Bucket policy propagation (Fixes #2930) (#2932)

Fixes a serialisation bug - encoding/gob does not directly support
serializing `map[string]interface{}`, so we serialise to JSON and send a
byte array in the RPC call, and deserialize and update on the receiver.

cmd/s3-peer-client.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"encoding/json"
 	"fmt"
 	"path"
 	"sync"
@@ -213,7 +214,12 @@ func S3PeersUpdateBucketListener(bucket string, lcfg []listenerConfig) {
 // S3PeersUpdateBucketPolicy - Sends update bucket policy request to
 // all peers. Currently we log an error and continue.
 func S3PeersUpdateBucketPolicy(bucket string, pCh policyChange) {
-	setBPPArgs := &SetBPPArgs{Bucket: bucket, PCh: pCh}
+	byts, err := json.Marshal(pCh)
+	if err != nil {
+		errorIf(err, "Failed to marshal policyChange - this is a BUG!")
+		return
+	}
+	setBPPArgs := &SetBPPArgs{Bucket: bucket, PChBytes: byts}
 	peers := globalS3Peers.GetPeers()
 	errsMap := globalS3Peers.SendRPC(peers, "S3.SetBucketPolicyPeer", setBPPArgs)
 	for peer, err := range errsMap {

cmd/s3-peer-rpc-handlers.go

@@ -16,7 +16,10 @@
 
 package cmd
 
-import "time"
+import (
+	"encoding/json"
+	"time"
+)
 
 func (s3 *s3PeerAPIHandlers) LoginHandler(args *RPCLoginArgs, reply *RPCLoginReply) error {
 	jwt, err := newJWT(defaultInterNodeJWTExpiry)
@@ -128,8 +131,8 @@ type SetBPPArgs struct {
 
 	Bucket string
 
-	// policy config
-	PCh policyChange
+	// Policy change (serialized to JSON)
+	PChBytes []byte
 }
 
 // tell receiving server to update a bucket policy
@@ -145,5 +148,10 @@ func (s3 *s3PeerAPIHandlers) SetBucketPolicyPeer(args SetBPPArgs, reply *Generic
 		return errServerNotInitialized
 	}
 
-	return globalBucketPolicies.SetBucketPolicy(args.Bucket, args.PCh)
+	var pCh policyChange
+	if err := json.Unmarshal(args.PChBytes, &pCh); err != nil {
+		return err
+	}
+
+	return globalBucketPolicies.SetBucketPolicy(args.Bucket, pCh)
 }