Fix set_auto_conf with single quotes

[demonolock]

This patch improves an PostgresNode::set_auto_conf method

New implementation does the following things:

• escaping '\n', '\r', '\t', '\b' and '\' symbols
• translating bool-values into 'on|off'
• saving a presentation of values those were not changed

This patch closes a problem with storing a command line with quotes in postgres' configuration files.

A test is provided.

---

It is a temporary solution to exist problems. In the future we should work with configuration files a more cleverly:

• do not reorder declarations
• do not remove comments

[dmitry-lipetsk]

Postgres' functions for escaping and unescaping configuration property values.

/*
* Strip the quotes surrounding the given string, and collapse any embedded
* '' sequences and backslash escapes.
*/
char * DeescapeQuotedString(const char *s)

https://github.com/postgres/postgres/blob/e3fa2b037c6f0f435838e99200050dc54c306085/src/backend/utils/misc/guc-file.l#L653

---

/*
 * Escape (by doubling) any single quotes or backslashes in given string
 *
*/
char* escape_single_quotes_ascii(const char *src)

https://github.com/postgres/postgres/blob/1acf10549e64c6a52ced570d712fcba1a2f5d1ec/src/port/quotes.c#L33

[demonolock]

Ошибки flake8
./testgres/node.py:1637:20: E721 do not compare types, for exact checks use is / is not, for instance checks use isinstance()
./testgres/node.py:1702:16: E721 do not compare types, for exact checks use is / is not, for instance checks use isinstance()

[dmitry-lipetsk]

flake8 error:

./build/lib/testgres/node.py:1637:20: E721 do not compare types, for exact checks use is / is not, for instance checks use isinstance()

It is a really interesting problem.

Flake does not like:

testgres/testgres/node.py

Line 1637 in ee7dc91

assert type(option) == str

but doesn't mind it:

testgres/testgres/node.py

Line 1644 in ee7dc91

if valueType == str:

For me - it need to configure flake and disable E721.

https://stackoverflow.com/questions/52395064/e721-do-not-compare-types-use-isinstance-error

you should just ignore the linter because it's not suggesting anything useful to you.

In my experience Python linters are blunt tools and implemented fairly naively.

What I do not use isinstance:

Never use isinstance() to validate types, one example is that True and False are considered instances of int

[dmitry-lipetsk]

https://www.flake8rules.com/rules/E721.html

A object should be be compared to a type by using isinstance. This is because isinstance can handle subclasses as well.

They are really thinking that know what I want :)

[dmitry-lipetsk]

This patch was tested with pg_probackup2 test system. All is OK.