Helper function LedgerMaster::getLedgerHash to walk the chain.

modules/ripple_app/ledger/LedgerMaster.cpp

@@ -776,7 +776,7 @@ void LedgerMaster::tryPublish ()
 
             if (!ledger && (++acq < 4))
             { // We can try to acquire the ledger we need
-	        InboundLedger::pointer acq = getApp().getInboundLedgers ().findCreate (hash, seq);
+                InboundLedger::pointer acq = getApp().getInboundLedgers ().findCreate (hash, seq);
 
                 if (!acq->isDone ())
                 {
@@ -800,7 +800,7 @@ void LedgerMaster::tryPublish ()
             if (ledger && (ledger->getLedgerSeq() == (mPubLedger->getLedgerSeq() + 1)))
             { // We acquired the next ledger we need to publish
                 ledger->setValidated();
-	        mPubLedger = ledger;
+                mPubLedger = ledger;
                 mPubLedgers.push_back (mPubLedger);
             }
 
@@ -824,6 +824,36 @@ void LedgerMaster::tryPublish ()
     }
 }
 
+uint256 LedgerMaster::getLedgerHash(uint32 desiredSeq, Ledger::ref knownGoodLedger)
+{ // Get the hash of the valid ledger with a particular sequence, given a subsequent ledger known valid
+
+    assert(desiredSeq < knownGoodLedger->getLedgerSeq());
+
+    uint256 hash = knownGoodLedger->getLedgerHash(desiredSeq);
+
+    if (hash.isZero ())
+    { // Not directly in the given ledger
+
+        uint32 seq = (desiredSeq + 255) % 256;
+        assert(seq < desiredSeq);
+
+        uint256 i = knownGoodLedger->getLedgerHash(seq);
+        if (i.isNonZero())
+        {
+            Ledger::pointer l = getLedgerByHash(i);
+            if (l)
+            {
+                hash = l->getLedgerHash(desiredSeq);
+                assert (hash.isNonZero());
+            }
+        }
+        else
+            assert(false);
+    }
+
+    return hash;
+}
+
 void LedgerMaster::pubThread ()
 {
     std::list<Ledger::pointer> ledgers;

modules/ripple_app/ledger/LedgerMaster.h

@@ -150,6 +150,8 @@ public:
         mCompleteLedgers.setRange (minV, maxV);
     }
 
+    uint256 getLedgerHash(uint32 desiredSeq, Ledger::ref knownGoodLedger);
+
     void addHeldTransaction (Transaction::ref trans);
     void fixMismatch (Ledger::ref ledger);