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
$ . "$TESTDIR/narrow-library.sh"
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [narrow]
> serveellipses=True
> EOF
$ mkdir dir
$ mkdir dir/src
$ cd dir/src
$ for x in `$TESTDIR/seq.py 20`; do echo $x > "f$x"; hg add "f$x"; hg commit -m "Commit src $x"; done
$ cd ..
$ mkdir tests
$ cd tests
$ for x in `$TESTDIR/seq.py 20`; do echo $x > "t$x"; hg add "t$x"; hg commit -m "Commit test $x"; done
$ cd ../../..
narrow clone a file, f10
$ hg clone --narrow ssh://user@dummy/master narrow --noupdate --include "dir/src/f10"
requesting all changes
adding changesets
adding manifests
adding file changes
added 3 changesets with 1 changes to 1 files
new changesets *:* (glob)
$ cd narrow
$ cat .hg/requires | grep -v generaldelta
dotencode
fncache
narrowhg-experimental
revlogv1
store
testonly-simplestore (reposimplestore !)
$ hg tracked
I path:dir/src/f10
$ hg tracked
I path:dir/src/f10
$ hg update
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ find * | sort
dir
dir/src
dir/src/f10
$ cat dir/src/f10
10
$ cd ..
narrow clone with a newline should fail
$ hg clone --narrow ssh://user@dummy/master narrow_fail --noupdate --include 'dir/src/f10
> '
requesting all changes
abort: newlines are not allowed in narrowspec paths
[255]
narrow clone a directory, tests/, except tests/t19
$ hg clone --narrow ssh://user@dummy/master narrowdir --noupdate --include "dir/tests/" --exclude "dir/tests/t19"
requesting all changes
adding changesets
adding manifests
adding file changes
added 21 changesets with 19 changes to 19 files
new changesets *:* (glob)
$ cd narrowdir
$ hg tracked
I path:dir/tests
X path:dir/tests/t19
$ hg tracked
I path:dir/tests
X path:dir/tests/t19
$ hg update
19 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ find * | sort
dir
dir/tests
dir/tests/t1
dir/tests/t10
dir/tests/t11
dir/tests/t12
dir/tests/t13
dir/tests/t14
dir/tests/t15
dir/tests/t16
dir/tests/t17
dir/tests/t18
dir/tests/t2
dir/tests/t20
dir/tests/t3
dir/tests/t4
dir/tests/t5
dir/tests/t6
dir/tests/t7
dir/tests/t8
dir/tests/t9
$ cd ..
narrow clone everything but a directory (tests/)
$ hg clone --narrow ssh://user@dummy/master narrowroot --noupdate --exclude "dir/tests"
requesting all changes
adding changesets
adding manifests
adding file changes
added 21 changesets with 20 changes to 20 files
new changesets *:* (glob)
$ cd narrowroot
$ hg tracked
I path:.
X path:dir/tests
$ hg tracked
I path:.
X path:dir/tests
$ hg update
20 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ find * | sort
dir
dir/src
dir/src/f1
dir/src/f10
dir/src/f11
dir/src/f12
dir/src/f13
dir/src/f14
dir/src/f15
dir/src/f16
dir/src/f17
dir/src/f18
dir/src/f19
dir/src/f2
dir/src/f20
dir/src/f3
dir/src/f4
dir/src/f5
dir/src/f6
dir/src/f7
dir/src/f8
dir/src/f9
$ cd ..
narrow clone no paths at all
$ hg clone --narrow ssh://user@dummy/master narrowempty --noupdate
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files
new changesets * (glob)
$ cd narrowempty
$ hg tracked
$ hg update
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ ls
$ cd ..
simple clone
$ hg clone ssh://user@dummy/master simpleclone
requesting all changes
adding changesets
adding manifests
adding file changes
added 40 changesets with 40 changes to 40 files
new changesets * (glob)
updating to branch default
40 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd simpleclone
$ find * | sort
dir
dir/src
dir/src/f1
dir/src/f10
dir/src/f11
dir/src/f12
dir/src/f13
dir/src/f14
dir/src/f15
dir/src/f16
dir/src/f17
dir/src/f18
dir/src/f19
dir/src/f2
dir/src/f20
dir/src/f3
dir/src/f4
dir/src/f5
dir/src/f6
dir/src/f7
dir/src/f8
dir/src/f9
dir/tests
dir/tests/t1
dir/tests/t10
dir/tests/t11
dir/tests/t12
dir/tests/t13
dir/tests/t14
dir/tests/t15
dir/tests/t16
dir/tests/t17
dir/tests/t18
dir/tests/t19
dir/tests/t2
dir/tests/t20
dir/tests/t3
dir/tests/t4
dir/tests/t5
dir/tests/t6
dir/tests/t7
dir/tests/t8
dir/tests/t9
$ cd ..
Testing the --narrowspec flag to clone
$ cat >> narrowspecs <<EOF
> %include foo
> [include]
> path:dir/tests/
> dir/src/f12
> EOF
$ hg clone ssh://user@dummy/master specfile --narrowspec narrowspecs
reading narrowspec from '$TESTTMP/narrowspecs'
abort: cannot specify other files using '%include' in narrowspec
[255]
$ cat > narrowspecs <<EOF
> [include]
> path:dir/tests/
> file:dir/src/f12
> EOF
$ hg clone ssh://user@dummy/master specfile --narrowspec narrowspecs
reading narrowspec from '$TESTTMP/narrowspecs'
requesting all changes
adding changesets
adding manifests
adding file changes
added 21 changesets with 20 changes to 20 files
new changesets f93383bb3e99:26ce255d5b5d
updating to branch default
20 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd specfile
$ hg tracked
I path:dir/tests
I path:file:dir/src/f12
$ cd ..