FileOutputBuffer.h revision 353358 
1//=== FileOutputBuffer.h - File Output Buffer -------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// Utility for creating a in-memory buffer that will be written to a file.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_SUPPORT_FILEOUTPUTBUFFER_H
14#define LLVM_SUPPORT_FILEOUTPUTBUFFER_H
15
16#include "llvm/ADT/SmallString.h"
17#include "llvm/ADT/StringRef.h"
18#include "llvm/Support/DataTypes.h"
19#include "llvm/Support/Error.h"
20#include "llvm/Support/FileSystem.h"
21
22namespace llvm {
23/// FileOutputBuffer - This interface provides simple way to create an in-memory
24/// buffer which will be written to a file. During the lifetime of these
25/// objects, the content or existence of the specified file is undefined. That
26/// is, creating an OutputBuffer for a file may immediately remove the file.
27/// If the FileOutputBuffer is committed, the target file's content will become
28/// the buffer content at the time of the commit.  If the FileOutputBuffer is
29/// not committed, the file will be deleted in the FileOutputBuffer destructor.
30class FileOutputBuffer {
31public:
32  enum {
33    /// set the 'x' bit on the resulting file
34    F_executable = 1,
35  };
36
37  /// Factory method to create an OutputBuffer object which manages a read/write
38  /// buffer of the specified size. When committed, the buffer will be written
39  /// to the file at the specified path.
40  ///
41  /// When F_modify is specified and \p FilePath refers to an existing on-disk
42  /// file \p Size may be set to -1, in which case the entire file is used.
43  /// Otherwise, the file shrinks or grows as necessary based on the value of
44  /// \p Size.  It is an error to specify F_modify and Size=-1 if \p FilePath
45  /// does not exist.
46  static Expected<std::unique_ptr<FileOutputBuffer>>
47  create(StringRef FilePath, size_t Size, unsigned Flags = 0);
48
49  /// Returns a pointer to the start of the buffer.
50  virtual uint8_t *getBufferStart() const = 0;
51
52  /// Returns a pointer to the end of the buffer.
53  virtual uint8_t *getBufferEnd() const = 0;
54
55  /// Returns size of the buffer.
56  virtual size_t getBufferSize() const = 0;
57
58  /// Returns path where file will show up if buffer is committed.
59  StringRef getPath() const { return FinalPath; }
60
61  /// Flushes the content of the buffer to its file and deallocates the
62  /// buffer.  If commit() is not called before this object's destructor
63  /// is called, the file is deleted in the destructor. The optional parameter
64  /// is used if it turns out you want the file size to be smaller than
65  /// initially requested.
66  virtual Error commit() = 0;
67
68  /// If this object was previously committed, the destructor just deletes
69  /// this object.  If this object was not committed, the destructor
70  /// deallocates the buffer and the target file is never written.
71  virtual ~FileOutputBuffer() {}
72
73  /// This removes the temporary file (unless it already was committed)
74  /// but keeps the memory mapping alive.
75  virtual void discard() {}
76
77protected:
78  FileOutputBuffer(StringRef Path) : FinalPath(Path) {}
79
80  std::string FinalPath;
81};
82} // end namespace llvm
83
84#endif
85