Check for duplicate txins in CheckTransaction. #443

1. 
   TheBlueMatt commented at 12:20 pm on July 31, 2011: member

   These should be invalid.
2. Check for duplicate txins in CheckTransaction. 33208fb557
3. 
   groffer commented at 10:03 pm on August 2, 2011: none

   CheckBlock calls this function. Won’t this cause a fork in the blockchain if the network doesn’t upgrade as a whole and a transaction that runs afoul of this check is included in a block?
4. 
   sipa commented at 10:07 pm on August 2, 2011: member

   Such a transaction should already cause the block it is included in to be invalid, as ConnectInputs will detect the duplicate use of the same prevout. This patch just causes such cases to be detected in an earlier stage, before it enters the memory pool.
5. 
   TheBlueMatt commented at 10:12 pm on August 2, 2011: member

   If a transaction with a duplicate input is in a block, the chain should be forked (or people are making money out of nothing). Also, no transactions with duplicate inputs get put in blocks…someone tried it a couple weeks ago, but the txes never ended up in blocks. Im assuming there is a check somewhere later on that prevented them from getting added to a block, though I haven’t done any digging on the matter. This is really to prevent such obviously invalid transactions from getting relayed.
6. 
   groffer commented at 10:19 pm on August 2, 2011: none

   Right, looks like the vSpent check in ConnectInputs takes care of it.
7. gavinandresen referenced this in commit 4e5d88ce26 on Aug 8, 2011
8. gavinandresen merged this on Aug 8, 2011
9. gavinandresen closed this on Aug 8, 2011

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10. dexX7 referenced this in commit c637a27dd7 on Jan 9, 2017
11. ptschip referenced this in commit fd9ccdef13 on Apr 19, 2017
12. kallewoof referenced this in commit e63e500658 on Oct 4, 2019
13. rajarshimaitra referenced this in commit 2d076f1420 on Aug 5, 2021
14. DrahtBot locked this on Sep 8, 2021

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