os: fix os.open_file('text.txt', 'wb', 0o666), add test (#15420)

vlib/os/const_nix.c.v

@@ -1,16 +1,15 @@
 module os
 
-// File modes
 const (
-	o_rdonly   = 0o00000000 // open the file read-only.
-	o_wronly   = 0o00000001 // open the file write-only.
-	o_rdwr     = 0o00000002 // open the file read-write.
-	o_binary   = 0o00000000 // input and output is not translated; the default on unix
-	o_create   = 0o00000100 // create a new file if none exists.
-	o_excl     = 0o00000200 // used with o_create, file must not exist.
-	o_noctty   = 0o00000400 // if file is terminal, don't make it the controller terminal
-	o_trunc    = 0o00001000 // truncate regular writable file when opened.
-	o_append   = 0o00002000 // append data to the file when writing.
-	o_nonblock = 0o00004000 // prevents blocking when opening files
-	o_sync     = 0o04010000 // open for synchronous I/O.
+	o_binary   = 0 // input and output is not translated; the default on unix
+	o_rdonly   = C.O_RDONLY // open the file read-only.
+	o_wronly   = C.O_WRONLY // open the file write-only.
+	o_rdwr     = C.O_RDWR // open the file read-write.
+	o_create   = C.O_CREAT // create a new file if none exists.
+	o_excl     = C.O_EXCL // used with o_create, file must not exist.
+	o_noctty   = C.O_NOCTTY // if file is terminal, don't make it the controller terminal
+	o_trunc    = C.O_TRUNC // truncate regular writable file when opened.
+	o_append   = C.O_APPEND // append data to the file when writing.
+	o_nonblock = C.O_NONBLOCK // prevents blocking when opening files
+	o_sync     = C.O_SYNC // open for synchronous I/O.
 )

vlib/os/file.c.v

@@ -54,28 +54,41 @@ fn fix_windows_path(path string) string {
 // open_file can be used to open or create a file with custom flags and permissions and returns a `File` object.
 pub fn open_file(path string, mode string, options ...int) ?File {
 	mut flags := 0
+	mut seek_to_end := false
 	for m in mode {
 		match m {
-			`w` { flags |= o_create | o_trunc }
-			`a` { flags |= o_create | o_append }
-			`r` { flags |= o_rdonly }
-			`b` { flags |= o_binary }
-			`s` { flags |= o_sync }
-			`n` { flags |= o_nonblock }
-			`c` { flags |= o_noctty }
-			`+` { flags |= o_rdwr }
+			`w` {
+				flags |= o_create | o_trunc | o_wronly
+			}
+			`a` {
+				flags |= o_create | o_append | o_wronly
+				seek_to_end = true
+			}
+			`r` {
+				flags |= o_rdonly
+			}
+			`b` {
+				flags |= o_binary
+			}
+			`s` {
+				flags |= o_sync
+			}
+			`n` {
+				flags |= o_nonblock
+			}
+			`c` {
+				flags |= o_noctty
+			}
+			`+` {
+				flags &= ~o_wronly
+				flags |= o_rdwr
+			}
 			else {}
 		}
 	}
 	if mode == 'r+' {
 		flags = o_rdwr
 	}
-	if mode == 'w' {
-		flags = o_wronly | o_create | o_trunc
-	}
-	if mode == 'a' {
-		flags = o_wronly | o_create | o_append
-	}
 	mut permission := 0o666
 	if options.len > 0 {
 		permission = options[0]
@@ -92,10 +105,19 @@ pub fn open_file(path string, mode string, options ...int) ?File {
 	if fd == -1 {
 		return error(posix_get_error_msg(C.errno))
 	}
-	cfile := C.fdopen(fd, &char(mode.str))
+	fdopen_mode := mode.replace('b', '')
+	cfile := C.fdopen(fd, &char(fdopen_mode.str))
 	if isnil(cfile) {
 		return error('Failed to open or create file "$path"')
 	}
+	if seek_to_end {
+		// ensure appending will work, even on bsd/macos systems:
+		$if windows {
+			C._fseeki64(cfile, 0, C.SEEK_END)
+		} $else {
+			C.fseeko(cfile, 0, C.SEEK_END)
+		}
+	}
 	return File{
 		cfile: cfile
 		fd: fd

vlib/os/file_test.v

@@ -388,7 +388,7 @@ fn test_reopen() ? {
 	f2.reopen(tfile1, 'r')?
 	assert !f2.eof()
 
-	z := f2.read(mut line_buffer)?
+	z := f2.read(mut line_buffer) or { panic(err) }
 	assert f2.eof()
 	assert z > 0
 	content := line_buffer#[..z].bytestr()
@@ -406,3 +406,16 @@ fn test_eof() ? {
 	f.read_bytes(100)
 	assert f.eof()
 }
+
+fn test_open_file_wb_ab() ? {
+	os.rm(tfile) or {}
+	mut wfile := os.open_file('text.txt', 'wb', 0o666)?
+	wfile.write_string('hello')?
+	wfile.close()
+	assert os.read_file('text.txt')? == 'hello'
+	//
+	mut afile := os.open_file('text.txt', 'ab', 0o666)?
+	afile.write_string('hello')?
+	afile.close()
+	assert os.read_file('text.txt')? == 'hellohello'
+}