1 package p9p
2 
3 import (
4 	"io"
5 
6 	"context"
7 )
8 
9 // ReaddirAll reads all the directory entries for the resource fid.
10 func ReaddirAll(session Session, fid Fid) ([]Dir, error) {
11 	panic("not implemented")
12 }
13 
14 // Readdir helps one to implement the server-side of Session.Read on
15 // directories.
16 type Readdir struct {
17 	nextfn func() (Dir, error)
18 	buf    *Dir // one-item buffer
19 	codec  Codec
20 	offset int64
21 }
22 
23 // NewReaddir returns a new Readdir to assist implementing server-side Readdir.
24 // The codec will be used to decode messages with Dir entries. The provided
25 // function next will be called until io.EOF is returned.
26 func NewReaddir(codec Codec, next func() (Dir, error)) *Readdir {
27 	return &Readdir{
28 		nextfn: next,
29 		codec:  codec,
30 	}
31 }
32 
33 // NewFixedReaddir returns a Readdir that will returned a fixed set of
34 // directory entries.
35 func NewFixedReaddir(codec Codec, dir []Dir) *Readdir {
36 	dirs := make([]Dir, len(dir))
37 	copy(dirs, dir) // make our own copy!
38 
39 	return NewReaddir(codec,
40 		func() (Dir, error) {
41 			if len(dirs) == 0 {
42 				return Dir{}, io.EOF
43 			}
44 
45 			d := dirs[0]
46 			dirs = dirs[1:]
47 			return d, nil
48 		})
49 }
50 
51 func (rd *Readdir) Read(ctx context.Context, p []byte, offset int64) (n int, err error) {
52 	if rd.offset != offset {
53 		return 0, ErrBadoffset
54 	}
55 
56 	p = p[:0:len(p)]
57 	for len(p) < cap(p) {
58 		var d Dir
59 		if rd.buf != nil {
60 			d = *rd.buf
61 			rd.buf = nil
62 		} else {
63 			d, err = rd.nextfn()
64 			if err != nil {
65 				goto done
66 			}
67 		}
68 
69 		var dp []byte
70 		dp, err = rd.codec.Marshal(d)
71 		if err != nil {
72 			goto done
73 		}
74 
75 		if len(p)+len(dp) > cap(p) {
76 			// will over fill buffer. save item and exit.
77 			rd.buf = &d
78 			goto done
79 		}
80 
81 		p = append(p, dp...)
82 	}
83 
84 done:
85 	if err == io.EOF {
86 		// Don't let io.EOF escape. EOF is indicated by a zero-length result
87 		// with no error.
88 		err = nil
89 	}
90 
91 	rd.offset += int64(len(p))
92 	return len(p), err
93 }