commit.go: support multi-line header continuations #10
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ttaylorr
commented
Mar 8, 2019
| for _, hdr := range c.ExtraHeaders { | ||
| n3, err := fmt.Fprintf(to, "%s %s\n", hdr.K, hdr.V) | ||
| n3, err := fmt.Fprintf(to, "%s %s\n", | ||
| hdr.K, strings.Replace(hdr.V, "\n", "\n ", -1)) |
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In future versions of Go, this line can be replaced with strings.ReplaceAll(hdr.V, "\n", "\n "), but this was introduced in Go 1.12, which we don't build against yet.
bk2204
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Mar 8, 2019
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Overall, I think this is a great improvement and I'm excited to see it. I'd like to see an additional test, though, to make sure we round-trip things properly and to help us avoid breaking things in the future.
When Git wishes to continue one or more of a commit's extra headers on
more than a single line, it writes out the following:
parent: <SHA-1>
tree: <SHA-1>
gpgsig: -----BEGIN PGP SIGNATURE-----
<signature>
-----END PGP SIGNATURE-----
Our current parsing implementation does not handle this correctly, based
on a misunderstanding that one line is equivalent to one extra header,
and vice versa.
In fact, the situation presently is even more dire than not parsing the
'gpgsig' header incorrectly: we'll split the signature end ending line
into their own "headers" and in doing so trim off the leading
whitespace. In practice, this means that we can corrupt commits when
round-tripping them in many interesting ways [1].
To address the situation, we do two things:
1. Teach gitobj that when we are parsing extra headers for a commit,
_and_ a header line begins with a single whitespace character, we
are in fact continuing the last known header.
2. Likewise, teach gitobj that when encoding a commit which has an
extra header whose value contains a LF character, replace each LF
with a leading space, to round trip commits of this form
successfully.
Together, (1) and (2) means that we parse the 'gpgsig' header in the
above example as a _single_ entry in the commit's 'ExtraHeaders' field,
as expected.
[1]: git-lfs/git-lfs#3530
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When parsing an extra header that is continued over multiple lines, an earlier check on the length of whitespace-separated fields caused the loop to terminate early, dropping continuation lines that consist only of whitespace. Tweak the logic slightly in order to capture these, and allow us to successfully round-trip commit parsing.
bk2204
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Mar 11, 2019
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This looks great! Thanks for adding the new test.
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When Git wishes to continue one or more of a commit's extra headers on
more than a single line, it writes out the following:
Our current parsing implementation does not handle this correctly, based
on a misunderstanding that one line is equivalent to one extra header,
and vice versa.
In fact, the situation presently is even more dire than not parsing the
'gpgsig' header incorrectly: we'll split the signature end ending line
into their own "headers" and in doing so trim off the leading
whitespace. In practice, this means that we can corrupt commits when
round-tripping them in many interesting ways [1].
To address the situation, we do two things:
Teach gitobj that when we are parsing extra headers for a commit,
and a header line begins with a single whitespace character, we
are in fact continuing the last known header.
Likewise, teach gitobj that when encoding a commit which has an
extra header whose value contains a LF character, replace each LF
with a leading space, to round trip commits of this form
successfully.
Together, (1) and (2) means that we parse the 'gpgsig' header in the
above example as a single entry in the commit's 'ExtraHeaders' field,
as expected.
[1]: git-lfs/git-lfs#3530
/cc @git-lfs/core, especially @bk2204
/cc git-lfs/git-lfs#3530