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    /// Don't use mmap and instead write an in-memory buffer to a file when this
37    /// buffer is closed.
38    F_no_mmap = 2,
39  };
40
41  /// Factory method to create an OutputBuffer object which manages a read/write
42  /// buffer of the specified size. When committed, the buffer will be written
43  /// to the file at the specified path.
44  ///
45  /// When F_modify is specified and \p FilePath refers to an existing on-disk
46  /// file \p Size may be set to -1, in which case the entire file is used.
47  /// Otherwise, the file shrinks or grows as necessary based on the value of
48  /// \p Size.  It is an error to specify F_modify and Size=-1 if \p FilePath
49  /// does not exist.
50  static Expected<std::unique_ptr<FileOutputBuffer>>
51  create(StringRef FilePath, size_t Size, unsigned Flags = 0);
52
53  /// Returns a pointer to the start of the buffer.
54  virtual uint8_t *getBufferStart() const = 0;
55
56  /// Returns a pointer to the end of the buffer.
57  virtual uint8_t *getBufferEnd() const = 0;
58
59  /// Returns size of the buffer.
60  virtual size_t getBufferSize() const = 0;
61
62  /// Returns path where file will show up if buffer is committed.
63  StringRef getPath() const { return FinalPath; }
64
65  /// Flushes the content of the buffer to its file and deallocates the
66  /// buffer.  If commit() is not called before this object's destructor
67  /// is called, the file is deleted in the destructor. The optional parameter
68  /// is used if it turns out you want the file size to be smaller than
69  /// initially requested.
70  virtual Error commit() = 0;
71
72  /// If this object was previously committed, the destructor just deletes
73  /// this object.  If this object was not committed, the destructor
74  /// deallocates the buffer and the target file is never written.
75  virtual ~FileOutputBuffer() {}
76
77  /// This removes the temporary file (unless it already was committed)
78  /// but keeps the memory mapping alive.
79  virtual void discard() {}
80
81protected:
82  FileOutputBuffer(StringRef Path) : FinalPath(Path) {}
83
84  std::string FinalPath;
85};
86} // end namespace llvm
87
88#endif
89