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/
server.go
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/
server.go
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// Copyright 2013 Francisco Souza. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"encoding/json"
"flag"
"github.com/fsouza/lb"
"github.com/howeyc/fsnotify"
"log"
"net/http"
"os"
"strings"
"sync"
)
type jsonRule struct {
Domain string
Backends []string
}
type Rule struct {
Domain string
Backend *lb.LoadBalancer
}
type Server struct {
rules []Rule
rmut sync.RWMutex
}
func NewServer(ruleFile string) (*Server, error) {
rules, err := loadRules(ruleFile)
if err != nil {
return nil, err
}
s := Server{rules: rules}
w, err := fsnotify.NewWatcher()
if err != nil {
log.Printf("Warning: frontend server is not watching rule file %q. Reason: %s", ruleFile, err)
return &s, nil
}
err = w.Watch(ruleFile)
if err != nil {
log.Printf("Warning: frontend server is not watching rule file %q. Reason: %s", ruleFile, err)
return &s, nil
}
go func() {
for {
select {
case e := <-w.Event:
if e.IsModify() {
if rules, err := loadRules(ruleFile); err == nil {
s.rmut.Lock()
s.rules = rules
s.rmut.Unlock()
}
}
case <-w.Error:
}
}
}()
return &s, nil
}
func (s *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
if req.Host == "" {
http.Error(w, "Missing Host header", http.StatusBadRequest)
return
}
var rule Rule
s.rmut.RLock()
for _, r := range s.rules {
if req.Host == r.Domain || strings.HasSuffix(req.Host, "."+r.Domain) {
rule = r
break
}
}
s.rmut.RUnlock()
if rule.Domain == "" {
http.Error(w, "Page not found", http.StatusNotFound)
return
}
rule.Backend.ServeHTTP(w, req)
}
func loadRules(file string) ([]Rule, error) {
f, err := os.Open(file)
if err != nil {
return nil, err
}
defer f.Close()
var rs []jsonRule
err = json.NewDecoder(f).Decode(&rs)
if err != nil {
return nil, &invalidRuleError{err}
}
rules := make([]Rule, len(rs))
for i, r := range rs {
balancer, err := lb.NewLoadBalancer(r.Backends...)
if err != nil {
return nil, &invalidRuleError{err}
}
rules[i] = Rule{Domain: r.Domain, Backend: balancer}
}
return rules, nil
}
type invalidRuleError struct {
err error
}
func (e *invalidRuleError) Error() string {
return "Invalid rule file: " + e.err.Error()
}
func main() {
var listen, rulesFile string
flag.StringVar(&listen, "listen", ":8080", "Address to listen to HTTP requests.")
flag.StringVar(&rulesFile, "rules", "", "JSON file to load rules from. You must provide it.")
flag.Parse()
if rulesFile == "" {
flag.Usage()
os.Exit(2)
}
server, err := NewServer(rulesFile)
if err != nil {
log.Fatal(err)
}
http.Handle("/", server)
if err := http.ListenAndServe(listen, nil); err != nil {
log.Fatal(err)
}
}