various bug fixes and minor improvements

- Fix static responder so it doesn't replace its own headers config,
  and instead replaces the actual response header values
- caddyhttp.ResponseRecorder type optionally buffers response
- Add interface guards to ensure regexp matchers get provisioned
- Use default HTTP port if one is not explicitly set
- Encode middleware writes status code 200 if not written upstream
- Templates and markdown only try to execute on text responses
- Static file server sets Content-Type based on file extension only
  (this whole thing -- MIME sniffing, etc -- needs more configurability)

modules/caddyhttp/markdown/markdown.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"net/http"
 	"strconv"
+	"strings"
 	"sync"
 
 	"gopkg.in/russross/blackfriday.v2"
@@ -28,12 +29,19 @@ func (m Markdown) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyht
 	buf.Reset()
 	defer bufPool.Put(buf)
 
-	rr := caddyhttp.NewResponseRecorder(w, buf)
+	shouldBuf := func(status int) bool {
+		return strings.HasPrefix(w.Header().Get("Content-Type"), "text/")
+	}
 
-	err := next.ServeHTTP(rr, r)
+	rec := caddyhttp.NewResponseRecorder(w, buf, shouldBuf)
+
+	err := next.ServeHTTP(rec, r)
 	if err != nil {
 		return err
 	}
+	if !rec.Buffered() {
+		return nil
+	}
 
 	output := blackfriday.Run(buf.Bytes())
 
@@ -43,7 +51,7 @@ func (m Markdown) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyht
 	w.Header().Del("Etag")          // don't know a way to quickly generate etag for dynamic content
 	w.Header().Del("Last-Modified") // useless for dynamic content since it's always changing
 
-	w.WriteHeader(rr.Status())
+	w.WriteHeader(rec.Status())
 	w.Write(output)
 
 	return nil