[Yuvi1192p]

Problem and Context

Closes #59.

Previously, requesting a database dump via /export/dump buffered the entire database in memory with SELECT * FROM ${table}; and new Blob([dumpContent]). For databases larger than a few megabytes or databases up to 10GB, this caused Cloudflare Workers to run out of memory (OOM) or trigger the 30-second execution wall time limit.

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Solution & Architecture

This PR introduces an $O(1)$ memory streaming architecture for SQLite database dumps with two complementary execution paths:

1. Incremental Streaming Generator (generateDumpChunks)

• Replaces unbounded full-table queries with paginated iteration using LIMIT 1000 OFFSET ${offset}.
• SQLite file header (SQLite format 3\0) is yielded first, followed by each table's schema definition (SELECT sql FROM sqlite_master), and then row INSERT statements chunk by chunk.
• Table data is never materialized in worker memory at once.

2. SQL Literal Escaping (escapeSqlValue)

• Properly serializes all SQLite data types:
  • null / undefined -> NULL
  • number / bigint -> numeric string literals
  • boolean -> 1 / 0
  • ArrayBuffer / Uint8Array -> X'...' hex BLOB literals
  • string -> single-quote escaped '...'

3. Direct HTTP Streaming

• When accessed directly via GET /export/dump, chunks are piped directly to the caller using a standard ReadableStream with headers:
  • Content-Type: application/x-sqlite3
  • Content-Disposition: attachment; filename="database_dump.sql"

4. Background R2 Multipart Offload

• When ?location=r2 or ?r2=true is requested:
  • Validates presence of DATABASE_DUMP_BUCKET binding (R2Bucket), returning 400 with descriptive error if missing.
  • Generates ISO timestamped key dump_YYYYMMDD-HHMMSS.sql.
  • Buffers chunks until R2's 5 MiB part size threshold is reached and flushes parts incrementally via createMultipartUpload, uploadPart, and complete.
  • Aborts multipart upload if an error occurs to prevent orphaned parts in the bucket.
  • If executionContext.waitUntil is available (Cloudflare Worker runtime), offloads the work to the background, returning 202 Accepted ({ key, status: "accepted" }) immediately so large dumps are unaffected by HTTP timeouts.
  • Notifies an optional callback URL via POST once upload completes.

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Verification & Test Matrix

• Comprehensive unit test suite in src/export/dump.test.ts with 17 tests covering:
  • formatDumpTimestamp: UTC zero-padding and formatting.
  • escapeSqlValue: null, numbers, bigints, booleans, BLOBs, single quote escaping.
  • generateDumpChunks: pagination across multiple pages with LIMIT/OFFSET.
  • dumpDatabaseRoute: HTTP streaming, empty database, tables without data, 500 error propagation.
  • R2 offload: 400 error on missing bucket, multipart upload lifecycle, upload abort on failure, 202 accepted background execution with waitUntil, webhook callback dispatch.
• Vitest Result: 17/17 passed (100%).
• Codebase formatted via Prettier and zero TypeScript errors in implementation files.

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/claim #59

Signed-off-by: Swapnil Jadhav yuvi.jadhav92@gmail.com