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main.go
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package main
import (
"fmt"
"log"
"net"
"net/http"
"net/url"
"os"
"strings"
"sync"
"time"
)
func main() {
port, addr := os.Getenv("PORT"), os.Getenv("LISTEN_ADDR")
if port == "" {
port = "8080"
}
googleSheetsID := os.Getenv("GOOGLE_SHEET_ID")
sheetName := os.Getenv("SHEET_NAME")
homeRedirect := os.Getenv("HOME_REDIRECT")
ttlVal := os.Getenv("CACHE_TTL")
ttl := time.Second * 5
if ttlVal != "" {
v, err := time.ParseDuration(ttlVal)
if err != nil {
log.Fatalf("failed to parse CACHE_TTL as duration: %v", err)
}
ttl = v
}
srv := &server{
db: &cachedURLMap{
ttl: ttl,
sheet: &sheetsProvider{
googleSheetsID: googleSheetsID,
sheetName: sheetName,
},
},
homeRedirect: homeRedirect,
}
http.HandleFunc("/", srv.handler)
listenAddr := net.JoinHostPort(addr, port)
log.Printf("starting server at %s; ttl=%v", listenAddr, ttl)
err := http.ListenAndServe(listenAddr, nil)
log.Fatal(err)
}
type server struct {
db *cachedURLMap
homeRedirect string
}
type URLMap map[string]*url.URL
type cachedURLMap struct {
sync.RWMutex
v URLMap
lastUpdate time.Time
ttl time.Duration
sheet *sheetsProvider
}
func (c *cachedURLMap) Get(query string) (*url.URL, error) {
if err := c.refresh(); err != nil {
return nil, err
}
c.RLock()
defer c.RUnlock()
return c.v[query], nil
}
func (c *cachedURLMap) refresh() error {
c.Lock()
defer c.Unlock()
if time.Since(c.lastUpdate) <= c.ttl {
return nil
}
rows, err := c.sheet.Query()
if err != nil {
return err
}
c.v = urlMap(rows)
c.lastUpdate = time.Now()
return nil
}
func (s *server) handler(w http.ResponseWriter, req *http.Request) {
if req.URL.Path == "/" {
s.home(w, req)
return
}
s.redirect(w, req)
}
func (s *server) home(w http.ResponseWriter, req *http.Request) {
if s.homeRedirect != "" {
http.Redirect(w, req, s.homeRedirect, http.StatusFound)
return
}
w.WriteHeader(http.StatusNotFound)
fmt.Fprintf(w, `<!DOCTYPE html>
<html><head><title>Not found</title></head><body><h1>Not found :(</h1>
<p>This is home page for a URL redirector service.</p>
<p>The URL is missing the shortcut in the path.</p>
</body></html>`)
}
func (s *server) redirect(w http.ResponseWriter, req *http.Request) {
if req.Body != nil {
defer req.Body.Close()
}
redirTo, err := s.findRedirect(req.URL)
if err != nil {
writeError(w, http.StatusInternalServerError, "failed to find redirect: %v", err)
return
}
if redirTo == nil {
w.WriteHeader(http.StatusNotFound)
fmt.Fprintf(w, "404 not found")
return
}
log.Printf("redirecting=%q to=%q", req.URL, redirTo.String())
http.Redirect(w, req, redirTo.String(), http.StatusFound) // no permanent redirects
}
func (s *server) findRedirect(req *url.URL) (*url.URL, error) {
path := strings.TrimPrefix(req.Path, "/")
segments := strings.Split(path, "/")
var discard []string
for len(segments) > 0 {
query := strings.Join(segments, "/")
v, err := s.db.Get(query)
if err != nil {
return nil, err
}
if v != nil {
return prepRedirect(v, strings.Join(discard, "/"), req.Query()), nil
}
discard = append([]string{segments[len(segments)-1]}, discard...)
segments = segments[:len(segments)-1]
}
return nil, nil
}
func prepRedirect(base *url.URL, addPath string, query url.Values) *url.URL {
if addPath != "" {
if !strings.HasSuffix(base.Path, "/") {
base.Path += "/"
}
base.Path += addPath
}
qs := base.Query()
for k := range query {
qs.Add(k, query.Get(k))
}
base.RawQuery = qs.Encode()
return base
}
func urlMap(in [][]interface{}) URLMap {
out := make(URLMap)
for _, row := range in {
if len(row) < 2 {
continue
}
k, ok := row[0].(string)
if !ok || k == "" {
continue
}
v, ok := row[1].(string)
if !ok || v == "" {
continue
}
k = strings.ToLower(k)
u, err := url.Parse(v)
if err != nil {
log.Printf("warn: %s=%s url invalid", k, v)
continue
}
_, exists := out[k]
if exists {
log.Printf("warn: shortcut %q redeclared, overwriting", k)
}
out[k] = u
}
return out
}
func writeError(w http.ResponseWriter, code int, msg string, vals ...interface{}) {
w.WriteHeader(code)
fmt.Fprintf(w, msg, vals...)
}