cborutil: implement sans I/O decoder
The vendored CBOR package decodes by calling read(n) on an object.
There are a number of disadvantages to this:
* Uses blocking I/O. If sufficient data is not available, the decoder
will hang until it is.
* No support for partial reads. If the read(n) returns less data than
requested, the decoder raises an error.
* Requires the use of a file like object. If the original data is in
say a buffer, we need to "cast" it to e.g. a BytesIO to appease the
decoder.
In addition, the vendored CBOR decoder doesn't provide flexibility
that we desire. Specifically:
* It buffers indefinite length bytestrings instead of streaming them.
* It doesn't allow limiting the set of types that can be decoded. This
property is useful when implementing a "hardened" decoder that is
less susceptible to abusive input.
* It doesn't provide sufficient "hook points" and introspection to
institute checks around behavior. These are useful for implementing
a "hardened" decoder.
This all adds up to a reasonable set of justifications for writing our
own decoder.
So, this commit implements our own CBOR decoder.
At the heart of the decoder is a function that decodes a single "item"
from a buffer. This item can be a complete simple value or a special
value, such as "start of array." Using this function, we can build a
decoder that effectively iterates over the stream of decoded items and
builds up higher-level values, such as arrays, maps, sets, and indefinite
length bytestrings. And we can do this without performing I/O in the
decoder itself.
The core of the sans I/O decoder will probably not be used directly.
Instead, it is expected that we'll build utility functions for invoking
the decoder given specific input types. This will allow extreme
flexibility in how data is delivered to the decoder.
I'm pretty happy with the state of the decoder modulo the TODO items
to track wanted features to help with a "hardened" decoder. The one
thing I could be convinced to change is the handling of semantic tags.
Since we only support a single semantic tag (sets), I thought it would
be easier to handle them inline in decodeitem(). This is simpler now.
But if we add support for other semantic tags, it will likely be easier
to move semantic tag handling outside of decodeitem(). But, properly
supporting semantic tags opens up a whole can of worms, as many
semantic tags imply new types. I'm optimistic we won't need these in
Mercurial. But who knows.
I'm also pretty happy with the test coverage. Writing comprehensive
tests for partial decoding did flush out a handful of bugs. One
general improvement to testing would be fuzz testing for partial
decoding. I may implement that later. I also anticipate switching the
wire protocol code to this new decoder will flush out any lingering
bugs.
Differential Revision: https://phab.mercurial-scm.org/D4414
Test the EOL hook
$ hg init main
$ cat > main/.hg/hgrc <<EOF
> [hooks]
> pretxnchangegroup = python:hgext.eol.hook
> EOF
$ hg clone main fork
updating to branch default
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd fork
Create repo
$ cat > .hgeol <<EOF
> [patterns]
> mixed.txt = BIN
> crlf.txt = CRLF
> **.txt = native
> EOF
$ hg add .hgeol
$ hg commit -m 'Commit .hgeol'
$ printf "first\nsecond\nthird\n" > a.txt
$ hg add a.txt
$ hg commit -m 'LF a.txt'
$ hg push ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 2 files
$ printf "first\r\nsecond\r\nthird\n" > a.txt
$ hg commit -m 'CRLF a.txt'
$ hg push ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
error: pretxnchangegroup hook failed: end-of-line check failed:
a.txt in a8ee6548cd86 should not have CRLF line endings
transaction abort!
rollback completed
abort: end-of-line check failed:
a.txt in a8ee6548cd86 should not have CRLF line endings
[255]
$ printf "first\nsecond\nthird\n" > a.txt
$ hg commit -m 'LF a.txt (fixed)'
$ hg push ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 1 files
$ printf "first\nsecond\nthird\n" > crlf.txt
$ hg add crlf.txt
$ hg commit -m 'LF crlf.txt'
$ hg push ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
error: pretxnchangegroup hook failed: end-of-line check failed:
crlf.txt in 004ba2132725 should not have LF line endings
transaction abort!
rollback completed
abort: end-of-line check failed:
crlf.txt in 004ba2132725 should not have LF line endings
[255]
$ printf "first\r\nsecond\r\nthird\r\n" > crlf.txt
$ hg commit -m 'CRLF crlf.txt (fixed)'
$ hg push ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 1 files
$ printf "first\r\nsecond" > b.txt
$ hg add b.txt
$ hg commit -m 'CRLF b.txt'
$ hg push ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
error: pretxnchangegroup hook failed: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
transaction abort!
rollback completed
abort: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
[255]
$ hg up -r -2
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ printf "some\nother\nfile" > c.txt
$ hg add c.txt
$ hg commit -m "LF c.txt, b.txt doesn't exist here"
created new head
$ hg push -f ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 2 files (+1 heads)
error: pretxnchangegroup hook failed: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
transaction abort!
rollback completed
abort: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
[255]
Test checkheadshook alias
$ cat > ../main/.hg/hgrc <<EOF
> [hooks]
> pretxnchangegroup = python:hgext.eol.checkheadshook
> EOF
$ hg push -f ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 2 files (+1 heads)
error: pretxnchangegroup hook failed: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
transaction abort!
rollback completed
abort: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
[255]
We can fix the head and push again
$ hg up 6
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ printf "first\nsecond" > b.txt
$ hg ci -m "remove CRLF from b.txt"
$ hg push -f ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 3 changesets with 3 changes to 2 files (+1 heads)
$ hg -R ../main rollback
repository tip rolled back to revision 5 (undo push)
Test it still fails with checkallhook
$ cat > ../main/.hg/hgrc <<EOF
> [hooks]
> pretxnchangegroup = python:hgext.eol.checkallhook
> EOF
$ hg push -f ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 3 changesets with 3 changes to 2 files (+1 heads)
error: pretxnchangegroup hook failed: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
transaction abort!
rollback completed
abort: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
[255]
But we can push the clean head
$ hg push -r7 -f ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
Test multiple files/revisions output
$ printf "another\r\nbad\r\none" > d.txt
$ hg add d.txt
$ hg ci -m "add d.txt"
$ hg push -f ../main
pushing to ../main
searching for changes
adding changesets
adding manifests
adding file changes
added 3 changesets with 3 changes to 2 files (+1 heads)
error: pretxnchangegroup hook failed: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
d.txt in a7040e68714f should not have CRLF line endings
transaction abort!
rollback completed
abort: end-of-line check failed:
b.txt in fbcf9b1025f5 should not have CRLF line endings
d.txt in a7040e68714f should not have CRLF line endings
[255]
$ cd ..