os/fileio: Add ability to use os/fileio.c for file descriptors

Code imported from #6299

2 files changed, 98 insertions, 4 deletions

diff --git a/src/nvim/os/fileio.c b/src/nvim/os/fileio.c
index d16746b7bf..0ed0ae87e3 100644
--- a/src/nvim/os/fileio.c
+++ b/src/nvim/os/fileio.c
@@ -49,7 +49,6 @@ int file_open(FileDescriptor *const ret_fp, const char *const fname,
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
 {
   int os_open_flags = 0;
-  int fd;
   TriState wr = kNone;
   // -V:FLAG:501
 #define FLAG(flags, flag, fcntl_flags, wrval, cond) \
@@ -74,14 +73,35 @@ int file_open(FileDescriptor *const ret_fp, const char *const fname,
   FLAG(flags, kFileNoSymlink, O_NOFOLLOW, kNone, true);
 #endif
 #undef FLAG
+  // wr is used for kFileReadOnly flag, but on
+  // QB:neovim-qb-slave-ubuntu-12-04-64bit it still errors out with
+  // `error: variable ‘wr’ set but not used [-Werror=unused-but-set-variable]`
+  (void)wr;
 
-  fd = os_open(fname, os_open_flags, mode);
+  const int fd = os_open(fname, os_open_flags, mode);
 
   if (fd < 0) {
     return fd;
   }
+  return file_open_fd(ret_fp, fd, (wr == kTrue));
+}
 
-  ret_fp->wr = (wr == kTrue);
+/// Wrap file descriptor with FileDescriptor structure
+///
+/// @warning File descriptor wrapped like this must not be accessed by other
+///          means.
+///
+/// @param[out]  ret_fp  Address where information needed for reading from or
+///                      writing to a file is saved
+/// @param[in]  fd  File descriptor to wrap.
+/// @param[in]  wr  True if fd is opened for writing only, false if it is read
+///                 only.
+///
+/// @return Error code (@see os_strerror()) or 0. Currently always returns 0.
+int file_open_fd(FileDescriptor *const ret_fp, const int fd, const bool wr)
+  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
+{
+  ret_fp->wr = wr;
   ret_fp->fd = fd;
   ret_fp->eof = false;
   ret_fp->rv = rbuffer_new(kRWBufferSize);
@@ -115,6 +135,26 @@ FileDescriptor *file_open_new(int *const error, const char *const fname,
   return fp;
 }
 
+/// Like file_open_fd(), but allocate and return ret_fp
+///
+/// @param[out]  error  Error code, @see os_strerror(). Is set to zero on
+///                     success.
+/// @param[in]  fd  File descriptor to wrap.
+/// @param[in]  wr  True if fd is opened for writing only, false if it is read
+///                 only.
+///
+/// @return [allocated] Opened file or NULL in case of error.
+FileDescriptor *file_open_fd_new(int *const error, const int fd, const bool wr)
+  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_MALLOC FUNC_ATTR_WARN_UNUSED_RESULT
+{
+  FileDescriptor *const fp = xmalloc(sizeof(*fp));
+  if ((*error = file_open_fd(fp, fd, wr)) != 0) {
+    xfree(fp);
+    return NULL;
+  }
+  return fp;
+}
+
 /// Close file and free its buffer
 ///
 /// @param[in,out]  fp  File to close.
diff --git a/test/unit/os/fileio_spec.lua b/test/unit/os/fileio_spec.lua
index a33a9637ee..d9c98e8afa 100644
--- a/test/unit/os/fileio_spec.lua
+++ b/test/unit/os/fileio_spec.lua
@@ -6,8 +6,10 @@ local itp = helpers.gen_itp(it)
 local eq = helpers.eq
 local ffi = helpers.ffi
 local cimport = helpers.cimport
+local cppimport = helpers.cppimport
 
-local m = cimport('./src/nvim/os/fileio.h')
+local m = cimport('./src/nvim/os/os.h', './src/nvim/os/fileio.h')
+cppimport('fcntl.h')
 
 local fcontents = ''
 for i = 0, 255 do
@@ -58,6 +60,18 @@ local function file_open_new(fname, flags, mode)
   return ret1[0], ret2
 end
 
+local function file_open_fd(fd, flags)
+  local ret2 = ffi.new('FileDescriptor')
+  local ret1 = m.file_open_fd(ret2, fd, flags)
+  return ret1, ret2
+end
+
+local function file_open_fd_new(fd, flags)
+  local ret1 = ffi.new('int[?]', 1, {0})
+  local ret2 = ffi.gc(m.file_open_fd_new(ret1, fd, flags), nil)
+  return ret1[0], ret2
+end
+
 local function file_write(fp, buf)
   return m.file_write(fp, buf, #buf)
 end
@@ -96,6 +110,46 @@ local function file_skip(fp, size)
   return m.file_skip(fp, size)
 end
 
+describe('file_open_fd', function()
+  itp('can use file descriptor returned by os_open for reading', function()
+    local fd = m.os_open(file1, m.kO_RDONLY, 0)
+    local err, fp = file_open_fd(fd, false)
+    eq(0, err)
+    eq({#fcontents, fcontents}, {file_read(fp, #fcontents)})
+    eq(0, m.file_close(fp, false))
+  end)
+  itp('can use file descriptor returned by os_open for writing', function()
+    eq(nil, lfs.attributes(filec))
+    local fd = m.os_open(filec, m.kO_WRONLY + m.kO_CREAT, 384)
+    local err, fp = file_open_fd(fd, true)
+    eq(0, err)
+    eq(4, file_write(fp, 'test'))
+    eq(0, m.file_close(fp, false))
+    eq(4, lfs.attributes(filec).size)
+    eq('test', io.open(filec):read('*a'))
+  end)
+end)
+
+describe('file_open_fd_new', function()
+  itp('can use file descriptor returned by os_open for reading', function()
+    local fd = m.os_open(file1, m.kO_RDONLY, 0)
+    local err, fp = file_open_fd_new(fd, false)
+    eq(0, err)
+    eq({#fcontents, fcontents}, {file_read(fp, #fcontents)})
+    eq(0, m.file_free(fp, false))
+  end)
+  itp('can use file descriptor returned by os_open for writing', function()
+    eq(nil, lfs.attributes(filec))
+    local fd = m.os_open(filec, m.kO_WRONLY + m.kO_CREAT, 384)
+    local err, fp = file_open_fd_new(fd, true)
+    eq(0, err)
+    eq(4, file_write(fp, 'test'))
+    eq(0, m.file_free(fp, false))
+    eq(4, lfs.attributes(filec).size)
+    eq('test', io.open(filec):read('*a'))
+  end)
+end)
+
 describe('file_open', function()
   itp('can create a rwx------ file with kFileCreate', function()
     local err, fp = file_open(filec, m.kFileCreate, 448)