Sebastian Nagel commented on NUTCH-2549:

Thanks, [~gbouchar], for the long list of issues affecting protocol-http 
(partially also protocol-httpclient), I know it was for sure hard work to 
prepare this list by digging into fetcher logs.

I would recommend to split this issue into multiple subissues. It's easier to 
discuss every point in a single issue and address it in a single commit. Could 
you open the subissues? Or let us know if we should do it, thanks. In general, 
the length of the list rises the question whether it wouldn't better to rewrite 
the protocol plugin from scratch using a library. Suggestions are welcome!

Two notes:
 - the Protocol interface does not support modifying URLs, it should be handled 
by URL normalizers (eg. urlnormalizer-basic). URLs are used as keys in CrawlDb 
and segments and should therefor correspond with the URLs actually fetched.
 - it's a good idea to skip the content in case of redirects, 404s etc. But 
this should be optional, as some crawlers may want to store this content.

> protocol-http does not behave the same as browsers
> --------------------------------------------------
>                 Key: NUTCH-2549
>                 URL: https://issues.apache.org/jira/browse/NUTCH-2549
>             Project: Nutch
>          Issue Type: Bug
>            Reporter: Gerard Bouchar
>            Priority: Major
> We identified the following issues in protocol-http (a plugin implementing 
> the HTTP protocol):
>  * It fails if an url's path does not start with '/'
>  ** Example: [http://news.fx678.com?171|http://news.fx678.com/?171] (browsers 
> correctly rewrite the url as [http://news.fx678.com/?171], while nutch tries 
> to send an invalid HTTP request starting with *GET ?171 HTTP/1.0*.
>  * It advertises its requests as being HTTP/1.0, but sends an 
> _Accept-Encoding_ request header, that is defined only in HTTP/1.1. This 
> confuses some web servers
>  ** Example: 
> [http://www.hansamanuals.com/main/english/none/theconf___987/manuals/version___82/hwconvindex.htm]
>  * If a server send sends a redirection (3XX status code, with a Location 
> header), protocol-http tries to parse the HTTP response body anyway. Thus, if 
> an error occurs while decoding the body, the redirection is not followed and 
> the information is lost. Browsers follow the redirection and close the socket 
> soon as they can.
>  ** Example: [http://www.webarcelona.net/es/blog?page=2]
>  * Some servers invalidly send an HTTP body directly without a status line or 
> headers. Browsers handle that, protocol-http doesn't:
>  ** Example: [https://app.unitymedia.de/]
>  * Some servers invalidly add colons after the HTTP status code in the status 
> line (they can send _HTTP/1.1 404: Not found_ instead of _HTTP/1.1 404 Not 
> found_ for instance). Browsers can handle that.
>  * Some servers invalidly send headers that span over multiple line. In that 
> case, browsers simply ignore the subsequent lines, but protocol-http throws 
> an error, thus preventing us from fetching the contents of the page.
>  * There is no limit over the size of the HTTP headers it reads. A bogus 
> server could send an infinite stream of different HTTP headers and cause the 
> fetcher to go out of memory, or send the same HTTP header repeatedly and 
> cause the fetcher to timeout.
>  * The same goes for the HTTP status line: no check is made concerning its 
> size.
>  * While reading chunked content, if the content size becomes larger than 
> {color:#9876aa}http{color}.getMaxContent(), instead of just stopping, it 
> tries to read a new chunk before having read the previous one completely, 
> resulting in a '{color:#333333}bad chunk length' error.{color}
> {color:#333333}Additionally (and that concerns protocol-httpclient as well), 
> when reading http headers, for each header, the SpellCheckedMetadata class 
> computes a Levenshtein distance between it and every  known header in the 
> HttpHeaders interface. Not only is that slow, non-standard, and non-conform 
> to browsers' behavior, but it also causes bugs and prevents us from accessing 
> the real headers sent by the HTTP server.{color}
>  * {color:#333333}Example: [http://www.taz.de/!443358/] . The server sends a 
> *Client-Transfer-Encoding: chunked* header, but SpellCheckedMetadata corrects 
> it to *Transfer-Encoding: chunked*. Then, HttpResponse (in protocol-http) 
> tries to read the HTTP body as chunked, whereas it is not.{color}

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