wasip2: Handle the O_APPEND flag (WebAssembly#671)

I'm a bit surprised the Python test suite didn't cover this, but this
nonetheless was broken and needed fixing.

Author: alexcrichton

libc-bottom-half/sources/wasip2_file.c

@@ -86,11 +86,20 @@ static int file_get_write_stream(void *data,
   file_t *file = (file_t *)data;
   if (file->write_stream.__handle == 0) {
     filesystem_error_code_t error_code;
-    bool ok = filesystem_method_descriptor_write_via_stream(
-        filesystem_borrow_descriptor(file->file_handle),
-        file->offset,
-        &file->write_stream,
-        &error_code);
+    bool ok;
+
+    if (file->oflag & O_APPEND) {
+      ok = filesystem_method_descriptor_append_via_stream(
+          filesystem_borrow_descriptor(file->file_handle),
+          &file->write_stream,
+          &error_code);
+    } else {
+      ok = filesystem_method_descriptor_write_via_stream(
+          filesystem_borrow_descriptor(file->file_handle),
+          file->offset,
+          &file->write_stream,
+          &error_code);
+    }
     if (!ok) {
       translate_error(error_code);
       return -1;
@@ -138,33 +147,53 @@ static int file_fstat(void *data, struct stat *buf) {
   return 0;
 }
 
+static int file_seek_end(file_t *file) {
+  filesystem_descriptor_stat_t stat;
+  filesystem_error_code_t error;
+  bool ok = filesystem_method_descriptor_stat(filesystem_borrow_descriptor(file->file_handle),
+      &stat,
+      &error);
+  if (!ok) {
+    translate_error(error);
+    return -1;
+  }
+  file->offset = (off_t) stat.size;
+  return 0;
+}
+
 static off_t file_seek(void *data, off_t offset, int whence) {
   file_t *file = (file_t *)data;
+
+  // If this file is in append mode, reset our knowledge of the current cursor
+  // to the current end of the file.
+  if ((file->oflag & O_APPEND) && file_seek_end(file) < 0)
+    return -1;
+
+  off_t result;
   switch (whence) {
     case SEEK_SET:
-      file->offset = offset;
+      result = offset;
       break;
     case SEEK_CUR:
-      file->offset += offset;
+      result = file->offset + offset;
       break;
     case SEEK_END: {
-      // Get the file metadata
-      filesystem_descriptor_stat_t stat;
-      filesystem_error_code_t error;
-      bool ok = filesystem_method_descriptor_stat(filesystem_borrow_descriptor(file->file_handle),
-                                                  &stat,
-                                                  &error);
-      if (!ok) {
-        translate_error(error);
+      // If we're in append mode we already reset to the end, but if we're not
+      // in append mode then do the reset to the end here.
+      if (!(file->oflag & O_APPEND) && file_seek_end(file) < 0)
         return -1;
-      }
-      file->offset = ((off_t) stat.size) + offset;
+      result = file->offset + offset;
       break;
     }
     default:
       errno = EINVAL;
       return -1;
   }
+  if (result < 0) {
+    errno = EINVAL;
+    return -1;
+  }
+  file->offset = result;
   file_close_streams(data);
   return file->offset;
 }

test/CMakeLists.txt

@@ -278,6 +278,7 @@ endfunction()
 if (NOT TARGET_TRIPLE MATCHES "-threads")
   add_wasilibc_test(access.c FS)
 endif()
+add_wasilibc_test(append.c FS)
 add_wasilibc_test(argv_two_args.c ARGV foo bar)
 add_wasilibc_test(clock_nanosleep.c)
 add_wasilibc_test(chdir.c FS)

test/src/append.c

@@ -0,0 +1,47 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/uio.h>
+#include "test.h"
+
+#define TEST(c) do { \
+	errno = 0; \
+	if (!(c)) \
+		t_error("%s failed (errno = %d)\n", #c, errno); \
+} while(0)
+
+int main(void) {
+  char tmp[] = "testsuite-XXXXXX";
+  int fd;
+  TEST((fd = open(tmp, O_RDWR | O_CREAT | O_EXCL | O_APPEND, 0600)) > 2);
+
+  TEST(write(fd, "Hello, world!", 13) == 13);
+  TEST(lseek(fd, 0, SEEK_CUR) == 13);
+  TEST(lseek(fd, 0, SEEK_SET) == 0);
+  TEST(write(fd, "Hello, world!", 13) == 13);
+  TEST(lseek(fd, 0, SEEK_CUR) == 26);
+  TEST(lseek(fd, 0, SEEK_SET) == 0);
+
+  TEST(close(fd) == 0);
+
+  int read_fd;
+  TEST((read_fd = open(tmp, O_RDONLY)) > 2);
+
+  char buf[30];
+  TEST(read(read_fd, buf, 30) == 26);
+  TEST(memcmp(buf, "Hello, world!Hello, world!", 26) == 0);
+
+  TEST((fd = open(tmp, O_RDWR | O_APPEND, 0600)) > 2);
+  TEST(write(fd, "hi", 2) == 2);
+  TEST(close(fd) == 0);
+
+  TEST(lseek(read_fd, 0, SEEK_SET) == 0);
+  TEST(read(read_fd, buf, 30) == 28);
+  TEST(memcmp(buf, "Hello, world!Hello, world!hi", 28) == 0);
+
+  return t_status;
+}

test/src/lseek.c

@@ -21,6 +21,11 @@ int main(void) {
   TEST(lseek(fd, 0, SEEK_SET) == 0);
   TEST(lseek(fd, 0, SEEK_CUR) == 0);
 
+  TEST(lseek(fd, -1, SEEK_END) == -1);
+  TEST(lseek(fd, -1, SEEK_CUR) == -1);
+  TEST(lseek(fd, -1, SEEK_SET) == -1);
+  TEST(lseek(fd, 0, SEEK_CUR) == 0);
+
   TEST(write(fd, "Hello, World!", 13) == 13);
   TEST(lseek(fd, 0, SEEK_CUR) == 13);
   TEST(lseek(fd, 0, SEEK_SET) == 0);