Implement Atom feed

Implements: https://todo.sr.ht/~cnx/phylactery/2

5 files changed, 216 insertions, 31 deletions

diff --git a/README.md b/README.md
index c98f657..118af79 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@ Phylactery is a web server rendering comic books directly from ZIP archives.
 
 ## Installation
 
-    go build -o $prefix/bin/phylactery main.go
+    go build -o $prefix/bin/phylactery *.go
 
 ## Usage
 
@@ -14,7 +14,7 @@ to the listening address and run `phylactery`.
 
 ## Hacking
 
-    PHYLACTERY_LIBRARY=/path/to/library PHYLACTERY_ADDRESS=:42069 go run main.go
+    PHYLACTERY_LIBRARY=/path/to/library PHYLACTERY_ADDRESS=:42069 go run *.go
 
 ## Contributing
 
diff --git a/atom.go b/atom.go
new file mode 100644
index 0000000..d905348
--- /dev/null
+++ b/atom.go
@@ -0,0 +1,129 @@
+// Atom feed synthesizer
+// Copyright (C) 2022  Nguyễn Gia Phong
+//
+// This file is part of Phylactery.
+//
+// Phylactery is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Phylactery is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with Phylactery.  If not, see <https://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"archive/zip"
+	"encoding/xml"
+	"net/http"
+	"os"
+	"path"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Type Img represents an XHTML img tag.
+type Img struct {
+	Src string `xml:"src,attr"`
+	Alt string `xml:"alt,attr"`
+}
+
+// Type Div represents an XHTML div tag.
+type Div struct {
+	NS  string `xml:"xmlns,attr"`
+	Img []Img  `xml:"img"`
+}
+
+// Type AtomLink represents an atom:link element.
+type AtomLink struct {
+	Rel  string `xml:"rel,attr"`
+	Href string `xml:"href,attr"`
+}
+
+// Type AtomContent represents an atom:content element.
+type AtomContent struct {
+	Type string `xml:"type,attr"`
+	Div  Div    `xml:"div"`
+}
+
+// Type AtomEntry represents an Atom Entry Document.
+type AtomEntry struct {
+	Title   string      `xml:"title"`
+	ID      string      `xml:"id"`
+	Link    []AtomLink  `xml:"link"`
+	Updated time.Time   `xml:"updated"`
+	Content AtomContent `xml:"content"`
+}
+
+// Type AtomFeed represents an Atom Feed Document.
+type AtomFeed struct {
+	XMLName xml.Name    `xml:"http://www.w3.org/2005/Atom feed"`
+	Title   string      `xml:"title"`
+	ID      string      `xml:"id"`
+	Link    []AtomLink  `xml:"link"`
+	Updated time.Time   `xml:"updated"`
+	Author  string      `xml:"author>name"`
+	Entry   []AtomEntry `xml:"entry"`
+}
+
+// Function synthesizeAtom generates an Atom feed for given directory.
+func synthesizeAtom(r *http.Request, dir string, updated time.Time) AtomFeed {
+	baseURL := "http://" + r.Host
+	if r.TLS != nil {
+		baseURL = "https" + baseURL[4:]
+	}
+	var entries []AtomEntry
+	filepath.WalkDir(dir, func(p string, d os.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return nil
+		}
+		name := strings.TrimPrefix(p, dir)[1:]
+		u := escape(baseURL + path.Join(r.URL.Path, name))
+		var images []Img
+		cbz, err := zip.OpenReader(p)
+		if err != nil {
+			return nil
+		}
+		defer cbz.Close()
+		for i, f := range cbz.File {
+			if isImageFile(f) {
+				continue
+			}
+			images = append(images,
+				Img{u + "?entry=" + strconv.Itoa(i), f.Name})
+		}
+
+		info, _ := d.Info()
+		entries = append(entries, AtomEntry{
+			Title:   name,
+			ID:      name,
+			Link:    []AtomLink{{"alternate", u}},
+			Updated: info.ModTime(),
+			Content: AtomContent{
+				"xhtml",
+				Div{"http://www.w3.org/1999/xhtml", images},
+			},
+		})
+		return nil
+	})
+
+	id := escape(baseURL + r.URL.Path)
+	return AtomFeed{
+		Title: r.URL.Path[1 : len(r.URL.Path)-1],
+		ID:    id,
+		Link: []AtomLink{
+			{"alternate", id},
+			{"self", id + "?feed=atom"},
+		},
+		Updated: updated,
+		Entry:   entries,
+	}
+}
diff --git a/misc.go b/misc.go
new file mode 100644
index 0000000..700256c
--- /dev/null
+++ b/misc.go
@@ -0,0 +1,52 @@
+// Miscellaneous utilities
+// Copyright (C) 2022  Nguyễn Gia Phong
+//
+// This file is part of Phylactery.
+//
+// Phylactery is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Phylactery is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with Phylactery.  If not, see <https://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"archive/zip"
+	"net/http"
+	"os"
+	"strings"
+)
+
+// Function escape ensures that question marks in path
+// are not recognized as URL parameters.
+func escape(name string) string {
+	return strings.ReplaceAll(name, "?", "%3f")
+}
+
+// Function find searches for the directory entry of given name.
+func find(entries []os.DirEntry, name string) int {
+	for i, entry := range entries {
+		if entry.Name() == name {
+			return i
+		}
+	}
+	return -1
+}
+
+// Function isImageFile detects if given file is an image.
+func isImageFile(file *zip.File) bool {
+	image, _ := file.Open()
+	defer image.Close()
+	buf := make([]byte, 512)
+	n, _ := image.Read(buf)
+	mime := http.DetectContentType(buf[:n])
+	return strings.HasPrefix(mime, "image/")
+}
diff --git a/main.go b/serv.go
index dfc01a5..f7e05dc 100644
--- a/main.go
+++ b/serv.go
@@ -21,6 +21,7 @@ package main
 import (
 	"archive/zip"
 	"embed"
+	"encoding/xml"
 	"html/template"
 	"io"
 	"log"
@@ -45,9 +46,9 @@ type Page struct {
 
 // Type Archive represents a comic book zip archive.
 type Archive struct {
-	Title   string
-	Prev    string
-	Next    string
+	Title string
+	Prev  string
+	Next  string
 }
 
 // Type Directory represents a library directory in file system.
@@ -56,28 +57,14 @@ type Directory struct {
 	Entries []string
 }
 
-// Function escape ensures that question marks in path
-// are not recognized as URL parameters.
-func escape(name string) template.URL {
-	return template.URL(strings.Replace(name, "?", "%3f", -1))
-}
-
-// Function find searches for the directory entry of given name.
-func find(entries []os.DirEntry, name string) int {
-	for i, entry := range entries {
-		if entry.Name() == name {
-			return i
-		}
-	}
-	return -1
-}
-
 // Function main starts Phylactery serving comics from PHYLACTERY_LIBRARY
-// and listening on PHYLACTERY_ADDRESS.
+// and listening on PHYLACTERY_ADDRESS to serve at PHYLACTERY_BASE_URL.
 func main() {
 	http.Handle("/static/", http.FileServer(http.FS(static)))
 	t, err := template.New("").Funcs(template.FuncMap{
-		"escape": escape,
+		"escape": func(name string) template.URL {
+			return template.URL(escape(name))
+		},
 	}).ParseFS(templates, "templates/*.html")
 	if err != nil {
 		log.Fatal(err)
@@ -90,6 +77,7 @@ func main() {
 			http.NotFound(w, r)
 			return
 		}
+		r.ParseForm()
 
 		if stat.IsDir() {
 			// Redirect URL without a trailing slash
@@ -100,6 +88,27 @@ func main() {
 				return
 			}
 
+			// Encode Atom feed
+			if feedFormat, isFeed := r.Form["feed"]; isFeed {
+				if r.URL.Path == "/" {
+					http.Error(w, "no feed for /",
+						http.StatusBadRequest)
+					return
+				}
+				if feedFormat[0] != "atom" {
+					http.Error(w, "unsupported feed format",
+						http.StatusUnsupportedMediaType)
+					return
+				}
+				w.Header().Set("Content-Type",
+					"application/atom+xml")
+				io.WriteString(w, xml.Header)
+				enc := xml.NewEncoder(w)
+				enc.Indent("", "  ")
+				enc.Encode(synthesizeAtom(r, p, stat.ModTime()))
+				return
+			}
+
 			// Render directory page
 			entries, _ := os.ReadDir(p)
 			var names []string
@@ -130,7 +139,6 @@ func main() {
 		defer cbz.Close()
 
 		// Respond with an image inside the CBZ
-		r.ParseForm()
 		if entry, isImage := r.Form["entry"]; isImage {
 			i, err := strconv.Atoi(entry[0])
 			if err != nil || i < 0 || i >= len(cbz.File) {
@@ -155,15 +163,10 @@ func main() {
 			next = entries[index+1].Name()
 		}
 		t.ExecuteTemplate(w, "archive-head.html",
-			Archive{ stat.Name(), prev, next })
+			Archive{stat.Name(), prev, next})
 
 		for i, f := range cbz.File {
-			image, _ := cbz.File[i].Open()
-			defer image.Close()
-			buf := make([]byte, 512)
-			n, _ := image.Read(buf)
-			mime := http.DetectContentType(buf[:n])
-			if strings.HasPrefix(mime, "image/") {
+			if isImageFile(f) {
 				t.ExecuteTemplate(w, "archive-page.html",
 					Page{i, f.Name})
 			}
diff --git a/templates/directory.html b/templates/directory.html
index 570e526..15ee01c 100644
--- a/templates/directory.html
+++ b/templates/directory.html
@@ -1,5 +1,6 @@
 {{template "base-head.html" -}}
 <link rel=stylesheet href=/static/directory.css>
+<link rel='alternate' type='application/atom+xml' href='?feed=atom'>
 <title>{{.Title}}</title>
 <body>
   <main>