SQLite: do not ask for the metadata of a column that has no table - #38976

Fixes #27776

the issue asks whether the column metadata calls in GetStream can be handed a null , and they can .

what happens

GetStream looks for a rowid column so it can hand back a SqliteBlob . for a value that came from an expression there is no underlying column , so sqlite3_column_database_name , sqlite3_column_table_name and sqlite3_column_origin_name all answer null . i printed them for SELECT 42, substr("Content", 1, 3) FROM "Case" :

ordinal=0 name=42                         db=<null> table=<null> origin=<null>
ordinal=1 name=substr("Content", 1, 3)    db=<null> table=<null> origin=<null>

the search starts from a null database and table name , so the literal in column 0 matches it , and its null origin name goes into sqlite3_table_column_metadata . sqlite answers SQLITE_MISUSE and GetStream throws :

Microsoft.Data.Sqlite.SqliteException : SQLite Error 21: 'bad parameter or other API misuse'
   at Microsoft.Data.Sqlite.SqliteDataRecord.GetStream(Int32 ordinal) in SqliteDataRecord.cs:341

the same expression on its own is fine , because there is no second column for the search to reach . that is why the report says removing the 42 makes it work . it is also why a real column sitting next to a literal is fine , a non null table name does not match the literal's null one .

this is the ado.net repro of ericsink/SQLitePCL.raw#479 , which asked whether the bug was in the wrapper or in the caller . it is the caller .

the fix

a column with no database or table name has no row to open a blob on , so return the MemoryStream , which is what already happens when no rowid column is found :

if (blobDatabaseName == null
    || blobTableName == null)
{
    return new MemoryStream(GetCachedBlob(ordinal), false);
}

GetTextReader and GetFieldValue<Stream> both go through GetStream , so they are fixed with it .

tests

three , next to the existing GetStream ones .

• GetStream_works_when_expression_and_a_literal_in_the_same_query , the report's shape . throws SQLITE_MISUSE on main , gives a MemoryStream with the right three bytes after
• GetTextReader_works_when_expression_and_a_literal_in_the_same_query , same path through the text reader . same before and after
• GetStream_Blob_works_when_a_literal_is_in_the_same_query , a real blob column with a literal beside it . passes on main and after , so the guard is not swallowing the blob case

on main that is 2 failures out of 714 , and both are the two above . with the change Microsoft.Data.Sqlite.sqlite3.Tests is 707 pass , sqlite3mc 708 pass , EFCore.Sqlite.Tests 896 pass , all 0 failed . EFCore.Sqlite.FunctionalTests is 38042 pass , and its 177 failures are all mod_spatialite.dylib not being installed on this mac , the same 177 as before the change .

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