xref: /aosp_15_r20/external/pigweed/pw_stream/public/pw_stream/null_stream.h (revision 61c4878ac05f98d0ceed94b57d316916de578985)
1 // Copyright 2020 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // the License at
6 //
7 //     https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14 #pragma once
15 
16 #include <cstddef>
17 
18 #include "pw_bytes/span.h"
19 #include "pw_polyfill/language_feature_macros.h"
20 #include "pw_span/span.h"
21 #include "pw_status/status.h"
22 #include "pw_status/status_with_size.h"
23 #include "pw_stream/stream.h"
24 
25 namespace pw::stream {
26 
27 // Stream that silently drops written data and returns nothing on reads, similar
28 // to /dev/null.
29 class NullStream final : public SeekableReaderWriter {
30  public:
31   // Gives access to a global NullStream instance. It is not necessary to have
32   // multiple NullStream instances since they have no state and do nothing.
Instance()33   static NullStream& Instance() {
34     PW_CONSTINIT static NullStream stream;
35     return stream;
36   }
37 
38  private:
DoWrite(ConstByteSpan)39   Status DoWrite(ConstByteSpan) final { return OkStatus(); }
DoRead(ByteSpan)40   StatusWithSize DoRead(ByteSpan) final { return StatusWithSize::OutOfRange(); }
DoSeek(ptrdiff_t,Whence)41   Status DoSeek(ptrdiff_t, Whence) final { return OkStatus(); }
42 };
43 
44 // Same as NullStream, but tracks the number of bytes written.
45 class CountingNullStream final : public SeekableReaderWriter {
46  public:
CountingNullStream()47   constexpr CountingNullStream() : bytes_written_(0) {}
48 
bytes_written()49   size_t bytes_written() const { return bytes_written_; }
50 
51  private:
DoWrite(ConstByteSpan data)52   Status DoWrite(ConstByteSpan data) final {
53     bytes_written_ += data.size();
54     return OkStatus();
55   }
56 
DoRead(ByteSpan)57   StatusWithSize DoRead(ByteSpan) final { return StatusWithSize::OutOfRange(); }
DoSeek(ptrdiff_t,Whence)58   Status DoSeek(ptrdiff_t, Whence) final { return OkStatus(); }
59 
60   size_t bytes_written_;
61 };
62 
63 }  // namespace pw::stream
64