Details
Major Description
I tried running Nutch on my Synology NAS. As SMB protocol is not contained in Nutch, I turned on FTP service on the NAS and configured Nutch to crawl ftp://nas.
The experience gives me varying results which seem to point to problems within Nutch. However this may need further evaluation.
As some files could not be downloaded and I could not see a good error message I changed the method org.apache.nutch.protocol.ftp.FTP.getProtocolOutput(Text, CrawlDatum) to not only return protocol status but send the full exception and stack trace to the logs:
{{ } catch (Exception e) {
LOG.warn("Could not get {}", url, e);
return new ProtocolOutput(null, new ProtocolStatus(e));
}
}}
With this modification I suddenly see such messages in the logfile:
{{2017-11-09 23:44:56,135 WARN org.apache.nutch.protocol.ftp.Ftp - Error:
java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.LinkedList.checkElementIndex(LinkedList.java:555)
at java.util.LinkedList.get(LinkedList.java:476)
at org.apache.nutch.protocol.ftp.FtpResponse.getFileAsHttpResponse(FtpResponse.java:327)
at org.apache.nutch.protocol.ftp.FtpResponse.<init>(FtpResponse.java:267)
at org.apache.nutch.protocol.ftp.Ftp.getProtocolOutput(Ftp.java:133)
at org.apache.nutch.fetcher.FetcherThread.run(FetcherThread.java:340)
2017-11-09 23:44:56,135 ERROR org.apache.nutch.protocol.ftp.Ftp - Could not get protocol output for ftp://nas/MediaPC/boot/memtest86+.elf
org.apache.nutch.protocol.ftp.FtpException: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at org.apache.nutch.protocol.ftp.FtpResponse.<init>(FtpResponse.java:309)
at org.apache.nutch.protocol.ftp.Ftp.getProtocolOutput(Ftp.java:133)
at org.apache.nutch.fetcher.FetcherThread.run(FetcherThread.java:340)
Caused by: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.LinkedList.checkElementIndex(LinkedList.java:555)
at java.util.LinkedList.get(LinkedList.java:476)
at org.apache.nutch.protocol.ftp.FtpResponse.getFileAsHttpResponse(FtpResponse.java:327)
}}
I cannot tell what the URLs showing this problems have in common. They seem to be regular files, however a lot of other regular files can be fetched and parsed successfully. As far as I understand the source code, at least one outgoing link is expected:
{{
FTPFile ftpFile = (FTPFile) list.get(0);
}}
Can this be safely assumed for all files? Or should there rather be a check if outgoing links were found?