Add warning to future segwit version address generation/parsing

Author: junderw

src/address.js

@@ -13,6 +13,11 @@ const FUTURE_SEGWIT_MIN_SIZE = 2;
 const FUTURE_SEGWIT_MAX_VERSION = 16;
 const FUTURE_SEGWIT_MIN_VERSION = 1;
 const FUTURE_SEGWIT_VERSION_DIFF = 0x50;
+const FUTURE_SEGWIT_VERSION_WARNING =
+  'WARNING: Sending to a future segwit version address can lead to loss of funds. ' +
+  'End users MUST be warned carefully in the GUI and asked if they wish to proceed ' +
+  'with caution. Wallets should verify the segwit version from the output of fromBech32, ' +
+  'then decide when it is safe to use which version of segwit.';
 function _toFutureSegwitAddress(output, network) {
   const data = output.slice(2);
   if (
@@ -28,6 +33,7 @@ function _toFutureSegwitAddress(output, network) {
     throw new TypeError('Invalid version for segwit address');
   if (output[1] !== data.length)
     throw new TypeError('Invalid script for segwit address');
+  console.warn(FUTURE_SEGWIT_VERSION_WARNING);
   return toBech32(data, version, network.bech32);
 }
 function fromBase58Check(address) {
@@ -128,11 +134,13 @@ function toOutputScript(address, network) {
         decodeBech32.version <= FUTURE_SEGWIT_MAX_VERSION &&
         decodeBech32.data.length >= FUTURE_SEGWIT_MIN_SIZE &&
         decodeBech32.data.length <= FUTURE_SEGWIT_MAX_SIZE
-      )
+      ) {
+        console.warn(FUTURE_SEGWIT_VERSION_WARNING);
         return bscript.compile([
           decodeBech32.version + FUTURE_SEGWIT_VERSION_DIFF,
           decodeBech32.data,
         ]);
+      }
     }
   }
   throw new Error(address + ' has no matching Script');

ts_src/address.ts

@@ -23,6 +23,11 @@ const FUTURE_SEGWIT_MIN_SIZE: number = 2;
 const FUTURE_SEGWIT_MAX_VERSION: number = 16;
 const FUTURE_SEGWIT_MIN_VERSION: number = 1;
 const FUTURE_SEGWIT_VERSION_DIFF: number = 0x50;
+const FUTURE_SEGWIT_VERSION_WARNING: string =
+  'WARNING: Sending to a future segwit version address can lead to loss of funds. ' +
+  'End users MUST be warned carefully in the GUI and asked if they wish to proceed ' +
+  'with caution. Wallets should verify the segwit version from the output of fromBech32, ' +
+  'then decide when it is safe to use which version of segwit.';
 
 function _toFutureSegwitAddress(output: Buffer, network: Network): string {
   const data = output.slice(2);
@@ -44,6 +49,8 @@ function _toFutureSegwitAddress(output: Buffer, network: Network): string {
   if (output[1] !== data.length)
     throw new TypeError('Invalid script for segwit address');
 
+  console.warn(FUTURE_SEGWIT_VERSION_WARNING);
+
   return toBech32(data, version, network.bech32);
 }
 
@@ -163,11 +170,14 @@ export function toOutputScript(address: string, network?: Network): Buffer {
         decodeBech32.version <= FUTURE_SEGWIT_MAX_VERSION &&
         decodeBech32.data.length >= FUTURE_SEGWIT_MIN_SIZE &&
         decodeBech32.data.length <= FUTURE_SEGWIT_MAX_SIZE
-      )
+      ) {
+        console.warn(FUTURE_SEGWIT_VERSION_WARNING);
+
         return bscript.compile([
           decodeBech32.version + FUTURE_SEGWIT_VERSION_DIFF,
           decodeBech32.data,
         ]);
+      }
     }
   }