Mercurial > hg
annotate mercurial/state.py @ 39559:07b58266bce3
wireprotov2: implement commands as a generator of objects
Previously, wire protocol version 2 inherited version 1's model of
having separate types to represent the results of different wire
protocol commands.
As I implemented more powerful commands in future commits, I found
I was using a common pattern of returning a special type to hold a
generator. This meant the command function required a closure to
do most of the work. That made logic flow more difficult to follow.
I also noticed that many commands were effectively a sequence of
objects to be CBOR encoded.
I think it makes sense to define version 2 commands as generators.
This way, commands can simply emit the data structures they wish to
send to the client. This eliminates the need for a closure in
command functions and removes encoding from the bodies of commands.
As part of this commit, the handling of response objects has been
moved into the serverreactor class. This puts the reactor in the
driver's seat with regards to CBOR encoding and error handling.
Having error handling in the function that emits frames is
particularly important because exceptions in that function can lead
to things getting in a bad state: I'm fairly certain that uncaught
exceptions in the frame generator were causing deadlocks.
I also introduced a dedicated error type for explicit error reporting
in command handlers. This will be used in subsequent commits.
There's still a bit of work to be done here, especially around
formalizing the error handling "protocol." I've added yet another
TODO to track this so we don't forget.
Test output changed because we're using generators and no longer know
we are at the end of the data until we hit the end of the generator.
This means we can't emit the end-of-stream flag until we've exhausted
the generator. Hence the introduction of 0-sized end-of-stream frames.
Differential Revision: https://phab.mercurial-scm.org/D4472
author | Gregory Szorc <gregory.szorc@gmail.com> |
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date | Wed, 05 Sep 2018 09:06:40 -0700 |
parents | 5bfab9400daf |
children | 050ea8eb42a5 |
rev | line source |
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1 # state.py - writing and reading state files in Mercurial |
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2 # |
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3 # Copyright 2018 Pulkit Goyal <pulkitmgoyal@gmail.com> |
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4 # |
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5 # This software may be used and distributed according to the terms of the |
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6 # GNU General Public License version 2 or any later version. |
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7 |
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8 """ |
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9 This file contains class to wrap the state for commands and other |
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10 related logic. |
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11 |
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12 All the data related to the command state is stored as dictionary in the object. |
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13 The class has methods using which the data can be stored to disk in a file under |
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14 .hg/ directory. |
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15 |
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16 We store the data on disk in cbor, for which we use the third party cbor library |
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17 to serialize and deserialize data. |
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18 """ |
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19 |
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20 from __future__ import absolute_import |
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21 |
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22 from . import ( |
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23 error, |
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24 util, |
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25 ) |
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26 from .utils import ( |
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27 cborutil, |
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28 ) |
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29 |
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30 class cmdstate(object): |
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31 """a wrapper class to store the state of commands like `rebase`, `graft`, |
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32 `histedit`, `shelve` etc. Extensions can also use this to write state files. |
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33 |
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34 All the data for the state is stored in the form of key-value pairs in a |
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35 dictionary. |
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36 |
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37 The class object can write all the data to a file in .hg/ directory and |
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38 can populate the object data reading that file. |
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39 |
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40 Uses cbor to serialize and deserialize data while writing and reading from |
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41 disk. |
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42 """ |
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43 |
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44 def __init__(self, repo, fname): |
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45 """ repo is the repo object |
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46 fname is the file name in which data should be stored in .hg directory |
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47 """ |
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48 self._repo = repo |
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49 self.fname = fname |
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50 |
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51 def read(self): |
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52 """read the existing state file and return a dict of data stored""" |
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53 return self._read() |
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54 |
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55 def save(self, version, data): |
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56 """write all the state data stored to .hg/<filename> file |
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57 |
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58 we use third-party library cbor to serialize data to write in the file. |
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59 """ |
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60 if not isinstance(version, int): |
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61 raise error.ProgrammingError("version of state file should be" |
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62 " an integer") |
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63 |
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64 with self._repo.vfs(self.fname, 'wb', atomictemp=True) as fp: |
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65 fp.write('%d\n' % version) |
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66 for chunk in cborutil.streamencode(data): |
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67 fp.write(chunk) |
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68 |
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69 def _read(self): |
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70 """reads the state file and returns a dictionary which contain |
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71 data in the same format as it was before storing""" |
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72 with self._repo.vfs(self.fname, 'rb') as fp: |
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73 try: |
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74 int(fp.readline()) |
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75 except ValueError: |
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76 raise error.CorruptedState("unknown version of state file" |
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77 " found") |
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78 |
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79 return cborutil.decodeall(fp.read())[0] |
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80 |
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81 def delete(self): |
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82 """drop the state file if exists""" |
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83 util.unlinkpath(self._repo.vfs.join(self.fname), ignoremissing=True) |
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84 |
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85 def exists(self): |
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86 """check whether the state file exists or not""" |
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87 return self._repo.vfs.exists(self.fname) |