1 files changed, 49 insertions, 0 deletions
diff --git a/gemini/gemtext/sub.go b/gemini/gemtext/sub.go
index 365d41b..5030291 100644
--- a/gemini/gemtext/sub.go
+++ b/gemini/gemtext/sub.go
@@ -2,13 +2,18 @@ package gemtext
 
 import (
 	"bytes"
+	"context"
 	"html/template"
 	"io"
+	"mime"
 	"net/url"
 	"regexp"
 	"strconv"
 	"strings"
 	"time"
+
+	"tildegit.org/tjp/sliderule/gemini"
+	"tildegit.org/tjp/sliderule/internal/types"
 )
 
 // GmisubToAtom converts a gemini document to Atom format.
@@ -28,6 +33,50 @@ func GmisubToAtom(doc Document, location url.URL, out io.Writer) error {
 	return nil
 }
 
+// AutoAtom is a middleware which builds atom feeds for any gemtext pages.
+//
+// It looks for requests ending with the '.atom' extension, passes through the request
+// with the extension clipped off, then if the response is in gemtext it converts it to
+// an Atom feed according to the gmisub spec at
+// gemini://gemini.circumlunar.space/docs/companion/subscription.gmi
+var AutoAtom = types.Middleware(func(h types.Handler) types.Handler {
+	return types.HandlerFunc(func(ctx context.Context, request *types.Request) *types.Response {
+		if !strings.HasSuffix(request.Path, ".atom") {
+			return h.Handle(ctx, request)
+		}
+
+		req := *request
+		u := *request.URL
+		u.Path = strings.TrimSuffix(u.Path, ".atom")
+		req.URL = &u
+
+		response := h.Handle(ctx, &req)
+		if response.Status != gemini.StatusSuccess {
+			return response
+		}
+
+		mtype, _, err := mime.ParseMediaType(response.Meta.(string))
+		if err != nil || mtype != "text/gemini" {
+			return response
+		}
+
+		defer func() {
+			_ = response.Close()
+		}()
+
+		doc, err := Parse(response.Body)
+		if err != nil {
+			return gemini.Failure(err)
+		}
+
+		buf := &bytes.Buffer{}
+		if err := GmisubToAtom(doc, *request.URL, buf); err != nil {
+			return gemini.Failure(err)
+		}
+		return gemini.Success("application/atom+xml; charset=utf-8", buf)
+	})
+})
+
 type gmiSub struct {
 	ID       template.URL
 	Title    string