Merge pull request #2424 from gsathya/fix_append_bug

Fix append bug

4 files changed, 34 insertions, 5 deletions

diff --git a/AUTHORS b/AUTHORS
index d356a05b..5930c012 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -144,4 +144,4 @@ a license to everyone to use it as detailed in LICENSE.)
 * Jason Green <jason@transgaming.com> (copyright owned by TransGaming, Inc.)
 * Ningxin Hu <ningxin.hu@intel.com> (copyright owned by Intel)
 * Nicolas Guillemot <nlguillemot@gmail.com>
-
+* Sathyanarayanan Gunasekaran <gsathya.ceg@gmail.com> (copyright owned by Mozilla Foundation)
diff --git a/src/library_fs.js b/src/library_fs.js
index 1fff6348..d825892c 100644
--- a/src/library_fs.js
+++ b/src/library_fs.js
@@ -1077,6 +1077,10 @@ mergeInto(LibraryManager.library, {
       if (!stream.stream_ops.write) {
         throw new FS.ErrnoError(ERRNO_CODES.EINVAL);
       }
+      if (stream.flags & {{{ cDefine('O_APPEND') }}}) {
+        // seek to the end before writing in append mode
+        FS.llseek(stream, 0, {{{ cDefine('SEEK_END') }}});
+      }
       var seeking = true;
       if (typeof position === 'undefined') {
         position = stream.position;
@@ -1084,10 +1088,6 @@ mergeInto(LibraryManager.library, {
       } else if (!stream.seekable) {
         throw new FS.ErrnoError(ERRNO_CODES.ESPIPE);
       }
-      if (stream.flags & {{{ cDefine('O_APPEND') }}}) {
-        // seek to the end before writing in append mode
-        FS.llseek(stream, 0, {{{ cDefine('SEEK_END') }}});
-      }
       var bytesWritten = stream.stream_ops.write(stream, buffer, offset, length, position, canOwn);
       if (!seeking) stream.position += bytesWritten;
       try {
diff --git a/tests/fs/test_append.c b/tests/fs/test_append.c
new file mode 100644
index 00000000..27909ba3
--- /dev/null
+++ b/tests/fs/test_append.c
@@ -0,0 +1,24 @@
+#include<assert.h>
+#include<stdio.h>
+
+int main (int argc, char *argv[])
+{
+   FILE *fp;
+   int res;
+   long len;
+
+   fp = fopen("testappend", "wb+");
+   res = fwrite("1234567890", 10, 1, fp);
+   fclose(fp);
+
+   fp = fopen("testappend", "ab+");
+   res = fwrite("1234567890", 10, 1, fp);
+
+   fseek(fp, -7, SEEK_END);
+   len = ftell(fp);
+   assert(len == 13);
+   fclose(fp);
+
+   puts("success");
+   return 0;
+}
diff --git a/tests/test_core.py b/tests/test_core.py
index 13b6c0f3..08e3594e 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -4348,6 +4348,11 @@ def process(filename):
     out = path_from_root('tests', 'fs', 'test_writeFile.out')
     self.do_run_from_file(src, out)
 
+  def test_fs_append(self):
+    if self.emcc_args is None: return self.skip('requires emcc')
+    src = open(path_from_root('tests', 'fs', 'test_append.c'), 'r').read()
+    self.do_run(src, 'success', force_c=True)
+
   def test_unistd_access(self):
     self.clear()
     if not self.is_emscripten_abi(): return self.skip('asmjs-unknown-emscripten needed for inline js')