doc: add comment explaining initial header request
Add a comment that explains why the initial "getheader" requests are made starting from the block preceding the currently best one. Thanks to sdaftuar for the explanation!
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11
src/main.cpp
11
src/main.cpp
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@ -4955,7 +4955,16 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
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if ((nSyncStarted == 0 && fFetch) || pindexBestHeader->GetBlockTime() > GetAdjustedTime() - 24 * 60 * 60) {
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state.fSyncStarted = true;
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nSyncStarted++;
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CBlockIndex *pindexStart = pindexBestHeader->pprev ? pindexBestHeader->pprev : pindexBestHeader;
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const CBlockIndex *pindexStart = pindexBestHeader;
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/* If possible, start at the block preceding the currently
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best known header. This ensures that we always get a
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non-empty list of headers back as long as the peer
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is up-to-date. With a non-empty response, we can initialise
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the peer's known best block. This wouldn't be possible
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if we requested starting at pindexBestHeader and
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got back an empty response. */
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if (pindexStart->pprev)
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pindexStart = pindexStart->pprev;
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LogPrint("net", "initial getheaders (%d) to peer=%d (startheight:%d)\n", pindexStart->nHeight, pto->id, pto->nStartingHeight);
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pto->PushMessage("getheaders", chainActive.GetLocator(pindexStart), uint256());
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}
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