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
$ hg init repo
$ cd repo
$ cat > a <<EOF
> c
> c
> a
> a
> b
> a
> a
> c
> c
> EOF
$ hg ci -Am adda
adding a
$ cat > a <<EOF
> c
> c
> a
> a
> dd
> a
> a
> c
> c
> EOF
default context
$ hg diff --nodates
diff -r cf9f4ba66af2 a
--- a/a
+++ b/a
@@ -2,7 +2,7 @@
c
a
a
-b
+dd
a
a
c
invalid --unified
$ hg diff --nodates -U foo
abort: diff context lines count must be an integer, not 'foo'
[255]
$ hg diff --nodates -U 2
diff -r cf9f4ba66af2 a
--- a/a
+++ b/a
@@ -3,5 +3,5 @@
a
a
-b
+dd
a
a
$ hg --config diff.unified=2 diff --nodates
diff -r cf9f4ba66af2 a
--- a/a
+++ b/a
@@ -3,5 +3,5 @@
a
a
-b
+dd
a
a
$ hg diff --nodates -U 1
diff -r cf9f4ba66af2 a
--- a/a
+++ b/a
@@ -4,3 +4,3 @@
a
-b
+dd
a
invalid diff.unified
$ hg --config diff.unified=foo diff --nodates
abort: diff context lines count must be an integer, not 'foo'
[255]
noprefix config and option
$ hg --config diff.noprefix=True diff --nodates
diff -r cf9f4ba66af2 a
--- a
+++ a
@@ -2,7 +2,7 @@
c
a
a
-b
+dd
a
a
c
$ hg diff --noprefix --nodates
diff -r cf9f4ba66af2 a
--- a
+++ a
@@ -2,7 +2,7 @@
c
a
a
-b
+dd
a
a
c
noprefix config disabled in plain mode, but option still enabled
$ HGPLAIN=1 hg --config diff.noprefix=True diff --nodates
diff -r cf9f4ba66af2 a
--- a/a
+++ b/a
@@ -2,7 +2,7 @@
c
a
a
-b
+dd
a
a
c
$ HGPLAIN=1 hg diff --noprefix --nodates
diff -r cf9f4ba66af2 a
--- a
+++ a
@@ -2,7 +2,7 @@
c
a
a
-b
+dd
a
a
c
$ cd ..
0 lines of context hunk header matches gnu diff hunk header
$ hg init diffzero
$ cd diffzero
$ cat > f1 << EOF
> c2
> c4
> c5
> EOF
$ hg commit -Am0
adding f1
$ cat > f2 << EOF
> c1
> c2
> c3
> c4
> EOF
$ mv f2 f1
$ hg diff -U0 --nodates
diff -r 55d8ff78db23 f1
--- a/f1
+++ b/f1
@@ -0,0 +1,1 @@
+c1
@@ -1,0 +3,1 @@
+c3
@@ -3,1 +4,0 @@
-c5
$ hg diff -U0 --nodates --git
diff --git a/f1 b/f1
--- a/f1
+++ b/f1
@@ -0,0 +1,1 @@
+c1
@@ -1,0 +3,1 @@
+c3
@@ -3,1 +4,0 @@
-c5
$ hg diff -U0 --nodates -p
diff -r 55d8ff78db23 f1
--- a/f1
+++ b/f1
@@ -0,0 +1,1 @@
+c1
@@ -1,0 +3,1 @@ c2
+c3
@@ -3,1 +4,0 @@ c4
-c5
$ echo a > f1
$ hg ci -m movef2
Test diff headers terminating with TAB when necessary (issue3357)
Regular diff --nodates, file creation
$ hg mv f1 'f 1'
$ echo b > 'f 1'
$ hg diff --nodates 'f 1'
diff -r 7574207d0d15 f 1
--- /dev/null
+++ b/f 1
@@ -0,0 +1,1 @@
+b
Git diff, adding space
$ hg diff --git
diff --git a/f1 b/f 1
rename from f1
rename to f 1
--- a/f1
+++ b/f 1
@@ -1,1 +1,1 @@
-a
+b
Git diff, adding extended headers
$ hg diff --git --config experimental.extendedheader.index=7 --config experimental.extendedheader.similarity=True
diff --git a/f1 b/f 1
similarity index 0%
rename from f1
rename to f 1
index 7898192..6178079 100644
--- a/f1
+++ b/f 1
@@ -1,1 +1,1 @@
-a
+b
$ hg diff --git --config experimental.extendedheader.index=-1
invalid length for extendedheader.index: '-1'
diff --git a/f1 b/f 1
rename from f1
rename to f 1
--- a/f1
+++ b/f 1
@@ -1,1 +1,1 @@
-a
+b
$ hg diff --git --config experimental.extendedheader.index=whatever
invalid value for extendedheader.index: 'whatever'
diff --git a/f1 b/f 1
rename from f1
rename to f 1
--- a/f1
+++ b/f 1
@@ -1,1 +1,1 @@
-a
+b
Git diff with noprefix
$ hg --config diff.noprefix=True diff --git --nodates
diff --git f1 f 1
rename from f1
rename to f 1
--- f1
+++ f 1
@@ -1,1 +1,1 @@
-a
+b
noprefix config disabled in plain mode, but option still enabled
$ HGPLAIN=1 hg --config diff.noprefix=True diff --git --nodates
diff --git a/f1 b/f 1
rename from f1
rename to f 1
--- a/f1
+++ b/f 1
@@ -1,1 +1,1 @@
-a
+b
$ HGPLAIN=1 hg diff --git --noprefix --nodates
diff --git f1 f 1
rename from f1
rename to f 1
--- f1
+++ f 1
@@ -1,1 +1,1 @@
-a
+b
Regular diff --nodates, file deletion
$ hg ci -m addspace
$ hg mv 'f 1' f1
$ echo a > f1
$ hg diff --nodates 'f 1'
diff -r ca50fe67c9c7 f 1
--- a/f 1
+++ /dev/null
@@ -1,1 +0,0 @@
-b
Git diff, removing space
$ hg diff --git
diff --git a/f 1 b/f1
rename from f 1
rename to f1
--- a/f 1
+++ b/f1
@@ -1,1 +1,1 @@
-b
+a
showfunc diff
$ cat > f1 << EOF
> int main() {
> int a = 0;
> int b = 1;
> int c = 2;
> int d = 3;
> return a + b + c + d;
> }
> EOF
$ hg commit -m addfunction
$ cat > f1 << EOF
> int main() {
> int a = 0;
> int b = 1;
> int c = 2;
> int e = 3;
> return a + b + c + e;
> }
> EOF
$ hg diff --git
diff --git a/f1 b/f1
--- a/f1
+++ b/f1
@@ -2,6 +2,6 @@
int a = 0;
int b = 1;
int c = 2;
- int d = 3;
- return a + b + c + d;
+ int e = 3;
+ return a + b + c + e;
}
$ hg diff --config diff.showfunc=True --git
diff --git a/f1 b/f1
--- a/f1
+++ b/f1
@@ -2,6 +2,6 @@ int main() {
int a = 0;
int b = 1;
int c = 2;
- int d = 3;
- return a + b + c + d;
+ int e = 3;
+ return a + b + c + e;
}
If [diff] git is set to true, but the user says --no-git, we should
*not* get git diffs
$ hg diff --nodates --config diff.git=1 --no-git
diff -r f2c7c817fa55 f1
--- a/f1
+++ b/f1
@@ -2,6 +2,6 @@
int a = 0;
int b = 1;
int c = 2;
- int d = 3;
- return a + b + c + d;
+ int e = 3;
+ return a + b + c + e;
}
$ cd ..
Long function names should be abbreviated, but multi-byte character shouldn't
be broken up
$ hg init longfunc
$ cd longfunc
>>> with open('a', 'wb') as f:
... f.write(b'a' * 39 + b'bb' + b'\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b' 0 b\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b'a' * 39 + b'\xc3\xa0' + b'\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b' 0 a with grave (single code point)\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b'a' * 39 + b'a\xcc\x80' + b'\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b' 0 a with grave (composition)\n') and None
... f.write(b' .\n' * 3) and None
$ hg ci -qAm0
>>> with open('a', 'wb') as f:
... f.write(b'a' * 39 + b'bb' + b'\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b' 1 b\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b'a' * 39 + b'\xc3\xa0' + b'\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b' 1 a with grave (single code point)\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b'a' * 39 + b'a\xcc\x80' + b'\n') and None
... f.write(b' .\n' * 3) and None
... f.write(b' 1 a with grave (composition)\n') and None
... f.write(b' .\n' * 3) and None
$ hg ci -m1
$ hg diff -c1 --nodates --show-function
diff -r 3e92dd6fa812 -r a256341606cb a
--- a/a
+++ b/a
@@ -2,7 +2,7 @@ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab
.
.
.
- 0 b
+ 1 b
.
.
.
@@ -10,7 +10,7 @@ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\xc3\xa0 (esc)
.
.
.
- 0 a with grave (single code point)
+ 1 a with grave (single code point)
.
.
.
@@ -18,7 +18,7 @@ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\xcc\x80 (esc)
.
.
.
- 0 a with grave (composition)
+ 1 a with grave (composition)
.
.
.
$ cd ..