[Asterisk-code-review] func_odbc: acf_odbc_read() and cli_odbc_read() unicode support (...asterisk[master])

[Sean Bright]

Sean Bright has posted comments on this change. ( https://gerrit.asterisk.org/c/asterisk/+/12812 )

Change subject: func_odbc:  acf_odbc_read() and cli_odbc_read() unicode support
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Patch Set 4:

> Patch Set 4:
> 
> > Patch Set 4:
> > 
> > I think that the correct fix is going to be to modify ast_odbc_ast_str_SQLGetData() to retrieve the data in parts, as documented here:
> > 
> > https://docs.microsoft.com/en-us/sql/odbc/reference/syntax/sqlgetdata-function?view=sql-server-2017#retrieving-variable-length-data-in-parts
> 
> How about a fixed-length data in parts (ex. NCHAR)? Microsoft prohibits to retrieve the data in parts for a fixed-length data.

I think your original solution may be the best (except you should multiply by 4 instead of 3).

The problem is that the drivers are inconsistent and I'm sure they are not even consistent with themselves between releases. When using the "octet length" check, MySQL returns a value that is sufficient to store the bytes in UTF-8, while Microsoft's does not. Multiplying the number of potential characters - while not ideal - is a better solution than potentially adding different logic for each of the ODBC drivers.

Because UTF-8 can require up to 4 bytes per codepoint, I think we can consider the 4x factor as the worst-case scenario for Unicode data.

Alexei - thoughts?


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Gerrit-Project: asterisk
Gerrit-Branch: master
Gerrit-Change-Id: I50e86c8a277996f13d4a4b9b318ece0d60b279bf
Gerrit-Change-Number: 12812
Gerrit-PatchSet: 4
Gerrit-Owner: Boris P. Korzun <drtr0jan at yandex.ru>
Gerrit-Reviewer: Alexei Gradinari <alex2grad at gmail.com>
Gerrit-Reviewer: Boris P. Korzun <drtr0jan at yandex.ru>
Gerrit-Reviewer: Friendly Automation
Gerrit-Reviewer: George Joseph <gjoseph at digium.com>
Gerrit-CC: Sean Bright <sean.bright at gmail.com>
Gerrit-Comment-Date: Fri, 06 Sep 2019 14:06:30 +0000
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