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// Package chain provides a wrapper object storage backend to query a chain of
// backends.
package chain
import (
"errors"
"fmt"
"io"
"codeberg.org/lindenii/furgit/objectid"
"codeberg.org/lindenii/furgit/objectstore"
"codeberg.org/lindenii/furgit/objecttype"
)
// Chain queries multiple object databases in order.
type Chain struct {
backends []objectstore.Store
}
// New creates an ordered object database chain.
func New(backends ...objectstore.Store) *Chain {
return &Chain{
backends: append([]objectstore.Store(nil), backends...),
}
}
// ReadBytesFull reads a full serialized object from the first backend that has it.
func (chain *Chain) ReadBytesFull(id objectid.ObjectID) ([]byte, error) {
for i, backend := range chain.backends {
if backend == nil {
continue
}
full, err := backend.ReadBytesFull(id)
if err == nil {
return full, nil
}
if errors.Is(err, objectstore.ErrObjectNotFound) {
continue
}
return nil, fmt.Errorf("objectstore: backend %d read bytes full: %w", i, err)
}
return nil, objectstore.ErrObjectNotFound
}
// ReadBytesContent reads an object's type and content bytes from the first backend that has it.
func (chain *Chain) ReadBytesContent(id objectid.ObjectID) (objecttype.Type, []byte, error) {
for i, backend := range chain.backends {
if backend == nil {
continue
}
ty, content, err := backend.ReadBytesContent(id)
if err == nil {
return ty, content, nil
}
if errors.Is(err, objectstore.ErrObjectNotFound) {
continue
}
return objecttype.TypeInvalid, nil, fmt.Errorf("objectstore: backend %d read bytes content: %w", i, err)
}
return objecttype.TypeInvalid, nil, objectstore.ErrObjectNotFound
}
// ReadReaderFull reads a full serialized object stream from the first backend that has it.
func (chain *Chain) ReadReaderFull(id objectid.ObjectID) (io.ReadCloser, error) {
for i, backend := range chain.backends {
if backend == nil {
continue
}
reader, err := backend.ReadReaderFull(id)
if err == nil {
return reader, nil
}
if errors.Is(err, objectstore.ErrObjectNotFound) {
continue
}
return nil, fmt.Errorf("objectstore: backend %d read reader full: %w", i, err)
}
return nil, objectstore.ErrObjectNotFound
}
// ReadReaderContent reads an object's type, declared content length, and content stream from the first backend that has it.
func (chain *Chain) ReadReaderContent(id objectid.ObjectID) (objecttype.Type, int64, io.ReadCloser, error) {
for i, backend := range chain.backends {
if backend == nil {
continue
}
ty, size, reader, err := backend.ReadReaderContent(id)
if err == nil {
return ty, size, reader, nil
}
if errors.Is(err, objectstore.ErrObjectNotFound) {
continue
}
return objecttype.TypeInvalid, 0, nil, fmt.Errorf("objectstore: backend %d read reader content: %w", i, err)
}
return objecttype.TypeInvalid, 0, nil, objectstore.ErrObjectNotFound
}
// ReadSize reads object content length from the first backend that has it.
func (chain *Chain) ReadSize(id objectid.ObjectID) (int64, error) {
for i, backend := range chain.backends {
if backend == nil {
continue
}
size, err := backend.ReadSize(id)
if err == nil {
return size, nil
}
if errors.Is(err, objectstore.ErrObjectNotFound) {
continue
}
return 0, fmt.Errorf("objectstore: backend %d read size: %w", i, err)
}
return 0, objectstore.ErrObjectNotFound
}
// ReadHeader reads object header data from the first backend that has it.
func (chain *Chain) ReadHeader(id objectid.ObjectID) (objecttype.Type, int64, error) {
for i, backend := range chain.backends {
if backend == nil {
continue
}
ty, size, err := backend.ReadHeader(id)
if err == nil {
return ty, size, nil
}
if errors.Is(err, objectstore.ErrObjectNotFound) {
continue
}
return objecttype.TypeInvalid, 0, fmt.Errorf("objectstore: backend %d read header: %w", i, err)
}
return objecttype.TypeInvalid, 0, objectstore.ErrObjectNotFound
}
// Close closes all backends and joins close errors.
func (chain *Chain) Close() error {
var errs []error
for _, backend := range chain.backends {
if backend == nil {
continue
}
if err := backend.Close(); err != nil {
errs = append(errs, err)
}
}
return errors.Join(errs...)
}
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