Pickle protocol 3 allows to natively support all py bytes and string
types and is supported by zodbpickle/py on both py2 and py3 out of the
box. ZODB/py3 is using protocol=3 since 2013 and ZODB/py2 since 2018. In
other words nowdays protocol=3 is the default protocol with which
ZODB emits pickles, and it can be read practically everywhere.

The difference in between protocol=2 and protocol=3 is addition of
BINBYTES and SHORT_BINBYTES opcodes to represent bytes. Without those
opcodes bytes are encoded as

    `_codecs.encode(byt.decode('latin1'), 'latin1')`

which, when unpickled, results in bytes on py3 and str on py2.

Compared to using `BINBYTES byt` this form is much bigger in size, but
what is more important might turn bytes back into str when decoded and
reencoded on py2.

This form of bytes encoding is also not accepted by ZEO/py which rejects
it with

    2024-07-18T20:44:39 ERROR ZEO.asyncio.server Can't deserialize message
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/z/ZEO5/src/ZEO/asyncio/server.py", line 100, in message_received
        message_id, async_, name, args = self.decode(message)
      File "/home/kirr/src/wendelin/z/ZEO5/src/ZEO/asyncio/marshal.py", line 119, in pickle_server_decode
        return unpickler.load()  # msgid, flags, name, args
      File "/home/kirr/src/wendelin/z/ZEO5/src/ZEO/asyncio/marshal.py", line 176, in server_find_global
        raise ImportError("Module not allowed: %s" % (module,))
    ImportError: Module not allowed: _codecs

All in all using pickle protocol=3 is ok from both py2 and py3 point of
view, brings size optimization and correctness, and fixes ZEO and
probably other issues.

So let the pickles ZODB/go saves and other Go places emit be encoded with protocol=3 now as well.

For the reference, the

    // TODO 2 -> 3 since ZODB5 switched to it and uses zodbpickle.

is from 2019 added in a16c9e06 (go/zodb: Teach Persistent to serialize
itself).

ZEO/go client was asserting "method" field to be bytestring. As the
result interoperation with ZEO/py3 server was failing as e.g.

    2024-07-18T20:41:14 INFO ZEO.asyncio.server received handshake 'Z5'
    2024/07/18 20:41:14 zlink @ - /tmp/zeo2281880331/1.fs.zeosock: serveRecv1: decode: .0: method: got string; expected str
        zeo_test.go:221: openzeo /tmp/zeo2281880331/1.fs.zeosock: zeo: open /tmp/zeo2281880331/1.fs.zeosock: zlink @ - /tmp/zeo2281880331/1.fs.zeosock: call register: zlink is closed

because ZEO/py3 sends "method" as unicode.

-> Fix it by using pickle.AsString when decoding "method" field.

Similarly ZEO/go client was sending strings as bytestr, which on py3 decode to
unicode ok only if they are ASCII. Adjust string encoding to be emitted
as unicode always which works wrt both ZEO/py3 and ZEO/py2.

--------

ZEO/go client was sending binary ZRPC arguments as bytestr as well,
which was resulting in the following exception on ZEO/py3 side:

    2024-07-18T20:42:31 ERROR ZEO.asyncio.server Can't deserialize message
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/z/ZEO/src/ZEO/asyncio/server.py", line 102, in message_received
        message_id, async_, name, args = self.decode(message)
      File "/home/kirr/src/wendelin/z/ZEO/src/ZEO/asyncio/marshal.py", line 122, in pickle_server_decode
        return unpickler.load()  # msgid, flags, name, args
    UnicodeDecodeError: 'ascii' codec can't decode byte 0x85 in position 1: ordinal not in range(128)
    2024/07/18 20:42:31 zlink @ - /tmp/zeo627526011/1.fs.zeosock: recvPkt: EOF
        xtesting.go:361: load 0285cbac70a3d733:0000000000000001: returned err unexpected:
            have: /tmp/zeo627526011/1.fs.zeosock: load 0285cbac70a3d733:0000000000000001: zlink @ - /tmp/zeo627526011/1.fs.zeosock: call loadBefore: zlink is closed
            want: nil

-> Fix it by using pickle.Bytes which should be encoded as bytes in the
   pickle stream.

This fix is ok but depends on the next patch to upgrade ZODB
serialization protocol to 3, because on pickle protocol 2 bytes are
serialized as `_codecs.encode(byt.decode('latin1'), 'latin1')` and
ZEO/py forbids import of _codecs:

    2024-07-18T20:44:39 ERROR ZEO.asyncio.server Can't deserialize message
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/z/ZEO5/src/ZEO/asyncio/server.py", line 100, in message_received
        message_id, async_, name, args = self.decode(message)
      File "/home/kirr/src/wendelin/z/ZEO5/src/ZEO/asyncio/marshal.py", line 119, in pickle_server_decode
        return unpickler.load()  # msgid, flags, name, args
      File "/home/kirr/src/wendelin/z/ZEO5/src/ZEO/asyncio/marshal.py", line 176, in server_find_global
        raise ImportError("Module not allowed: %s" % (module,))
    ImportError: Module not allowed: _codecs

We will address this in the next patch.

go/zodb/zeo: Test it on all py2/py3 ZODB kinds of data we care about and wrt both ZEO/py2 and ZEO/py3

Similarly to FileStorage, fs1tools and other Go packages previously we
were testing ZEO/go client only with old FileStorage testdata generated
by python2 and pickle protocol=2. However even on py2 there are more
pickle protocols that are in use, and also there is python3.

We were also testing our ZEO/go client only wrt ZEO/py2 but there is
also ZEO/py3.

-> Adjust ZEO/go testing to automatically load and test against all ZODB
kinds from recently updated FileStorage testdata and wrt both ZEO/py2
and ZEO/py3.

All py2_pickle1, py2_pickle2, py2_pickle3 and py3_pickle3 are handled well out of the box.
However only ZEO/py2 succeeds: tests wrt ZEO/py3 server currently fail
and so are marked with "xfail".

We will fix tests for ZEO/py3 in the next patch.

Similarly to FileStorage, fs1tools and zodbtools previously we were testing
demo only with old FileStorage testdata generated by python2 and pickle
protocol=2. However even on py2 there are more pickle protocols that
are in use, and also there is python3.

-> Adjust demo testing to automatically load and test agains all ZODB
kinds from recently updated FileStorage testdata.

All py2_pickle1, py2_pickle2, py2_pickle3 and py3_pickle3 are handled well out of the box.

Like with FileStorage and fs1tools previously we were testing zodbtools/go only
with data generated by python2 and pickle protocol=2. However even on py2 there
are more pickle protocols that are in use, and also there is python3.

-> Modernize testdata generation to automatically pick up all ZODB kinds
   from recently-updated FileStorage/go testdata.

   Adjust tests on Go side to verify how zodbtools/go handle all generated zkinds.

All py2_pickle1, py2_pickle2, py2_pickle3 and py3_pickle3 are handled well out of the box.

Because else, py3_pickle3 tests fail e.g. as

        --- FAIL: TestFsDump/py3_pickle3/db=1 (0.00s)
            dump_test.go:70: fsdump: dump different:
                 Trans #00000 tid=0285cbac70a3d733 size=211 time=1979-01-03 21:00:26.400001 offset=117
                -    status='p' user=b'user0.12' description=b'step 0.12'
                +    status='p' user='user0.12' description='step 0.12'

        --- FAIL: TestFsDumpv/py3_pickle3/db=1 (0.00s)
            dump_test.go:70: fsdumpv: dump different:
                 ************************************************************
                -file identifier: b'FS30'
                +file identifier: 'FS30'

        ...

fs1tools/go sticks to py2 syntax because in my view it is more user
friendly. The preference of py2 or py3 syntax needs to be made anyway
because for fs1tools/go it is not possible to know beforehand to which
py kind its output will be compared against.

I think it is not very good for fstools/py output to be dependent on
python version. For the reference on this topic: output of zodbtools/py
is designed to be the same on both py2 and py3.

Like with FileStorage previously we were testing fs1tools only with data
generated by python2 and pickle protocol=2. However even on py2 there are
more pickle protocols that are in use, and also there is python3.

-> Modernize testdata generation to automatically pick up all ZODB kinds
   from recently-updated FileStorage/go testdata.

   Adjust tests on Go side to verify how fs1tools handles all generated zkinds.

py2_pickle1, py2_pickle2 and py2_pickle3 are handled well.
Tests for py3_pickle3 currently fail and so are marked with "xfail".

We will fix tests for py3_pickle3 in follow-up patches.

Like fsdump/py does.

https://github.com/zopefoundation/ZODB/commit/403f9869 started to print
size of every transaction record saying that it readded it. And indeed
this printing was there starting from
https://github.com/zopefoundation/ZODB/commit/06e757b3 authored in 2003.

Both commits use `size(txn) = trans._tend - trans._tpos` which is wrong
by 8 because during file iteration tpos points to the beginning of
transaction and tend points to tpos + tlen, but tlen is full
transaction length - 8:

https://github.com/zopefoundation/ZODB/blob/5.8.1/src/ZODB/FileStorage/FileStorage.py#L1997-L1998
https://github.com/zopefoundation/ZODB/blob/5.8.1/src/ZODB/FileStorage/format.py#L28

Mimic fsdump/py behaviour exactly for compatibility, even if it is a bit
buggy, since it was there for such a long time.

Without the fix TestFsDump was failing like this:

    --- FAIL: TestFsDump/db=1 (0.00s)
        dump_test.go:70: fsdump: dump different:
            -Trans #00000 tid=0285cbac258bf266 size=151 time=1979-01-03 21:00:08.800000 offset=52
            +Trans #00000 tid=0285cbac258bf266 time=1979-01-03 21:00:08.800000 offset=52
                 status=' ' user='' description='initial database creation'
               data #00000 oid=0000000000000000 size=61 class=persistent.mapping.PersistentMapping
             ...

https://github.com/zopefoundation/ZODB/commit/403f9869 adjusted fsdump
to emit size of transaction record. Everything else remains unchanged.

Our fsdump becomes broken, because it does not yet emit that size(txn).
We will fix it in the next patch.

We were saving index data with bytestrings inside index records. This
works for py2 but on py3 it causes failure on unpickling because, by default,
*STRING opcodes are unpickled into unicode on py3:

    === RUN   TestIndexSaveToPy/py2_pickle1/py3
    UnicodeDecodeError: 'ascii' codec can't decode byte 0x8d in position 25: ordinal not in range(128)

    The above exception was the direct cause of the following exception:

    Traceback (most recent call last):
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/fs1/./py/indexcmp", line 43, in <module>
        main()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/fs1/./py/indexcmp", line 30, in main
        d1 = fsIndex.load(path1)
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/fsIndex.py", line 138, in load
        v = unpickler.load()
    SystemError: <built-in method read of _io.BufferedReader object at 0x7fb631a86670> returned a result with an error set
        index_test.go:229: zodb/py read/compare index: exit status 1

-> Fix it by explicitly emitting index entries in binary form.

To be able to compare "index from py2 -> loaded into go -> saved by go ->
compared by py3" implement a bit of backward compatibility for  loading py2
index files on py3. Do this compatibility only for known-good py2 files, not
index produced by go code which is loaded by py3 without any compatibility
shims.

Python3 emits index entries using bytes, but index.go was expecting only
bytestrings. As the result loading index produced by py3 was failing
e.g. as

    index_test.go:201: index load: testdata/py3_pickle3/1.fs.index: pickle @6: invalid oidPrefix: type ogórek.Bytes

-> Fix it by accepting both bytes and bytestrings inside the index.

FileStorage/py2 saves data with FS21 magic, while FileStorage/py3 with
FS30 magic:

https://github.com/zopefoundation/ZODB/blob/5.8.1/src/ZODB/_compat.py#L25-L77

Up till now FileStorage/go was accepting only FS21 and so with
py3-generated data it was leading to e.g. the following failure:

    === RUN   TestEmptyDB/py3_pickle3
        filestorage_test.go:90: testdata/py3_pickle3/empty.fs: invalid fs1 magic "FS30"

-> Fix it by accepting both py2 and py3 FileStorage magics.

We do accept them both without any other change because FileStorage
format, even when it comes with those two different magic, is really the
same.

Previously we were testing FileStorage/go only with data generated by
python2 and pickle protocol=2. However even on py2 there are more pickle
protocols that are in use, and also there is python3.

-> Modernize py/gen-testdata to use run_with_all_zodb_pickle_kinds
   that was recently added as part of nexedi/zodbtools@f9d36ba7
   and generate test data with both python2 and python3. It is handy to
   use py2py3-venv(*) to prepare python environment to do that.

   Adjust tests on Go side to verify how FileStorage handles all generated zkinds.

py2_pickle1, py2_pickle2 and py2_pickle3 are handled well.
Tests for py3_pickle3 currently fail and so are marked with "xfail".

We will fix tests for py3_pickle3 in follow-up patches.

Old testdata are not yet removed because e.g. fs1tools and zodbdump
tests depend on them. We will remove old fs1 testdata after adjusting
tests in dependent packages step-by-step.

(*) see nexedi/zodbtools@fac2f190

Test for PyData.ClassName currently fails for py3_pickle3 zkind:

    === RUN   TestPyClassName/py3_pickle3
        pydata_test.go:50: class name for "\x80\x03X\x18\x00\x00\x00ZODB.tests.testSerializeq\x00X\x13\x00\x00\x00ClassWithoutNewargsq\x01\x86q\x02N\x86q\x03.":
            have: "?.?"
            want: "ZODB.tests.testSerialize.ClassWithoutNewargs"
        pydata_test.go:50: class name for "\x80\x03X\x18\x00\x00\x00ZODB.tests.testSerializeq\x00X\x10\x00\x00\x00ClassWithNewargsq\x01\x86q\x02K\x01\x85q\x03\x86q\x04.":
            have: "?.?"
            want: "ZODB.tests.testSerialize.ClassWithNewargs"

This happens because classname decoder was expecting class and module
names to come as py2 bytestrings, while py3 emits them as unicode.

-> Fix it by accepting both py2 bytestring and unicode for class and
module names.

Previously we were testing PyData only with data generated by python2
and pickle protocol=2. However even on py2 there are more pickle
protocols that are in use, and also there is python3.

-> Modernize py/pydata-gen-testdata to use run_with_all_zodb_pickle_kinds
   that was recently added as part of nexedi/zodbtools@f9d36ba7
   and generate test data with both python2 and python3. It is handy to
   use py2py3-venv(*) to prepare python environment to do that.

   Adjust tests on Go side to verify how PyData handles all generated
   zkinds.

py2_pickle1, py2_pickle2 and py2_pickle3 are handled well.
Tests for py3_pickle3 currently fail and so are marked with "xfail".

We will fix tests for py3_pickle3 in the next patch.

(*) see nexedi/zodbtools@fac2f190

Tests, that want to verify something wrt both py2 and py3 will do
WithEachPy(tested_func) which will run tested_func two times:

1) under environment where python on $PATH points to python2, and
2) under environment where python on $PATH points to python3.

Client tests will now need to use just "python" instead of e.g.
"python2" or "python3" to run some python program, and each time
"python" will correspond to current phase of WithEachPy execution.

This will be soon handy to test things wrt e.g. ZEO/py2 and ZEO/py3
servers and similar situations.

Tests that merely want to use some python program just for their inner
working, for example to run `zodb commit`, no longer indicate their
preference for py2. For such tests it is a matter of preference in
pre-setup environment to where "python" points.

For the reference under environments created with py2py3-venv(*) default
"python" currently points to "python2".

(*) see nexedi/zodbtools@fac2f190

ZTestData is Go counterpart of ztestdata on zodbtools/py side from
https://lab.nexedi.com/nexedi/zodbtools/-/blob/f9d36ba7/zodbtools/test/conftest.py#L31-65
that was recently added in nexedi/zodbtools@bf772ce0.

On Go side each ZTestData describes testdata files on the filesystem +
carry arbitrary extra information. For example FileStorage tests will
use it to place there "what is expected to load" information
corresponding to on-filesystem database.

Currently with the only utility to retrieve map keys in sorted order.

We will need this in several tests in follow-up patches.

Similarly to ZODB/py which provides u64 and p64 utilities. Add
zodbpickle.Pack64 for symmetry.

Because without StrictUnicode both bytestrings (str from py2) and
unicode (unicode from py2 and str from py3) load into the same Go type
string so it becomes impossible to distinguish them from each other.
Re-saving data, thus, also generally introduces changes as e.g.
string loaded via bytestring will be saved as unicode when pickling with
protocol 3. Or a loaded unicode will be saved as bytestring with
pickling via protocol=2.

-> Switching to StrictUnicode mode solves all those problems.

Please see updated documentatin for zodbpickle.go and
https://github.com/kisielk/og-rek/commit/b28613c2 for more details about
StrictUnicode mode.

For ZODB/go this is change in behaviour exposed to outside. However
there is currently only one known ZODB/go user - WCFS in Wendelin.core -
and that user will be updated correspondingly as well.

We already have 3 places where we create picklers and unpicklers:
zodb/pydata.go, fs1/index.go and zeo/proto.go and they are already
diverging a bit: for example pydata was explicitly specifying protocol
for pickle encoder, while other places were using defaults.

We will soon want to use StrictUnicode option for all picklers and
unpicklers we create, which means it is better to keep this
customization only in one place instead of copy-pasting it in between
callsites increasing the possibility for divergence and errors.

-> Move the code to create pickler and unpickler to internal zodbpickle
package as a preparatory step for that.

For the reference: this package is merely a wrapper around ogórek, not a
fork of any code like zodbpickle/py is.

We will soon want to use generics and `any` which are available only for go >= 1.18 .

The other changes in go.sum and go.mod are there because after just

    -go 1.14
    +go 1.18

the build stopped to work and asked to do `go mod tidy`

ogórek.AsInt64 was added in https://github.com/kisielk/og-rek/commit/010fbd2e
with functionality similar to what we had in pickletools.Xint64 before.

This brings in support for StrictUnicode mode, AsInt64, AsBytes and
AsString helpers, and other fixes.

See https://github.com/kisielk/og-rek/compare/v1.2.0...7d520718eea5 for
details.

So that building and using ZODB/go works not only in GOPATH mode.

Offload drivers from handling options such as ?read-only=1 and force
them to deal with such options only via DriverOptions, never zurl.

See added comment for details.

/reviewed-by @levin.zimmermann
/reviewed-on !4

go/neo/neonet: Fix client handshake not to accept server encoding if it is different from what client indicated

If the peers encoding is different than our encoding two different
scenarios can happen, because the handshake order is undefined (e.g.
we don't know if our handshake is received before the peer sends its
handshake):

1. Our handshake is received before peer sends its handshake, NEO/py
closes connection if it sees unexpected magic, version, etc.

2. The client already sends a handshake before it proceeds our handshake.
In this case it initally sends us it version, we can extract its encoding,
and only later, once it proceeded our handshake with the bad encoding,
it closes the connection.

Before this patch case (2) wasn't handled correctly by the automatic
encoding detection of 'DialLink'. 'DialLink' simply accepted the
different-than-expected encoding, but once the peer proceeded the nodes
handshake the peer closed the connection and the initially established
and returned link was immediately closed again. Due to this it was good
luck whether connecting with a peer different with an encoding different
from the expected one worked or didn't work (it depended on which handshake
was faster). Now 'DialLink' should reliably find the correct encoding
and return a stable link.

--------

kirr: this is based on the following original patch by Levin: levin.zimmermann/neoppod@f6b59772

I updated documentation throughout correspondingly and also added
corresponding handshake-specific test in the previous patch.

See !5 and b2da69e2
(go/neo/neonet: Demonstrate problem in handshake with NEO/py) for more
in-depth description of the problem.

Levin Zimmerman discovered that sometimes NEO/py accepts our handshake
hello with encoding 'M', then replies its owh handshake ehlo with
encoding 'N' and then further terminates the connection. In other words
it looks like that the handshake went successful, but it actually did
not and NEO/py terminates the link after some time.

This manifests itself e.g. as infrequent TestLoad failures on t branch
with the following output:

=== RUN   TestLoad/py/!ssl
I: runneo.py: /tmp/neo776618506/1 !ssl: started master(s): 127.0.0.1:21151
=== RUN   TestLoad/py/!ssl/enc=N(dialTryOrder=N,M)
    client_test.go:598: skip: does not excercise client redial
=== RUN   TestLoad/py/!ssl/enc=N(dialTryOrder=M,N)
    xtesting.go:330: load 0285cbac258bf266:0000000000000000: returned err unexpected:
        have: neo://127.0.0.1:21151/1: load 0285cbac258bf266:0000000000000000: dial S1: dial 127.0.0.1:40345 (STORAGE): 127.0.0.1:56678 - 127.0.0.1:40345: request identification: 127.0.0.1:56678 - 127.0.0.1:40345 .1: recv: EOF
        want: nil
    xtesting.go:330: load 0285cbac258bf266:0000000000000000: returned tid unexpected: 0000000000000000  ; want: 0285cbac258bf266
    xtesting.go:330: load 0285cbac258bf266:0000000000000000: returned buf = nil
    xtesting.go:339: load 0285cbac258bf265:0000000000000000: returned err unexpected:
        have: neo://127.0.0.1:21151/1: load 0285cbac258bf265:0000000000000000: dial S1: dial 127.0.0.1:40345 (STORAGE): 127.0.0.1:56688 - 127.0.0.1:40345: request identification: 127.0.0.1:56688 - 127.0.0.1:40345 .1: recv: EOF
        want: neo://127.0.0.1:21151/1: load 0285cbac258bf265:0000000000000000: 0000000000000000: object was not yet created
    ...
    client_test.go:588: NEO log tail:

        log file 'storage_0.log' tail:

        2023-07-17 17:21:57.1519 DEBUG     S1         connection completed for <ServerConnection(nid=None, address=127.0.0.1:51230, handler=IdentificationHandler, fd=20, server) at 7f3583fd4f50> (from 127.0.0.1:40345)
        2023-07-17 17:21:57.1537 WARNING   S1         Protocol version mismatch with <ServerConnection(nid=None, address=127.0.0.1:51230, handler=IdentificationHandler, fd=20, server) at 7f3583fd4f50>
        2023-07-17 17:21:57.1548 DEBUG     S1         connection closed for <ServerConnection(nid=None, address=127.0.0.1:51230, handler=IdentificationHandler, closed, server) at 7f3583fd4f50>
        2023-07-17 17:21:57.1551 WARNING   S1         A connection was lost during identification
        2023-07-17 17:22:00.1582 DEBUG     S1         accepted a connection from 127.0.0.1:51236
        2023-07-17 17:22:00.1585 DEBUG     S1         connection completed for <ServerConnection(nid=None, address=127.0.0.1:51236, handler=IdentificationHandler, fd=20, server) at 7f3583fd4e90> (from 127.0.0.1:40345)
        2023-07-17 17:22:00.1604 WARNING   S1         Protocol version mismatch with <ServerConnection(nid=None, address=127.0.0.1:51236, handler=IdentificationHandler, fd=20, server) at 7f3583fd4e90>
        2023-07-17 17:22:00.1622 DEBUG     S1         connection closed for <ServerConnection(nid=None, address=127.0.0.1:51236, handler=IdentificationHandler, closed, server) at 7f3583fd4e90>
        2023-07-17 17:22:00.1625 WARNING   S1         A connection was lost during identification
        2023-07-17 17:22:03.1663 DEBUG     S1         accepted a connection from 127.0.0.1:51238
        2023-07-17 17:22:03.1666 DEBUG     S1         connection completed for <ServerConnection(nid=None, address=127.0.0.1:51238, handler=IdentificationHandler, fd=20, server) at 7f3583fd4d10> (from 127.0.0.1:40345)
        2023-07-17 17:22:03.1674 WARNING   S1         Protocol version mismatch with <ServerConnection(nid=None, address=127.0.0.1:51238, handler=IdentificationHandler, fd=20, server) at 7f3583fd4d10>
        2023-07-17 17:22:03.1688 DEBUG     S1         connection closed for <ServerConnection(nid=None, address=127.0.0.1:51238, handler=IdentificationHandler, closed, server) at 7f3583fd4d10>
        2023-07-17 17:22:03.1691 WARNING   S1         A connection was lost during identification
        2023-07-17 17:22:06.1714 DEBUG     S1         accepted a connection from 127.0.0.1:57072
        2023-07-17 17:22:06.1719 DEBUG     S1         connection completed for <ServerConnection(nid=None, address=127.0.0.1:57072, handler=IdentificationHandler, fd=20, server) at 7f3583fd4b50> (from 127.0.0.1:40345)
        2023-07-17 17:22:06.1727 WARNING   S1         Protocol version mismatch with <ServerConnection(nid=None, address=127.0.0.1:57072, handler=IdentificationHandler, fd=20, server) at 7f3583fd4b50>
        2023-07-17 17:22:06.1738 DEBUG     S1         connection closed for <ServerConnection(nid=None, address=127.0.0.1:57072, handler=IdentificationHandler, closed, server) at 7f3583fd4b50>
        2023-07-17 17:22:06.1738 WARNING   S1         A connection was lost during identification

        log file 'master_0.log' tail:

        2023-07-17 17:21:21.0799 PACKET    M1         #0x0012 NotifyNodeInformation          > A1 (127.0.0.1:37906)
        2023-07-17 17:21:21.0799 PACKET    M1          ! C0 | CLIENT |  | RUNNING | 2023-07-17 14:21:21.079838
        2023-07-17 17:21:21.0800 PACKET    M1         #0x0102 NotifyNodeInformation          > S1 (127.0.0.1:37918)
        2023-07-17 17:21:21.0800 PACKET    M1          ! C0 | CLIENT |  | RUNNING | 2023-07-17 14:21:21.079838
        2023-07-17 17:21:21.0801 DEBUG     M1         Handler changed on <ServerConnection(nid=None, address=127.0.0.1:37966, handler=ClientServiceHandler, fd=18, server) at 7f3584245910>
        2023-07-17 17:21:21.0802 PACKET    M1         #0x0001 AnswerRequestIdentification    > C0 (127.0.0.1:37966)
        2023-07-17 17:21:21.0804 PACKET    M1         #0x0000 NotifyNodeInformation          > C0 (127.0.0.1:37966)
        2023-07-17 17:21:21.0804 PACKET    M1          ! C0 | CLIENT  |                 | RUNNING | 2023-07-17 14:21:21.079838
        2023-07-17 17:21:21.0804 PACKET    M1          ! M1 | MASTER  | 127.0.0.1:21151 | RUNNING | None
        2023-07-17 17:21:21.0804 PACKET    M1          ! S1 | STORAGE | 127.0.0.1:40345 | RUNNING | 2023-07-17 14:21:18.737469
        2023-07-17 17:21:21.0805 PACKET    M1         #0x0002 NotifyPartitionTable           > C0 (127.0.0.1:37966)
        2023-07-17 17:21:21.0810 PACKET    M1         #0x0003 LastTransaction                < C0 (127.0.0.1:37966)
        2023-07-17 17:21:21.0811 PACKET    M1         #0x0003 AnswerLastTransaction          > C0 (127.0.0.1:37966)
        2023-07-17 17:22:06.2053 DEBUG     M1         <SocketConnectorIPv4 at 0x7f3584252d10 fileno 18 ('127.0.0.1', 21151), opened from ('127.0.0.1', 37966)> closed in recv
        2023-07-17 17:22:06.2056 DEBUG     M1         connection closed for <ServerConnection(nid=C0, address=127.0.0.1:37966, handler=ClientServiceHandler, closed, server) at 7f3584245910>
        2023-07-17 17:22:06.2058 PACKET    M1         #0x0014 NotifyNodeInformation          > A1 (127.0.0.1:37906)
        2023-07-17 17:22:06.2058 PACKET    M1          ! C0 | CLIENT |  | UNKNOWN | 2023-07-17 14:21:21.079838
        2023-07-17 17:22:06.2059 PACKET    M1         #0x0104 NotifyNodeInformation          > S1 (127.0.0.1:37918)
        2023-07-17 17:22:06.2059 PACKET    M1          ! C0 | CLIENT |  | UNKNOWN | 2023-07-17 14:21:21.079838

The problem is due to that my analysis from e407f725 (go/neo/neonet:
Rework handshake to differentiate client and server parts) turned out to
be incorrect. Quoting that patch:

    -> Rework handshake so that client always sends its hello first, and
    only then the server side replies. This matches actual NEO/py behaviour:

    https://lab.nexedi.com/nexedi/neoppod/blob/v1.12-67-g261dd4b4/neo/lib/connector.py#L293-294

    even though the "NEO protocol" states that

    	Handshake transmissions are not ordered with respect to each other and can go in parallel.

    	( https://neo.nexedi.com/P-NEO-Protocol.Specification.2019?portal_skin=CI_slideshow#/9/2 )

    If I recall correctly that sentence was authored by me in 2018 based on
    previous understanding of should-be full symmetry in-between client and
    server.

so here "This matches actual NEO/py behaviour" was wrong: even though
https://lab.nexedi.com/nexedi/neoppod/blob/v1.12-67-g261dd4b4/neo/lib/connector.py#L293-294
indeed says that

    #       The NEO protocol is such that a client connection is always the
    #       first to send a packet, as soon as the connection is established,

in reality it is not the case as SocketConnector always queues handshake
hello upon its creation before receiving anything from remote side:
https://lab.nexedi.com/nexedi/neoppod/blob/v1.12-93-gfd87e153/neo/lib/connector.py#L77-78 .
In practice this leads to that in non-SSL case NEO/py server might be
fast enough to send its prepared hello before receiving hello from us.
Levin also explains at !5 (comment 187429):

    I think what happens is this:

    the NEO protocol doesn't specify in which order handshakes happen after
    initial dial. If the peer sends a handshake before receiving our
    handshake and if this peers handshake is received by us, 'DialLink'
    assumes everything is fine (no err is returned), it breaks the loop and
    returns the link. But then, very little time later, when the peer
    finally receives our handshake, this looks strange for the peer and it
    closes the connection.

    So in my understanding this should be fixed by explicitly comparing the
    encodings between our expected one and what the peer provided us. If
    encodings don't match we should retry with a new encoding in order to
    prevent the peer from closing the connection.

    For me this also explains why sometimes the tests passed and sometimes
    didn't: it depended on which node was faster ('race condition').

-> In this patch we add correspondig handshake test that demonstrates
this problem. It currently fails as

--- FAIL: TestHandshake (0.01s)
    --- FAIL: TestHandshake/enc=N (0.00s)
        newlink_test.go:154: handshake encoding mismatch: client: unexpected error:
            have: <nil>
                 "<nil>"
            want: &neonet._HandshakeError{LocalRole:1, LocalAddr:net.pipeAddr{}, RemoteAddr:net.pipeAddr{}, Err:(*neonet._EncodingMismatchError)(0xc0000a4190)}
                 "pipe - pipe: handshake (client): protocol encoding mismatch: peer = 'M'  ; our side = 'N'"
    --- FAIL: TestHandshake/enc=M (0.00s)
        newlink_test.go:154: handshake encoding mismatch: client: unexpected error:
            have: <nil>
                 "<nil>"
            want: &neonet._HandshakeError{LocalRole:1, LocalAddr:net.pipeAddr{}, RemoteAddr:net.pipeAddr{}, Err:(*neonet._EncodingMismatchError)(0xc0001a22cc)}
                 "pipe - pipe: handshake (client): protocol encoding mismatch: peer = 'N'  ; our side = 'M'"

We will fix it in the next patch.

/reported-by @levin.zimmermann
/reported-on !5

go/neo/neonet: Dedicate an error type to indicate "protocol version mismatch" as handshake failure cause

We will soon need to detect if a handshake failure was due to mismatch
of protocol encodings and that would require introduction of dedicated
error type for that cause. As a preparatory step first refactor "version
mismatch cause" to follow the same style for symmetry.

This patch fixes a discrepancy between NEO/py and NEO/go: NEO/py expands
the '~' and the '~username' prefix in the file path of the TLS
certificate/key files [1]. This syntax is used in NEO/py SlapOS SR [2].
We need to fix this discrepancy in NEO/go in order to use TLS encryption
with NEO + WCFS.

[1] https://lab.nexedi.com/nexedi/neoppod/blob/7c539f0f/neo/lib/config.py#L149
and https://lab.nexedi.com/nexedi/neoppod/blob/fa63d856/neo/lib/app.py#L25-31

[2] https://lab.nexedi.com/nexedi/slapos/blob/397726e1/stack/erp5/instance-zodb-base.cfg.in#L18-20
and https://lab.nexedi.com/nexedi/slapos/blob/a8150a1a/software/neoppod/instance-neo-input-schema.json#L62

/reviewed-by @kirr
/reviewed-on !1

The xfilepath package supports resolving filepaths with a user prefix
to absolute paths: it converts '~' and '~username' to $HOME of user
(as it's done by for  instance bash). No builtin golang module supports this
functionality [1]. We need this functionality in order to imitate the
behaviour of NEO/py in NEO/go [2].

---

[1] https://stackoverflow.com/questions/47261719/how-can-i-resolve-a-relative-path-to-absolute-path-in-golang)
[2] nexedi/slapos!1307 (comment 17574)

/reviewed-by @kirr
/reviewed-on !1

Without parenthesis it was failing on py3:

	(neo) (py3.venv) (g.env) kirr@deca:~/src/neo/src/lab.nexedi.com/kirr/neo/go/neo/t$ ./neotest info-local
	date:   Wed, 18 May 2022 11:05:50 +0300
	xnode:  kirr@deca.navytux.spb.ru (2401:5180:0:af::1 192.168.0.3 (+ 1·ipv4))
	uname:  Linux deca 5.10.0-13-amd64 #1 SMP Debian 5.10.106-1 (2022-03-17) x86_64 GNU/Linux
	cpu:    Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz
	  File "<string>", line 1
	    print '%.2fGHz' % (400000 / 1E6)
	          ^
	SyntaxError: invalid syntax

On py3 dict.keys() returns iterator instead of list:

    $ ./tzodb.py zhash
    Traceback (most recent call last):
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/neo/t/./tzodb.py", line 141, in <module>
        main()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/neo/t/./tzodb.py", line 138, in main
        zhash()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/neo/t/./tzodb.py", line 59, in zhash
        optv, argv = getopt(sys.argv[2:], "h", ["help", "check=", "bench="] + hashRegistry.keys())
    TypeError: can only concatenate list (not "dict_keys") to list

With xurl.ParseQuery being simpler analog of url.ParseQuery.
Simpler: It returns regular map instead of url.Values by not allowing duplicates.

WCFS needs to know key coverage for every visited node.

WARNING: this is API change.

KeyRange represents [lo,hi) key range. It simplifies working with ranges
of keys. We will use it in the next commit.

KeyRange originated in WCFS and was copied from there:

https://lab.nexedi.com/kirr/wendelin.core/blob/57be0126/wcfs/internal/xbtree/blib/keyrange.go

We were already using math.Min<Key> in one place, but the number of such
places is going to increase. -> Keep min/max definition in only one place.

NOTE: db was already being closed in the test's code.

staticcheck says:

	xtesting.go:386:2: this value of err is never used (SA4006)