Subject: Re: [PATCH v5 2/3] gitweb: refactor If-Modified-Since handling

From: Jakub Narebski <[email-masked]>
Date: Tue, 27 Mar 2012 23:24:20 +0100

On Mon, 26 Mar 2012, W. Trevor King wrote:

> The current gitweb only generates Last-Modified and handles
> If-Modified-Since headers for the git_feed action.  This patch breaks
> the Last-Modified and If-Modified-Since handling code out from
> git_feed into a new function exit_if_unmodified_since.  This makes the
> code easy to reuse for other actions.

Nice description, and I think quite good name for a subroutine.  Well,
good enough; any more we would drown in bikeshed-ding.
> 
> Only gitweb actions which can easily calculate a modification time
> should use exit_if_unmodified_since, as the goal is to balance local
> processing time vs. upload bandwidth.

Good.
>
> Signed-off-by: W Trevor King <[email-masked]>
> ---
> Patch v4 1/3 is unchanged.  Should I mail it back in with a
> [PATCH v5 1/3] tag?
> 
> Changes since v4:
> * die_if_unmodified() -> exit_if_unmodified_since()
> * Added missing `&&` to tests for feed-last-modified (patch 2/3) and
>   snapshot-last-modified (patch 3/3).
> 
>  gitweb/gitweb.perl                       |   40 +++++++++++++++++------------
>  t/t9501-gitweb-standalone-http-status.sh |   27 +++++++++++++++++++-
>  2 files changed, 49 insertions(+), 18 deletions(-)
> 
> diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
> index 041da17..229f3da 100755
> --- a/gitweb/gitweb.perl
> +++ b/gitweb/gitweb.perl
> @@ -7003,6 +7003,28 @@ sub snapshot_name {
>  	return wantarray ? ($name, $name) : $name;
>  }
>  
> +sub exit_if_unmodified_since {
> +	my ($latest_epoch) = @_;

We could have made \%latest_date an optional parameter...

  +	my ($latest_epoch, $latest_date) = @_;

> +	our $cgi;
> +
> +	my $if_modified = $cgi->http('IF_MODIFIED_SINCE');
> +	if (defined $if_modified) {
> +		my $since;
> +		if (eval { require HTTP::Date; 1; }) {
> +			$since = HTTP::Date::str2time($if_modified);
> +		} elsif (eval { require Time::ParseDate; 1; }) {
> +			$since = Time::ParseDate::parsedate($if_modified, GMT => 1);
> +		}
> +		if (defined $since && $latest_epoch <= $since) {
> +			my %latest_date = parse_date($latest_epoch);

...and use it if provided

  +			my %latest_date = ref($latest_date) eq 'HASH' 
  +				? %$latest_date : parse_date($latest_epoch);

but something is to be said for simplicity.  We need epoch for comparison
anyway.

> +			print $cgi->header(
> +				-last_modified => $latest_date{'rfc2822'},
> +				-status => '304 Not Modified');

O.K. we lose some unnecessary headers; never mind that.  What is
important is here.

> +			goto DONE_GITWEB;
> +		}
> +	}
> +}
> +
>  sub git_snapshot {
>  	my $format = $input_params{'snapshot_format'};
>  	if (!@snapshot_fmts) {
> @@ -7820,24 +7842,8 @@ sub git_feed {
>  	if (defined($commitlist[0])) {
>  		%latest_commit = %{$commitlist[0]};
>  		my $latest_epoch = $latest_commit{'committer_epoch'};
> +		exit_if_unmodified_since($latest_epoch);
>  		%latest_date   = parse_date($latest_epoch, $latest_commit{'comitter_tz'});
> -		my $if_modified = $cgi->http('IF_MODIFIED_SINCE');
> -		if (defined $if_modified) {
> -			my $since;
> -			if (eval { require HTTP::Date; 1; }) {
> -				$since = HTTP::Date::str2time($if_modified);
> -			} elsif (eval { require Time::ParseDate; 1; }) {
> -				$since = Time::ParseDate::parsedate($if_modified, GMT => 1);
> -			}
> -			if (defined $since && $latest_epoch <= $since) {
> -				print $cgi->header(
> -					-type => $content_type,
> -					-charset => 'utf-8',
> -					-last_modified => $latest_date{'rfc2822'},
> -					-status => '304 Not Modified');
> -				return;
> -			}
> -		}
>  		print $cgi->header(
>  			-type => $content_type,
>  			-charset => 'utf-8',
> diff --git a/t/t9501-gitweb-standalone-http-status.sh b/t/t9501-gitweb-standalone-http-status.sh
> index 31076ed..0e49f29 100755
> --- a/t/t9501-gitweb-standalone-http-status.sh
> +++ b/t/t9501-gitweb-standalone-http-status.sh
> @@ -92,7 +92,7 @@ test_debug 'cat gitweb.output'
>  test_expect_success 'snapshots: bad tree-ish id (tagged object)' '
>  	echo object > tag-object &&
>  	git add tag-object &&
> -	git commit -m "Object to be tagged" &&
> +	test_tick && git commit -m "Object to be tagged" &&
>  	git tag tagged-object `git hash-object tag-object` &&
>  	gitweb_run "p=.git;a=snapshot;h=tagged-object;sf=tgz" &&
>  	grep "400 - Object is not a tree-ish" gitweb.output
> @@ -112,6 +112,31 @@ test_expect_success 'snapshots: bad object id' '
>  '
>  test_debug 'cat gitweb.output'
>  
> +# ----------------------------------------------------------------------
> +# modification times (Last-Modified and If-Modified-Since)
> +
> +test_expect_success 'modification: feed last-modified' '
> +	gitweb_run "p=.git;a=atom;h=master" &&
> +	grep "Status: 200 OK" gitweb.output &&
> +	grep "Last-modified: Thu, 7 Apr 2005 22:14:13 +0000" gitweb.output
> +'

All right.

What's that date from?  Wouldn't it be better to read it from commit
object with `git show -s --pretty=%cD HEAD` or postprocessed from
'%ct' timestamp?

> +test_debug 'cat gitweb.headers'
> +
> +test_expect_success 'modification: feed if-modified-since (modified)' '
> +	export HTTP_IF_MODIFIED_SINCE="Wed, 6 Apr 2005 22:14:13 +0000" &&
> +	gitweb_run "p=.git;a=atom;h=master" &&
> +	unset HTTP_IF_MODIFIED_SINCE &&
> +	grep "Status: 200 OK" gitweb.output
> +'

I think it *might* be better solution to use test_when_finished:

  +test_expect_success 'modification: feed if-modified-since (modified)' '
  +	export HTTP_IF_MODIFIED_SINCE="Wed, 6 Apr 2005 22:14:13 +0000" &&
  +	test_when_finished "unset HTTP_IF_MODIFIED_SINCE" &&
  +	gitweb_run "p=.git;a=atom;h=master" &&
  +	grep "Status: 200 OK" gitweb.output
  +'

I don't think we need sane_unset here.

> +test_debug 'cat gitweb.headers'
> +
> +test_expect_success 'modification: feed if-modified-since (unmodified)' '
> +	export HTTP_IF_MODIFIED_SINCE="Thu, 7 Apr 2005 22:14:13 +0000" &&
> +	gitweb_run "p=.git;a=atom;h=master" &&
> +	unset HTTP_IF_MODIFIED_SINCE &&
> +	grep "Status: 304 Not Modified" gitweb.output
> +'

Same here.

> +test_debug 'cat gitweb.headers'
>  
>  # ----------------------------------------------------------------------
>  # load checking
> -- 
> 1.7.3.4
> 

-- 
Jakub Narebski
Poland