union: Implement multiple writable remotes

backend/union/policy/rand.go

@@ -0,0 +1,83 @@
+package policy
+
+import (
+	"context"
+	"math/rand"
+
+	"github.com/rclone/rclone/backend/union/upstream"
+	"github.com/rclone/rclone/fs"
+)
+
+func init() {
+	registerPolicy("rand", &Rand{})
+}
+
+// Rand stands for random
+// Calls all and then randomizes. Returns one candidate.
+type Rand struct {
+	All
+}
+
+func (p *Rand) rand(upstreams []*upstream.Fs) *upstream.Fs {
+	return upstreams[rand.Intn(len(upstreams))]
+}
+
+func (p *Rand) randEntries(entries []upstream.Entry) upstream.Entry {
+	return entries[rand.Intn(len(entries))]
+}
+
+// Action category policy, governing the modification of files and directories
+func (p *Rand) Action(ctx context.Context, upstreams []*upstream.Fs, path string) ([]*upstream.Fs, error) {
+	upstreams, err := p.All.Action(ctx, upstreams, path)
+	if err != nil {
+		return nil, err
+	}
+	return []*upstream.Fs{p.rand(upstreams)}, nil
+}
+
+// ActionEntries is ACTION category policy but receving a set of candidate entries
+func (p *Rand) ActionEntries(entries ...upstream.Entry) ([]upstream.Entry, error) {
+	entries, err := p.All.ActionEntries(entries...)
+	if err != nil {
+		return nil, err
+	}
+	return []upstream.Entry{p.randEntries(entries)}, nil
+}
+
+// Create category policy, governing the creation of files and directories
+func (p *Rand) Create(ctx context.Context, upstreams []*upstream.Fs, path string) ([]*upstream.Fs, error) {
+	upstreams, err := p.All.Create(ctx, upstreams, path)
+	if err != nil {
+		return nil, err
+	}
+	return []*upstream.Fs{p.rand(upstreams)}, nil
+}
+
+// CreateEntries is CREATE category policy but receving a set of candidate entries
+func (p *Rand) CreateEntries(entries ...upstream.Entry) ([]upstream.Entry, error) {
+	entries, err := p.All.CreateEntries(entries...)
+	if err != nil {
+		return nil, err
+	}
+	return []upstream.Entry{p.randEntries(entries)}, nil
+}
+
+// Search category policy, governing the access to files and directories
+func (p *Rand) Search(ctx context.Context, upstreams []*upstream.Fs, path string) (*upstream.Fs, error) {
+	if len(upstreams) == 0 {
+		return nil, fs.ErrorObjectNotFound
+	}
+	upstreams, err := p.epall(ctx, upstreams, path)
+	if err != nil {
+		return nil, err
+	}
+	return p.rand(upstreams), nil
+}
+
+// SearchEntries is SEARCH category policy but receving a set of candidate entries
+func (p *Rand) SearchEntries(entries ...upstream.Entry) (upstream.Entry, error) {
+	if len(entries) == 0 {
+		return nil, fs.ErrorObjectNotFound
+	}
+	return p.randEntries(entries), nil
+}