Merge bitcoin/bitcoin#22383: rpc: Prefer to use txindex if available for GetTransaction

78f4c8b98eada337346ffb206339c3ebae4ff43b prefer to use txindex if available for GetTransaction (Jameson Lopp)

Pull request description:

  Fixes #22382

  Motivation: prevent excessive disk reads if txindex is enabled.

  Worth noting that this could be argued to be less of a bug and more of an issue of undefined behavior. If a user calls GetTransaction with the wrong block hash, what should happen?

ACKs for top commit:
  jonatack:
    ACK 78f4c8b98eada337346ffb206339c3ebae4ff43b
  theStack:
    Code review ACK 78f4c8b98eada337346ffb206339c3ebae4ff43b
  LarryRuane:
    tACK 78f4c8b98eada337346ffb206339c3ebae4ff43b
  luke-jr:
    utACK 78f4c8b98eada337346ffb206339c3ebae4ff43b
  jnewbery:
    utACK 78f4c8b98eada337346ffb206339c3ebae4ff43b
  rajarshimaitra:
    Code review ACK https://github.com/bitcoin/bitcoin/commit/78f4c8b98eada337346ffb206339c3ebae4ff43b
  lsilva01:
    Code Review ACK and Tested ACK https://github.com/bitcoin/bitcoin/pull/22383/commits/78f4c8b98eada337346ffb206339c3ebae4ff43b on Ubuntu 20.04

Tree-SHA512: af7db5b98cb2ae4897b28476b2fa243bf7e6f850750d9347062fe8013c5720986d1a3c808f80098e5289bd84b085de03c81a44e584dc28982f721c223651bfe0

1 files changed, 14 insertions, 9 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index 842687e4d6..4e7bc635da 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1158,6 +1158,20 @@ CTransactionRef GetTransaction(const CBlockIndex* const block_index, const CTxMe
 {
     LOCK(cs_main);
 
+    if (mempool && !block_index) {
+        CTransactionRef ptx = mempool->get(hash);
+        if (ptx) return ptx;
+    }
+    if (g_txindex) {
+        CTransactionRef tx;
+        uint256 block_hash;
+        if (g_txindex->FindTx(hash, block_hash, tx)) {
+            if (!block_index || block_index->GetBlockHash() == block_hash) {
+                hashBlock = block_hash;
+                return tx;
+            }
+        }
+    }
     if (block_index) {
         CBlock block;
         if (ReadBlockFromDisk(block, block_index, consensusParams)) {
@@ -1168,15 +1182,6 @@ CTransactionRef GetTransaction(const CBlockIndex* const block_index, const CTxMe
                 }
             }
         }
-        return nullptr;
-    }
-    if (mempool) {
-        CTransactionRef ptx = mempool->get(hash);
-        if (ptx) return ptx;
-    }
-    if (g_txindex) {
-        CTransactionRef tx;
-        if (g_txindex->FindTx(hash, hashBlock, tx)) return tx;
     }
     return nullptr;
 }