Use UTF-8 encoding for Windows?

[brodycj]

I discovered that the Windows platform version uses the UTF-16le internal database encoding while the other platform versions use the UTF-8 database encoding. The results of using the HEX function on TEXT string values indicate that Android/iOS WebKit Web SQL uses the UTF-8 encoding as well. I found the following official descriptions:

• http://www.sqlite.org/pragma.html#pragma_encoding
• "Support for UTF-8 and UTF-16" section of https://www.sqlite.org/version3.html

It is very clear in those and other places that the necessary conversions are done automatically and there should be no difference between UTF-8 and UTF-16 database encoding at the API level. However I discovered some hidden Gotchas:

• The result of using the sqlite HEX function with a string value is different depending on which internal database encoding is used.
• According to http://www.sqlite.org/pragma.html#pragma_encoding:
  • It is not possible to change the internal encoding of an existing sqlite database.
  • There is no way to ATTACH to a database created with a different encoding.
• According to https://www.sqlite.org/version3.html it should be possible for a developer to store and retrieve TEXT strings with ISO-8859 (Latin-1) encoded characters in case of UTF-8 database encoding.

From some research I discovered that it is generally more efficient to store the data in UTF-8 format:

• http://www.mimec.org/node/297
• http://sqlite.1065341.n5.nabble.com/UTF-16-API-a-second-class-citizen-td46048.html

For the reasons above I think it would be beneficial to fix the Windows version to use the UTF-8 encoding by default. (The easy way is to use PRAGMA encoding right after opening the database.) The user can then change the internal database encoding using PRAGMA encoding before writing any data. (See http://www.sqlite.org/pragma.html#pragma_encoding.)

ADDITIONAL IMPORTANT READING: http://sqlite.1065341.n5.nabble.com/UTF-16-API-a-second-class-citizen-td46048.html links to https://www.joelonsoftware.com/2003/10/08/the-absolute-minimum-every-software-developer-absolutely-positively-must-know-about-unicode-and-character-sets-no-excuses/ which looks like essential reading for all serious sqlite users.

[brodycj]

Excellent case at http://utf8everywhere.org/, found thanks to microsoft/cppwinrt#269.

Excellent discussion at: https://softwareengineering.stackexchange.com/questions/102205/should-utf-16-be-considered-harmful

[brodycj]

General solution:

• convert database file name from UTF-16 wstring to UTF-8 std::string (to get UTF-8 char *) needed to call sqlite3_open (or sqlite3_open_v2) instead of sqlite3_open16, as needed to create the database with UTF-8 TEXT encoding if it does not already exist ref: https://www.sqlite.org/c3ref/open.html

How to convert the database file name:

• solution for using std::wstring_convert described at: https://stackoverflow.com/questions/42739129/where-to-put-stdwstring-convertstdcodecvt-utf8wchar-t/42739727#42739727

[brodycj]

The test suite was updated to check the result of PRAGMA encoding, currently expected to report encoding value of UTF-16le on Windows, UTF-8 on all other platforms. In addition there is a number of HEX encoding tests that expect result of SQLite3 HEX function to show UTF-16le encoding on Windows plugin and (WebKit) Web SQL on Android 4.1-4.3, UTF-8 otherwise.

[brodycj]

I am a bit concerned by the thread at http://sqlite.1065341.n5.nabble.com/Filename-encoding-on-Unix-platforms-td102210.html, especially the comment by Richard Hipp in http://sqlite.1065341.n5.nabble.com/Filename-encoding-on-Unix-platforms-td102210.html#a102215.

My concern is that using various forms of conversion to deal with locale-specific or platform-specific character conversions, especially on the database file name, may lead to an unpleasant surprise down the road (when someone least expects it and is least prepared for it).

Further analysis may be needed to reduce the risk of such a surprise as much as possible on Windows.