coreapi: get going, add Cat() and Ls()

License: MIT
Signed-off-by: Lars Gierth <larsg@systemli.org>

interface.go

+package iface
+
+import (
+	"context"
+	"errors"
+	"io"
+
+	cid "gx/ipfs/QmXfiyr2RWEXpVDdaYnD2HNiBk6UBddsvEP4RPfXb6nGqY/go-cid"
+)
+
+// type CoreAPI interface {
+// 	ID() CoreID
+// 	Version() CoreVersion
+// }
+
+type Link struct {
+	Name string
+	Size uint64
+	Cid  *cid.Cid
+}
+
+type Reader interface {
+	io.ReadSeeker
+	io.Closer
+}
+
+type UnixfsAPI interface {
+	Cat(context.Context, string) (Reader, error)
+	Ls(context.Context, string) ([]*Link, error)
+}
+
+// type ObjectAPI interface {
+// 	New() (cid.Cid, Object)
+// 	Get(string) (Object, error)
+// 	Links(string) ([]*Link, error)
+// 	Data(string) (Reader, error)
+// 	Stat(string) (ObjectStat, error)
+// 	Put(Object) (cid.Cid, error)
+// 	SetData(string, Reader) (cid.Cid, error)
+// 	AppendData(string, Data) (cid.Cid, error)
+// 	AddLink(string, string, string) (cid.Cid, error)
+// 	RmLink(string, string) (cid.Cid, error)
+// }
+
+// type ObjectStat struct {
+// 	Cid            cid.Cid
+// 	NumLinks       int
+// 	BlockSize      int
+// 	LinksSize      int
+// 	DataSize       int
+// 	CumulativeSize int
+// }
+
+var ErrIsDir = errors.New("object is a directory")
+var ErrIsNonDag = errors.New("not a merkledag object")
+var ErrOffline = errors.New("can't resolve, ipfs node is offline")