patchvcs-svn: fix broken test 'keep content, but change mode'

> svn symlinks are files with "link destination" content and a
> "svn:special=*" property set. These are imported as blobs with
> "destination" content and S_IFLNK mode. When svn copy a file without
> altering it's content(but maybe altering it's mode), we reuse the blob
> object thus loosing or not adding the "link " prefix.
>
> But we take possible prefix into account when applying svn deltas. And
> this is the only place we ask fast-import for original blob. So pretend
> that we want to apply a zero delta to resolve the issue.
>
> There is some overhead due to using a temporary file to store such a small
> blob. But hopefully such node change is too rare to care.
>
> Signed-off-by: Dmitry Ivankov <divanorama@gmail.com>
> ---
> This could be done better if we just read the cat-blob to memory, added or
> removed the "link " prefix and wrote it to the stream, because the link
> destination should be a tiny string. But on the other hand it'd blow up
> if for some reason it's huge.
>
> And taking into account that changing file mode from/to link without a
> content change should be extremely rare anyway, I think it's ok.
>
> Maybe it is redundant to add svndiff0_identity function to just cat blob
> to a temporary file. The excuse is that svndiff.c is the only user of this
> temporary file and the cat-blob response, so keep it there.
>
> The patch base is svn-fe branch at git://repo.or.cz/git/jrn.git
> Not backporting it to git master because vcs-svn stuff differs quite much
> around this change.
>
>  t/t9010-svn-fe.sh     |    2 +-
>  vcs-svn/fast_export.c |    6 +++++-
>  vcs-svn/svndiff.c     |   17 +++++++++++++++++
>  vcs-svn/svndiff.h     |    1 +
>  vcs-svn/svndump.c     |   16 +++++++++++++++-
>  5 files changed, 39 insertions(+), 3 deletions(-)
>
> diff --git a/t/t9010-svn-fe.sh b/t/t9010-svn-fe.sh
> index b7eed24..b6bdfeb 100755
> --- a/t/t9010-svn-fe.sh
> +++ b/t/t9010-svn-fe.sh
> @@ -413,7 +413,7 @@ test_expect_success PIPE 'action: add node without text' '
>        try_dump textless.dump must_fail
>  '
>
> -test_expect_failure PIPE 'change file mode but keep old content' '
> +test_expect_success PIPE 'change file mode but keep old content' '
>        reinit_git &&
>        cat >expect <<-\EOF &&
>        OBJID
> diff --git a/vcs-svn/fast_export.c b/vcs-svn/fast_export.c
> index 19d7c34..8c7295f 100644
> --- a/vcs-svn/fast_export.c
> +++ b/vcs-svn/fast_export.c
> @@ -209,7 +209,11 @@ static long apply_delta(off_t len, struct line_buffer *input,
>                preimage.max_off += strlen("link ");
>                check_preimage_overflow(preimage.max_off, 1);
>        }
> -       if (svndiff0_apply(input, len, &preimage, out))
> +
> +       if (!input) {
> +               if (svndiff0_identity(&preimage, out))
> +                       die("cannot cat blob");
> +       } else if (svndiff0_apply(input, len, &preimage, out))
>                die("cannot apply delta");
>        if (old_data) {
>                /* Read the remainder of preimage and trailing newline. */
> diff --git a/vcs-svn/svndiff.c b/vcs-svn/svndiff.c
> index 9ee41bb..bf104db 100644
> --- a/vcs-svn/svndiff.c
> +++ b/vcs-svn/svndiff.c
> @@ -306,3 +306,20 @@ int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
>        }
>        return 0;
>  }
> +int svndiff0_identity(struct sliding_view *preimage, FILE *postimage)
> +{
> +       assert(preimage && postimage);
> +       off_t pre_off = 0;
> +
> +       while (pre_off != preimage->max_off) {
> +               size_t pre_len = 8192;
> +               if (pre_off + pre_len > preimage->max_off)
> +                       pre_len = preimage->max_off - pre_off;
> +               if (move_window(preimage, pre_off, pre_len) ||
> +                       write_strbuf(&preimage->buf, postimage))
> +                       return -1;
> +               pre_off += pre_len;
> +       }
> +
> +       return 0;
> +}
> diff --git a/vcs-svn/svndiff.h b/vcs-svn/svndiff.h
> index 74eb464..5afa3f2 100644
> --- a/vcs-svn/svndiff.h
> +++ b/vcs-svn/svndiff.h
> @@ -6,5 +6,6 @@ struct sliding_view;
>
>  extern int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
>                struct sliding_view *preimage, FILE *postimage);
> +extern int svndiff0_identity(struct sliding_view *preimage, FILE *postimage);
>
>  #endif
> diff --git a/vcs-svn/svndump.c b/vcs-svn/svndump.c
> index b1f4161..1e7ed48 100644
> --- a/vcs-svn/svndump.c
> +++ b/vcs-svn/svndump.c
> @@ -285,7 +285,21 @@ static void handle_node(void)
>                /* For the fast_export_* functions, NULL means empty. */
>                old_data = NULL;
>        if (!have_text) {
> -               fast_export_modify(node_ctx.dst.buf, node_ctx.type, old_data);
> +               /*
> +                * This is clean content copy in svn, but we alter the content
> +                * of symlinks (add/remove "link " prefix used by svn). So when
> +                * mode changes from/to symlink specify (recreate) data inline.
> +                */
> +               if (node_ctx.type != old_mode && (old_mode == REPO_MODE_LNK
> +                                       || node_ctx.type == REPO_MODE_LNK)) {
> +
> +                       fast_export_modify(node_ctx.dst.buf,
> +                                               node_ctx.type, "inline");
> +                       fast_export_blob_delta(node_ctx.type, old_mode,
> +                                               old_data, 0, NULL);
> +               } else
> +                       fast_export_modify(node_ctx.dst.buf,
> +                                               node_ctx.type, old_data);
>                return;
>        }
>        if (!node_ctx.text_delta) {
> --
> 1.7.3.4
>
>