include/llvm/Support/FileOutputBuffer.h

   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
  22 namespace 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.
  30 class FileOutputBuffer {
  31 public:
  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
  77 protected:
  78   FileOutputBuffer(StringRef Path) : FinalPath(Path) {}
  79
  80   std::string FinalPath;
  81 };
  82 } // end namespace llvm
  83
  84 #endif