1 files changed, 108 insertions, 0 deletions
diff --git a/lib/openlock.c b/lib/openlock.c
new file mode 100644
index 000000000..f913ef82f
--- /dev/null
+++ b/lib/openlock.c
@@ -0,0 +1,108 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 2019 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+#include "curl_setup.h"
+
+#ifdef HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
+#include <curl/curl.h>
+#include "openlock.h"
+
+/* The last 3 #include files should be in this order */
+#include "curl_printf.h"
+#include "curl_memory.h"
+#include "memdebug.h"
+
+/*
+ * Curl_openlock() opens a file for writing text and waits for the adivsory
+ * lock on it.
+ */
+
+#ifndef O_CLOEXEC
+/* this doesn't exist everywhere */
+#define O_CLOEXEC 0
+#endif
+
+CURLcode Curl_openlock(const char *file, struct openlock *o)
+{
+  int fd = -1;
+  FILE *out = NULL;
+  CURLcode result = CURLE_OK;
+
+  DEBUGASSERT(o);
+  o->fd = -1;
+  o->out = NULL;
+
+  fd = open(file, O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, 0666);
+  if(fd == -1) {
+    result = CURLE_WRITE_ERROR;
+    goto error;
+  }
+
+#ifdef HAVE_LOCKF
+  /* wait for advisory lock on the whole file */
+  if(lockf(fd, F_LOCK, 0)) {
+    result = CURLE_WRITE_ERROR;
+    goto error;
+  }
+#endif
+
+  out = fdopen(fd, FOPEN_WRITETEXT);
+  if(!out)
+    result = CURLE_WRITE_ERROR;
+  else {
+    o->fd = fd;
+    o->out = out;
+    return CURLE_OK;
+  }
+  error:
+  if(out)
+    /* fclose() will close the fd as well after fdopen */
+    fclose(out);
+  else if(fd != -1)
+    close(fd);
+  return result;
+}
+
+/*
+ * Truncate the file at the current position, then unlock and close it.
+ */
+void Curl_openunlock(struct openlock *o)
+{
+#ifdef HAVE_FTRUNCATE
+  long pos = ftell(o->out);
+  fflush(o->out);
+  if(ftruncate(o->fd, (off_t)pos))
+    /* ignoring the return code causes warnings ... */
+    pos = 0;
+#endif
+#ifdef HAVE_LOCKF
+  if(o->fd != -1) {
+    if(lockf(o->fd, F_ULOCK, 0)) {
+      o->fd = -1;
+    }
+  }
+#endif
+  if(o->out)
+    fclose(o->out);
+}