[net processing] Synchronize cfilter request handling with block filt…

…er index.

Since the block filter index is updated asynchronously by proxy of the
ValidationInterface queue, lazily synchronize the net thread with the
block filter index in case lookups fail.

Github-Pull: bitcoin#18876
Rebased-From: 5488ce9

src/index/base.h

@@ -84,13 +84,13 @@ class BaseIndex : public CValidationInterface
 
     virtual DB& GetDB() const = 0;
 
-    /// Get the name of the index for display in logs.
-    virtual const char* GetName() const = 0;
-
 public:
     /// Destructor interrupts sync thread if running and blocks until it exits.
     virtual ~BaseIndex();
 
+    /// Get the name of the index for display in logs.
+    virtual const char* GetName() const = 0;
+
     /// Returns whether index has completed the initial sync with the active chain.
     /// After returning true once, this function will return true on all subsequent calls.
     bool IsSynced() const { return m_synced; }

src/index/blockfilterindex.h

@@ -41,13 +41,13 @@ class BlockFilterIndex final : public BaseIndex
 
     BaseIndex::DB& GetDB() const override { return *m_db; }
 
-    const char* GetName() const override { return m_name.c_str(); }
-
 public:
     /** Constructs the index, which becomes available to be queried. */
     explicit BlockFilterIndex(BlockFilterType filter_type,
                               size_t n_cache_size, bool f_memory = false, bool f_wipe = false);
 
+    const char* GetName() const override { return m_name.c_str(); }
+
     BlockFilterType GetFilterType() const { return m_filter_type; }
 
     /** Get a single filter by block. */

src/index/txindex.h

@@ -30,15 +30,15 @@ class TxIndex final : public BaseIndex
 
     BaseIndex::DB& GetDB() const override;
 
-    const char* GetName() const override { return "txindex"; }
-
 public:
     /// Constructs the index, which becomes available to be queried.
     explicit TxIndex(size_t n_cache_size, bool f_memory = false, bool f_wipe = false);
 
     // Destructor is declared because this class contains a unique_ptr to an incomplete type.
     virtual ~TxIndex() override;
 
+    const char* GetName() const override { return "txindex"; }
+
     /// Look up a transaction by hash.
     ///
     /// @param[in]   tx_hash  The hash of the transaction to be returned.

src/net_processing.cpp

@@ -2022,6 +2022,10 @@ static bool PrepareBlockFilterRequest(CNode* pfrom, const CChainParams& chain_pa
         LogPrint(BCLog::NET, "Filter index for supported type %s not found\n", BlockFilterTypeName(filter_type));
         return false;
     }
+    if (!filter_index->BlockUntilSyncedToCurrentChain()) {
+        LogPrint(BCLog::NET, "%s is not ready yet\n", filter_index->GetName());
+        return false;
+    }
 
     return true;
 }