When people ask us for headers we do not have (over REST or RPC), do something reasonable.

Author: gwillen

src/node/blockstorage.cpp

@@ -412,6 +412,17 @@ bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus
     return true;
 }
 
+bool ReadBlockHeaderFromDisk(CBlockHeader& header, const CBlockIndex* pindex, const Consensus::Params& consensusParams)
+{
+    // Not very efficient: read a block and throw away all but the header.
+    CBlock tmp;
+    if (!ReadBlockFromDisk(tmp, pindex, consensusParams)) {
+        return false;
+    }
+    header = tmp.GetBlockHeader();
+    return true;
+}
+
 bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const FlatFilePos& pos, const CMessageHeader::MessageStartChars& message_start)
 {
     FlatFilePos hpos = pos;

src/node/blockstorage.h

@@ -49,7 +49,7 @@ extern bool fTrimHeaders;
 /** Minimum number of full untrimmed headers to keep, for blocks we have. */
 extern uint64_t nMustKeepFullHeaders;
 /** Target number of headers to download beyond the blocks we have. */
-// XXX: this currently only operates when in header trim mode, but it's really independent of that.
+// NOTE: this currently only operates when in header trim mode, but it's really independent of that.
 extern uint64_t nHeaderDownloadBuffer;
 
 //! Check whether the block associated with this index entry is pruned or not.
@@ -78,6 +78,8 @@ bool ReadBlockFromDisk(CBlock& block, const FlatFilePos& pos, const Consensus::P
 bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams);
 bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const FlatFilePos& pos, const CMessageHeader::MessageStartChars& message_start);
 bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const CBlockIndex* pindex, const CMessageHeader::MessageStartChars& message_start);
+// ELEMENTS:
+bool ReadBlockHeaderFromDisk(class CBlockHeader& header, const CBlockIndex* pindex, const Consensus::Params& consensusParams);
 
 bool UndoReadFromDisk(CBlockUndo& blockundo, const CBlockIndex* pindex);
 bool WriteUndoDataForBlock(const CBlockUndo& blockundo, BlockValidationState& state, CBlockIndex* pindex, const CChainParams& chainparams);

src/rest.cpp

@@ -221,7 +221,14 @@ static bool rest_headers(const std::any& context,
     case RetFormat::BINARY: {
         CDataStream ssHeader(SER_NETWORK, PROTOCOL_VERSION);
         for (const CBlockIndex *pindex : headers) {
-            ssHeader << pindex->GetBlockHeader();
+            if (pindex->trimmed()) {
+                CBlockHeader tmp;
+                ReadBlockHeaderFromDisk(tmp, pindex, Params().GetConsensus());
+                ssHeader << tmp;
+
+            } else {
+                ssHeader << pindex->GetBlockHeader();
+            }
         }
 
         std::string binaryHeader = ssHeader.str();
@@ -233,8 +240,14 @@ static bool rest_headers(const std::any& context,
     case RetFormat::HEX: {
         CDataStream ssHeader(SER_NETWORK, PROTOCOL_VERSION);
         for (const CBlockIndex *pindex : headers) {
-            ssHeader << pindex->GetBlockHeader();
-        }
+            if (pindex->trimmed()) {
+                CBlockHeader tmp;
+                ReadBlockHeaderFromDisk(tmp, pindex, Params().GetConsensus());
+                ssHeader << tmp;
+
+            } else {
+                ssHeader << pindex->GetBlockHeader();
+            }        }
 
         std::string strHex = HexStr(ssHeader) + "\n";
         req->WriteHeader("Content-Type", "text/plain");

src/rpc/blockchain.cpp

@@ -249,11 +249,23 @@ UniValue blockheaderToJSON(const CBlockIndex* tip, const CBlockIndex* blockindex
         result.pushKV("chainwork", blockindex->nChainWork.GetHex());
     } else {
         if (blockindex->dynafed_params().IsNull()) {
-            result.pushKV("signblock_witness_asm", ScriptToAsmStr(blockindex->get_proof().solution));
-            result.pushKV("signblock_witness_hex", HexStr(blockindex->get_proof().solution));
+            if (blockindex->trimmed()) {
+                result.pushKV("signblock_witness_asm", "<trimmed>");
+                result.pushKV("signblock_witness_hex", "<trimmed>");
+                result.pushKV("warning", "Fields missing due to -trim_headers flag.");
+            } else {
+                result.pushKV("signblock_witness_asm", ScriptToAsmStr(blockindex->get_proof().solution));
+                result.pushKV("signblock_witness_hex", HexStr(blockindex->get_proof().solution));
+            }
         } else {
-            result.pushKV("signblock_witness_hex", EncodeHexScriptWitness(blockindex->signblock_witness()));
-            result.pushKV("dynamic_parameters", dynaParamsToJSON(blockindex->dynafed_params()));
+            if (blockindex->trimmed()) {
+                result.pushKV("signblock_witness_hex", "<trimmed>");
+                result.pushKV("dynamic_parameters", "<trimmed>");
+                result.pushKV("warning", "Fields missing due to -trim_headers flag.");
+            } else {
+                result.pushKV("signblock_witness_hex", EncodeHexScriptWitness(blockindex->signblock_witness()));
+                result.pushKV("dynamic_parameters", dynaParamsToJSON(blockindex->dynafed_params()));
+            }
         }
     }
     result.pushKV("nTx", (uint64_t)blockindex->nTx);
@@ -266,7 +278,13 @@ UniValue blockheaderToJSON(const CBlockIndex* tip, const CBlockIndex* blockindex
 
 UniValue blockToJSON(const CBlock& block, const CBlockIndex* tip, const CBlockIndex* blockindex, bool txDetails)
 {
-    UniValue result = blockheaderToJSON(tip, blockindex);
+    UniValue result;
+    if (blockindex->trimmed()) {
+        CBlockIndex tmp = CBlockIndex(block.GetBlockHeader());  // XXX: lifetimes?
+        result = blockheaderToJSON(tip, &tmp);
+    } else {
+        result = blockheaderToJSON(tip, blockindex);
+    }
 
     result.pushKV("strippedsize", (int)::GetSerializeSize(block, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS));
     result.pushKV("size", (int)::GetSerializeSize(block, PROTOCOL_VERSION));
@@ -968,7 +986,13 @@ static RPCHelpMan getblockheader()
     if (!fVerbose)
     {
         CDataStream ssBlock(SER_NETWORK, PROTOCOL_VERSION);
-        ssBlock << pblockindex->GetBlockHeader();
+        if (pblockindex->trimmed()) {
+            CBlockHeader tmp;
+            ReadBlockHeaderFromDisk(tmp, pblockindex, Params().GetConsensus());
+            ssBlock << tmp;
+        } else {
+            ssBlock << pblockindex->GetBlockHeader();
+        }
         std::string strHex = HexStr(ssBlock);
         return strHex;
     }