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git: send more known refs, in hopes of smaller fetches

we used to only say we had the branches we were pulling,
but that meant that when pulling a new branch, we would
say we had nothing, leading to a lot of duplicate data
getting sent.

This change the 20 most recent local branches as refs
we know about, in the hopes that the remote can compute
a smaller delta.

The long term fix would be to write the request in
parallel with reading the response, which would allow
us to provide a great deal more information without
blocking, but this will do the job for now.

--- a/sys/src/cmd/git/get.c

+++ b/sys/src/cmd/git/get.c

@@ -5,6 +5,8 @@

 char *fetchbranch;

 char *upstream = "origin";

+Hash heads[64];

+int nheads;

 int listonly;

 /*

@@ -302,7 +304,7 @@

 			continue;

 		for(j = 0; j < i; j++)

 			if(hasheq(&want[i], &want[j]))

-				goto Next;

+				continue;

 		if((o = readobject(want[i])) != nil){

 			unref(o);

 			continue;

@@ -311,7 +313,6 @@

 			sysfatal("could not send want for %H", want[i]);

 		caps[0] = 0;

 		req = 1;

-Next:		continue;

 	}

 	flushpkt(c);

@@ -337,6 +338,22 @@

 		nsent++;

 	}

 	/*

+	 * The other branches we have probably make sense to send,

+	 * since often we'll be pulling a new branch with objects

+	 * that we already have; it's not entirely clear what we

+	 * want to do here.

+	 */

+	for(i = 0; i < nheads; i++){

+		if((o = readobject(heads[i])) == nil)

+			sysfatal("missing exected object: %H", have[i]);

+		if(fmtpkt(c, "have %H", o->hash) == -1)

+			sysfatal("write: %r");

+		enqueueparent(&haveq, o);

+		osadd(&hadobj, o);

+		unref(o);

+		nsent++;

+	}

+	/*

 	 * While we could short circuit this and check if upstream has

 	 * acked our objects, for the first 256 haves, this is simple

 	 * enough.

@@ -467,7 +484,14 @@

 	case 'u':	upstream=EARGF(usage());	break;

 	case 'd':	chattygit++;			break;

 	case 'l':	listonly++;			break;

-	default:	usage();			break;

+	case 'h':

+		if(nheads < nelem(heads))

+			if(hparse(&heads[nheads], EARGF(usage())) == 0)

+				nheads++;

+		break;

+	default:

+		usage();

+		break;

 	}ARGEND;

 	gitinit();

--- a/sys/src/cmd/git/pull

+++ b/sys/src/cmd/git/pull

@@ -9,7 +9,19 @@

 	dflag=()

 	if(! ~ $#debug 0)

 		dflag='-d'

-	{git/get $dflag -u $upstream $url >[2=3] || die $status} | awk '

+	heads=`$nl{

+		# safe to split in awk, branch names may not

+		# have spaces or newlines.

+		git/query `$nl{

+			cd .git/refs && \

+			walk -f -emp heads remotes | \

+			sort -rn | \

+			awk '{print $2}'

+		}

+	}

+	if(! ~ $#heads 0)

+		heads='-h'^$heads

+	{git/get $dflag -u $upstream $heads $url >[2=3] || die $status} | awk '

 	/^remote refs\/(heads|tags)\//{

 		ref=$2

 		hash=$3

-- 

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