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
#require svn13
$ svnupanddisplay()
> {
> (
> cd $1;
> svn up -q;
> svn st -v | sed 's/ */ /g' | sort
> limit=''
> if [ $2 -gt 0 ]; then
> limit="--limit=$2"
> fi
> svn log --xml -v $limit | $PYTHON "$TESTDIR/svnxml.py"
> )
> }
$ cat >> $HGRCPATH <<EOF
> [extensions]
> convert =
> EOF
$ hg init a
Add
$ echo a > a/a
$ mkdir -p a/d1/d2
$ echo b > a/d1/d2/b
$ hg --cwd a ci -d '0 0' -A -m 'add a file'
adding a
adding d1/d2/b
Modify
$ svn-safe-append.py a a/a
$ hg --cwd a ci -d '1 0' -m 'modify a file'
$ hg --cwd a tip -q
1:e0e2b8a9156b
$ hg convert -d svn a
assuming destination a-hg
initializing svn repository 'a-hg'
initializing svn working copy 'a-hg-wc'
scanning source...
sorting...
converting...
1 add a file
0 modify a file
$ svnupanddisplay a-hg-wc 2
2 1 test d1
2 1 test d1/d2
2 1 test d1/d2/b
2 2 test .
2 2 test a
revision: 2
author: test
msg: modify a file
M /a
revision: 1
author: test
msg: add a file
A /a
A /d1
A /d1/d2
A /d1/d2/b
$ ls a a-hg-wc
a:
a
d1
a-hg-wc:
a
d1
$ cmp a/a a-hg-wc/a
Rename
$ hg --cwd a mv a b
$ hg --cwd a ci -d '2 0' -m 'rename a file'
$ hg --cwd a tip -q
2:eb5169441d43
$ hg convert -d svn a
assuming destination a-hg
initializing svn working copy 'a-hg-wc'
scanning source...
sorting...
converting...
0 rename a file
$ svnupanddisplay a-hg-wc 1
3 1 test d1
3 1 test d1/d2
3 1 test d1/d2/b
3 3 test .
3 3 test b
revision: 3
author: test
msg: rename a file
D /a
A /b (from /a@2)
$ ls a a-hg-wc
a:
b
d1
a-hg-wc:
b
d1
Copy
$ hg --cwd a cp b c
$ hg --cwd a ci -d '3 0' -m 'copy a file'
$ hg --cwd a tip -q
3:60effef6ab48
$ hg convert -d svn a
assuming destination a-hg
initializing svn working copy 'a-hg-wc'
scanning source...
sorting...
converting...
0 copy a file
$ svnupanddisplay a-hg-wc 1
4 1 test d1
4 1 test d1/d2
4 1 test d1/d2/b
4 3 test b
4 4 test .
4 4 test c
revision: 4
author: test
msg: copy a file
A /c (from /b@3)
$ ls a a-hg-wc
a:
b
c
d1
a-hg-wc:
b
c
d1
$ hg --cwd a rm b
Remove
$ hg --cwd a ci -d '4 0' -m 'remove a file'
$ hg --cwd a tip -q
4:87bbe3013fb6
$ hg convert -d svn a
assuming destination a-hg
initializing svn working copy 'a-hg-wc'
scanning source...
sorting...
converting...
0 remove a file
$ svnupanddisplay a-hg-wc 1
5 1 test d1
5 1 test d1/d2
5 1 test d1/d2/b
5 4 test c
5 5 test .
revision: 5
author: test
msg: remove a file
D /b
$ ls a a-hg-wc
a:
c
d1
a-hg-wc:
c
d1
Executable
#if execbit
$ chmod +x a/c
#else
$ echo fake >> a/c
#endif
$ hg --cwd a ci -d '5 0' -m 'make a file executable'
#if execbit
$ hg --cwd a tip -q
5:ff42e473c340
#else
$ hg --cwd a tip -q
5:817a700c8cf1
#endif
$ hg convert -d svn a
assuming destination a-hg
initializing svn working copy 'a-hg-wc'
scanning source...
sorting...
converting...
0 make a file executable
$ svnupanddisplay a-hg-wc 1
6 1 test d1
6 1 test d1/d2
6 1 test d1/d2/b
6 6 test .
6 6 test c
revision: 6
author: test
msg: make a file executable
M /c
#if execbit
$ test -x a-hg-wc/c
#endif
#if symlink
Symlinks
$ ln -s a/missing a/link
$ hg --cwd a commit -Am 'add symlink'
adding link
$ hg --cwd a mv link newlink
$ hg --cwd a commit -m 'move symlink'
$ hg convert -d svn a a-svnlink
initializing svn repository 'a-svnlink'
initializing svn working copy 'a-svnlink-wc'
scanning source...
sorting...
converting...
7 add a file
6 modify a file
5 rename a file
4 copy a file
3 remove a file
2 make a file executable
1 add symlink
0 move symlink
$ svnupanddisplay a-svnlink-wc 1
8 1 test d1
8 1 test d1/d2
8 1 test d1/d2/b
8 6 test c
8 8 test .
8 8 test newlink
revision: 8
author: test
msg: move symlink
D /link
A /newlink (from /link@7)
Make sure our changes don't affect the rest of the test cases
$ hg --cwd a up 5
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg --cwd a --config extensions.strip= strip -r 6
saved backup bundle to $TESTTMP/a/.hg/strip-backup/bd4f7b7a7067-ed505e42-backup.hg
#endif
Convert with --full adds and removes files that didn't change
$ touch a/f
$ hg -R a ci -Aqmf
$ echo "rename c d" > filemap
$ hg convert -d svn a --filemap filemap --full
assuming destination a-hg
initializing svn working copy 'a-hg-wc'
scanning source...
sorting...
converting...
0 f
$ svnupanddisplay a-hg-wc 1
7 7 test .
7 7 test d
7 7 test f
revision: 7
author: test
msg: f
D /c
A /d
D /d1
A /f
$ rm -rf a a-hg a-hg-wc
Executable in new directory
$ hg init a
$ mkdir a/d1
$ echo a > a/d1/a
#if execbit
$ chmod +x a/d1/a
#else
$ echo fake >> a/d1/a
#endif
$ hg --cwd a ci -d '0 0' -A -m 'add executable file in new directory'
adding d1/a
$ hg convert -d svn a
assuming destination a-hg
initializing svn repository 'a-hg'
initializing svn working copy 'a-hg-wc'
scanning source...
sorting...
converting...
0 add executable file in new directory
$ svnupanddisplay a-hg-wc 1
1 1 test .
1 1 test d1
1 1 test d1/a
revision: 1
author: test
msg: add executable file in new directory
A /d1
A /d1/a
#if execbit
$ test -x a-hg-wc/d1/a
#endif
Copy to new directory
$ mkdir a/d2
$ hg --cwd a cp d1/a d2/a
$ hg --cwd a ci -d '1 0' -A -m 'copy file to new directory'
$ hg convert -d svn a
assuming destination a-hg
initializing svn working copy 'a-hg-wc'
scanning source...
sorting...
converting...
0 copy file to new directory
$ svnupanddisplay a-hg-wc 1
2 1 test d1
2 1 test d1/a
2 2 test .
2 2 test d2
2 2 test d2/a
revision: 2
author: test
msg: copy file to new directory
A /d2
A /d2/a (from /d1/a@1)
Branchy history
$ hg init b
$ echo base > b/b
$ hg --cwd b ci -d '0 0' -Ambase
adding b
$ svn-safe-append.py left-1 b/b
$ echo left-1 > b/left-1
$ hg --cwd b ci -d '1 0' -Amleft-1
adding left-1
$ svn-safe-append.py left-2 b/b
$ echo left-2 > b/left-2
$ hg --cwd b ci -d '2 0' -Amleft-2
adding left-2
$ hg --cwd b up 0
1 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ svn-safe-append.py right-1 b/b
$ echo right-1 > b/right-1
$ hg --cwd b ci -d '3 0' -Amright-1
adding right-1
created new head
$ svn-safe-append.py right-2 b/b
$ echo right-2 > b/right-2
$ hg --cwd b ci -d '4 0' -Amright-2
adding right-2
$ hg --cwd b up -C 2
3 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ hg --cwd b merge
merging b
warning: conflicts while merging b! (edit, then use 'hg resolve --mark')
2 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
[1]
$ hg --cwd b revert -r 2 b
$ hg --cwd b resolve -m b
(no more unresolved files)
$ hg --cwd b ci -d '5 0' -m 'merge'
Expect 4 changes
$ hg convert -d svn b
assuming destination b-hg
initializing svn repository 'b-hg'
initializing svn working copy 'b-hg-wc'
scanning source...
sorting...
converting...
5 base
4 left-1
3 left-2
2 right-1
1 right-2
0 merge
$ svnupanddisplay b-hg-wc 0
4 2 test left-1
4 3 test b
4 3 test left-2
4 4 test .
4 4 test right-1
4 4 test right-2
revision: 4
author: test
msg: merge
A /right-1
A /right-2
revision: 3
author: test
msg: left-2
M /b
A /left-2
revision: 2
author: test
msg: left-1
M /b
A /left-1
revision: 1
author: test
msg: base
A /b
Tags are not supported, but must not break conversion
$ rm -rf a a-hg a-hg-wc
$ hg init a
$ echo a > a/a
$ hg --cwd a ci -d '0 0' -A -m 'Add file a'
adding a
$ hg --cwd a tag -d '1 0' -m 'Tagged as v1.0' v1.0
$ hg convert -d svn a
assuming destination a-hg
initializing svn repository 'a-hg'
initializing svn working copy 'a-hg-wc'
scanning source...
sorting...
converting...
1 Add file a
0 Tagged as v1.0
writing Subversion tags is not yet implemented
$ svnupanddisplay a-hg-wc 2
2 1 test a
2 2 test .
2 2 test .hgtags
revision: 2
author: test
msg: Tagged as v1.0
A /.hgtags
revision: 1
author: test
msg: Add file a
A /a
$ rm -rf a a-hg a-hg-wc