Subject: Re: [PATCH] Add support for limiting number of lines generated in messages by post-receive-email

From: Marc Branchaud <[email-masked]>
Date: Mon, 12 Jul 2010 12:47:48 -0400

On 10-07-08 03:03 PM, Kevin P. Fleming wrote:
> We have become used to the features of svnmailer when used with Subversion,
> and one of those useful features is that it can limit the maximum length
> (in lines) of a commit email message. This is terribly useful since once the
> goes beyond a reasonable number of lines, nobody is going to read the remainder,
> and if they really want the entire contents of the commits, they can use
> git itself to get them using the revision IDs present in the message already.
> 
> This patch adds a new parameter to the post-receive-email hook script called
> 'maxlines', that defaults to 2048 if not specified. The entire message is
> filtered through a function that counts the number of lines generated
> (including headers), and any lines beyond the limit are suppressed; if any
> lines are suppressed, a final line is added indicating the number that
> were suppressed.

Hi Kevin,

I appreciate the work and the need you're addressing.  Thanks!

I do have a request though, which is to make this match the current
(unlimited) behavior by default instead of imposing an arbitrary (although
seemingly large) limit.

I admit I don't have a strong reason for this, mainly just a desire to not
force features on folks that don't need them.  IMHO the limit is a bit too
hidden and likely to surprise someone at an inopportune time.  Plus what
would someone do if they *want* no limit?

(FYI, we dealt with large-email syndrome by taking the diffs out of the
emails and using a custom format to embed a gitweb URL instead.  Folks who
care about the actual code change can browse the commit in gitweb.  This also
helped make it easier for humans to parse the emails and the commits they
contain.)

A couple more comments below...

> Signed-off-by: Kevin P. Fleming <[email-masked]>
> ---
>  contrib/hooks/post-receive-email |   31 ++++++++++++++++++++++++++++++-
>  1 files changed, 30 insertions(+), 1 deletions(-)
> 
> diff --git a/contrib/hooks/post-receive-email b/contrib/hooks/post-receive-email
> index 30ae63d..436c13f 100755
> --- a/contrib/hooks/post-receive-email
> +++ b/contrib/hooks/post-receive-email
> @@ -55,6 +55,11 @@
>  #     "t=%s; printf 'http://.../?id=%%s' \$t; echo;echo; git show -C \$t; echo"
>  #   Be careful if "..." contains things that will be expanded by shell "eval"
>  #   or printf.
> +# hooks.maxlines

Why not call this something like "hooks.maxemaillines"?  "maxlines" is so
generic that it might collide with something some other hook might use.

> +#   The maximum number of lines that should be included in the generated
> +#   email (including its headers). If not specified, defaults to 2048.
> +#   Lines beyond the limit are suppressed and counted, and a final
> +#   line is added indicating the number of suppressed lines.
>  #
>  # Notes
>  # -----
> @@ -642,6 +647,29 @@ show_new_revisions()
>  }
>  
>  
> +limit_lines()
> +{
> +    lines=0
> +    skipped=0
> +    limit=$(($1 - 2))
> +    while IFS="" read line
> +    do
> +	lines=$((lines + 1))
> +	if [ $lines -gt $limit ]
> +	then
> +	    skipped=$((skipped + 1))
> +	else
> +	    echo "$line"
> +	fi
> +    done
> +    if [ $skipped -ne 0 ]
> +    then
> +	echo
> +	echo "... $skipped lines suppressed ..."
> +    fi
> +}
> +
> +
>  send_mail()
>  {
>  	if [ -n "$envelopesender" ]; then
> @@ -679,6 +707,7 @@ announcerecipients=$(git config hooks.announcelist)
>  envelopesender=$(git config hooks.envelopesender)
>  emailprefix=$(git config hooks.emailprefix || echo '[SCM] ')
>  custom_showrev=$(git config hooks.showrev)
> +maxlines=$(git config hooks.maxlines || echo '2048')
>  
>  # --- Main loop
>  # Allow dual mode: run from the command line just like the update hook, or
> @@ -691,6 +720,6 @@ if [ -n "$1" -a -n "$2" -a -n "$3" ]; then
>  else
>  	while read oldrev newrev refname
>  	do
> -		generate_email $oldrev $newrev $refname | send_mail
> +		generate_email $oldrev $newrev $refname | limit_lines $maxlines | send_mail

I'm a little concerned about the performance hit of piping the output through
limit_lines(), which buffers all the lines in memory.  Folks who want large
emails might get bitten by this.

(That said, I don't know anything about the memory efficiency of the shell's
pipes, or if "git diff-tree" itself would suck up a lot of memory on a series
of huge patches.)

Maybe only pipe through limit_lines() if $maxlines > 0?

		M.