fix(export): stream database dump with LIMIT/OFFSET to fix large-DB failure (#59)

[Vinzz2303]

Fixes

Closes #59 — Database dumps do not work on large databases

Problem

The previous implementation loaded the entire database into a single string in memory before sending any HTTP response:

let dumpContent = 'SQLite format 3\0'
// ... all rows appended ...
const blob = new Blob([dumpContent], ...)
return new Response(blob, { headers })

This caused two failure modes on large databases:

• Memory exhaustion — Durable Objects have a 1 GB memory cap. Large databases cause OOM crashes mid-request.
• Gateway timeout — The response body is not sent until the entire dump is assembled. Cloudflare's 30-second limit fires before a single byte is delivered to the client.

Solution

1. Pre-flight metadata collection

Table names and CREATE TABLE schemas are collected before the stream opens. Any DB error returns a clean HTTP 500 (not a broken HTTP 200 with truncated body).

2. ReadableStream with LIMIT/OFFSET batching

Rows are fetched in pages of 1 000 rows and enqueued to a ReadableStream<Uint8Array> immediately. The HTTP response starts flowing after the first enqueue() call — eliminating the gateway-timeout problem entirely.

3. Event-loop yielding

await new Promise(r => setTimeout(r, 0)) is called between batches and between tables, preventing the Durable Object's single JS thread from being monopolised.

4. Correct value escaping

Type	Output
null / undefined	NULL
boolean	1 / 0
number	bare literal
Uint8Array (BLOB)	X'hexstring'
string	'single-quoted' with '' escaping

5. Exclude sqlite_ internal tables

The pre-flight query filters out sqlite_sequence, sqlite_stat1, etc. to produce a clean, importable dump.

Tests

9 tests — all passing (npx vitest run src/export/dump.test.ts):

• ✅ Streaming response has correct Content-Type and Transfer-Encoding: chunked headers
• ✅ Body contains CREATE TABLE + INSERT statements
• ✅ Empty database produces valid SQL preamble/epilogue only
• ✅ Tables with no rows are schema-only (no INSERT)
• ✅ Single quotes in strings are properly escaped
• ✅ NULL columns render as SQL NULL (new)
• ✅ Pagination: full 1 000-row batch followed by partial batch = 1 001 INSERT statements (new)
• ✅ Pre-flight DB error returns HTTP 500 (new)
• ✅ sqlite_ internal tables excluded from dump (new)

/claim #59

[Vinzz2303]

Hi team 👋 This PR is fully ready for review, featuring a streaming implementation with batching and 9 functional tests. Could you please check it out or approve the workflow to let tests run? Thank you!