> It matters (to me) because `wget`/`curl` plus `patch` is not some exotic lab setup.
If the point is to be able to do `curl https://...deadbeef.patch | patch -p1`, you can just change the extension provided to Github from `.patch` to `.diff`. That way, it just includes the hunks. E.g.
I don't see it as a problem with the email format, because I can't imagine someone just patching from an email without looking at the email first.
A nice thing about the fact that a group of hunks aren't a file format but rather a text format is that you can add comments and additional metadata, as well as embed the hunks in other texts. For example, the lines
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 15ba592236e845..725a49a0eee72e 100644
are not part of the hunk format. To `patch`, they're comments, and that allows git and potentially other utilities to extend the format.
This has come up multiple times before [1], and more generally it's come up hundreds of times with Unix style tools in general. It's always been a stupid idea for every tool to have its own barely documented file format.
This wouldn't be an issue if patches were XML or JSON with a well defined schema, but everything must be a boutique undocumented format in the world of Unix tools.
Maybe the worst part about this is that it can entirely come from a patch being exported by git and then imported straight back in to git. If you can't even handle your own undocumented format then what hope do other tools have that want to work with it?
While patch[0] has problems, the issue here is not that it is undocumented.
Git recently added this doc on roundtripping, and the problem is with git.
Any line that is of the form:
* three-dashes and end-of-line, or
* a line that begins with "diff -", or
* a line that begins with "Index: "
is taken as the beginning of a patch, and the commit log message is terminated before the first occurrence of such a line.
The patch isn't even the complicated forms with RCS, ClearCase, Perforce, or SCCS support, it is just doing what the pre-POSIX spec says.
The argument is if git should do input sanitation etc...
But `patch -p1` is doing exactly what was documented, even in the original Larry Wall usenet post of the program.
> This wouldn't be an issue if patches were XML or JSON with a well defined schema, but everything must be a boutique undocumented format in the world of Unix tools.
Patch files are readable by humans. Replacing them with XML or JSON would fix this problem, but at the expense of removing a core feature.
If, by "readable by humans", you mean "it would reliably fool humans as well", I'd say it's an ambiguity bug regardless of whether it's "a core feature" or not. A patch format, human-readable or not, should clearly indicate which part is the commit message and which part is an actual diff; it's not the case here.
Alright, allow me to disambiguate in your preferred format.
<?xml version="1.0" encoding="UTF-8"?> <claims> <claims_I_did_not_make description='Claims that I did not make or defend.'> <claim>Patch is perfect.</claim> <claim>Ambiguity is good.</claim> <claim>There are no better formats for conveying patches.</claim> </claims_I_did_not_make> <claims_I_did_make description='What I actually said.'> <claim>Patch files are readable by humans.</claim> <claim>Being readble by humans is useful.</claim> <claim>XML is painful for humans to read and write.</claim> <claim>JSON is painful for humans to read and write.</claim> <claim caveat='Actually this would require all parties to handle JSON or XML correctly which on further reflection I am not sure about. Still, it is a claim I initially made.'>JSON or XML would actually fix this problem in the format.</claim> </claims_I_did_make> <claims_I_did_not_make_but_am_open_to description='Things that were never specified but that I do not actually disagree with.'> <claim>The patch format could be improved.</claim> <claim>Formats should be unambiguous.</claim> <claim>Separating sections is good.</claim> </claims_I_did_not_make_but_am_open_to> </claims>
Haha, good one. Much like Makefiles, patch format precedes a lot of more modern things (by decades!) and is good enough to stick around. Unlike Makefiles, I've never seen tool gain any acceptance at all to replace patch.
And a lot of these older tools are not meant to be fed untrusted, unvetted input. The patch shown there confused me for quite a bit.
Or, more snarky: tee is also a huge security problem if you pipe untrusted input into `tee -a /etc/passwd`, such as `curl | tee -a /etc/passwd`. Not many things are safe with a `curl |` in front of them. I think yes might be?
> Maybe the worst part about this is that it can entirely come from a patch being exported by git and then imported straight back in to git.
No one wants to apply diffs in commit messages. But some people use this technique via email:
Finally fix it
---
Changes in v2:
- Proper formatting
- Remove irrelevant typo fix
They’ve used the `---` commit message delimiter in the commit message itself so that everything after it won’t be applied by git-am(1). So that’s intentional loss of round tripping.
Seems like this would probably be solved if github returned a patch file formatted like `git show` provides, specifically with the commit message indented? I do see that `git format-patch` doesn't do this indentation though.
In any case, agreed that it's not a great "feature" to use in-band signaling of when patch data starts, with no escaping. Confusion and misbehavior is pretty much guaranteed.
> Seems like this would probably be solved if github returned a patch file formatted like `git show` provides, specifically with the commit message indented? I do see that `git format-patch` doesn't do this indentation though.
This would be "solved" if the patch file only included the patch. That's pretty straightforward. The file github provides includes fake email headers for no particular reason. The commit message appears to be part of the subject header. The subject header is never terminated, so arguably applying this patch shouldn't do anything. (Because the actual patch data is also part of the email headers.) The other headers aren't terminated either, so actually there is no subject header. This shouldn't really matter, because the patch file isn't email, but it does seem to want to pretend to be.
The usual question to ask here would be "why are you applying patch files from an untrusted source?". If patch(1) was stricter about the format of its input files... applying patches from an untrusted source would still be a good way to get owned. If you think I can get you to patch inappropriate files by writing a fake diff into my commit message... wait until you see what I can do by writing those same changes into the real diff.
That's the output you get from `git format-patch --stdout -1 dd28283`. The idea is that it's suitable for emailing to a mailing list for review (hence the subject line beginning with [PATCH], and so on).
If you ask for colorized output with `git format-patch --color=always --stdout -1 dd28283` you'll see that `git format-patch` itself knows which bits are the commit message and which bits are the diff. (Well, of course it does, I guess.)
I suspect that if you sent a patch like this to the mailing list, they'd get mad at you. So `git format-patch` is working OK for its intended use-case. Arguably it's GitHub causing the problem here by "misusing" `git format-patch` as a way to deliver patches that are (these days) expected to be machine-readable — something you can just curl and pipe into `patch`. `git format-patch` doesn't do that.
That said, yeah, it's amusing that (as TFA says)
git format-patch -1 HEAD --stdout > 0001 ;
git checkout HEAD~ ;
git am 0001
isn't a clean round-trip. `git am` applies the fake diff.
> If you think I can get you to patch inappropriate files by writing a fake diff into my commit message... wait until you see what I can do by writing those same changes into the real diff.
git-am(1) (apply patches) delimits the commit message from the patch/diff by looking for (1) a line `---` or (2) a line that starts with `diff -` or (3) a line that starts with `Index:SP` (SP is space). Only the first rule is necessary for patches generated git-format-patch(1). But git-am(1) is for applying patches, and you are free to bring patches from some other system. That’s why, I suppose, there are multiple options.
This means that it will try to apply any unindented diffs in the commit message. But you’re fine if you indent the diff. (Newschool code fencers will have a worse time here.)
I imagine that this worked fine for changes that were authored by one person and submitted by another person via email, or by their friend, or by someone trying to resurrect a previous attempt at getting something upstreamed. Someone is likely to notice that examples diffs are getting applied. But it won’t work well at all if you are some software distributor who is using patch files to apply modifications to packages.
Recall that git-am(1) will not apply indented diffs. Well have a look at my GNU patch 2.7.6:
If the entire diff is indented by a consistent amount, if lines end in
CRLF, or if a diff is encapsulated one or more times by prepending "- "
to lines starting with "-" as specified by Internet RFC 934, this is
taken into account.
Some may say that patch(1) should work like a more straightforward importer. But I’ve been itching to point out something else.
If the point is to be able to do `curl https://...deadbeef.patch | patch -p1`, you can just change the extension provided to Github from `.patch` to `.diff`. That way, it just includes the hunks. E.g.
https://github.com/torvalds/linux/commit/dca922e019dd758b4c1...
I don't see it as a problem with the email format, because I can't imagine someone just patching from an email without looking at the email first.
A nice thing about the fact that a group of hunks aren't a file format but rather a text format is that you can add comments and additional metadata, as well as embed the hunks in other texts. For example, the lines
are not part of the hunk format. To `patch`, they're comments, and that allows git and potentially other utilities to extend the format.This wouldn't be an issue if patches were XML or JSON with a well defined schema, but everything must be a boutique undocumented format in the world of Unix tools.
Maybe the worst part about this is that it can entirely come from a patch being exported by git and then imported straight back in to git. If you can't even handle your own undocumented format then what hope do other tools have that want to work with it?
[1]: https://mas.to/@zekjur/116022397626943871
Git recently added this doc on roundtripping, and the problem is with git.
The patch isn't even the complicated forms with RCS, ClearCase, Perforce, or SCCS support, it is just doing what the pre-POSIX spec says.The argument is if git should do input sanitation etc...
But `patch -p1` is doing exactly what was documented, even in the original Larry Wall usenet post of the program.
[0] https://pubs.opengroup.org/onlinepubs/9799919799/utilities/p... [1] https://github.com/git/git/blob/94f057755b7941b321fd11fec1b2...
Patch files are readable by humans. Replacing them with XML or JSON would fix this problem, but at the expense of removing a core feature.
Or, more snarky: tee is also a huge security problem if you pipe untrusted input into `tee -a /etc/passwd`, such as `curl | tee -a /etc/passwd`. Not many things are safe with a `curl |` in front of them. I think yes might be?
No one wants to apply diffs in commit messages. But some people use this technique via email:
They’ve used the `---` commit message delimiter in the commit message itself so that everything after it won’t be applied by git-am(1). So that’s intentional loss of round tripping.I would personally use Git notes instead though.
Or MIME, even.
In any case, agreed that it's not a great "feature" to use in-band signaling of when patch data starts, with no escaping. Confusion and misbehavior is pretty much guaranteed.
This would be "solved" if the patch file only included the patch. That's pretty straightforward. The file github provides includes fake email headers for no particular reason. The commit message appears to be part of the subject header. The subject header is never terminated, so arguably applying this patch shouldn't do anything. (Because the actual patch data is also part of the email headers.) The other headers aren't terminated either, so actually there is no subject header. This shouldn't really matter, because the patch file isn't email, but it does seem to want to pretend to be.
The usual question to ask here would be "why are you applying patch files from an untrusted source?". If patch(1) was stricter about the format of its input files... applying patches from an untrusted source would still be a good way to get owned. If you think I can get you to patch inappropriate files by writing a fake diff into my commit message... wait until you see what I can do by writing those same changes into the real diff.
That's the output you get from `git format-patch --stdout -1 dd28283`. The idea is that it's suitable for emailing to a mailing list for review (hence the subject line beginning with [PATCH], and so on).
If you ask for colorized output with `git format-patch --color=always --stdout -1 dd28283` you'll see that `git format-patch` itself knows which bits are the commit message and which bits are the diff. (Well, of course it does, I guess.)
I suspect that if you sent a patch like this to the mailing list, they'd get mad at you. So `git format-patch` is working OK for its intended use-case. Arguably it's GitHub causing the problem here by "misusing" `git format-patch` as a way to deliver patches that are (these days) expected to be machine-readable — something you can just curl and pipe into `patch`. `git format-patch` doesn't do that.
That said, yeah, it's amusing that (as TFA says)
isn't a clean round-trip. `git am` applies the fake diff.> If you think I can get you to patch inappropriate files by writing a fake diff into my commit message... wait until you see what I can do by writing those same changes into the real diff.
Well put. :)
This means that it will try to apply any unindented diffs in the commit message. But you’re fine if you indent the diff. (Newschool code fencers will have a worse time here.)
I imagine that this worked fine for changes that were authored by one person and submitted by another person via email, or by their friend, or by someone trying to resurrect a previous attempt at getting something upstreamed. Someone is likely to notice that examples diffs are getting applied. But it won’t work well at all if you are some software distributor who is using patch files to apply modifications to packages.
Recall that git-am(1) will not apply indented diffs. Well have a look at my GNU patch 2.7.6:
Some may say that patch(1) should work like a more straightforward importer. But I’ve been itching to point out something else. Is it surprising if patch(1) is a bit DWIM?