Subject: Re: [PATCH] post-receive-email: optional message line count limit

From: Junio C Hamano <[email-masked]>
Date: Thu, 15 Jul 2010 10:36:55 -0700

"Kevin P. Fleming" <[email-masked]> writes:

> 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.
>
> Change the post-receive-email script to respond to an 'emailmaxlines' config key
> which, if specified, will limit the number of lines generated (including
> headers); any lines beyond the limit are suppressed, and a final line is added
> indicating the number that were suppressed.
> ---

Sign-off?

> diff --git a/contrib/hooks/post-receive-email b/contrib/hooks/post-receive-email
> index 30ae63d..4dc85c2 100755
> --- a/contrib/hooks/post-receive-email
> +++ b/contrib/hooks/post-receive-email
> @@ -642,6 +647,27 @@ show_new_revisions()
>  }
>  
>  
> +limit_lines()
> +{
> +	lines=0
> +	skipped=0
> +	while IFS="" read -r line
> +	do
> +		lines=$((lines + 1))
> +		if [ $lines -gt $1 ]
> +		then

Since this is a contrib/ material, I should probably be not so picky about
it, but the style used in this script seems to be to use "; then" tacked
at the end on the same line as "if" is on.  Which is different from the
main scripted Porcelains in git.git, but you would want to be consistent
with the local convention around your code.

> +			skipped=$((skipped + 1))
> +		else
> +			printf "%s\n" "$line"
> +		fi
> +	done
> +	if [ $skipped -ne 0 ]
> +	then
> +		echo "... $skipped lines suppressed ..."
> +	fi
> +}

The above makes me wonder if the nicety of saying "we are not showing
everything; instead we skipped N lines" is really worth the trouble of the
shell loop.  Otherwise, a lot simpler:

	limit_lines ()
        {
        	head -n "$1"
	}

would be sufficient.  I dunno, and I don't deeply care either way.

> @@ -679,6 +705,7 @@ 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.emailmaxlines)
>  
>  # --- Main loop
>  # Allow dual mode: run from the command line just like the update hook, or
> @@ -691,6 +718,10 @@ if [ -n "$1" -a -n "$2" -a -n "$3" ]; then
>  else
>  	while read oldrev newrev refname
>  	do
> -		generate_email $oldrev $newrev $refname | send_mail
> +		if [ -z "$maxlines" ]; then
> +			generate_email $oldrev $newrev $refname | send_mail
> +		else
> +			generate_email $oldrev $newrev $refname | limit_lines $maxlines | send_mail
> +		fi

Hmm, the above made me wonder how the raw message needs to be generated
differently depending on maxlines and eyeball the common part for three
times to spot there is no difference.  I wouldn't have if it were written
this way:

	generate_email $oldrev $newrev $refname |
        if ...; then
        	send_mail
	else
        	limit_lines ... | send_mail
	fi

But more importantly, I have a suspicion that this patch is hooking into a
wrong place.  Look at what generate_email does.  It consists of calls to

 - generate_email_header, that gives the To:/Subject:/etc and the header
   boilerplate;

 - generate_*_*_email, that gives the body of the message; and

 - generate_email_footer, that gives the standard "-- " signature line.

You would never want to shorten the output so much that the header is cut
in the middle.  What you are trying to shorten is the body of the message,
so it would make a lot more sense to cut only the generate_*_*_email part.

IOW, shouldn't the patch be more like this?

diff --git a/contrib/hooks/post-receive-email b/contrib/hooks/post-receive-email
index 30ae63d..d8964b6 100755
--- a/contrib/hooks/post-receive-email
+++ b/contrib/hooks/post-receive-email
@@ -84,6 +84,7 @@ generate_email()
 	oldrev=$(git rev-parse $1)
 	newrev=$(git rev-parse $2)
 	refname="$3"
+	maxlines=$4
 
 	# --- Interpret
 	# 0000->1234 (create)
@@ -192,7 +193,12 @@ generate_email()
 		fn_name=atag
 		;;
 	esac
-	generate_${change_type}_${fn_name}_email
+	if [ -z "$maxlines" ]; then
+		generate_${change_type}_${fn_name}_email
+	else
+		generate_${change_type}_${fn_name}_email |
+		limit_lines $maxlines
+	fi
 
 	generate_email_footer
 }
@@ -691,6 +697,6 @@ 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 $maxlines | send_mail
 	done
 fi