Merge pull request #124 from PierreF/retry-http

Retry on backend error

README.md

@@ -349,6 +349,19 @@ auth_opt_log_file /var/log/mosquitto/mosquitto.log
 
 If `log_dest` or `log_file` are invalid, or if there's an error opening the file (e.g. no permissions), logging will default to `stderr`.
 
+#### Retry
+
+By default, if backend had an error (and no other backend granted access), an error is returned to Mosquitto.
+
+It's possible to enable retry, which will immediately retry all configured backends. This could be useful if the
+backend may be behind a load-balancer (like HTTP backend) and one instance may fail:
+
+```
+auth_opt_retry_count 2
+```
+
+The above example will do up to 2 retries (3 calls in total considering the original one) if the responsible backend had an error or was down while performing the check.
+
 #### Prefixes
 
 Though the plugin may have multiple backends enabled, there's a way to specify which backend must be used for a given user: prefixes. When enabled, `prefixes` allow to check if the username contains a predefined prefix in the form prefix_username and use the configured backend for that prefix. Options to enable and set prefixes are the following:

go-auth.go

@@ -35,6 +35,7 @@ type AuthPlugin struct {
  customPluginHalt func()
  useCache bool
  checkPrefix bool
+ retryCount int
  prefixes map[string]string
  logLevel log.Level
  logDest string
@@ -120,6 +121,15 @@ func AuthPluginInit(keys []string, values []string, authOptsNum int) {
  authOpts[keys[i]] = values[i]
  }
 
+ if retryCount, ok := authOpts["retry_count"]; ok {
+ retry, err := strconv.ParseInt(retryCount, 10, 64)
+ if err == nil {
+ authPlugin.retryCount = int(retry)
+ } else {
+ log.Warningf("couldn't parse retryCount (err: %s), defaulting to 0", err)
+ }
+ }
+
  //Log and end program if backends are wrong
  if !backendsOk {
  log.Fatal("backends error")
@@ -520,7 +530,16 @@ func setCache(authOpts map[string]string) {
 
 //export AuthUnpwdCheck
 func AuthUnpwdCheck(username, password, clientid string) uint8 {
- ok, err := authUnpwdCheck(username, password, clientid)
+ var ok bool
+ var err error
+
+ for try := 0; try <= authPlugin.retryCount; try++ {
+ ok, err = authUnpwdCheck(username, password, clientid)
+ if err == nil {
+ break
+ }
+ }
+
  if err != nil {
  log.Error(err)
  return AuthError
@@ -608,7 +627,16 @@ func authUnpwdCheck(username, password, clientid string) (bool, error) {
 
 //export AuthAclCheck
 func AuthAclCheck(clientid, username, topic string, acc int) uint8 {
- ok, err := authAclCheck(clientid, username, topic, acc)
+ var ok bool
+ var err error
+
+ for try := 0; try <= authPlugin.retryCount; try++ {
+ ok, err = authAclCheck(clientid, username, topic, acc)
+ if err == nil {
+ break
+ }
+ }
+
  if err != nil {
  log.Error(err)
  return AuthError