eth: handler BlockHeadersMsg if statement is always true #14848
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This statement `len(headers) > 0 || !filter` is just always true and sometimes can be confusing. - when `len(headers) == 0`: `!filter` is true. - when `len(headers) == 1`: `len(headers) > 0` is true. - when `len(headers) > 1`: `len(headers) > 0` is true.
fjl
approved these changes
Jul 25, 2017
karalabe
reviewed
Jul 26, 2017
| @@ -444,11 +444,9 @@ func (pm *ProtocolManager) handleMsg(p *peer) error { | |||
| // Irrelevant of the fork checks, send the header to the fetcher just in case | |||
| headers = pm.fetcher.FilterHeaders(headers, time.Now()) | |||
| } | |||
| if len(headers) > 0 || !filter { | |||
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No, this is not always true, because headers is changed 2 lines above, and len(headers) becomes 0, while filter was true (hence !filter false).
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This is explicitly how the fetcher works, it keeps anything sent to it, and forwards the rest to the downloader. If the fetcher kept the header delivered, and forwards an empty slice to the downloader, the downloader will abort the sync thinking the peer doesn't have any more headers available.
karalabe
requested changes
Jul 26, 2017
sorpaas
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Jul 26, 2017
…not necessarily always true See ethereum/go-ethereum#14848 for an explanation of why the line `len(headers) > 0 || !filter` is added back. I still don't think we should check total difficulty of the peer with the fork header like ETH does. It might break light clients that only keep the last 256 blocks and does not prevent network attacks. See #313 for an explanation.
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This statement
len(headers) > 0 || !filteris just always true and sometimes can be confusing.len(headers) == 0:!filteris true.len(headers) == 1:len(headers) > 0is true.len(headers) > 1:len(headers) > 0is true.