curl: add --parallel-connectbagder/parallel-connect

Starting with this change when doing parallel transfers, without this
option set, curl will prefer to create new transfers multiplexed on an
existing connection rather than creating a brand new one.

--parallel-connect can be set to tell curl to prefer to use new
connections rather than to wait and try to multiplex.

libcurl-wise, this means that curl will set CURLOPT_PIPEWAIT by default
on parallel transfers.

Suggested-by: Tom van der Woerdt

6 files changed, 22 insertions, 1 deletions

diff --git a/docs/cmdline-opts/Makefile.inc b/docs/cmdline-opts/Makefile.inc
index c90e9c5fb..9743cafca 100644
--- a/docs/cmdline-opts/Makefile.inc
+++ b/docs/cmdline-opts/Makefile.inc
@@ -103,9 +103,10 @@ DPAGES =					\
   ntlm.d ntlm-wb.d				\
   oauth2-bearer.d				\
   output.d                                      \
+  parallel-connect.d                            \
+  parallel-max.d                                \
   parallel.d                                    \
   pass.d                			\
-  parallel-max.d                                \
   path-as-is.d					\
   pinnedpubkey.d				\
   post301.d					\
diff --git a/docs/cmdline-opts/parallel-connect.d b/docs/cmdline-opts/parallel-connect.d
new file mode 100644
index 000000000..a51e12e85
--- /dev/null
+++ b/docs/cmdline-opts/parallel-connect.d
@@ -0,0 +1,9 @@
+Long: parallel-connect
+Help: Prefer parallel connections to multiplexed ones
+Added: 7.68.0
+See-also: parallel parallel-max
+---
+When doing parallel transfers, this option will instruct curl that it should
+rather prefer opening up more connections in parallel rather than risk waiting
+to see if new transfers can be added as multiplexed streams on another
+connection.
diff --git a/src/tool_cfgable.h b/src/tool_cfgable.h
index 7232c35e3..4372cc6fc 100644
--- a/src/tool_cfgable.h
+++ b/src/tool_cfgable.h
@@ -300,6 +300,7 @@ struct GlobalConfig {
 #endif
   bool parallel;
   long parallel_max;
+  bool parallel_connect;
   struct OperationConfig *first;
   struct OperationConfig *current;
   struct OperationConfig *last;   /* Always last in the struct */
diff --git a/src/tool_getparam.c b/src/tool_getparam.c
index 3882cb97e..d49b7031b 100644
--- a/src/tool_getparam.c
+++ b/src/tool_getparam.c
@@ -321,6 +321,7 @@ static const struct LongShort aliases[]= {
   {"z",  "time-cond",                ARG_STRING},
   {"Z",  "parallel",                 ARG_BOOL},
   {"Zb", "parallel-max",             ARG_STRING},
+  {"Zc", "parallel-connect",         ARG_BOOL},
   {"#",  "progress-bar",             ARG_BOOL},
   {"#m", "progress-meter",           ARG_BOOL},
   {":",  "next",                     ARG_NONE},
@@ -2154,6 +2155,9 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
            (global->parallel_max < 1))
           global->parallel_max = PARALLEL_DEFAULT;
         break;
+      case 'c':   /* --parallel-connect */
+        global->parallel_connect = toggle;
+        break;
       }
       break;
     case 'z': /* time condition coming up */
diff --git a/src/tool_help.c b/src/tool_help.c
index 022956676..7de19dc8f 100644
--- a/src/tool_help.c
+++ b/src/tool_help.c
@@ -279,6 +279,8 @@ static const struct helptxt helptext[] = {
    "Write to file instead of stdout"},
   {"-Z, --parallel",
    "Perform transfers in parallel"},
+  {"    --parallel-connect",
+   "Prefer parallel connections to multiplexed ones"},
   {"    --parallel-max",
    "Maximum concurrency for parallel transfers"},
   {"    --pass <phrase>",
diff --git a/src/tool_operate.c b/src/tool_operate.c
index 3087d2d14..c0ca45756 100644
--- a/src/tool_operate.c
+++ b/src/tool_operate.c
@@ -1973,6 +1973,10 @@ static CURLcode add_parallel_transfers(struct GlobalConfig *global,
     if(result)
       break;
 
+    /* parallel connect means that we don't set PIPEWAIT since pipewait
+       will make libcurl prefer multiplexing */
+    (void)curl_easy_setopt(per->curl, CURLOPT_PIPEWAIT,
+                           global->parallel_connect ? 0L : 1L);
     (void)curl_easy_setopt(per->curl, CURLOPT_PRIVATE, per);
     (void)curl_easy_setopt(per->curl, CURLOPT_XFERINFOFUNCTION, xferinfo_cb);
     (void)curl_easy_setopt(per->curl, CURLOPT_XFERINFODATA, per);