xref: /aosp_15_r20/external/tink/cc/input_stream.h (revision e7b1675dde1b92d52ec075b0a92829627f2c52a5)
1 // Copyright 2018 Google Inc.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 //     http://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,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 //
15 ///////////////////////////////////////////////////////////////////////////////
16 
17 #ifndef TINK_INPUT_STREAM_H_
18 #define TINK_INPUT_STREAM_H_
19 
20 #include "tink/util/status.h"
21 #include "tink/util/statusor.h"
22 
23 namespace crypto {
24 namespace tink {
25 
26 // Abstract interface similar to an input stream, and to
27 // Protocol Buffers' google::protobuf::io::ZeroCopyInputStream.
28 class InputStream {
29  public:
30   InputStream() = default;
31   virtual ~InputStream() = default;
32 
33   // Obtains a chunk of data from the stream.
34   //
35   // Preconditions:
36   // * "data" is not NULL.
37   //
38   // Postconditions:
39   // * If the returned status is not OK, there is no more data to return
40   //   (status equal to OUT_OF_RANGE) or an error occurred
41   //   (status not in {OK, OUT_OF_RANGE}.  All errors are permanent.
42   // * Otherwise, the returned value is the number of bytes read and "data"
43   //   points to a buffer containing these bytes.
44   // * Ownership of this buffer remains with the stream, and the buffer
45   //   remains valid only until some other non-const method of the stream
46   //   is called or the stream is destroyed.
47   // * It is legal for the returned buffer to have zero size, as long as
48   //   repeatedly calling Next() eventually yields a buffer with non-zero
49   //   size or a non-OK status.
50   virtual crypto::tink::util::StatusOr<int> Next(const void** data) = 0;
51 
52   // Backs up a number of bytes, so that the next call to Next() returns
53   // data again that was already returned by the last call to Next().
54   // This is useful when writing procedures that are only supposed to read
55   // up to a certain point in the input, then return.  If Next() returns a
56   // buffer that goes beyond what you wanted to read, you can use BackUp()
57   // to return to the point where you intended to finish.
58   //
59   // Preconditions:
60   // * The last call to Next() must have returned status OK.
61   //   If there was no Next()-call yet, or the last one failed,
62   //   BackUp()-call is ignored.
63   // * count must be less than or equal to the size of the last buffer
64   //   returned by Next().  Non-positive count is ignored (no action on this
65   //   stream), and count larger than the size of the last buffer is treated
66   //   as equal to the size of the last buffer.
67   //
68   // Postconditions:
69   // * The last "count" bytes of the last buffer returned by Next() will be
70   //   pushed back into the stream.  Subsequent calls to Next() will return
71   //   the same data again before producing new data.
72   // * Repeated calls to BackUp() accumulate:
73   //      BackUp(a);
74   //      Backup(b);
75   //   is equivalent to
76   //      Backup(c);
77   //   with c = max(0, a) + max(0, b).
78   // * The actual result of BackUp()-call can be verified via Position().
79   virtual void BackUp(int count) = 0;
80 
81   // Returns the current byte position in the stream.
82   //
83   // Preconditions:
84   // * The last call to Next() ended with status in {OK, OUT_OF_RANGE}.
85   //
86   // Postconditions:
87   // * Position equal to i means that the next call to Next() will
88   //   return a data buffer starting at (i+1)st byte of the stream (if any).
89   // * If the last call to Next() reached end of stream (status OUT_OF_RANGE),
90   //   then returned value is the total number of bytes in the stream.
91   // * If the last call to Next() ended with a failure, -1 is returned;
92   virtual int64_t Position() const = 0;
93 };
94 
95 }  // namespace tink
96 }  // namespace crypto
97 
98 #endif  // TINK_INPUT_STREAM_H_
99