url: Add option CURLOPT_HAPPY_EYEBALLS_TIMEOUT

- Add new option CURLOPT_HAPPY_EYEBALLS_TIMEOUT to set libcurl's happy
  eyeball timeout value.

- Add new optval macro CURL_HET_DEFAULT to represent the default happy
  eyeballs timeout value (currently 200 ms).

- Add new tool option --happy-eyeballs-timeout-ms to expose
  CURLOPT_HAPPY_EYEBALLS_TIMEOUT. The -ms suffix is used because the
  other -timeout options in the tool expect seconds not milliseconds.

Closes https://github.com/curl/curl/pull/2260

src/tool_cfgable.c

@@ -42,6 +42,7 @@ void config_init(struct OperationConfig* config)
   config->proto_redir_present = FALSE;
   config->proto_default = NULL;
   config->tcp_nodelay = TRUE; /* enabled by default */
+  config->happy_eyeballs_timeout_ms = CURL_HET_DEFAULT;
 }
 
 static void free_config_fields(struct OperationConfig *config)

src/tool_cfgable.h

@@ -250,6 +250,8 @@ struct OperationConfig {
   curl_error synthetic_error;     /* if non-zero, it overrides any libcurl
                                      error */
   bool ssh_compression;           /* enable/disable SSH compression */
+  long happy_eyeballs_timeout_ms; /* happy eyeballs timeout in milliseconds.
+                                     0 is valid. default: CURL_HET_DEFAULT. */
   struct GlobalConfig *global;
   struct OperationConfig *prev;
   struct OperationConfig *next;   /* Always last in the struct */

src/tool_getparam.c

@@ -190,6 +190,7 @@ static const struct LongShort aliases[]= {
   {"$X", "tls-max",                  ARG_STRING},
   {"$Y", "suppress-connect-headers", ARG_BOOL},
   {"$Z", "compressed-ssh",           ARG_BOOL},
+  {"$~", "happy-eyeballs-timeout-ms", ARG_STRING},
   {"0",   "http1.0",                 ARG_NONE},
   {"01",  "http1.1",                 ARG_NONE},
   {"02",  "http2",                   ARG_NONE},
@@ -1111,6 +1112,12 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
       case 'Z': /* --compressed-ssh */
         config->ssh_compression = toggle;
         break;
+      case '~': /* --happy-eyeballs-timeout-ms */
+        err = str2unum(&config->happy_eyeballs_timeout_ms, nextarg);
+        if(err)
+          return err;
+        /* 0 is a valid value for this timeout */
+        break;
       }
       break;
     case '#': /* --progress-bar */

src/tool_help.c

@@ -160,6 +160,8 @@ static const struct helptxt helptext[] = {
    "Put the post data in the URL and use GET"},
   {"-g, --globoff",
    "Disable URL sequences and ranges using {} and []"},
+  {"    --happy-eyeballs-timeout-ms",
+   "How long to wait in milliseconds for IPv6 before trying IPv4"},
   {"-I, --head",
    "Show document info only"},
   {"-H, --header <header/@file>",

src/tool_operate.c

@@ -1440,6 +1440,11 @@ static CURLcode operate_do(struct GlobalConfig *global,
         if(config->tftp_no_options)
           my_setopt(curl, CURLOPT_TFTP_NO_OPTIONS, 1L);
 
+        /* new in 7.59.0 */
+        if(config->happy_eyeballs_timeout_ms != CURL_HET_DEFAULT)
+          my_setopt(curl, CURLOPT_HAPPY_EYEBALLS_TIMEOUT,
+                    config->happy_eyeballs_timeout_ms);
+
         /* initialize retry vars for loop below */
         retry_sleep_default = (config->retry_delay) ?
           config->retry_delay*1000L : RETRY_SLEEP_DEFAULT; /* ms */