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
$ echo "[extensions]" >> $HGRCPATH
$ echo "largefiles =" >> $HGRCPATH
Create the repository outside $HOME since largefiles write to
$HOME/.cache/largefiles.
$ hg init test
$ cd test
$ echo "root" > root
$ hg add root
$ hg commit -m "Root commit" --config extensions.largefiles=!
Ensure that .hg/largefiles isn't created before largefiles are added
#if unix-permissions
$ chmod 555 .hg
#endif
$ hg status
#if unix-permissions
$ chmod 755 .hg
#endif
$ test -f .hg/largefiles
[1]
$ echo "large" > foo
$ hg add --large foo
$ hg commit -m "Add foo as a largefile"
$ hg update -r 0
getting changed largefiles
0 largefiles updated, 1 removed
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo "normal" > foo
$ hg add foo
$ hg commit -m "Add foo as normal file"
created new head
Normal file in the working copy, keeping the normal version:
$ echo "n" | hg merge --config ui.interactive=Yes
remote turned local normal file foo into a largefile
use (l)argefile or keep (n)ormal file? n
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg status
$ cat foo
normal
Normal file in the working copy, keeping the largefile version:
$ hg update -q -C
$ echo "l" | hg merge --config ui.interactive=Yes
remote turned local normal file foo into a largefile
use (l)argefile or keep (n)ormal file? l
getting changed largefiles
1 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg status
M foo
$ hg diff --nodates
diff -r fa129ab6b5a7 .hglf/foo
--- /dev/null
+++ b/.hglf/foo
@@ -0,0 +1,1 @@
+7f7097b041ccf68cc5561e9600da4655d21c6d18
diff -r fa129ab6b5a7 foo
--- a/foo
+++ /dev/null
@@ -1,1 +0,0 @@
-normal
$ cat foo
large
Largefile in the working copy, keeping the normal version:
$ hg update -q -C -r 1
$ echo "n" | hg merge --config ui.interactive=Yes
remote turned local largefile foo into a normal file
keep (l)argefile or use (n)ormal file? n
getting changed largefiles
0 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg status
M foo
$ hg diff --nodates
diff -r ff521236428a .hglf/foo
--- a/.hglf/foo
+++ /dev/null
@@ -1,1 +0,0 @@
-7f7097b041ccf68cc5561e9600da4655d21c6d18
diff -r ff521236428a foo
--- /dev/null
+++ b/foo
@@ -0,0 +1,1 @@
+normal
$ cat foo
normal
Largefile in the working copy, keeping the largefile version:
$ hg update -q -C -r 1
$ echo "l" | hg merge --config ui.interactive=Yes
remote turned local largefile foo into a normal file
keep (l)argefile or use (n)ormal file? l
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg status
$ cat foo
large
Whatever ... commit something so we can invoke merge when updating
$ hg commit -m '3: Merge'
Updating from largefile to normal - no reason to prompt
$ hg up -r 2
getting changed largefiles
0 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat foo
normal
(the update above used to leave the working dir in a very weird state - clean it
$ hg up -qr null
$ hg up -qr 2
)
Updating from normal to largefile - no reason to prompt
$ hg up -r 3
getting changed largefiles
1 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat foo
large
$ cd ..
Systematic testing of merges involving largefiles:
Ancestor: normal Parent: normal-id Parent: large result: large
Ancestor: normal Parent: normal2 Parent: large result: ?
Ancestor: large Parent: large-id Parent: normal result: normal
Ancestor: large Parent: large2 Parent: normal result: ?
All cases should try merging both ways.
Prepare test repo:
$ hg init merges
$ cd merges
prepare cases with "normal" ancestor:
$ hg up -qr null
$ echo normal > f
$ hg ci -Aqm "normal-ancestor"
$ hg tag -l "normal-ancestor"
$ touch f2
$ hg ci -Aqm "normal-id"
$ hg tag -l "normal-id"
$ echo normal2 > f
$ hg ci -m "normal2"
$ hg tag -l "normal2"
$ echo normal > f
$ hg ci -Aqm "normal-same"
$ hg tag -l "normal-same"
$ hg up -qr "normal-ancestor"
$ hg rm f
$ echo large > f
$ hg add --large f
$ hg ci -qm "large"
$ hg tag -l "large"
prepare cases with "large" ancestor:
$ hg up -qr null
$ echo large > f
$ hg add --large f
$ hg ci -qm "large-ancestor"
$ hg tag -l "large-ancestor"
$ touch f2
$ hg ci -Aqm "large-id"
$ hg tag -l "large-id"
$ echo large2 > f
$ hg ci -m "large2"
$ hg tag -l "large2"
$ echo large > f
$ hg ci -Aqm "large-same"
$ hg tag -l "large-same"
$ hg up -qr "large-ancestor"
$ hg rm f
$ echo normal > f
$ hg ci -qAm "normal"
$ hg tag -l "normal"
$ hg log -GT '{tags}'
@ normal tip
|
| o large-same
| |
| o large2
| |
| o large-id
|/
o large-ancestor
o large
|
| o normal-same
| |
| o normal2
| |
| o normal-id
|/
o normal-ancestor
Ancestor: normal Parent: normal-id Parent: large result: large
$ hg up -Cqr normal-id
$ hg merge -r large
getting changed largefiles
1 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
large
swap
$ hg up -Cqr large
$ hg merge -r normal-id
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
large
Ancestor: normal Parent: normal-same Parent: large result: large
$ hg up -Cqr normal-same
$ hg merge -r large
getting changed largefiles
1 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
large
swap
$ hg up -Cqr large
$ hg merge -r normal-same
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
large
Ancestor: normal Parent: normal2 Parent: large result: ?
(annoying extra prompt ... but it do not do any serious harm)
$ hg up -Cqr normal2
$ hg merge -r large
remote turned local normal file f into a largefile
use (l)argefile or keep (n)ormal file? l
getting changed largefiles
1 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
large
$ hg up -Cqr normal2
$ echo n | hg merge -r large --config ui.interactive=Yes
remote turned local normal file f into a largefile
use (l)argefile or keep (n)ormal file? n
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
normal2
swap
$ hg up -Cqr large
$ hg merge -r normal2
remote turned local largefile f into a normal file
keep (l)argefile or use (n)ormal file? l
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
large
$ hg up -Cqr large
$ echo n | hg merge -r normal2 --config ui.interactive=Yes
remote turned local largefile f into a normal file
keep (l)argefile or use (n)ormal file? n
getting changed largefiles
0 largefiles updated, 0 removed
2 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
normal2
Ancestor: large Parent: large-id Parent: normal result: normal
$ hg up -Cqr large-id
$ hg merge -r normal
getting changed largefiles
0 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
normal
swap
$ hg up -Cqr normal
$ hg merge -r large-id
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
normal
Ancestor: large Parent: large-same Parent: normal result: normal
$ hg up -Cqr large-same
$ hg merge -r normal
getting changed largefiles
0 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
normal
swap
$ hg up -Cqr normal
$ hg merge -r large-same
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
normal
Ancestor: large Parent: large2 Parent: normal result: ?
(annoying extra prompt ... but it do not do any serious harm)
$ hg up -Cqr large2
$ hg merge -r normal
remote turned local largefile f into a normal file
keep (l)argefile or use (n)ormal file? l
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
large2
$ hg up -Cqr large2
$ echo n | hg merge -r normal --config ui.interactive=Yes
remote turned local largefile f into a normal file
keep (l)argefile or use (n)ormal file? n
getting changed largefiles
0 largefiles updated, 0 removed
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
normal
swap
$ hg up -Cqr normal
$ hg merge -r large2
remote turned local normal file f into a largefile
use (l)argefile or keep (n)ormal file? l
getting changed largefiles
1 largefiles updated, 0 removed
2 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
large2
$ hg up -Cqr normal
$ echo n | hg merge -r large2 --config ui.interactive=Yes
remote turned local normal file f into a largefile
use (l)argefile or keep (n)ormal file? n
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat f
normal
$ cd ..