Message-ID: <8620df11-96e4-4ca3-8f3c-33a479260961@joeconway.com>
Date: Wed, 6 Dec 2023 18:09:30 -0500
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: Emitting JSON to file using COPY TO
Content-Language: en-US
From: Joe Conway <mail@joeconway.com>
To: Daniel Verite <daniel@manitou-mail.org>,
 Andrew Dunstan <andrew@dunslane.net>
Cc: Davin Shearer <davin@apache.org>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>
References: <b3a73eca-ec3b-4b64-b6c2-82418bb16701@manitou-mail.org>
 <b7d8c88b-d175-44ca-a323-ec2f5c3cd37d@joeconway.com>
Autocrypt: addr=mail@joeconway.com; keydata=
 xsFNBEpXMCsBEADDnXUQzjlyi/cX02Gtdy2CLcroE5CsC7DJKdOBDbfgn0kfiIYoV5JniG4l
 VyzZUodY8yUAagqLYolh0UkBzs9N+qkm7erde4ypw3jzVQ37BuzIvk3nMUbuDZDgxWqX+nVS
 sKc+BQ5BpzgCHg48leoRO2ohjvYnUhgH3j2rFZCzaj6qQ7mv+XoxOJmUlVQtG06Jwkk7Vu14
 7U9nMMM6hyUKzVnmCphnlcMNo26UyVU70MwFfFJgcI0c5fpp8byN56eD6VJVnufO5WAuEhzE
 qcrSJR2FAlmM90GBY+6vP29twLDCHuSFvrnujNCx/BvCC/a3/gPvyAFp4JtMm9eXAmq3m/Kw
 94nTJXVdcbQeQQDp3KIG7MmWS4lnGvPn8v0CjgNaLvZXFLo1FgmUVsyEq1Lww4iRLa6sbpXJ
 ESx15UEue1k1YZM9C+4F/o3aeKNsAienjw2EXFzcaxIg/C4P493VMi3Qa8ycVxR5iYhUbYdo
 DFIUQhbFNsYfrtW/qZAELT3FCYFpZYG01e9Hj+cBrXXgyDDkQ5Lq4mlvmkRvuxn61V6Au4HA
 0sJiCox5pM1FvzT+aI8HY1BYaiB9Pl4fhpKgmhhlSuglk9v39S4jmlUIb45iLAUVpeNM6Qjm
 69pf5da9sm4aGFa7YlDSKf/WcU7z9ITZxsilOi2n7YJiwG7kTQARAQABzSRKb3NlcGggRSBD
 b253YXkgPG1haWxAam9lY29ud2F5LmNvbT7CwXoEEwEIACQCGwMCHgECF4AFCwkIBwMFFQoJ
 CAsFFgIDAQAFAlWTVvUCGQEACgkQMyt+aLaZQ0oPCQ/9HyRewMyvAIJRmoXoLAr8AoFLId6R
 qBJnNX0Lll0RLZui65aQ0+exwX7aH7TxWR16B2gWX3OmLfGT8XITOoG+zt9zsEpLvNkHchkF
 T/jyAcbuRj5WX9hamZgMbjXAJeCdlhW+fRA9Upb0w4dgBjqK5OgsqMikASL7t2vogHl9H08j
 vSoQLW+8wTnSBXBeBTBwB7xLIin5WVivzFHUCrnD2UsjeBIW3fmGdpTAjSxRzG+UPYVwXQ8F
 FLt7DpEytvLWapmZWMRdj0WZ/Q3SOO/Ed0yFqbzuwKaWcFrQBNeS2Sig+FefBNS98f9Hx7ku
 H3DW34qX/zSSdDh0jLs7X3PkIgF6BZR2TxaCwHPP9ERDiDaUInC9U7We1iZE1DjW8rLMEVJB
 hY0ClrrF67pnUKTbcU+uajpPn+2Jl74T0Set/XxpHZ4cezcJuqg31R8vHZgd5cf1WKP0D0pc
 qiuS02BBFkNCs1jQ+raTWcDuE6F1mUO2nvjUBN9r4y5DUbCNSqLKeAe/aA6JaSDkBpoXKdNS
 +c4rbzbktWkfUW8EhVlCGzNpy4ezEoVsqV2Ex7fNoxsE2vnSylLT9hycAmYf8ryMvniRZqnD
 T4JgLenIcQlkhB896T7wApOXfD8OJj1/XFxAfPi6vdlsr81uoxuB4euLp8IyduwLORRUogO9
 zmAXG5jOwU0ESlcyJwEQAOkTBb9yDhJbMUgvhM11rZwT5tm4Y9TqtEHn0Zy3t9g7bdFFpMva
 v/KENd3oAtLFpMDf+H3AggFk4ftUwJwiVgJ88ilvCynJUGXiuYIaexY4DLgn4xpnuiEpYEFV
 dWnlw7dWVTc62exfqIz9bSWRzwfBCY9ruYGEb4RDPDSNSAVyI7sxHzef2asiYxIcxrTrw5Vu
 gWNlPZcV5/EJ6PUvATjBF2TBkXV7KOciQng2tsQGrGMkY5mduNqwpuh6zfPcVF8LeObe96wv
 5ZhPRpO79nef7hnK2lJogp3JIo558Jlbz9WHtQEMZR85+bUhtI825QyNAFz3Jrn7NMgvDikc
 2OrWo7YMgMC5hDSWVFqA6/EQCNnDWGABWgeYHZFpnPwsvUWIYdhSilUuj/Tuzvz9ZmucFNbQ
 bauDQw6VQ38ofGnoYDZFJsGncprB8dBi4tDrIQ+1RlIh6C2Z/eMipqJOT26+spluTjouvnKT
 0S5yOgyX0PjbsysgwQdCGNJLHOjhHbSpSmOLaduV3CQo/0+DHT/TBjYfIXjTWouY9TkGxG4e
 NrxU0u2xAy5bMqOPmsFdjLTWlQUlF/fTMhB54XwI3FHWgnSnXZzStDTmTebLNdT/ftgliAzA
 81uMj49j0exv731/v+7udLA1bV8gnZ01zQCASDpWiRQR3fgwcugSUqgRABEBAAHCwV8EGAEI
 AAkFAkpXMicCGwwACgkQMyt+aLaZQ0pwAQ//bjcWnZg/jjRQ9gbZUGMqniItZYRglBMKIqt4
 Fia379JmHwTvavnFkJ8XMZ56UB0FIrgS+sUkRH6cPRQR+7Qi392LD021DXgSsz9CwFHjFyBG
 HwLEOTRcfYQbtJy0shHDJB4aQTOX3ERDH1PsvJNuevmQMzS0DWFav9+xMz9rKP4N+HffoBIZ
 E0C1xIE43nD4eLsbycte9sVIrmlNuUti3qUxJAQw8HwfJ6ZbBInHxquApR16uD1u99o6Xlnd
 FrDlY22tRmHCM0bR81GfGNdcU3Uo+rG/R/k4qa7s9/dgKvMbyH3fHhp/ceKag80Xo8IFurRl
 0ZJP3sHJ2QDHCVLat7jRZ+43hi1WlIhFbrgn6IyI0i7XR/W8JjrC5MsKq4TUwGH077sU/kcH
 YebVJZRbUUst2hAGHDFVBcG12qoKf+ltL9qXJc1y7BGeCoUW6QjOpljpq6ZL4FQUsM0RSRjs
 5egE3szPcIf5SyPK6WDOApoAq6M7BBFMGDZwEylYMtr0YekA1u86UA9D2xwLHEbBBp/uiby1
 c9JbPJ1Pn8zJP8WZNeRw4Q9TtqVK09+oLirMUSpIDd6KdZ1VgRxOK2re7tjDvkVuYsSrsiJ+
 1iJNEnp9iK0ok0DlJpSCe6KhkxpaTdeoWMXdKuJWec0NIqoAd54ZgBPnr+UPxTixgPq/p6Q=
In-Reply-To: <b7d8c88b-d175-44ca-a323-ec2f5c3cd37d@joeconway.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Archived-At: <https://www.postgresql.org/message-id/8620df11-96e4-4ca3-8f3c-33a479260961%40joeconway.com>
Precedence: bulk

On 12/6/23 14:47, Joe Conway wrote:
> On 12/6/23 13:59, Daniel Verite wrote:
>> 	Andrew Dunstan wrote:
>> 
>>> IMNSHO, we should produce either a single JSON 
>>> document (the ARRAY case) or a series of JSON documents, one per row 
>>> (the LINES case).
>> 
>> "COPY Operations" in the doc says:
>> 
>> " The backend sends a CopyOutResponse message to the frontend, followed
>>     by zero or more CopyData messages (always one per row), followed by
>>     CopyDone".
>> 
>> In the ARRAY case, the first messages with the copyjsontest
>> regression test look like this (tshark output):
>> 
>> PostgreSQL
>>      Type: CopyOut response
>>      Length: 13
>>      Format: Text (0)
>>      Columns: 3
>> 	Format: Text (0)
>> PostgreSQL
>>      Type: Copy data
>>      Length: 6
>>      Copy data: 5b0a
>> PostgreSQL
>>      Type: Copy data
>>      Length: 76
>>      Copy data:
>> 207b226964223a312c226631223a226c696e652077697468205c2220696e2069743a2031…
>> 
>> The first Copy data message with contents "5b0a" does not qualify
>> as a row of data with 3 columns as advertised in the CopyOut
>> message. Isn't that a problem?
> 
> 
> Is it a real problem, or just a bit of documentation change that I missed?
> 
> Anything receiving this and looking for a json array should know how to
> assemble the data correctly despite the extra CopyData messages.

Hmm, maybe the real problem here is that Columns do not equal "3" for 
the json mode case -- that should really say "1" I think, because the 
row is not represented as 3 columns but rather 1 json object.

Does that sound correct?

Assuming yes, there is still maybe an issue that there are two more 
"rows" that actual output rows (the "[" and the "]"), but maybe those 
are less likely to cause some hazard?

-- 
Joe Conway
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com