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
$ cat >> $HGRCPATH <<EOF
> [extensions]
> rebase=
>
> [alias]
> tlog = log --template "{rev}: {node|short} '{desc}' {branches}\n"
> tglog = tlog --graph
> EOF
$ hg init a
$ cd a
$ mkdir d
$ echo a > a
$ hg ci -Am A
adding a
$ echo b > d/b
$ hg ci -Am B
adding d/b
$ hg mv d d-renamed
moving d/b to d-renamed/b
$ hg ci -m 'rename B'
$ hg up -q -C 1
$ hg mv a a-renamed
$ echo x > d/x
$ hg add d/x
$ hg ci -m 'rename A'
created new head
$ hg tglog
@ 3: 73a3ee40125d 'rename A'
|
| o 2: 220d0626d185 'rename B'
|/
o 1: 3ab5da9a5c01 'B'
|
o 0: 1994f17a630e 'A'
Rename is tracked:
$ hg tlog -p --git -r tip
3: 73a3ee40125d 'rename A'
diff --git a/a b/a-renamed
rename from a
rename to a-renamed
diff --git a/d/x b/d/x
new file mode 100644
--- /dev/null
+++ b/d/x
@@ -0,0 +1,1 @@
+x
Rebase the revision containing the rename:
$ hg rebase -s 3 -d 2
rebasing 3:73a3ee40125d "rename A" (tip)
saved backup bundle to $TESTTMP/a/.hg/strip-backup/73a3ee40125d-1d78ebcf-rebase.hg
$ hg tglog
@ 3: 032a9b75e83b 'rename A'
|
o 2: 220d0626d185 'rename B'
|
o 1: 3ab5da9a5c01 'B'
|
o 0: 1994f17a630e 'A'
Rename is not lost:
$ hg tlog -p --git -r tip
3: 032a9b75e83b 'rename A'
diff --git a/a b/a-renamed
rename from a
rename to a-renamed
diff --git a/d-renamed/x b/d-renamed/x
new file mode 100644
--- /dev/null
+++ b/d-renamed/x
@@ -0,0 +1,1 @@
+x
Rebased revision does not contain information about b (issue3739)
$ hg log -r 3 --debug
changeset: 3:032a9b75e83bff1dcfb6cbfa4ef50a704bf1b569
tag: tip
phase: draft
parent: 2:220d0626d185f372d9d8f69d9c73b0811d7725f7
parent: -1:0000000000000000000000000000000000000000
manifest: 3:035d66b27a1b06b2d12b46d41a39adb7a200c370
user: test
date: Thu Jan 01 00:00:00 1970 +0000
files+: a-renamed d-renamed/x
files-: a
extra: branch=default
extra: rebase_source=73a3ee40125d6f0f347082e5831ceccb3f005f8a
description:
rename A
$ cd ..
$ hg init b
$ cd b
$ echo a > a
$ hg ci -Am A
adding a
$ echo b > b
$ hg ci -Am B
adding b
$ hg cp b b-copied
$ hg ci -Am 'copy B'
$ hg up -q -C 1
$ hg cp a a-copied
$ hg ci -m 'copy A'
created new head
$ hg tglog
@ 3: 0a8162ff18a8 'copy A'
|
| o 2: 39e588434882 'copy B'
|/
o 1: 6c81ed0049f8 'B'
|
o 0: 1994f17a630e 'A'
Copy is tracked:
$ hg tlog -p --git -r tip
3: 0a8162ff18a8 'copy A'
diff --git a/a b/a-copied
copy from a
copy to a-copied
Rebase the revision containing the copy:
$ hg rebase -s 3 -d 2
rebasing 3:0a8162ff18a8 "copy A" (tip)
saved backup bundle to $TESTTMP/b/.hg/strip-backup/0a8162ff18a8-dd06302a-rebase.hg
$ hg tglog
@ 3: 98f6e6dbf45a 'copy A'
|
o 2: 39e588434882 'copy B'
|
o 1: 6c81ed0049f8 'B'
|
o 0: 1994f17a630e 'A'
Copy is not lost:
$ hg tlog -p --git -r tip
3: 98f6e6dbf45a 'copy A'
diff --git a/a b/a-copied
copy from a
copy to a-copied
Rebased revision does not contain information about b (issue3739)
$ hg log -r 3 --debug
changeset: 3:98f6e6dbf45ab54079c2237fbd11066a5c41a11d
tag: tip
phase: draft
parent: 2:39e588434882ff77d01229d169cdc77f29e8855e
parent: -1:0000000000000000000000000000000000000000
manifest: 3:2232f329d66fffe3930d43479ae624f66322b04d
user: test
date: Thu Jan 01 00:00:00 1970 +0000
files+: a-copied
extra: branch=default
extra: rebase_source=0a8162ff18a8900df8df8ef7ac0046955205613e
description:
copy A
$ cd ..
Test rebase across repeating renames:
$ hg init repo
$ cd repo
$ echo testing > file1.txt
$ hg add file1.txt
$ hg ci -m "Adding file1"
$ hg rename file1.txt file2.txt
$ hg ci -m "Rename file1 to file2"
$ echo Unrelated change > unrelated.txt
$ hg add unrelated.txt
$ hg ci -m "Unrelated change"
$ hg rename file2.txt file1.txt
$ hg ci -m "Rename file2 back to file1"
$ hg update -r -2
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo Another unrelated change >> unrelated.txt
$ hg ci -m "Another unrelated change"
created new head
$ hg tglog
@ 4: b918d683b091 'Another unrelated change'
|
| o 3: 1ac17e43d8aa 'Rename file2 back to file1'
|/
o 2: 480101d66d8d 'Unrelated change'
|
o 1: be44c61debd2 'Rename file1 to file2'
|
o 0: 8ce9a346991d 'Adding file1'
$ hg rebase -s 4 -d 3
rebasing 4:b918d683b091 "Another unrelated change" (tip)
saved backup bundle to $TESTTMP/repo/.hg/strip-backup/b918d683b091-3024bc57-rebase.hg
$ hg diff --stat -c .
unrelated.txt | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)
$ cd ..
Verify that copies get preserved (issue4192).
$ hg init copy-gets-preserved
$ cd copy-gets-preserved
$ echo a > a
$ hg add a
$ hg commit --message "File a created"
$ hg copy a b
$ echo b > b
$ hg commit --message "File b created as copy of a and modified"
$ hg copy b c
$ echo c > c
$ hg commit --message "File c created as copy of b and modified"
$ hg copy c d
$ echo d > d
$ hg commit --message "File d created as copy of c and modified"
Note that there are four entries in the log for d
$ hg tglog --follow d
@ 3: 421b7e82bb85 'File d created as copy of c and modified'
|
o 2: 327f772bc074 'File c created as copy of b and modified'
|
o 1: 79d255d24ad2 'File b created as copy of a and modified'
|
o 0: b220cd6d2326 'File a created'
Update back to before we performed copies, and inject an unrelated change.
$ hg update 0
0 files updated, 0 files merged, 3 files removed, 0 files unresolved
$ echo unrelated > unrelated
$ hg add unrelated
$ hg commit --message "Unrelated file created"
created new head
$ hg update 4
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
Rebase the copies on top of the unrelated change.
$ hg rebase --source 1 --dest 4
rebasing 1:79d255d24ad2 "File b created as copy of a and modified"
rebasing 2:327f772bc074 "File c created as copy of b and modified"
rebasing 3:421b7e82bb85 "File d created as copy of c and modified"
saved backup bundle to $TESTTMP/copy-gets-preserved/.hg/strip-backup/79d255d24ad2-a2265555-rebase.hg
$ hg update 4
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
There should still be four entries in the log for d
$ hg tglog --follow d
@ 4: dbb9ba033561 'File d created as copy of c and modified'
|
o 3: af74b229bc02 'File c created as copy of b and modified'
|
o 2: 68bf06433839 'File b created as copy of a and modified'
:
o 0: b220cd6d2326 'File a created'
Same steps as above, but with --collapse on rebase to make sure the
copy records collapse correctly.
$ hg co 1
0 files updated, 0 files merged, 3 files removed, 0 files unresolved
$ echo more >> unrelated
$ hg ci -m 'unrelated commit is unrelated'
created new head
$ hg rebase -s 2 --dest 5 --collapse
rebasing 2:68bf06433839 "File b created as copy of a and modified"
rebasing 3:af74b229bc02 "File c created as copy of b and modified"
merging b and c to c
rebasing 4:dbb9ba033561 "File d created as copy of c and modified"
merging c and d to d
saved backup bundle to $TESTTMP/copy-gets-preserved/.hg/strip-backup/68bf06433839-dde37595-rebase.hg
$ hg co tip
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
This should show both revision 3 and 0 since 'd' was transitively a
copy of 'a'.
$ hg tglog --follow d
@ 3: 5a46b94210e5 'Collapsed revision
: * File b created as copy of a and modified
: * File c created as copy of b and modified
: * File d created as copy of c and modified'
o 0: b220cd6d2326 'File a created'
$ cd ..