implement .dbtotxt and dbpage vtab

[Pavan-Nambi]

closes #3833

turso> create table t(x);
turso> select * from sqlite_dbpage;
┌──────┬───────────────────────────────────────────────────────────────────────┐
│ pgno │ data                                                                  │
├──────┼───────────────────────────────────────────────────────────────────────┤
│    1 │ SQLite format 3@  ���0… │
├──────┼───────────────────────────────────────────────────────────────────────┤
… │  2 │
└──────┴───────────────────────────────────────────────────────────────────────┘
turso> .dbtotxt
| size 8192 pagesize 4096 filename 1qazq
| page 1 offset 0
|      0: 53 51 4c 69 74 65 20 66 6f 72 6d 61 74 20 33 00   SQLite format 3.
|     16: 10 00 02 02 00 40 20 20 00 00 00 01 00 00 00 02   .....@  ........
|     32: 00 00 00 00 00 00 00 00 00 00 00 01 00 00 00 04   ................
|     48: ff ff f8 30 00 00 00 00 00 00 00 01 00 00 00 00   ...0............
|     80: 00 00 00 00 00 00 00 00 00 00 00 00 00 2e 7e 58   ..............~X
|     96: 00 2e 7e 58 0d 00 00 00 01 0f de 00 0f de 00 00   ..~X............
|   4048: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 20 01   .............. .
|   4064: 06 17 0f 0f 01 31 74 61 62 6c 65 74 74 02 43 52   .....1tablett.CR
|   4080: 45 41 54 45 20 54 41 42 4c 45 20 74 20 28 78 29   EATE TABLE t (x)
| page 2 offset 4096
|      0: 0d 00 00 00 00 10 00 00 00 00 00 00 00 00 00 00   ................
| end 1qazq
turso>

sqlite dont support this but i think this is nice to have a --page flag

turso> .dbtotxt --page 2
| size 8192 pagesize 4096 filename :memory:
| page 2 offset 4096
|      0: 0d 00 00 00 00 10 00 00 00 00 00 00 00 00 00 00   ................
| end :memory:
turso>

Note:

sqlite allows to write into sqlite_db_page , we do not yet, - issue #3836 - i'm not really sure why this is needed, so i didn't bothered with it.

❯ sqlite3 --unsafe-testing /tmp/1qaz
SQLite version 3.50.4 2025-07-30 19:33:53
Enter ".help" for usage hints.
sqlite> INSERT INTO sqlite_dbpage(pgno, data) VALUES(1000, NULL);
sqlite> SELECT pgno FROM sqlite_dbpage WHERE schema='main';
1
2
sqlite> INSERT INTO sqlite_dbpage(pgno, data) VALUES(1, NULL);
Runtime error: bad page value
sqlite> INSERT INTO sqlite_dbpage(pgno, data) VALUES(2, NULL);
sqlite> SELECT pgno FROM sqlite_dbpage WHERE schema='main';
Runtime error: database disk image is malformed (11)
sqlite>

[Pavan-Nambi]

If used on empty db, we currently get this error but it is due to #3441

turso> .dbtotxt
| size 0 pagesize 4096 filename wed
/****** ERROR: Database is empty, header does not exist - page 1 should've been allocated before this ******/
turso>

[Pavan-Nambi]

I m thinking maybe it would be nice if we could do smthng like

.dbtotxt --page-no 2

and we only display page 2 , sqlite dont have this, but i had this issue in large dbs i have to scroll forever or pipe it into a file and read from file

[Pavan-Nambi]

turso> .dbtotxt --page 2
| size 8192 pagesize 4096 filename :memory:
| page 2 offset 4096
|      0: 0d 00 00 00 00 10 00 00 00 00 00 00 00 00 00 00   ................
| end :memory:
turso>

[Pavan-Nambi]

Maybe i am getting ahead of myself but why cant we just use a seperate screen for this? for eg: similar to how .manual command shows it in a seperate screen? - would also be nice cus terminal be clean.

if anyone think this is a good idea, please let me know and i will do that. for now i am not doing it as i am not really sure if its good or bad thing.