From 9da9e37f32e0e06f99d18c62540d0d9d44f3ce44 Mon Sep 17 00:00:00 2001
From: Jan-Lukas Else <mail@jlelse.de>
Date: Tue, 22 Dec 2020 22:15:29 +0100
Subject: [PATCH] Short URLs

---
 databaseMigrations.go |  9 ++++++
 http.go               |  3 ++
 posts.go              |  1 +
 postsFuncs.go         |  8 ++++++
 render.go             |  3 ++
 shortPath.go          | 64 +++++++++++++++++++++++++++++++++++++++++++
 telegram.go           |  2 +-
 templates/post.gohtml |  1 +
 8 files changed, 90 insertions(+), 1 deletion(-)
 create mode 100644 shortPath.go

diff --git a/databaseMigrations.go b/databaseMigrations.go
index b2e23cf..f238f66 100644
--- a/databaseMigrations.go
+++ b/databaseMigrations.go
@@ -97,6 +97,15 @@ func migrateDb() error {
 					return err
 				},
 			},
+			&migrator.Migration{
+				Name: "00008",
+				Func: func(tx *sql.Tx) error {
+					_, err := tx.Exec(`
+					create table shortpath (id integer primary key autoincrement, path text not null, unique(path));
+					`)
+					return err
+				},
+			},
 		),
 	)
 	if err != nil {
diff --git a/http.go b/http.go
index 1c516a9..8d684a0 100644
--- a/http.go
+++ b/http.go
@@ -173,6 +173,9 @@ func buildHandler() (http.Handler, error) {
 		r.With(cacheMiddleware).Get(path, serveAsset)
 	}
 
+	// Short paths
+	r.With(cacheMiddleware).Get("/s/{id:[0-9a-fA-F]+}", redirectToLongPath)
+
 	paginationPath := "/page/{page:[0-9-]+}"
 	feedPath := ".{feed:rss|json|atom}"
 
diff --git a/posts.go b/posts.go
index d558f47..ce8af11 100644
--- a/posts.go
+++ b/posts.go
@@ -51,6 +51,7 @@ func servePost(w http.ResponseWriter, r *http.Request) {
 	if canonical == "" {
 		canonical = p.fullURL()
 	}
+	w.Header().Add("Link", fmt.Sprintf("<%s>; rel=shortlink", p.shortURL()))
 	render(w, templatePost, &renderData{
 		blogString: p.Blog,
 		Canonical:  canonical,
diff --git a/postsFuncs.go b/postsFuncs.go
index a0a69ed..e3092bb 100644
--- a/postsFuncs.go
+++ b/postsFuncs.go
@@ -12,6 +12,14 @@ func (p *post) fullURL() string {
 	return appConfig.Server.PublicAddress + p.Path
 }
 
+func (p *post) shortURL() string {
+	s, err := shortenPath(p.Path)
+	if err != nil {
+		return ""
+	}
+	return appConfig.Server.PublicAddress + s
+}
+
 func (p *post) firstParameter(parameter string) (result string) {
 	if pp := p.Parameters[parameter]; len(pp) > 0 {
 		result = pp[0]
diff --git a/render.go b/render.go
index df2064e..64b4ae0 100644
--- a/render.go
+++ b/render.go
@@ -85,6 +85,9 @@ func initRendering() error {
 			})
 			return mentions
 		},
+		"shorturl": func(p *post) string {
+			return p.shortURL()
+		},
 		// Others
 		"dateformat": func(date string, format string) string {
 			d, err := dateparse.ParseLocal(date)
diff --git a/shortPath.go b/shortPath.go
new file mode 100644
index 0000000..04dfa62
--- /dev/null
+++ b/shortPath.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"net/http"
+	"strconv"
+
+	"github.com/go-chi/chi"
+)
+
+func shortenPath(p string) (string, error) {
+	if p == "" {
+		return "", errors.New("empty path")
+	}
+	id := getShortPathID(p)
+	if id == -1 {
+		_, err := appDbExec("insert or ignore into shortpath (path) values (@path)", sql.Named("path", p))
+		if err != nil {
+			return "", err
+		}
+		id = getShortPathID(p)
+	}
+	if id == -1 {
+		return "", errors.New("failed to retrieve short path for " + p)
+	}
+	return fmt.Sprintf("/s/%x", id), nil
+}
+
+func getShortPathID(p string) (id int) {
+	if p == "" {
+		return -1
+	}
+	row, err := appDbQueryRow("select id from shortpath where path = @path", sql.Named("path", p))
+	if err != nil {
+		return -1
+	}
+	err = row.Scan(&id)
+	if err != nil {
+		return -1
+	}
+	return id
+}
+
+func redirectToLongPath(rw http.ResponseWriter, r *http.Request) {
+	id, err := strconv.ParseInt(chi.URLParam(r, "id"), 16, 64)
+	if err != nil {
+		serve404(rw, r)
+		return
+	}
+	row, err := appDbQueryRow("select path from shortpath where id = @id", sql.Named("id", id))
+	if err != nil {
+		serve404(rw, r)
+		return
+	}
+	var path string
+	err = row.Scan(&path)
+	if err != nil {
+		serve404(rw, r)
+		return
+	}
+	http.Redirect(rw, r, path, http.StatusFound)
+}
diff --git a/telegram.go b/telegram.go
index eab36b7..7731151 100644
--- a/telegram.go
+++ b/telegram.go
@@ -35,7 +35,7 @@ func (p *post) tgPost() {
 		message.WriteString(title)
 		message.WriteString("\n\n")
 	}
-	message.WriteString(p.fullURL())
+	message.WriteString(p.shortURL())
 	sendTelegramMessage(message.String(), tg.BotToken, tg.ChatID)
 }
 
diff --git a/templates/post.gohtml b/templates/post.gohtml
index 6e01a4a..5dc516a 100644
--- a/templates/post.gohtml
+++ b/templates/post.gohtml
@@ -1,6 +1,7 @@
 {{ define "title" }}
   <title>{{ with p .Data "title" }}{{ . }} - {{end}}{{ .Blog.Title }}</title>
   {{ include "postheadmeta" . }}
+  {{ with shorturl .Data }}<link rel="shortlink" href="{{ . }}">{{ end }}
 {{ end }}
 
 {{ define "main" }}