curl: add --skip-existing

With this option, the entire download is skipped if the selected target
filename already exists when the opertion is about to begin.

Test 994, 995 and 996 verify.

Ref: #11012
Closes #13993

src/tool_cfgable.h

@@ -302,6 +302,7 @@ struct OperationConfig {
   struct State state;             /* for create_transfer() */
   bool rm_partial;                /* on error, remove partially written output
                                      files */
+  bool skip_existing;
 #ifdef USE_ECH
   char *ech;                      /* Config set by --ech keywords */
   char *ech_config;               /* Config set by "--ech esl:" option */

src/tool_getparam.c

@@ -287,6 +287,7 @@ static const struct LongShort aliases[]= {
   {"show-error",                 ARG_BOOL, 'S', C_SHOW_ERROR},
   {"show-headers",               ARG_BOOL, 'i', C_SHOW_HEADERS},
   {"silent",                     ARG_BOOL, 's', C_SILENT},
+  {"skip-existing",              ARG_BOOL, ' ', C_SKIP_EXISTING},
   {"socks4",                     ARG_STRG, ' ', C_SOCKS4},
   {"socks4a",                    ARG_STRG, ' ', C_SOCKS4A},
   {"socks5",                     ARG_STRG, ' ', C_SOCKS5},
@@ -2435,6 +2436,9 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
     case C_SILENT: /* --silent */
       global->silent = toggle;
       break;
+    case C_SKIP_EXISTING: /* --skip-existing */
+      config->skip_existing = toggle;
+      break;
     case C_SHOW_ERROR: /* --show-error */
       global->showerror = toggle;
       break;

src/tool_getparam.h

@@ -242,6 +242,7 @@ typedef enum {
   C_SHOW_ERROR,
   C_SHOW_HEADERS,
   C_SILENT,
+  C_SKIP_EXISTING,
   C_SOCKS4,
   C_SOCKS4A,
   C_SOCKS5,

src/tool_listhelp.c

@@ -662,6 +662,9 @@ const struct helptxt helptext[] = {
   {"-s, --silent",
    "Silent mode",
    CURLHELP_IMPORTANT | CURLHELP_VERBOSE},
+  {"    --skip-existing",
+   "Skip download if local file already exists",
+   CURLHELP_CURL | CURLHELP_OUTPUT},
   {"    --socks4 <host[:port]>",
    "SOCKS4 proxy on given host + port",
    CURLHELP_PROXY},

src/tool_operate.c

@@ -460,6 +460,9 @@ static CURLcode post_per_transfer(struct GlobalConfig *global,
   if(per->infdopen)
     close(per->infd);
 
+  if(per->skip)
+    goto skip;
+
 #ifdef __VMS
   if(is_vms_shell()) {
     /* VMS DCL shell behavior */
@@ -731,7 +734,7 @@ noretry:
     curl_easy_getinfo(curl, CURLINFO_FILETIME_T, &filetime);
     setfiletime(filetime, outs->filename, global);
   }
-
+skip:
   /* Write the --write-out data before cleanup but after result is final */
   if(config->writeout)
     ourWriteOut(config, per, result);
@@ -1197,6 +1200,15 @@ static CURLcode single_transfer(struct GlobalConfig *global,
               break;
           }
 
+          if(per->outfile && config->skip_existing) {
+            struct_stat fileinfo;
+            if(!stat(per->outfile, &fileinfo)) {
+              /* file is present */
+              notef(global, "skips transfer, \"%s\" exists locally",
+                    per->outfile);
+              per->skip = TRUE;
+            }
+          }
           if((urlnode->flags & GETOUT_USEREMOTE)
              && config->content_disposition) {
             /* Our header callback MIGHT set the filename */
@@ -2611,25 +2623,29 @@ static CURLcode serial_transfers(struct GlobalConfig *global,
     long delay_ms;
     bool bailout = FALSE;
     struct timeval start;
-    result = pre_transfer(global, per);
-    if(result)
-      break;
 
-    if(global->libcurl) {
-      result = easysrc_perform();
+    start = tvnow();
+    if(!per->skip) {
+      result = pre_transfer(global, per);
       if(result)
         break;
-    }
-    start = tvnow();
-#ifdef DEBUGBUILD
-    if(getenv("CURL_FORBID_REUSE"))
-      (void)curl_easy_setopt(per->curl, CURLOPT_FORBID_REUSE, 1L);
 
-    if(global->test_event_based)
-      result = curl_easy_perform_ev(per->curl);
-    else
+      if(global->libcurl) {
+        result = easysrc_perform();
+        if(result)
+          break;
+      }
+
+#ifdef DEBUGBUILD
+      if(getenv("CURL_FORBID_REUSE"))
+        (void)curl_easy_setopt(per->curl, CURLOPT_FORBID_REUSE, 1L);
+
+      if(global->test_event_based)
+        result = curl_easy_perform_ev(per->curl);
+      else
 #endif
-      result = curl_easy_perform(per->curl);
+        result = curl_easy_perform(per->curl);
+    }
 
     returncode = post_per_transfer(global, per, result, &retry, &delay_ms);
     if(retry) {

src/tool_operate.h

@@ -44,25 +44,16 @@ struct per_transfer {
   char *this_url;
   unsigned int urlnum; /* the index of the given URL */
   char *outfile;
-  bool infdopen; /* TRUE if infd needs closing */
   int infd;
-  bool noprogress;
   struct ProgressData progressbar;
   struct OutStruct outs;
   struct OutStruct heads;
   struct OutStruct etag_save;
   struct HdrCbData hdrcbdata;
   long num_headers;
-  bool was_last_header_empty;
-
-  bool added; /* set TRUE when added to the multi handle */
   time_t startat; /* when doing parallel transfers, this is a retry transfer
                      that has been set to sleep until this time before it
                      should get started (again) */
-  bool abort; /* when doing parallel transfers and this is TRUE then a critical
-                 error (eg --fail-early) has occurred in another transfer and
-                 this transfer will be aborted in the progress callback */
-
   /* for parallel progress bar */
   curl_off_t dltotal;
   curl_off_t dlnow;
@@ -77,6 +68,15 @@ struct per_transfer {
   char *uploadfile;
   char *errorbuffer; /* allocated and assigned while this is used for a
                         transfer */
+  bool infdopen; /* TRUE if infd needs closing */
+  bool noprogress;
+  bool was_last_header_empty;
+
+  bool added; /* set TRUE when added to the multi handle */
+  bool abort; /* when doing parallel transfers and this is TRUE then a critical
+                 error (eg --fail-early) has occurred in another transfer and
+                 this transfer will be aborted in the progress callback */
+  bool skip;  /* considered already done */
 };
 
 CURLcode operate(struct GlobalConfig *config, int argc, argv_item_t argv[]);