curl: add --no-clobber

Does not overwrite output files if they already exist

Closes #7708
Co-authored-by: Daniel Stenberg

src/tool_cb_wrt.c

@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2022, 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
@@ -48,50 +48,86 @@
 #define OPENMODE S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH
 #endif
 
-/* create a local file for writing, return TRUE on success */
+/* create/open a local file for writing, return TRUE on success */
 bool tool_create_output_file(struct OutStruct *outs,
                              struct OperationConfig *config)
 {
   struct GlobalConfig *global;
   FILE *file = NULL;
+  char *fname = outs->filename;
+  char *aname = NULL;
   DEBUGASSERT(outs);
   DEBUGASSERT(config);
   global = config->global;
-  if(!outs->filename || !*outs->filename) {
+  if(!fname || !*fname) {
     warnf(global, "Remote filename has no length!\n");
     return FALSE;
   }
 
-  if(outs->is_cd_filename) {
-    /* don't overwrite existing files */
+  if(config->output_dir && outs->is_cd_filename) {
+    aname = aprintf("%s/%s", config->output_dir, fname);
+    if(!aname) {
+      errorf(global, "out of memory\n");
+      return FALSE;
+    }
+    fname = aname;
+  }
+
+  if(config->file_clobber_mode == CLOBBER_ALWAYS ||
+     (config->file_clobber_mode == CLOBBER_DEFAULT &&
+      !outs->is_cd_filename)) {
+    /* open file for writing */
+    file = fopen(fname, "wb");
+  }
+  else {
     int fd;
-    char *name = outs->filename;
-    char *aname = NULL;
-    if(config->output_dir) {
-      aname = aprintf("%s/%s", config->output_dir, name);
-      if(!aname) {
+    do {
+      fd = open(fname, O_CREAT | O_WRONLY | O_EXCL | O_BINARY, OPENMODE);
+      /* Keep retrying in the hope that it isn't interrupted sometime */
+    } while(fd == -1 && errno == EINTR);
+    if(config->file_clobber_mode == CLOBBER_NEVER && fd == -1) {
+      int next_num = 1;
+      size_t len = strlen(fname);
+      char *newname = malloc(len + 13); /* nul + 1-11 digits + dot */
+      if(!newname) {
         errorf(global, "out of memory\n");
         return FALSE;
       }
-      name = aname;
+      memcpy(newname, fname, len);
+      newname[len] = '.';
+      while(fd == -1 && /* haven't sucessfully opened a file */
+            (errno == EEXIST || errno == EISDIR) &&
+            /* because we keep having files that already exist */
+            next_num < 100 /* and we haven't reached the retry limit */ ) {
+        curlx_msnprintf(newname + len + 1, 12, "%d", next_num);
+        next_num++;
+        do {
+          fd = open(newname, O_CREAT | O_WRONLY | O_EXCL | O_BINARY, OPENMODE);
+          /* Keep retrying in the hope that it isn't interrupted sometime */
+        } while(fd == -1 && errno == EINTR);
+      }
+      outs->filename = newname; /* remember the new one */
+      outs->alloc_filename = TRUE;
     }
-    fd = open(name, O_CREAT | O_WRONLY | O_EXCL | O_BINARY, OPENMODE);
+    /* An else statement to not overwrite existing files and not retry with
+       new numbered names (which would cover
+       config->file_clobber_mode == CLOBBER_DEFAULT && outs->is_cd_filename)
+       is not needed because we would have failed earlier, in the while loop
+       and `fd` would now be -1 */
     if(fd != -1) {
       file = fdopen(fd, "wb");
       if(!file)
         close(fd);
     }
-    free(aname);
   }
-  else
-    /* open file for writing */
-    file = fopen(outs->filename, "wb");
 
   if(!file) {
-    warnf(global, "Failed to create the file %s: %s\n", outs->filename,
+    warnf(global, "Failed to open the file %s: %s\n", fname,
           strerror(errno));
+    free(aname);
     return FALSE;
   }
+  free(aname);
   outs->s_isreg = TRUE;
   outs->fopened = TRUE;
   outs->stream = file;

src/tool_cfgable.c

@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2022, 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
@@ -45,6 +45,7 @@ void config_init(struct OperationConfig *config)
   config->happy_eyeballs_timeout_ms = CURL_HET_DEFAULT;
   config->http09_allowed = FALSE;
   config->ftp_skip_ip = TRUE;
+  config->file_clobber_mode = CLOBBER_DEFAULT;
 }
 
 static void free_config_fields(struct OperationConfig *config)

src/tool_cfgable.h

@@ -290,6 +290,15 @@ struct OperationConfig {
   bool haproxy_protocol;          /* whether to send HAProxy protocol v1 */
   bool disallow_username_in_url;  /* disallow usernames in URLs */
   char *aws_sigv4;
+  enum {
+    CLOBBER_DEFAULT, /* Provides compatability with previous versions of curl,
+                        by using the default behavior for -o, -O, and -J.
+                        If those options would have overwritten files, like
+                        -o and -O would, then overwrite them. In the case of
+                        -J, this will not overwrite any files. */
+    CLOBBER_NEVER, /* If the file exists, always fail */
+    CLOBBER_ALWAYS /* If the file exists, always overwrite it */
+  } file_clobber_mode;
   struct GlobalConfig *global;
   struct OperationConfig *prev;
   struct OperationConfig *next;   /* Always last in the struct */

src/tool_getparam.c

@@ -314,6 +314,7 @@ static const struct LongShort aliases[]= {
   {"O",  "remote-name",              ARG_NONE},
   {"Oa", "remote-name-all",          ARG_BOOL},
   {"Ob", "output-dir",               ARG_STRING},
+  {"Oc", "clobber",                  ARG_BOOL},
   {"p",  "proxytunnel",              ARG_BOOL},
   {"P",  "ftp-port",                 ARG_STRING},
   {"q",  "disable",                  ARG_BOOL},
@@ -1999,10 +2000,7 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
     case 'N':
       /* disable the output I/O buffering. note that the option is called
          --buffer but is mostly used in the negative form: --no-buffer */
-      if(longopt)
-        config->nobuffer = (!toggle)?TRUE:FALSE;
-      else
-        config->nobuffer = toggle;
+      config->nobuffer = longopt ? !toggle : TRUE;
       break;
     case 'O': /* --remote-name */
       if(subletter == 'a') { /* --remote-name-all */
@@ -2013,6 +2011,10 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
         GetStr(&config->output_dir, nextarg);
         break;
       }
+      else if(subletter == 'c') { /* --clobber / --no-clobber */
+        config->file_clobber_mode = toggle ? CLOBBER_ALWAYS : CLOBBER_NEVER;
+        break;
+      }
       /* FALLTHROUGH */
     case 'o': /* --output */
       /* output file */

src/tool_help.c

@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2022, 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

src/tool_listhelp.c

@@ -385,6 +385,9 @@ const struct helptxt helptext[] = {
   {"-N, --no-buffer",
    "Disable buffering of the output stream",
    CURLHELP_CURL},
+  {"    --no-clobber",
+   "Do not overwrite files that already exist",
+   CURLHELP_CURL | CURLHELP_OUTPUT},
   {"    --no-keepalive",
    "Disable TCP keepalive on the connection",
    CURLHELP_CONNECTION},