Accept any sequence of PUSHDATAs in OP_RETURN outputs

Previously only one PUSHDATA was allowed, needlessly limiting
applications such as matching OP_RETURN contents with bloom filters that
operate on a per-PUSHDATA level. Now any combination that passes
IsPushOnly() is allowed, so long as the total size of the scriptPubKey
is less than 42 bytes. (unchanged modulo non-minimal PUSHDATA encodings)

Also, this fixes the odd bug where previously the PUSHDATA could be
replaced by any single opcode, even sigops consuming opcodes such as
CHECKMULTISIG. (20 sigops!)

Author: petertodd

src/policy/policy.cpp

@@ -49,7 +49,9 @@ bool IsStandard(const CScript& scriptPubKey, txnouttype& whichType)
             return false;
         if (m < 1 || m > n)
             return false;
-    }
+    } else if (whichType == TX_NULL_DATA &&
+               (!GetBoolArg("-datacarrier", true) || scriptPubKey.size() > nMaxDatacarrierBytes))
+          return false;
 
     return whichType != TX_NONSTANDARD;
 }

src/script/script.cpp

@@ -144,7 +144,7 @@ const char* GetOpName(opcodetype opcode)
     case OP_INVALIDOPCODE          : return "OP_INVALIDOPCODE";
 
     // Note:
-    //  The template matching params OP_SMALLDATA/etc are defined in opcodetype enum
+    //  The template matching params OP_SMALLINTEGER/etc are defined in opcodetype enum
     //  as kind of implementation hack, they are *NOT* real opcodes.  If found in real
     //  Script, just let the default: case deal with them.
 

src/script/script.h

@@ -167,7 +167,6 @@ enum opcodetype
 
 
     // template matching params
-    OP_SMALLDATA = 0xf9,
     OP_SMALLINTEGER = 0xfa,
     OP_PUBKEYS = 0xfb,
     OP_PUBKEYHASH = 0xfd,

src/script/standard.cpp

@@ -51,11 +51,6 @@ bool Solver(const CScript& scriptPubKey, txnouttype& typeRet, vector<vector<unsi
 
         // Sender provides N pubkeys, receivers provides M signatures
         mTemplates.insert(make_pair(TX_MULTISIG, CScript() << OP_SMALLINTEGER << OP_PUBKEYS << OP_SMALLINTEGER << OP_CHECKMULTISIG));
-
-        // Empty, provably prunable, data-carrying output
-        if (GetBoolArg("-datacarrier", true))
-            mTemplates.insert(make_pair(TX_NULL_DATA, CScript() << OP_RETURN << OP_SMALLDATA));
-        mTemplates.insert(make_pair(TX_NULL_DATA, CScript() << OP_RETURN));
     }
 
     vSolutionsRet.clear();
@@ -70,6 +65,16 @@ bool Solver(const CScript& scriptPubKey, txnouttype& typeRet, vector<vector<unsi
         return true;
     }
 
+    // Provably prunable, data-carrying output
+    //
+    // So long as script passes the IsUnspendable() test and all but the first
+    // byte passes the IsPushOnly() test we don't care what exactly is in the
+    // script.
+    if (scriptPubKey.size() >= 1 && scriptPubKey[0] == OP_RETURN && scriptPubKey.IsPushOnly(scriptPubKey.begin()+1)) {
+        typeRet = TX_NULL_DATA;
+        return true;
+    }
+
     // Scan templates
     const CScript& script1 = scriptPubKey;
     BOOST_FOREACH(const PAIRTYPE(txnouttype, CScript)& tplate, mTemplates)
@@ -142,12 +147,6 @@ bool Solver(const CScript& scriptPubKey, txnouttype& typeRet, vector<vector<unsi
                 else
                     break;
             }
-            else if (opcode2 == OP_SMALLDATA)
-            {
-                // small pushdata, <= nMaxDatacarrierBytes
-                if (vch1.size() > nMaxDatacarrierBytes)
-                    break;
-            }
             else if (opcode1 != opcode2 || vch1 != vch2)
             {
                 // Others must match exactly

src/script/standard.h

@@ -25,7 +25,7 @@ class CScriptID : public uint160
     CScriptID(const uint160& in) : uint160(in) {}
 };
 
-static const unsigned int MAX_OP_RETURN_RELAY = 80;      //! bytes
+static const unsigned int MAX_OP_RETURN_RELAY = 83; //! bytes (+1 for OP_RETURN, +2 for the pushdata opcodes)
 extern unsigned nMaxDatacarrierBytes;
 
 /**

src/test/transaction_tests.cpp

@@ -351,12 +351,29 @@ BOOST_AUTO_TEST_CASE(test_IsStandard)
     t.vout[0].scriptPubKey = CScript() << OP_1;
     BOOST_CHECK(!IsStandardTx(t, reason));
 
-    // 80-byte TX_NULL_DATA (standard)
+    // MAX_OP_RETURN_RELAY-byte TX_NULL_DATA (standard)
     t.vout[0].scriptPubKey = CScript() << OP_RETURN << ParseHex("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef3804678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38");
+    BOOST_CHECK_EQUAL(MAX_OP_RETURN_RELAY, t.vout[0].scriptPubKey.size());
     BOOST_CHECK(IsStandardTx(t, reason));
 
-    // 81-byte TX_NULL_DATA (non-standard)
+    // MAX_OP_RETURN_RELAY+1-byte TX_NULL_DATA (non-standard)
     t.vout[0].scriptPubKey = CScript() << OP_RETURN << ParseHex("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef3804678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef3800");
+    BOOST_CHECK_EQUAL(MAX_OP_RETURN_RELAY + 1, t.vout[0].scriptPubKey.size());
+    BOOST_CHECK(!IsStandardTx(t, reason));
+
+    // Data payload can be encoded in any way...
+    t.vout[0].scriptPubKey = CScript() << OP_RETURN << ParseHex("");
+    BOOST_CHECK(IsStandardTx(t, reason));
+    t.vout[0].scriptPubKey = CScript() << OP_RETURN << ParseHex("00") << ParseHex("01");
+    BOOST_CHECK(IsStandardTx(t, reason));
+    // OP_RESERVED *is* considered to be a PUSHDATA type opcode by IsPushOnly()!
+    t.vout[0].scriptPubKey = CScript() << OP_RETURN << OP_RESERVED << -1 << 0 << ParseHex("01") << 2 << 3 << 4 << 5 << 6 << 7 << 8 << 9 << 10 << 11 << 12 << 13 << 14 << 15 << 16;
+    BOOST_CHECK(IsStandardTx(t, reason));
+    t.vout[0].scriptPubKey = CScript() << OP_RETURN << 0 << ParseHex("01") << 2 << ParseHex("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
+    BOOST_CHECK(IsStandardTx(t, reason));
+
+    // ...so long as it only contains PUSHDATA's
+    t.vout[0].scriptPubKey = CScript() << OP_RETURN << OP_RETURN;
     BOOST_CHECK(!IsStandardTx(t, reason));
 
     // TX_NULL_DATA w/o PUSHDATA