[experiment] add alternative wasm sqlite3 implementation available via build-tag (#2863)

This allows for building GoToSocial with [SQLite transpiled to WASM](https://github.com/ncruces/go-sqlite3) and accessed through [Wazero](https://wazero.io/).

vendor/github.com/ncruces/go-sqlite3/blob.go

@@ -0,0 +1,250 @@
+package sqlite3
+
+import (
+	"io"
+
+	"github.com/ncruces/go-sqlite3/internal/util"
+)
+
+// ZeroBlob represents a zero-filled, length n BLOB
+// that can be used as an argument to
+// [database/sql.DB.Exec] and similar methods.
+type ZeroBlob int64
+
+// Blob is an handle to an open BLOB.
+//
+// It implements [io.ReadWriteSeeker] for incremental BLOB I/O.
+//
+// https://sqlite.org/c3ref/blob.html
+type Blob struct {
+	c      *Conn
+	bytes  int64
+	offset int64
+	handle uint32
+}
+
+var _ io.ReadWriteSeeker = &Blob{}
+
+// OpenBlob opens a BLOB for incremental I/O.
+//
+// https://sqlite.org/c3ref/blob_open.html
+func (c *Conn) OpenBlob(db, table, column string, row int64, write bool) (*Blob, error) {
+	c.checkInterrupt()
+	defer c.arena.mark()()
+	blobPtr := c.arena.new(ptrlen)
+	dbPtr := c.arena.string(db)
+	tablePtr := c.arena.string(table)
+	columnPtr := c.arena.string(column)
+
+	var flags uint64
+	if write {
+		flags = 1
+	}
+
+	r := c.call("sqlite3_blob_open", uint64(c.handle),
+		uint64(dbPtr), uint64(tablePtr), uint64(columnPtr),
+		uint64(row), flags, uint64(blobPtr))
+
+	if err := c.error(r); err != nil {
+		return nil, err
+	}
+
+	blob := Blob{c: c}
+	blob.handle = util.ReadUint32(c.mod, blobPtr)
+	blob.bytes = int64(c.call("sqlite3_blob_bytes", uint64(blob.handle)))
+	return &blob, nil
+}
+
+// Close closes a BLOB handle.
+//
+// It is safe to close a nil, zero or closed Blob.
+//
+// https://sqlite.org/c3ref/blob_close.html
+func (b *Blob) Close() error {
+	if b == nil || b.handle == 0 {
+		return nil
+	}
+
+	r := b.c.call("sqlite3_blob_close", uint64(b.handle))
+
+	b.handle = 0
+	return b.c.error(r)
+}
+
+// Size returns the size of the BLOB in bytes.
+//
+// https://sqlite.org/c3ref/blob_bytes.html
+func (b *Blob) Size() int64 {
+	return b.bytes
+}
+
+// Read implements the [io.Reader] interface.
+//
+// https://sqlite.org/c3ref/blob_read.html
+func (b *Blob) Read(p []byte) (n int, err error) {
+	if b.offset >= b.bytes {
+		return 0, io.EOF
+	}
+
+	avail := b.bytes - b.offset
+	want := int64(len(p))
+	if want > avail {
+		want = avail
+	}
+
+	defer b.c.arena.mark()()
+	ptr := b.c.arena.new(uint64(want))
+
+	r := b.c.call("sqlite3_blob_read", uint64(b.handle),
+		uint64(ptr), uint64(want), uint64(b.offset))
+	err = b.c.error(r)
+	if err != nil {
+		return 0, err
+	}
+	b.offset += want
+	if b.offset >= b.bytes {
+		err = io.EOF
+	}
+
+	copy(p, util.View(b.c.mod, ptr, uint64(want)))
+	return int(want), err
+}
+
+// WriteTo implements the [io.WriterTo] interface.
+//
+// https://sqlite.org/c3ref/blob_read.html
+func (b *Blob) WriteTo(w io.Writer) (n int64, err error) {
+	if b.offset >= b.bytes {
+		return 0, nil
+	}
+
+	want := int64(1024 * 1024)
+	avail := b.bytes - b.offset
+	if want > avail {
+		want = avail
+	}
+
+	defer b.c.arena.mark()()
+	ptr := b.c.arena.new(uint64(want))
+
+	for want > 0 {
+		r := b.c.call("sqlite3_blob_read", uint64(b.handle),
+			uint64(ptr), uint64(want), uint64(b.offset))
+		err = b.c.error(r)
+		if err != nil {
+			return n, err
+		}
+
+		mem := util.View(b.c.mod, ptr, uint64(want))
+		m, err := w.Write(mem[:want])
+		b.offset += int64(m)
+		n += int64(m)
+		if err != nil {
+			return n, err
+		}
+		if int64(m) != want {
+			return n, io.ErrShortWrite
+		}
+
+		avail = b.bytes - b.offset
+		if want > avail {
+			want = avail
+		}
+	}
+	return n, nil
+}
+
+// Write implements the [io.Writer] interface.
+//
+// https://sqlite.org/c3ref/blob_write.html
+func (b *Blob) Write(p []byte) (n int, err error) {
+	defer b.c.arena.mark()()
+	ptr := b.c.arena.bytes(p)
+
+	r := b.c.call("sqlite3_blob_write", uint64(b.handle),
+		uint64(ptr), uint64(len(p)), uint64(b.offset))
+	err = b.c.error(r)
+	if err != nil {
+		return 0, err
+	}
+	b.offset += int64(len(p))
+	return len(p), nil
+}
+
+// ReadFrom implements the [io.ReaderFrom] interface.
+//
+// https://sqlite.org/c3ref/blob_write.html
+func (b *Blob) ReadFrom(r io.Reader) (n int64, err error) {
+	want := int64(1024 * 1024)
+	avail := b.bytes - b.offset
+	if l, ok := r.(*io.LimitedReader); ok && want > l.N {
+		want = l.N
+	}
+	if want > avail {
+		want = avail
+	}
+	if want < 1 {
+		want = 1
+	}
+
+	defer b.c.arena.mark()()
+	ptr := b.c.arena.new(uint64(want))
+
+	for {
+		mem := util.View(b.c.mod, ptr, uint64(want))
+		m, err := r.Read(mem[:want])
+		if m > 0 {
+			r := b.c.call("sqlite3_blob_write", uint64(b.handle),
+				uint64(ptr), uint64(m), uint64(b.offset))
+			err := b.c.error(r)
+			if err != nil {
+				return n, err
+			}
+			b.offset += int64(m)
+			n += int64(m)
+		}
+		if err == io.EOF {
+			return n, nil
+		}
+		if err != nil {
+			return n, err
+		}
+
+		avail = b.bytes - b.offset
+		if want > avail {
+			want = avail
+		}
+		if want < 1 {
+			want = 1
+		}
+	}
+}
+
+// Seek implements the [io.Seeker] interface.
+func (b *Blob) Seek(offset int64, whence int) (int64, error) {
+	switch whence {
+	default:
+		return 0, util.WhenceErr
+	case io.SeekStart:
+		break
+	case io.SeekCurrent:
+		offset += b.offset
+	case io.SeekEnd:
+		offset += b.bytes
+	}
+	if offset < 0 {
+		return 0, util.OffsetErr
+	}
+	b.offset = offset
+	return offset, nil
+}
+
+// Reopen moves a BLOB handle to a new row of the same database table.
+//
+// https://sqlite.org/c3ref/blob_reopen.html
+func (b *Blob) Reopen(row int64) error {
+	err := b.c.error(b.c.call("sqlite3_blob_reopen", uint64(b.handle), uint64(row)))
+	b.bytes = int64(b.c.call("sqlite3_blob_bytes", uint64(b.handle)))
+	b.offset = 0
+	return err
+}