gcc/d/dmd/common/file.d - gcc - Git at Google

 /**
  * File utilities.
  *
  * Functions and objects dedicated to file I/O and management. TODO: Move here artifacts
  * from places such as root/ so both the frontend and the backend have access to them.
  *
  * Copyright: Copyright (C) 1999-2022 by The D Language Foundation, All Rights Reserved
  * Authors:   Walter Bright, https://www.digitalmars.com
  * License:   $(LINK2 https://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
  * Source:    $(LINK2 https://github.com/dlang/dmd/blob/master/src/dmd/common/file.d, common/_file.d)
  * Documentation: https://dlang.org/phobos/dmd_common_file.html
  * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/dmd/common/file.d
  */

 module dmd.common.file;

 import core.stdc.errno : errno;
 import core.stdc.stdio : fprintf, remove, rename, stderr;
 import core.stdc.stdlib : exit;
 import core.stdc.string : strerror;
 import core.sys.windows.winbase;
 import core.sys.windows.winnt;
 import core.sys.posix.fcntl;
 import core.sys.posix.unistd;

 import dmd.common.string;

 nothrow:

 /**
 Encapsulated management of a memory-mapped file.

 Params:
 Datum = the mapped data type: Use a POD of size 1 for read/write mapping
 and a `const` version thereof for read-only mapping. Other primitive types
 should work, but have not been yet tested.
 */
 struct FileMapping(Datum)
 {
     static assert(__traits(isPOD, Datum) && Datum.sizeof == 1,
         "Not tested with other data types yet. Add new types with care.");

     version(Posix) enum invalidHandle = -1;
     else version(Windows) enum invalidHandle = INVALID_HANDLE_VALUE;

     // state {
     /// Handle of underlying file
     private auto handle = invalidHandle;
     /// File mapping object needed on Windows
     version(Windows) private HANDLE fileMappingObject = invalidHandle;
     /// Memory-mapped array
     private Datum[] data;
     /// Name of underlying file, zero-terminated
     private const(char)* name;
     // state }

   nothrow:

     /**
     Open `filename` and map it in memory. If `Datum` is `const`, opens for
     read-only and maps the content in memory; no error is issued if the file
     does not exist. This makes it easy to treat a non-existing file as empty.

     If `Datum` is mutable, opens for read/write (creates file if it does not
     exist) and fails fatally on any error.

     Due to quirks in `mmap`, if the file is empty, `handle` is valid but `data`
     is `null`. This state is valid and accounted for.

     Params:
     filename = the name of the file to be mapped in memory
     */
     this(const char* filename)
     {
         version (Posix)
         {
             import core.sys.posix.sys.mman;
             import core.sys.posix.fcntl : open, O_CREAT, O_RDONLY, O_RDWR, S_IRGRP, S_IROTH, S_IRUSR, S_IWUSR;

             handle = open(filename, is(Datum == const) ? O_RDONLY : (O_CREAT | O_RDWR),
                 S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);

             if (handle == invalidHandle)
             {
                 static if (is(Datum == const))
                 {
                     // No error, nonexisting file in read mode behaves like an empty file.
                     return;
                 }
                 else
                 {
                     fprintf(stderr, "open(\"%s\") failed: %s\n", filename, strerror(errno));
                     exit(1);
                 }
             }

             const size = fileSize(handle);

             if (size > 0 && size != ulong.max && size <= size_t.max)
             {
                 auto p = mmap(null, cast(size_t) size, is(Datum == const) ? PROT_READ : PROT_WRITE, MAP_SHARED, handle, 0);
                 if (p == MAP_FAILED)
                 {
                     fprintf(stderr, "mmap(null, %zu) for \"%s\" failed: %s\n", cast(size_t) size, filename, strerror(errno));
                     exit(1);
                 }
                 // The cast below will always work because it's gated by the `size <= size_t.max` condition.
                 data = cast(Datum[]) p[0 .. cast(size_t) size];
             }
         }
         else version(Windows)
         {
             static if (is(Datum == const))
             {
                 enum createFileMode = GENERIC_READ;
                 enum openFlags = OPEN_EXISTING;
             }
             else
             {
                 enum createFileMode = GENERIC_READ | GENERIC_WRITE;
                 enum openFlags = CREATE_ALWAYS;
             }

             handle = filename.asDString.extendedPathThen!(p => CreateFileW(p.ptr, createFileMode, 0, null, openFlags, FILE_ATTRIBUTE_NORMAL, null));
             if (handle == invalidHandle)
             {
                 static if (is(Datum == const))
                 {
                     return;
                 }
                 else
                 {
                     fprintf(stderr, "CreateFileW() failed for \"%s\": %d\n", filename, GetLastError());
                     exit(1);
                 }
             }
             createMapping(filename, fileSize(handle));
         }
         else static assert(0);

         // Save the name for later. Technically there's no need: on Linux one can use readlink on /proc/self/fd/NNN.
         // On BSD and OSX one can use fcntl with F_GETPATH. On Windows one can use GetFileInformationByHandleEx.
         // But just saving the name is simplest, fastest, and most portable...
         import core.stdc.string : strlen;
         import core.stdc.stdlib : malloc;
         import core.stdc.string : memcpy;
         const totalNameLength = filename.strlen() + 1;
         auto namex = cast(char*) malloc(totalNameLength);
         if (!namex)
         {
             fprintf(stderr, "FileMapping: Out of memory.");
             exit(1);
         }
         name = cast(char*) memcpy(namex, filename, totalNameLength);
     }

     /**
     Common code factored opportunistically. Windows only. Assumes `handle` is
     already pointing to an opened file. Initializes the `fileMappingObject`
     and `data` members.

     Params:
     filename = the file to be mapped
     size = the size of the file in bytes
     */
     version(Windows) private void createMapping(const char* filename, ulong size)
     {
         assert(size <= size_t.max || size == ulong.max);
         assert(handle != invalidHandle);
         assert(data is null);
         assert(fileMappingObject == invalidHandle);

         if (size == 0 || size == ulong.max)
             return;

         static if (is(Datum == const))
         {
             enum fileMappingFlags = PAGE_READONLY;
             enum mapViewFlags = FILE_MAP_READ;
         }
         else
         {
             enum fileMappingFlags = PAGE_READWRITE;
             enum mapViewFlags = FILE_MAP_WRITE;
         }

         fileMappingObject = CreateFileMappingW(handle, null, fileMappingFlags, 0, 0, null);
         if (!fileMappingObject)
         {
             fprintf(stderr, "CreateFileMappingW(%p) failed for %llu bytes of \"%s\": %d\n",
                 handle, size, filename, GetLastError());
             fileMappingObject = invalidHandle;  // by convention always use invalidHandle, not null
             exit(1);
         }
         auto p = MapViewOfFile(fileMappingObject, mapViewFlags, 0, 0, 0);
         if (!p)
         {
             fprintf(stderr, "MapViewOfFile() failed for \"%s\": %d\n", filename, GetLastError());
             exit(1);
         }
         data = cast(Datum[]) p[0 .. cast(size_t) size];
     }

     // Not copyable or assignable (for now).
     @disable this(const FileMapping!Datum rhs);
     @disable void opAssign(const ref FileMapping!Datum rhs);

     /**
     Frees resources associated with this mapping. However, it does not deallocate the name.
     */
     ~this() pure nothrow
     {
         if (!active)
             return;
         fakePure({
             version (Posix)
             {
                 import core.sys.posix.sys.mman : munmap;
                 import core.sys.posix.unistd : close;

                 // Cannot call fprintf from inside a destructor, so exiting silently.

                 if (data.ptr && munmap(cast(void*) data.ptr, data.length) != 0)
                 {
                     exit(1);
                 }
                 data = null;
                 if (handle != invalidHandle && close(handle) != 0)
                 {
                     exit(1);
                 }
                 handle = invalidHandle;
             }
             else version(Windows)
             {
                 if (data.ptr !is null && UnmapViewOfFile(cast(void*) data.ptr) == 0)
                 {
                     exit(1);
                 }
                 data = null;
                 if (fileMappingObject != invalidHandle && CloseHandle(fileMappingObject) == 0)
                 {
                     exit(1);
                 }
                 fileMappingObject = invalidHandle;
                 if (handle != invalidHandle && CloseHandle(handle) == 0)
                 {
                     exit(1);
                 }
                 handle = invalidHandle;
             }
             else static assert(0);
         });
     }

     /**
     Returns the zero-terminated file name associated with the mapping. Can NOT
     be saved beyond the lifetime of `this`.
     */
     private const(char)* filename() const pure @nogc @safe nothrow { return name; }

     /**
     Frees resources associated with this mapping. However, it does not deallocate the name.
     Reinitializes `this` as a fresh object that can be reused.
     */
     void close()
     {
         __dtor();
         handle = invalidHandle;
         version(Windows) fileMappingObject = invalidHandle;
         data = null;
         name = null;
     }

     /**
     Deletes the underlying file and frees all resources associated.
     Reinitializes `this` as a fresh object that can be reused.

     This function does not abort if the file cannot be deleted, but does print
     a message on `stderr` and returns `false` to the caller. The underlying
     rationale is to give the caller the option to continue execution if
     deleting the file is not important.

     Returns: `true` iff the file was successfully deleted. If the file was not
     deleted, prints a message to `stderr` and returns `false`.
     */
     static if (!is(Datum == const))
     bool discard()
     {
         // Truncate file to zero so unflushed buffers are not flushed unnecessarily.
         resize(0);
         auto deleteme = name;
         close();
         // In-memory resource freed, now get rid of the underlying temp file.
         version(Posix)
         {
             import core.sys.posix.unistd : unlink;
             if (unlink(deleteme) != 0)
             {
                 fprintf(stderr, "unlink(\"%s\") failed: %s\n", filename, strerror(errno));
                 return false;
             }
         }
         else version(Windows)
         {
             import core.sys.windows.winbase;
             if (deleteme.asDString.extendedPathThen!(p => DeleteFileW(p.ptr)) == 0)
             {
                 fprintf(stderr, "DeleteFileW error %d\n", GetLastError());
                 return false;
             }
         }
         else static assert(0);
         return true;
     }

     /**
     Queries whether `this` is currently associated with a file.

     Returns: `true` iff there is an active mapping.
     */
     bool active() const pure @nogc nothrow
     {
         return handle !is invalidHandle;
     }

     /**
     Queries the length of the file associated with this mapping.  If not
     active, returns 0.

     Returns: the length of the file, or 0 if no file associated.
     */
     size_t length() const pure @nogc @safe nothrow { return data.length; }

     /**
     Get a slice to the contents of the entire file.

     Returns: the contents of the file. If not active, returns the `null` slice.
     */
     auto opSlice() pure @nogc @safe nothrow { return data; }

     /**
     Resizes the file and mapping to the specified `size`.

     Params:
     size = new length requested
     */
     static if (!is(Datum == const))
     void resize(size_t size) pure
     {
         assert(handle != invalidHandle);
         fakePure({
             version(Posix)
             {
                 import core.sys.posix.unistd : ftruncate;
                 import core.sys.posix.sys.mman;

                 if (data.length)
                 {
                     assert(data.ptr, "Corrupt memory mapping");
                     // assert(0) here because it would indicate an internal error
                     munmap(cast(void*) data.ptr, data.length) == 0 || assert(0);
                     data = null;
                 }
                 if (ftruncate(handle, size) != 0)
                 {
                     fprintf(stderr, "ftruncate() failed for \"%s\": %s\n", filename, strerror(errno));
                     exit(1);
                 }
                 if (size > 0)
                 {
                     auto p = mmap(null, size, PROT_WRITE, MAP_SHARED, handle, 0);
                     if (cast(ssize_t) p == -1)
                     {
                         fprintf(stderr, "mmap() failed for \"%s\": %s\n", filename, strerror(errno));
                         exit(1);
                     }
                     data = cast(Datum[]) p[0 .. size];
                 }
             }
             else version(Windows)
             {
                 // Per documentation, must unmap first.
                 if (data.length > 0 && UnmapViewOfFile(cast(void*) data.ptr) == 0)
                 {
                     fprintf(stderr, "UnmapViewOfFile(%p) failed for memory mapping of \"%s\": %d\n",
                         data.ptr, filename, GetLastError());
                     exit(1);
                 }
                 data = null;
                 if (fileMappingObject != invalidHandle && CloseHandle(fileMappingObject) == 0)
                 {
                     fprintf(stderr, "CloseHandle() failed for memory mapping of \"%s\": %d\n", filename, GetLastError());
                     exit(1);
                 }
                 fileMappingObject = invalidHandle;
                 LARGE_INTEGER biggie;
                 biggie.QuadPart = size;
                 if (SetFilePointerEx(handle, biggie, null, FILE_BEGIN) == 0 || SetEndOfFile(handle) == 0)
                 {
                     fprintf(stderr, "SetFilePointer() failed for \"%s\": %d\n", filename, GetLastError());
                     exit(1);
                 }
                 createMapping(name, size);
             }
             else static assert(0);
         });
     }

     /**
     Unconditionally and destructively moves the underlying file to `filename`.
     If the operation succeeds, returns true. Upon failure, prints a message to
     `stderr` and returns `false`. In all cases it closes the underlying file.

     Params: filename = zero-terminated name of the file to move to.

     Returns: `true` iff the operation was successful.
     */
     bool moveToFile(const char* filename)
     {
         assert(name !is null);

         // Fetch the name and then set it to `null` so it doesn't get deallocated
         auto oldname = name;
         import core.stdc.stdlib;
         scope(exit) free(cast(void*) oldname);
         name = null;
         close();

         // Rename the underlying file to the target, no copy necessary.
         version(Posix)
         {
             if (.rename(oldname, filename) != 0)
             {
                 fprintf(stderr, "rename(\"%s\", \"%s\") failed: %s\n", oldname, filename, strerror(errno));
                 return false;
             }
         }
         else version(Windows)
         {
             import core.sys.windows.winbase;
             auto r = oldname.asDString.extendedPathThen!(
                 p1 => filename.asDString.extendedPathThen!(p2 => MoveFileExW(p1.ptr, p2.ptr, MOVEFILE_REPLACE_EXISTING))
             );
             if (r == 0)
             {
                 fprintf(stderr, "MoveFileExW(\"%s\", \"%s\") failed: %d\n", oldname, filename, GetLastError());
                 return false;
             }
         }
         else static assert(0);
         return true;
     }
 }

 /// Write a file, returning `true` on success.
 extern(D) static bool writeFile(const(char)* name, const void[] data) nothrow
 {
     version (Posix)
     {
         int fd = open(name, O_CREAT | O_WRONLY | O_TRUNC, (6 << 6) | (4 << 3) | 4);
         if (fd == -1)
             goto err;
         if (.write(fd, data.ptr, data.length) != data.length)
             goto err2;
         if (close(fd) == -1)
             goto err;
         return true;
     err2:
         close(fd);
         .remove(name);
     err:
         return false;
     }
     else version (Windows)
     {
         DWORD numwritten; // here because of the gotos
         const nameStr = name.asDString;
         // work around Windows file path length limitation
         // (see documentation for extendedPathThen).
         HANDLE h = nameStr.extendedPathThen!
             (p => CreateFileW(p.ptr,
                                 GENERIC_WRITE,
                                 0,
                                 null,
                                 CREATE_ALWAYS,
                                 FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN,
                                 null));
         if (h == INVALID_HANDLE_VALUE)
             goto err;

         if (WriteFile(h, data.ptr, cast(DWORD)data.length, &numwritten, null) != TRUE)
             goto err2;
         if (numwritten != data.length)
             goto err2;
         if (!CloseHandle(h))
             goto err;
         return true;
     err2:
         CloseHandle(h);
         nameStr.extendedPathThen!(p => DeleteFileW(p.ptr));
     err:
         return false;
     }
     else
     {
         static assert(0);
     }
 }

 /// Touch a file to current date
 bool touchFile(const char* namez)
 {
     version (Windows)
     {
         FILETIME ft = void;
         SYSTEMTIME st = void;
         GetSystemTime(&st);
         SystemTimeToFileTime(&st, &ft);

         import core.stdc.string : strlen;

         // get handle to file
         HANDLE h = namez[0 .. namez.strlen()].extendedPathThen!(p => CreateFile(p.ptr,
             FILE_WRITE_ATTRIBUTES, FILE_SHARE_READ | FILE_SHARE_WRITE,
             null, OPEN_EXISTING,
             FILE_ATTRIBUTE_NORMAL, null));
         if (h == INVALID_HANDLE_VALUE)
             return false;

         const f = SetFileTime(h, null, null, &ft); // set last write time

         if (!CloseHandle(h))
             return false;

         return f != 0;
     }
     else version (Posix)
     {
         import core.sys.posix.utime;
         return utime(namez, null) == 0;
     }
     else
         static assert(0);
 }

 // Feel free to make these public if used elsewhere.
 /**
 Size of a file in bytes.
 Params: fd = file handle
 Returns: file size in bytes, or `ulong.max` on any error.
 */
 version (Posix)
 private ulong fileSize(int fd)
 {
     import core.sys.posix.sys.stat;
     stat_t buf;
     if (fstat(fd, &buf) == 0)
         return buf.st_size;
     return ulong.max;
 }

 /// Ditto
 version (Windows)
 private ulong fileSize(HANDLE fd)
 {
     ulong result;
     if (GetFileSizeEx(fd, cast(LARGE_INTEGER*) &result) == 0)
         return result;
     return ulong.max;
 }

 /**
 Runs a non-pure function or delegate as pure code. Use with caution.

 Params:
 fun = the delegate to run, usually inlined: `fakePure({ ... });`

 Returns: whatever `fun` returns.
 */
 private auto ref fakePure(F)(scope F fun) pure
 {
     mixin("alias PureFun = " ~ F.stringof ~ " pure;");
     return (cast(PureFun) fun)();
 }
	/**
	* File utilities.
	*
	* Functions and objects dedicated to file I/O and management. TODO: Move here artifacts
	* from places such as root/ so both the frontend and the backend have access to them.
	*
	* Copyright: Copyright (C) 1999-2022 by The D Language Foundation, All Rights Reserved
	* Authors: Walter Bright, https://www.digitalmars.com
	* License: $(LINK2 https://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
	* Source: $(LINK2 https://github.com/dlang/dmd/blob/master/src/dmd/common/file.d, common/_file.d)
	* Documentation: https://dlang.org/phobos/dmd_common_file.html
	* Coverage: https://codecov.io/gh/dlang/dmd/src/master/src/dmd/common/file.d
	*/

	module dmd.common.file;

	import core.stdc.errno : errno;
	import core.stdc.stdio : fprintf, remove, rename, stderr;
	import core.stdc.stdlib : exit;
	import core.stdc.string : strerror;
	import core.sys.windows.winbase;
	import core.sys.windows.winnt;
	import core.sys.posix.fcntl;
	import core.sys.posix.unistd;

	import dmd.common.string;

	nothrow:

	/**
	Encapsulated management of a memory-mapped file.

	Params:
	Datum = the mapped data type: Use a POD of size 1 for read/write mapping
	and a `const` version thereof for read-only mapping. Other primitive types
	should work, but have not been yet tested.
	*/
	struct FileMapping(Datum)
	{
	static assert(__traits(isPOD, Datum) && Datum.sizeof == 1,
	"Not tested with other data types yet. Add new types with care.");

	version(Posix) enum invalidHandle = -1;
	else version(Windows) enum invalidHandle = INVALID_HANDLE_VALUE;

	// state {
	/// Handle of underlying file
	private auto handle = invalidHandle;
	/// File mapping object needed on Windows
	version(Windows) private HANDLE fileMappingObject = invalidHandle;
	/// Memory-mapped array
	private Datum[] data;
	/// Name of underlying file, zero-terminated
	private const(char)* name;
	// state }

	nothrow:

	/**
	Open `filename` and map it in memory. If `Datum` is `const`, opens for
	read-only and maps the content in memory; no error is issued if the file
	does not exist. This makes it easy to treat a non-existing file as empty.

	If `Datum` is mutable, opens for read/write (creates file if it does not
	exist) and fails fatally on any error.

	Due to quirks in `mmap`, if the file is empty, `handle` is valid but `data`
	is `null`. This state is valid and accounted for.

	Params:
	filename = the name of the file to be mapped in memory
	*/
	this(const char* filename)
	{
	version (Posix)
	{
	import core.sys.posix.sys.mman;
	import core.sys.posix.fcntl : open, O_CREAT, O_RDONLY, O_RDWR, S_IRGRP, S_IROTH, S_IRUSR, S_IWUSR;

	handle = open(filename, is(Datum == const) ? O_RDONLY : (O_CREAT \| O_RDWR),
	S_IRUSR \| S_IWUSR \| S_IRGRP \| S_IROTH);

	if (handle == invalidHandle)
	{
	static if (is(Datum == const))
	{
	// No error, nonexisting file in read mode behaves like an empty file.
	return;
	}
	else
	{
	fprintf(stderr, "open(\"%s\") failed: %s\n", filename, strerror(errno));
	exit(1);
	}
	}

	const size = fileSize(handle);

	if (size > 0 && size != ulong.max && size <= size_t.max)
	{
	auto p = mmap(null, cast(size_t) size, is(Datum == const) ? PROT_READ : PROT_WRITE, MAP_SHARED, handle, 0);
	if (p == MAP_FAILED)
	{
	fprintf(stderr, "mmap(null, %zu) for \"%s\" failed: %s\n", cast(size_t) size, filename, strerror(errno));
	exit(1);
	}
	// The cast below will always work because it's gated by the `size <= size_t.max` condition.
	data = cast(Datum[]) p[0 .. cast(size_t) size];
	}
	}
	else version(Windows)
	{
	static if (is(Datum == const))
	{
	enum createFileMode = GENERIC_READ;
	enum openFlags = OPEN_EXISTING;
	}
	else
	{
	enum createFileMode = GENERIC_READ \| GENERIC_WRITE;
	enum openFlags = CREATE_ALWAYS;
	}

	handle = filename.asDString.extendedPathThen!(p => CreateFileW(p.ptr, createFileMode, 0, null, openFlags, FILE_ATTRIBUTE_NORMAL, null));
	if (handle == invalidHandle)
	{
	static if (is(Datum == const))
	{
	return;
	}
	else
	{
	fprintf(stderr, "CreateFileW() failed for \"%s\": %d\n", filename, GetLastError());
	exit(1);
	}
	}
	createMapping(filename, fileSize(handle));
	}
	else static assert(0);

	// Save the name for later. Technically there's no need: on Linux one can use readlink on /proc/self/fd/NNN.
	// On BSD and OSX one can use fcntl with F_GETPATH. On Windows one can use GetFileInformationByHandleEx.
	// But just saving the name is simplest, fastest, and most portable...
	import core.stdc.string : strlen;
	import core.stdc.stdlib : malloc;
	import core.stdc.string : memcpy;
	const totalNameLength = filename.strlen() + 1;
	auto namex = cast(char*) malloc(totalNameLength);
	if (!namex)
	{
	fprintf(stderr, "FileMapping: Out of memory.");
	exit(1);
	}
	name = cast(char*) memcpy(namex, filename, totalNameLength);
	}

	/**
	Common code factored opportunistically. Windows only. Assumes `handle` is
	already pointing to an opened file. Initializes the `fileMappingObject`
	and `data` members.

	Params:
	filename = the file to be mapped
	size = the size of the file in bytes
	*/
	version(Windows) private void createMapping(const char* filename, ulong size)
	{
	assert(size <= size_t.max \|\| size == ulong.max);
	assert(handle != invalidHandle);
	assert(data is null);
	assert(fileMappingObject == invalidHandle);

	if (size == 0 \|\| size == ulong.max)
	return;

	static if (is(Datum == const))
	{
	enum fileMappingFlags = PAGE_READONLY;
	enum mapViewFlags = FILE_MAP_READ;
	}
	else
	{
	enum fileMappingFlags = PAGE_READWRITE;
	enum mapViewFlags = FILE_MAP_WRITE;
	}

	fileMappingObject = CreateFileMappingW(handle, null, fileMappingFlags, 0, 0, null);
	if (!fileMappingObject)
	{
	fprintf(stderr, "CreateFileMappingW(%p) failed for %llu bytes of \"%s\": %d\n",
	handle, size, filename, GetLastError());
	fileMappingObject = invalidHandle; // by convention always use invalidHandle, not null
	exit(1);
	}
	auto p = MapViewOfFile(fileMappingObject, mapViewFlags, 0, 0, 0);
	if (!p)
	{
	fprintf(stderr, "MapViewOfFile() failed for \"%s\": %d\n", filename, GetLastError());
	exit(1);
	}
	data = cast(Datum[]) p[0 .. cast(size_t) size];
	}

	// Not copyable or assignable (for now).
	@disable this(const FileMapping!Datum rhs);
	@disable void opAssign(const ref FileMapping!Datum rhs);

	/**
	Frees resources associated with this mapping. However, it does not deallocate the name.
	*/
	~this() pure nothrow
	{
	if (!active)
	return;
	fakePure({
	version (Posix)
	{
	import core.sys.posix.sys.mman : munmap;
	import core.sys.posix.unistd : close;

	// Cannot call fprintf from inside a destructor, so exiting silently.

	if (data.ptr && munmap(cast(void*) data.ptr, data.length) != 0)
	{
	exit(1);
	}
	data = null;
	if (handle != invalidHandle && close(handle) != 0)
	{
	exit(1);
	}
	handle = invalidHandle;
	}
	else version(Windows)
	{
	if (data.ptr !is null && UnmapViewOfFile(cast(void*) data.ptr) == 0)
	{
	exit(1);
	}
	data = null;
	if (fileMappingObject != invalidHandle && CloseHandle(fileMappingObject) == 0)
	{
	exit(1);
	}
	fileMappingObject = invalidHandle;
	if (handle != invalidHandle && CloseHandle(handle) == 0)
	{
	exit(1);
	}
	handle = invalidHandle;
	}
	else static assert(0);
	});
	}

	/**
	Returns the zero-terminated file name associated with the mapping. Can NOT
	be saved beyond the lifetime of `this`.
	*/
	private const(char)* filename() const pure @nogc @safe nothrow { return name; }

	/**
	Frees resources associated with this mapping. However, it does not deallocate the name.
	Reinitializes `this` as a fresh object that can be reused.
	*/
	void close()
	{
	__dtor();
	handle = invalidHandle;
	version(Windows) fileMappingObject = invalidHandle;
	data = null;
	name = null;
	}

	/**
	Deletes the underlying file and frees all resources associated.
	Reinitializes `this` as a fresh object that can be reused.

	This function does not abort if the file cannot be deleted, but does print
	a message on `stderr` and returns `false` to the caller. The underlying
	rationale is to give the caller the option to continue execution if
	deleting the file is not important.

	Returns: `true` iff the file was successfully deleted. If the file was not
	deleted, prints a message to `stderr` and returns `false`.
	*/
	static if (!is(Datum == const))
	bool discard()
	{
	// Truncate file to zero so unflushed buffers are not flushed unnecessarily.
	resize(0);
	auto deleteme = name;
	close();
	// In-memory resource freed, now get rid of the underlying temp file.
	version(Posix)
	{
	import core.sys.posix.unistd : unlink;
	if (unlink(deleteme) != 0)
	{
	fprintf(stderr, "unlink(\"%s\") failed: %s\n", filename, strerror(errno));
	return false;
	}
	}
	else version(Windows)
	{
	import core.sys.windows.winbase;
	if (deleteme.asDString.extendedPathThen!(p => DeleteFileW(p.ptr)) == 0)
	{
	fprintf(stderr, "DeleteFileW error %d\n", GetLastError());
	return false;
	}
	}
	else static assert(0);
	return true;
	}

	/**
	Queries whether `this` is currently associated with a file.

	Returns: `true` iff there is an active mapping.
	*/
	bool active() const pure @nogc nothrow
	{
	return handle !is invalidHandle;
	}

	/**
	Queries the length of the file associated with this mapping. If not
	active, returns 0.

	Returns: the length of the file, or 0 if no file associated.
	*/
	size_t length() const pure @nogc @safe nothrow { return data.length; }

	/**
	Get a slice to the contents of the entire file.

	Returns: the contents of the file. If not active, returns the `null` slice.
	*/
	auto opSlice() pure @nogc @safe nothrow { return data; }

	/**
	Resizes the file and mapping to the specified `size`.

	Params:
	size = new length requested
	*/
	static if (!is(Datum == const))
	void resize(size_t size) pure
	{
	assert(handle != invalidHandle);
	fakePure({
	version(Posix)
	{
	import core.sys.posix.unistd : ftruncate;
	import core.sys.posix.sys.mman;

	if (data.length)
	{
	assert(data.ptr, "Corrupt memory mapping");
	// assert(0) here because it would indicate an internal error
	munmap(cast(void*) data.ptr, data.length) == 0 \|\| assert(0);
	data = null;
	}
	if (ftruncate(handle, size) != 0)
	{
	fprintf(stderr, "ftruncate() failed for \"%s\": %s\n", filename, strerror(errno));
	exit(1);
	}
	if (size > 0)
	{
	auto p = mmap(null, size, PROT_WRITE, MAP_SHARED, handle, 0);
	if (cast(ssize_t) p == -1)
	{
	fprintf(stderr, "mmap() failed for \"%s\": %s\n", filename, strerror(errno));
	exit(1);
	}
	data = cast(Datum[]) p[0 .. size];
	}
	}
	else version(Windows)
	{
	// Per documentation, must unmap first.
	if (data.length > 0 && UnmapViewOfFile(cast(void*) data.ptr) == 0)
	{
	fprintf(stderr, "UnmapViewOfFile(%p) failed for memory mapping of \"%s\": %d\n",
	data.ptr, filename, GetLastError());
	exit(1);
	}
	data = null;
	if (fileMappingObject != invalidHandle && CloseHandle(fileMappingObject) == 0)
	{
	fprintf(stderr, "CloseHandle() failed for memory mapping of \"%s\": %d\n", filename, GetLastError());
	exit(1);
	}
	fileMappingObject = invalidHandle;
	LARGE_INTEGER biggie;
	biggie.QuadPart = size;
	if (SetFilePointerEx(handle, biggie, null, FILE_BEGIN) == 0 \|\| SetEndOfFile(handle) == 0)
	{
	fprintf(stderr, "SetFilePointer() failed for \"%s\": %d\n", filename, GetLastError());
	exit(1);
	}
	createMapping(name, size);
	}
	else static assert(0);
	});
	}

	/**
	Unconditionally and destructively moves the underlying file to `filename`.
	If the operation succeeds, returns true. Upon failure, prints a message to
	`stderr` and returns `false`. In all cases it closes the underlying file.

	Params: filename = zero-terminated name of the file to move to.

	Returns: `true` iff the operation was successful.
	*/
	bool moveToFile(const char* filename)
	{
	assert(name !is null);

	// Fetch the name and then set it to `null` so it doesn't get deallocated
	auto oldname = name;
	import core.stdc.stdlib;
	scope(exit) free(cast(void*) oldname);
	name = null;
	close();

	// Rename the underlying file to the target, no copy necessary.
	version(Posix)
	{
	if (.rename(oldname, filename) != 0)
	{
	fprintf(stderr, "rename(\"%s\", \"%s\") failed: %s\n", oldname, filename, strerror(errno));
	return false;
	}
	}
	else version(Windows)
	{
	import core.sys.windows.winbase;
	auto r = oldname.asDString.extendedPathThen!(
	p1 => filename.asDString.extendedPathThen!(p2 => MoveFileExW(p1.ptr, p2.ptr, MOVEFILE_REPLACE_EXISTING))
	);
	if (r == 0)
	{
	fprintf(stderr, "MoveFileExW(\"%s\", \"%s\") failed: %d\n", oldname, filename, GetLastError());
	return false;
	}
	}
	else static assert(0);
	return true;
	}
	}

	/// Write a file, returning `true` on success.
	extern(D) static bool writeFile(const(char)* name, const void[] data) nothrow
	{
	version (Posix)
	{
	int fd = open(name, O_CREAT \| O_WRONLY \| O_TRUNC, (6 << 6) \| (4 << 3) \| 4);
	if (fd == -1)
	goto err;
	if (.write(fd, data.ptr, data.length) != data.length)
	goto err2;
	if (close(fd) == -1)
	goto err;
	return true;
	err2:
	close(fd);
	.remove(name);
	err:
	return false;
	}
	else version (Windows)
	{
	DWORD numwritten; // here because of the gotos
	const nameStr = name.asDString;
	// work around Windows file path length limitation
	// (see documentation for extendedPathThen).
	HANDLE h = nameStr.extendedPathThen!
	(p => CreateFileW(p.ptr,
	GENERIC_WRITE,
	0,
	null,
	CREATE_ALWAYS,
	FILE_ATTRIBUTE_NORMAL \| FILE_FLAG_SEQUENTIAL_SCAN,
	null));
	if (h == INVALID_HANDLE_VALUE)
	goto err;

	if (WriteFile(h, data.ptr, cast(DWORD)data.length, &numwritten, null) != TRUE)
	goto err2;
	if (numwritten != data.length)
	goto err2;
	if (!CloseHandle(h))
	goto err;
	return true;
	err2:
	CloseHandle(h);
	nameStr.extendedPathThen!(p => DeleteFileW(p.ptr));
	err:
	return false;
	}
	else
	{
	static assert(0);
	}
	}

	/// Touch a file to current date
	bool touchFile(const char* namez)
	{
	version (Windows)
	{
	FILETIME ft = void;
	SYSTEMTIME st = void;
	GetSystemTime(&st);
	SystemTimeToFileTime(&st, &ft);

	import core.stdc.string : strlen;

	// get handle to file
	HANDLE h = namez[0 .. namez.strlen()].extendedPathThen!(p => CreateFile(p.ptr,
	FILE_WRITE_ATTRIBUTES, FILE_SHARE_READ \| FILE_SHARE_WRITE,
	null, OPEN_EXISTING,
	FILE_ATTRIBUTE_NORMAL, null));
	if (h == INVALID_HANDLE_VALUE)
	return false;

	const f = SetFileTime(h, null, null, &ft); // set last write time

	if (!CloseHandle(h))
	return false;

	return f != 0;
	}
	else version (Posix)
	{
	import core.sys.posix.utime;
	return utime(namez, null) == 0;
	}
	else
	static assert(0);
	}

	// Feel free to make these public if used elsewhere.
	/**
	Size of a file in bytes.
	Params: fd = file handle
	Returns: file size in bytes, or `ulong.max` on any error.
	*/
	version (Posix)
	private ulong fileSize(int fd)
	{
	import core.sys.posix.sys.stat;
	stat_t buf;
	if (fstat(fd, &buf) == 0)
	return buf.st_size;
	return ulong.max;
	}

	/// Ditto
	version (Windows)
	private ulong fileSize(HANDLE fd)
	{
	ulong result;
	if (GetFileSizeEx(fd, cast(LARGE_INTEGER*) &result) == 0)
	return result;
	return ulong.max;
	}

	/**
	Runs a non-pure function or delegate as pure code. Use with caution.

	Params:
	fun = the delegate to run, usually inlined: `fakePure({ ... });`

	Returns: whatever `fun` returns.
	*/
	private auto ref fakePure(F)(scope F fun) pure
	{
	mixin("alias PureFun = " ~ F.stringof ~ " pure;");
	return (cast(PureFun) fun)();
	}