do not enforce 1/3 validator power change

leave it to the app

Refs #1022

docs/app-development.rst

@@ -409,11 +409,10 @@ to update the validator set. To add a new validator or update an existing one,
 simply include them in the list returned in the EndBlock response. To remove
 one, include it in the list with a ``power`` equal to ``0``. Tendermint core
 will take care of updating the validator set. Note the change in voting power
-must be strictly less than 1/3 per block. Otherwise it will be impossible for a
-light client to prove the transition externally. See the `light client docs
+must be strictly less than 1/3 per block if you want a light client to be able
+to prove the transition externally. See the `light client docs
 <https://godoc.org/github.com/tendermint/tendermint/lite#hdr-How_We_Track_Validators>`__
-for details on how it tracks validators. Tendermint core will fail with an
-error if the change in voting power is more or equal than 1/3.
+for details on how it tracks validators.
 
 .. container:: toggle
 

state/execution.go

@@ -1,7 +1,6 @@
 package state
 
 import (
-	"errors"
 	"fmt"
 
 	fail "github.com/ebuchman/fail-test"
@@ -238,18 +237,10 @@ func execBlockOnProxyApp(logger log.Logger, proxyAppConn proxy.AppConnConsensus,
 	return abciResponses, nil
 }
 
+// If more or equal than 1/3 of total voting power changed in one block, then
+// a light client could never prove the transition externally. See
+// ./lite/doc.go for details on how a light client tracks validators.
 func updateValidators(currentSet *types.ValidatorSet, updates []abci.Validator) error {
-	// If more or equal than 1/3 of total voting power changed in one block, then
-	// a light client could never prove the transition externally. See
-	// ./lite/doc.go for details on how a light client tracks validators.
-	vp23, err := changeInVotingPowerMoreOrEqualToOneThird(currentSet, updates)
-	if err != nil {
-		return err
-	}
-	if vp23 {
-		return errors.New("the change in voting power must be strictly less than 1/3")
-	}
-
 	for _, v := range updates {
 		pubkey, err := crypto.PubKeyFromBytes(v.PubKey) // NOTE: expects go-wire encoded pubkey
 		if err != nil {
@@ -288,42 +279,6 @@ func updateValidators(currentSet *types.ValidatorSet, updates []abci.Validator)
 	return nil
 }
 
-func changeInVotingPowerMoreOrEqualToOneThird(currentSet *types.ValidatorSet, updates []abci.Validator) (bool, error) {
-	threshold := currentSet.TotalVotingPower() * 1 / 3
-	acc := int64(0)
-
-	for _, v := range updates {
-		pubkey, err := crypto.PubKeyFromBytes(v.PubKey) // NOTE: expects go-wire encoded pubkey
-		if err != nil {
-			return false, err
-		}
-
-		address := pubkey.Address()
-		power := int64(v.Power)
-		// mind the overflow from int64
-		if power < 0 {
-			return false, fmt.Errorf("Power (%d) overflows int64", v.Power)
-		}
-
-		_, val := currentSet.GetByAddress(address)
-		if val == nil {
-			acc += power
-		} else {
-			np := val.VotingPower - power
-			if np < 0 {
-				np = -np
-			}
-			acc += np
-		}
-
-		if acc >= threshold {
-			return true, nil
-		}
-	}
-
-	return false, nil
-}
-
 // updateState returns a new State updated according to the header and responses.
 func updateState(s State, blockID types.BlockID, header *types.Header,
 	abciResponses *ABCIResponses) (State, error) {

state/state_test.go

@@ -375,73 +375,6 @@ func makeParams(blockBytes, blockTx, blockGas, txBytes,
 	}
 }
 
-func TestLessThanOneThirdOfVotingPowerPerBlockEnforced(t *testing.T) {
-	testCases := []struct {
-		initialValSetSize int
-		shouldErr         bool
-		valUpdatesFn      func(vals *types.ValidatorSet) []abci.Validator
-	}{
-		///////////// 1 val (vp: 10) => less than 3 is ok ////////////////////////
-		// adding 1 validator => 10
-		0: {1, false, func(vals *types.ValidatorSet) []abci.Validator {
-			return []abci.Validator{
-				{PubKey: pk(), Power: 2},
-			}
-		}},
-		1: {1, true, func(vals *types.ValidatorSet) []abci.Validator {
-			return []abci.Validator{
-				{PubKey: pk(), Power: 3},
-			}
-		}},
-		2: {1, true, func(vals *types.ValidatorSet) []abci.Validator {
-			return []abci.Validator{
-				{PubKey: pk(), Power: 100},
-			}
-		}},
-
-		///////////// 3 val (vp: 30) => less than 10 is ok ////////////////////////
-		// adding and removing validator => 20
-		3: {3, true, func(vals *types.ValidatorSet) []abci.Validator {
-			_, firstVal := vals.GetByIndex(0)
-			return []abci.Validator{
-				{PubKey: firstVal.PubKey.Bytes(), Power: 0},
-				{PubKey: pk(), Power: 10},
-			}
-		}},
-		// adding 1 validator => 10
-		4: {3, true, func(vals *types.ValidatorSet) []abci.Validator {
-			return []abci.Validator{
-				{PubKey: pk(), Power: 10},
-			}
-		}},
-		// adding 2 validators => 8
-		5: {3, false, func(vals *types.ValidatorSet) []abci.Validator {
-			return []abci.Validator{
-				{PubKey: pk(), Power: 4},
-				{PubKey: pk(), Power: 4},
-			}
-		}},
-	}
-
-	for i, tc := range testCases {
-		tearDown, stateDB, state := setupTestCase(t)
-		state.Validators = genValSet(tc.initialValSetSize)
-		SaveState(stateDB, state)
-		height := state.LastBlockHeight + 1
-		block := makeBlock(state, height)
-		abciResponses := &ABCIResponses{
-			EndBlock: &abci.ResponseEndBlock{ValidatorUpdates: tc.valUpdatesFn(state.Validators)},
-		}
-		state, err := updateState(state, types.BlockID{block.Hash(), types.PartSetHeader{}}, block.Header, abciResponses)
-		if tc.shouldErr {
-			assert.Error(t, err, "#%d", i)
-		} else {
-			assert.NoError(t, err, "#%d", i)
-		}
-		tearDown(t)
-	}
-}
-
 func pk() []byte {
 	return crypto.GenPrivKeyEd25519().PubKey().Bytes()
 }