feat(all): Add example chain implementation

CHANGELOG.md

@@ -8,6 +8,7 @@ This changelog was created using the `clu` binary
 
 ### Improvements
 
+- (all) [#30](https://github.com/evmos/os/pull/30) Add example chain implementation and ante handlers.
 - (ci) [#35](https://github.com/evmos/os/pull/35) Disable dependabot temporarily.
 - (contracts) [#24](https://github.com/evmos/os/pull/24) Add contracts directory and compilation script.
 - (cli) [#23](https://github.com/evmos/os/pull/23) Add client, cmd and version packages.

ante/cosmos/authz.go

@@ -0,0 +1,91 @@
+// Copyright Tharsis Labs Ltd.(Evmos)
+// SPDX-License-Identifier:ENCL-1.0(https://github.com/evmos/evmos/blob/main/LICENSE)
+
+package cosmos
+
+import (
+	"fmt"
+
+	errorsmod "cosmossdk.io/errors"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	errortypes "github.com/cosmos/cosmos-sdk/types/errors"
+	"github.com/cosmos/cosmos-sdk/x/authz"
+)
+
+// maxNestedMsgs defines a cap for the number of nested messages on a MsgExec message
+const maxNestedMsgs = 7
+
+// AuthzLimiterDecorator blocks certain msg types from being granted or executed
+// within the authorization module.
+type AuthzLimiterDecorator struct {
+	// disabledMsgTypes is the type urls of the msgs to block.
+	disabledMsgTypes []string
+}
+
+// NewAuthzLimiterDecorator creates a decorator to block certain msg types from being granted or executed within authz.
+func NewAuthzLimiterDecorator(disabledMsgTypes ...string) AuthzLimiterDecorator {
+	return AuthzLimiterDecorator{
+		disabledMsgTypes: disabledMsgTypes,
+	}
+}
+
+func (ald AuthzLimiterDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (newCtx sdk.Context, err error) {
+	if err := ald.checkDisabledMsgs(tx.GetMsgs(), false, 1); err != nil {
+		return ctx, errorsmod.Wrapf(errortypes.ErrUnauthorized, err.Error())
+	}
+	return next(ctx, tx, simulate)
+}
+
+// checkDisabledMsgs iterates through the msgs and returns an error if it finds any unauthorized msgs.
+//
+// When searchOnlyInAuthzMsgs is enabled, only authz MsgGrant and MsgExec are blocked, if they contain unauthorized msg types.
+// Otherwise, any msg matching the disabled types are blocked, regardless of being in an authz msg or not.
+//
+// This method is recursive as MsgExec's can wrap other MsgExecs. The check for nested messages is performed up to the
+// maxNestedMsgs threshold. If there are more than that limit, it returns an error
+func (ald AuthzLimiterDecorator) checkDisabledMsgs(msgs []sdk.Msg, isAuthzInnerMsg bool, nestedLvl int) error {
+	if nestedLvl >= maxNestedMsgs {
+		return fmt.Errorf("found more nested msgs than permitted; got: %d, expected: <%d", nestedLvl, maxNestedMsgs)
+	}
+	for _, msg := range msgs {
+		switch msg := msg.(type) {
+		case *authz.MsgExec:
+			innerMsgs, err := msg.GetMessages()
+			if err != nil {
+				return err
+			}
+			nestedLvl++
+			if err := ald.checkDisabledMsgs(innerMsgs, true, nestedLvl); err != nil {
+				return err
+			}
+		case *authz.MsgGrant:
+			authorization, err := msg.GetAuthorization()
+			if err != nil {
+				return err
+			}
+
+			url := authorization.MsgTypeURL()
+			if ald.isDisabledMsg(url) {
+				return fmt.Errorf("found disabled msg type: %s", url)
+			}
+		default:
+			url := sdk.MsgTypeURL(msg)
+			if isAuthzInnerMsg && ald.isDisabledMsg(url) {
+				return fmt.Errorf("found disabled msg type: %s", url)
+			}
+		}
+	}
+	return nil
+}
+
+// isDisabledMsg returns true if the given message is in the list of restricted
+// messages from the AnteHandler.
+func (ald AuthzLimiterDecorator) isDisabledMsg(msgTypeURL string) bool {
+	for _, disabledType := range ald.disabledMsgTypes {
+		if msgTypeURL == disabledType {
+			return true
+		}
+	}
+
+	return false
+}