blockstorage: return an error code from `ReadRawBlock()`

diff --git a/src/bench/readwriteblock.cpp b/src/bench/readwriteblock.cpp
index 4ca5b8eb..a742a1e8 100644
--- a/src/bench/readwriteblock.cpp
+++ b/src/bench/readwriteblock.cpp
@@ -57,11 +57,9 @@ static void ReadRawBlockBench(benchmark::Bench& bench)
     const auto testing_setup{MakeNoLogFileContext<const TestingSetup>(ChainType::MAIN)};
     auto& blockman{testing_setup->m_node.chainman->m_blockman};
     const auto pos{blockman.WriteBlock(CreateTestBlock(), 413'567)};
-    std::vector<std::byte> block_data;
-    blockman.ReadRawBlock(block_data, pos); // warmup
     bench.run([&] {
-        const auto success{blockman.ReadRawBlock(block_data, pos)};
-        assert(success);
+        const auto res{blockman.ReadRawBlock(pos)};
+        assert(res);
     });
 }
 
diff --git a/src/init.cpp b/src/init.cpp
index b35c6b72..1a0cd79f 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1759,7 +1759,11 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     g_zmq_notification_interface = CZMQNotificationInterface::Create(
         [&chainman = node.chainman](std::vector<std::byte>& block, const CBlockIndex& index) {
             assert(chainman);
-            return chainman->m_blockman.ReadRawBlock(block, WITH_LOCK(cs_main, return index.GetBlockPos()));
+            if (auto ret{chainman->m_blockman.ReadRawBlock(WITH_LOCK(cs_main, return index.GetBlockPos()))}) {
+                block = std::move(*ret);
+                return true;
+            }
+            return false;
         });
 
     if (g_zmq_notification_interface) {
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index c8bc4a84..00acebd1 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -2276,8 +2276,9 @@ void PeerManagerImpl::ProcessGetBlockData(CNode& pfrom, Peer& peer, const CInv&
     } else if (inv.IsMsgWitnessBlk()) {
         // Fast-path: in this case it is possible to serve the block directly from disk,
         // as the network format matches the format on disk
-        std::vector<std::byte> block_data;
-        if (!m_chainman.m_blockman.ReadRawBlock(block_data, block_pos)) {
+        if (const auto block_data{m_chainman.m_blockman.ReadRawBlock(block_pos)}) {
+            MakeAndPushMessage(pfrom, NetMsgType::BLOCK, std::span{*block_data});
+        } else {
             if (WITH_LOCK(m_chainman.GetMutex(), return m_chainman.m_blockman.IsBlockPruned(*pindex))) {
                 LogDebug(BCLog::NET, "Block was pruned before it could be read, %s\n", pfrom.DisconnectMsg(fLogIPs));
             } else {
@@ -2286,7 +2287,6 @@ void PeerManagerImpl::ProcessGetBlockData(CNode& pfrom, Peer& peer, const CInv&
             pfrom.fDisconnect = true;
             return;
         }
-        MakeAndPushMessage(pfrom, NetMsgType::BLOCK, std::span{block_data});
         // Don't set pblock as we've sent the block
     } else {
         // Send block from disk
diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index d2a4c620..0927eb85 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -1006,14 +1006,14 @@ bool BlockManager::ReadBlock(CBlock& block, const FlatFilePos& pos, const std::o
     block.SetNull();
 
     // Open history file to read
-    std::vector<std::byte> block_data;
-    if (!ReadRawBlock(block_data, pos)) {
+    const auto block_data{ReadRawBlock(pos)};
+    if (!block_data) {
         return false;
     }
 
     try {
         // Read block
-        SpanReader{block_data} >> TX_WITH_WITNESS(block);
+        SpanReader{*block_data} >> TX_WITH_WITNESS(block);
     } catch (const std::exception& e) {
         LogError("Deserialize or I/O error - %s at %s while reading block", e.what(), pos.ToString());
         return false;
@@ -1048,19 +1048,19 @@ bool BlockManager::ReadBlock(CBlock& block, const CBlockIndex& index) const
     return ReadBlock(block, block_pos, index.GetBlockHash());
 }
 
-bool BlockManager::ReadRawBlock(std::vector<std::byte>& block, const FlatFilePos& pos) const
+BlockManager::ReadRawBlockResult BlockManager::ReadRawBlock(const FlatFilePos& pos) const
 {
     if (pos.nPos < STORAGE_HEADER_BYTES) {
         // If nPos is less than STORAGE_HEADER_BYTES, we can't read the header that precedes the block data
         // This would cause an unsigned integer underflow when trying to position the file cursor
         // This can happen after pruning or default constructed positions
         LogError("Failed for %s while reading raw block storage header", pos.ToString());
-        return false;
+        return util::Unexpected{ReadRawError::IO};
     }
     AutoFile filein{OpenBlockFile({pos.nFile, pos.nPos - STORAGE_HEADER_BYTES}, /*fReadOnly=*/true)};
     if (filein.IsNull()) {
         LogError("OpenBlockFile failed for %s while reading raw block", pos.ToString());
-        return false;
+        return util::Unexpected{ReadRawError::IO};
     }
 
     try {
@@ -1072,23 +1072,22 @@ bool BlockManager::ReadRawBlock(std::vector<std::byte>& block, const FlatFilePos
         if (blk_start != GetParams().MessageStart()) {
             LogError("Block magic mismatch for %s: %s versus expected %s while reading raw block",
                 pos.ToString(), HexStr(blk_start), HexStr(GetParams().MessageStart()));
-            return false;
+            return util::Unexpected{ReadRawError::IO};
         }
 
         if (blk_size > MAX_SIZE) {
             LogError("Block data is larger than maximum deserialization size for %s: %s versus %s while reading raw block",
                 pos.ToString(), blk_size, MAX_SIZE);
-            return false;
+            return util::Unexpected{ReadRawError::IO};
         }
 
-        block.resize(blk_size); // Zeroing of memory is intentional here
-        filein.read(block);
+        std::vector<std::byte> data(blk_size); // Zeroing of memory is intentional here
+        filein.read(data);
+        return data;
     } catch (const std::exception& e) {
         LogError("Read from block file failed: %s for %s while reading raw block", e.what(), pos.ToString());
-        return false;
+        return util::Unexpected{ReadRawError::IO};
     }
-
-    return true;
 }
 
 FlatFilePos BlockManager::WriteBlock(const CBlock& block, int nHeight)
diff --git a/src/node/blockstorage.h b/src/node/blockstorage.h
index 9ba7873c..1ce7e8f6 100644
--- a/src/node/blockstorage.h
+++ b/src/node/blockstorage.h
@@ -17,6 +17,7 @@
 #include <streams.h>
 #include <sync.h>
 #include <uint256.h>
+#include <util/expected.h>
 #include <util/fs.h>
 #include <util/hasher.h>
 
@@ -169,6 +170,9 @@ struct BlockfileCursor {
 
 std::ostream& operator<<(std::ostream& os, const BlockfileCursor& cursor);
 
+enum class ReadRawError {
+    IO,
+};
 
 /**
  * Maintains a tree of blocks (stored in `m_block_index`) which is consulted
@@ -302,6 +306,7 @@ private:
 
 public:
     using Options = kernel::BlockManagerOpts;
+    using ReadRawBlockResult = util::Expected<std::vector<std::byte>, ReadRawError>;
 
     explicit BlockManager(const util::SignalInterrupt& interrupt, Options opts);
 
@@ -455,7 +460,7 @@ public:
     /** Functions for disk access for blocks */
     bool ReadBlock(CBlock& block, const FlatFilePos& pos, const std::optional<uint256>& expected_hash) const;
     bool ReadBlock(CBlock& block, const CBlockIndex& index) const;
-    bool ReadRawBlock(std::vector<std::byte>& block, const FlatFilePos& pos) const;
+    ReadRawBlockResult ReadRawBlock(const FlatFilePos& pos) const;
 
     bool ReadBlockUndo(CBlockUndo& blockundo, const CBlockIndex& index) const;
 
diff --git a/src/rest.cpp b/src/rest.cpp
index 40a07ba1..4883e26d 100644
--- a/src/rest.cpp
+++ b/src/rest.cpp
@@ -416,20 +416,23 @@ static bool rest_block(const std::any& context,
         pos = pblockindex->GetBlockPos();
     }
 
-    std::vector<std::byte> block_data{};
-    if (!chainman.m_blockman.ReadRawBlock(block_data, pos)) {
-        return RESTERR(req, HTTP_NOT_FOUND, hashStr + " not found");
+    const auto block_data{chainman.m_blockman.ReadRawBlock(pos)};
+    if (!block_data) {
+        switch (block_data.error()) {
+        case node::ReadRawError::IO: return RESTERR(req, HTTP_INTERNAL_SERVER_ERROR, "I/O error reading " + hashStr);
+        }
+        assert(false);
     }
 
     switch (rf) {
     case RESTResponseFormat::BINARY: {
         req->WriteHeader("Content-Type", "application/octet-stream");
-        req->WriteReply(HTTP_OK, block_data);
+        req->WriteReply(HTTP_OK, *block_data);
         return true;
     }
 
     case RESTResponseFormat::HEX: {
-        const std::string strHex{HexStr(block_data) + "\n"};
+        const std::string strHex{HexStr(*block_data) + "\n"};
         req->WriteHeader("Content-Type", "text/plain");
         req->WriteReply(HTTP_OK, strHex);
         return true;
@@ -437,7 +440,7 @@ static bool rest_block(const std::any& context,
 
     case RESTResponseFormat::JSON: {
         CBlock block{};
-        DataStream block_stream{block_data};
+        DataStream block_stream{*block_data};
         block_stream >> TX_WITH_WITNESS(block);
         UniValue objBlock = blockToJSON(chainman.m_blockman, block, *tip, *pblockindex, tx_verbosity, chainman.GetConsensus().powLimit);
         std::string strJSON = objBlock.write() + "\n";
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 8f283ff4..c68bfb8c 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -680,7 +680,6 @@ static CBlock GetBlockChecked(BlockManager& blockman, const CBlockIndex& blockin
 
 static std::vector<std::byte> GetRawBlockChecked(BlockManager& blockman, const CBlockIndex& blockindex)
 {
-    std::vector<std::byte> data{};
     FlatFilePos pos{};
     {
         LOCK(cs_main);
@@ -688,13 +687,10 @@ static std::vector<std::byte> GetRawBlockChecked(BlockManager& blockman, const C
         pos = blockindex.GetBlockPos();
     }
 
-    if (!blockman.ReadRawBlock(data, pos)) {
-        // Block not found on disk. This shouldn't normally happen unless the block was
-        // pruned right after we released the lock above.
-        throw JSONRPCError(RPC_MISC_ERROR, "Block not found on disk");
-    }
-
-    return data;
+    if (auto data{blockman.ReadRawBlock(pos)}) return std::move(*data);
+    // Block not found on disk. This shouldn't normally happen unless the block was
+    // pruned right after we released the lock above.
+    throw JSONRPCError(RPC_MISC_ERROR, "Block not found on disk");
 }
 
 static CBlockUndo GetUndoChecked(BlockManager& blockman, const CBlockIndex& blockindex)