sql/pgwire: explicitly handle 0, 1 or n format codes

[dt]

refactored slightly to explicitly handle the cases allowed by the spec and check for a few
invalid cases that we were previously allowing (eg 0 < format codes < params).

Unfortunately hard to write a test with current setup because of lib/pq, but verified by using the failing php example.

Fixes #5758.

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This change is

[bdarnell]

We can't easily test this from go but we should still be able to add it to acceptance/php_test.go.

[tamird]

agree we need an acceptance test that tickles this.

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Reviewed 1 of 1 files at r1.
Review status: all files reviewed at latest revision, 4 unresolved discussions.

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sql/pgwire/v3.go, line 496 [r1] (raw file):
link to it: http://www.postgresql.org/docs/current/static/protocol-message-formats.html

also, do we use multiline comments like this anywhere else?

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sql/pgwire/v3.go, line 509 [r1] (raw file):
this should be a switch now, and the 0 case can just be a no-op

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sql/pgwire/v3.go, line 563 [r1] (raw file):
ditto. also in both cases we need to give context explaining what the docs are referring to when they say "This"

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sql/pgwire/v3.go, line 577 [r1] (raw file):
also a switch

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Comments from the review on Reviewable.io

[tbg]

Thanks for fixing this so quickly! cc @jseldess

[dt]

Hm, maybe we should make all the examples acceptance tests.

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Review status: all files reviewed at latest revision, 4 unresolved discussions, all commit checks successful.

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sql/pgwire/v3.go, line 496 [r1] (raw file):
Done.

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sql/pgwire/v3.go, line 509 [r1] (raw file):
Done.

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sql/pgwire/v3.go, line 563 [r1] (raw file):
Done.

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sql/pgwire/v3.go, line 577 [r1] (raw file):
Done.

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Comments from the review on Reviewable.io

[bdarnell]

We need to find some solution for testing the examples; adding them to the acceptance tests would be one way to do it. See cockroachdb/docs#182

[tamird]

LGTM with the test

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Reviewed 1 of 1 files at r2.
Review status: all files reviewed at latest revision, 1 unresolved discussion.

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sql/pgwire/v3.go, line 565 [r2] (raw file):
To match the above:

"From the docs on number of result-column format codes to bind:"

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Comments from the review on Reviewable.io

[tamird]

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Reviewed 2 of 2 files at r3.
Review status: all files reviewed at latest revision, 2 unresolved discussions.

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acceptance/php_test.go, line 41 [r3] (raw file):
separate this with a blank line?

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Comments from the review on Reviewable.io