Re: [PATCH] connect: tighten check for unexpected early hang up (Re: [PATCH v3 2/2] connect: advertized capability is not a ref)

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 8, 2016, 16:42 UTC
Message-ID: <xmqqinu6jqc5.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20160908015040.GF25016@google.com>

Jonathan Nieder <jrnieder@gmail.com> writes:

Show 14 quoted lines

> Jonathan Nieder wrote:
>
>> Subject: connect: tighten check for unexpected early hang up
> [...]
>> @@ -131,7 +131,7 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
>>  				  PACKET_READ_GENTLE_ON_EOF |
>>  				  PACKET_READ_CHOMP_NEWLINE);
>>  		if (len < 0)
>> -			die_initial_contact(got_at_least_one_head);
>> +			die_initial_contact(first_line);
>
> This should say !first_line.
>
> I'll add tests if the patch seems like a good idea.

I tried to write one-paragraph comment for the die_initial_contact() function, like so:

    +/*
    + * A remote end that is unwilling to talk to us would not give
    + * any response to us before hanging up.  After seeing some
    + * response, we know the hang-up is unexpected.
    + */
    +static void die_initial_contact(int saw_any_response)

but then I got stuck.

We may know that after seeing any response (not necessarily a ref, but .have or shallow) the other end is willing to talk to us, but the reverse is not necessarily true (it may be willing to talk to us, but the network between us may have prevented it from doing so). For that reason, the above comment is inappropriate for a function that takes a bool and gives an "unexpected hung-up" or an "unreachable, possible ACL or problems" message.

So my second attempt was to comment on the variable that keeps track of the status of the conversation, which turned out to be better (attached).

I think I fixed your "oops, the bool needs polarity flip". A test may be a good idea, but I am not sure how you plan to produce a failure after sending some response.

-- >8 --
From: Jonathan Nieder <jrnieder@gmail.com>
Date: Wed, 7 Sep 2016 18:45:55 -0700
Subject: [PATCH] connect: tighten check for unexpected early hang up

A server hanging up immediately to mark access being denied does not send any .have refs, shallow lines, or anything else before hanging up. If the server has sent anything, then the hangup is unexpected.

That is, if the server hangs up after a shallow line but before sending any refs, then git should tell me so:

	fatal: The remote end hung up upon initial contact

instead of suggesting an access control problem:

	fatal: Could not read from remote repository.
	Please make sure you have the correct access rights
	and the repository exists.

Noticed while examining this code. This case isn't likely to come up in practice but tightening the check makes the code easier to read and manipulate.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 connect.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/connect.c b/connect.c
index c53f3f1..067cf40 100644
--- a/connect.c
+++ b/connect.c
@@ -43,9 +43,9 @@ int check_ref_type(const struct ref *ref, int flags)
 	return check_ref(ref->name, flags);
 }
 
-static void die_initial_contact(int got_at_least_one_head)
+static void die_initial_contact(int unexpected)
 {
-	if (got_at_least_one_head)
+	if (unexpected)
 		die("The remote end hung up upon initial contact");
 	else
 		die("Could not read from remote repository.\n\n"
@@ -115,10 +115,17 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 			      struct sha1_array *shallow_points)
 {
 	struct ref **orig_list = list;
-	int got_at_least_one_head = 0;
+
+	/*
+	 * A hang-up after seeing some response from the other end
+	 * means that it is unexpected, as we know the other end is
+	 * willing to talk to us.  A hang-up before seeing any
+	 * response does not necessarily mean an ACL problem, though.
+	 */
+	int saw_response;
 
 	*list = NULL;
-	for (;;) {
+	for (saw_response = 0; ; saw_response = 1) {
 		struct ref *ref;
 		struct object_id old_oid;
 		char *name;
@@ -131,7 +138,7 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 				  PACKET_READ_GENTLE_ON_EOF |
 				  PACKET_READ_CHOMP_NEWLINE);
 		if (len < 0)
-			die_initial_contact(got_at_least_one_head);
+			die_initial_contact(saw_response);
 
 		if (!len)
 			break;
@@ -171,7 +178,6 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 		oidcpy(&ref->old_oid, &old_oid);
 		*list = ref;
 		list = &ref->next;
-		got_at_least_one_head = 1;
 	}
 
 	annotate_refs_with_symref_info(*orig_list);

-- 
2.10.0-267-g7db2ae3