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

18 files changed, 125 insertions, 5 deletions

diff --git a/docs/cmdline-opts/Makefile.inc b/docs/cmdline-opts/Makefile.inc
index 9891f3717..778149ca3 100644
--- a/docs/cmdline-opts/Makefile.inc
+++ b/docs/cmdline-opts/Makefile.inc
@@ -12,7 +12,9 @@ DPAGES = abstract-unix-socket.d anyauth.d append.d basic.d cacert.d capath.d cer
   form.d form-string.d ftp-account.d ftp-alternative-to-user.d          \
   ftp-create-dirs.d ftp-method.d ftp-pasv.d ftp-port.d ftp-pret.d       \
   ftp-skip-pasv-ip.d ftp-ssl-ccc.d ftp-ssl-ccc-mode.d ftp-ssl-control.d \
-  get.d globoff.d head.d header.d help.d hostpubmd5.d http1.0.d         \
+  get.d globoff.d                                                       \
+  happy-eyeballs-timeout-ms.d                                           \
+  head.d header.d help.d hostpubmd5.d http1.0.d                         \
   http1.1.d http2.d http2-prior-knowledge.d ignore-content-length.d     \
   include.d insecure.d interface.d ipv4.d ipv6.d junk-session-cookies.d \
   keepalive-time.d key.d key-type.d krb.d libcurl.d limit-rate.d        \
diff --git a/docs/cmdline-opts/happy-eyeballs-timeout-ms.d b/docs/cmdline-opts/happy-eyeballs-timeout-ms.d
new file mode 100644
index 000000000..ec9a8c228
--- /dev/null
+++ b/docs/cmdline-opts/happy-eyeballs-timeout-ms.d
@@ -0,0 +1,17 @@
+Long: happy-eyeballs-timeout-ms
+Arg: <milliseconds>
+Help: How long to wait in milliseconds for IPv6 before trying IPv4
+Added: 7.59.0
+---
+Happy eyeballs is an algorithm that attempts to connect to both IPv4 and IPv6
+addresses for dual-stack hosts, preferring IPv6 first for the number of
+milliseconds. If the IPv6 address cannot be connected to within that time then
+a connection attempt is made to the IPv4 address in parallel. The first
+connection to be established is the one that is used.
+
+The range of suggested useful values is limited. Happy Eyeballs RFC 6555 says
+"It is RECOMMENDED that connection attempts be paced 150-250 ms apart to
+balance human factors against network load." libcurl currently defaults to
+200 ms. Firefox and Chrome currently default to 300 ms.
+
+If this option is used several times, the last one will be used.
diff --git a/docs/libcurl/curl_easy_setopt.3 b/docs/libcurl/curl_easy_setopt.3
index 0249e6bbc..72ef2886a 100644
--- a/docs/libcurl/curl_easy_setopt.3
+++ b/docs/libcurl/curl_easy_setopt.3
@@ -577,6 +577,8 @@ Mode for creating new remote directories. See \fICURLOPT_NEW_DIRECTORY_PERMS(3)\
 .SH TELNET OPTIONS
 .IP CURLOPT_TELNETOPTIONS
 TELNET options. See \fICURLOPT_TELNETOPTIONS(3)\fP
+.IP CURLOPT_HAPPY_EYEBALLS_TIMEOUT
+Timeout for happy eyeballs. See \fICURLOPT_HAPPY_EYEBALLS_TIMEOUT(3)\fP
 .SH RETURN VALUE
 \fICURLE_OK\fP (zero) means that the option was set properly, non-zero means an
 error occurred as \fI<curl/curl.h>\fP defines. See the \fIlibcurl-errors(3)\fP
diff --git a/docs/libcurl/opts/CURLOPT_HAPPY_EYEBALLS_TIMEOUT.3 b/docs/libcurl/opts/CURLOPT_HAPPY_EYEBALLS_TIMEOUT.3
new file mode 100644
index 000000000..d4fa1505b
--- /dev/null
+++ b/docs/libcurl/opts/CURLOPT_HAPPY_EYEBALLS_TIMEOUT.3
@@ -0,0 +1,59 @@
+.\" **************************************************************************
+.\" *                                  _   _ ____  _
+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
+.\" *                            | (__| |_| |  _ <| |___
+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2015, 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.haxx.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.
+.\" *
+.\" **************************************************************************
+.\"
+.TH CURLOPT_HAPPY_EYEBALLS_TIMEOUT 3 "1 Feb 2018" "libcurl 7.59.0" "curl_easy_setopt options"
+.SH NAME
+CURLOPT_HAPPY_EYEBALLS_TIMEOUT \- head start for ipv6 for happy eyeballs
+.SH SYNOPSIS
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HAPPY_EYEBALLS_TIMEOUT, long timeout);
+.SH DESCRIPTION
+Happy eyeballs is an algorithm that attempts to connect to both IPv4 and IPv6
+addresses for dual-stack hosts, preferring IPv6 first for \fItimeout\fP
+milliseconds. If the IPv6 address cannot be connected to within that time then
+a connection attempt is made to the IPv4 address in parallel. The first
+connection to be established is the one that is used.
+
+The range of suggested useful values for \fItimeout\fP is limited. Happy
+Eyeballs RFC 6555 says "It is RECOMMENDED that connection attempts be paced
+150-250 ms apart to balance human factors against network load." libcurl
+currently defaults to 200 ms. Firefox and Chrome currently default to 300 ms.
+.SH DEFAULT
+CURL_HET_DEFAULT (currently defined as 200L)
+.SH EXAMPLE
+.nf
+CURL *curl = curl_easy_init();
+if(curl) {
+  curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
+  curl_easy_setopt(curl, CURLOPT_HAPPY_EYEBALLS_TIMEOUT, 300L);
+
+  curl_easy_perform(curl);
+
+  /* always cleanup */
+  curl_easy_cleanup(curl);
+}
+.fi
+.SH AVAILABILITY
+Added in 7.59.0
+.SH RETURN VALUE
+Returns CURLE_OK
diff --git a/docs/libcurl/opts/Makefile.inc b/docs/libcurl/opts/Makefile.inc
index 22a54c399..d0597500a 100644
--- a/docs/libcurl/opts/Makefile.inc
+++ b/docs/libcurl/opts/Makefile.inc
@@ -136,6 +136,7 @@ man_MANS =                                      \
   CURLOPT_FTP_USE_EPSV.3                        \
   CURLOPT_FTP_USE_PRET.3                        \
   CURLOPT_GSSAPI_DELEGATION.3                   \
+  CURLOPT_HAPPY_EYEBALLS_TIMEOUT.3              \
   CURLOPT_HEADER.3                              \
   CURLOPT_HEADERDATA.3                          \
   CURLOPT_HEADERFUNCTION.3                      \
diff --git a/docs/libcurl/symbols-in-versions b/docs/libcurl/symbols-in-versions
index ac3dadee3..44f111b05 100644
--- a/docs/libcurl/symbols-in-versions
+++ b/docs/libcurl/symbols-in-versions
@@ -403,6 +403,7 @@ CURLOPT_FTP_USE_EPRT            7.10.5
 CURLOPT_FTP_USE_EPSV            7.9.2
 CURLOPT_FTP_USE_PRET            7.20.0
 CURLOPT_GSSAPI_DELEGATION       7.22.0
+CURLOPT_HAPPY_EYEBALLS_TIMEOUT  7.59.0
 CURLOPT_HEADER                  7.1
 CURLOPT_HEADERDATA              7.10
 CURLOPT_HEADERFUNCTION          7.7.2
@@ -741,6 +742,7 @@ CURL_GLOBAL_DEFAULT             7.8
 CURL_GLOBAL_NOTHING             7.8
 CURL_GLOBAL_SSL                 7.8
 CURL_GLOBAL_WIN32               7.8.1
+CURL_HET_DEFAULT                7.59.0
 CURL_HTTPPOST_BUFFER            7.46.0
 CURL_HTTPPOST_CALLBACK          7.46.0
 CURL_HTTPPOST_FILENAME          7.46.0
diff --git a/include/curl/curl.h b/include/curl/curl.h
index 7cab0a16c..a592a0e4d 100644
--- a/include/curl/curl.h
+++ b/include/curl/curl.h
@@ -791,6 +791,11 @@ typedef enum {
    SSL backends where such behavior is present. */
 #define CURLSSLOPT_NO_REVOKE (1<<1)
 
+/* The default connection attempt delay in milliseconds for happy eyeballs.
+   CURLOPT_HAPPY_EYEBALLS_TIMEOUT.3 and happy-eyeballs-timeout-ms.d document
+   this value, keep them in sync. */
+#define CURL_HET_DEFAULT 200L
+
 #ifndef CURL_NO_OLDIES /* define this to test if your app builds with all
                           the obsolete stuff removed! */
 
@@ -1825,6 +1830,9 @@ typedef enum {
      seconds since 1 Jan 1970. */
   CINIT(TIMEVALUE_LARGE, OFF_T, 270),
 
+  /* Head start in milliseconds to give happy eyeballs. */
+  CINIT(HAPPY_EYEBALLS_TIMEOUT, LONG, 271),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;
 
diff --git a/lib/connect.c b/lib/connect.c
index c3add43cc..1a27ae135 100644
--- a/lib/connect.c
+++ b/lib/connect.c
@@ -783,7 +783,8 @@ CURLcode Curl_is_connected(struct connectdata *conn,
 
       /* should we try another protocol family? */
       if(i == 0 && conn->tempaddr[1] == NULL &&
-         Curl_timediff(now, conn->connecttime) >= HAPPY_EYEBALLS_TIMEOUT) {
+         (Curl_timediff(now, conn->connecttime) >=
+          data->set.happy_eyeballs_timeout)) {
         trynextip(conn, sockindex, 1);
       }
     }
@@ -1206,7 +1207,8 @@ CURLcode Curl_connecthost(struct connectdata *conn,  /* context */
   }
 
   data->info.numconnects++; /* to track the number of connections made */
-  Curl_expire(conn->data, HAPPY_EYEBALLS_TIMEOUT, EXPIRE_HAPPY_EYEBALLS);
+  Curl_expire(conn->data, data->set.happy_eyeballs_timeout,
+              EXPIRE_HAPPY_EYEBALLS);
 
   return CURLE_OK;
 }
diff --git a/lib/connect.h b/lib/connect.h
index 4c038874e..193dc6397 100644
--- a/lib/connect.h
+++ b/lib/connect.h
@@ -41,8 +41,6 @@ timediff_t Curl_timeleft(struct Curl_easy *data,
                          bool duringconnect);
 
 #define DEFAULT_CONNECT_TIMEOUT 300000 /* milliseconds == five minutes */
-#define HAPPY_EYEBALLS_TIMEOUT     200 /* milliseconds to wait between
-                                          IPv4/IPv6 connection attempts */
 
 /*
  * Used to extract socket and connectdata struct for the most recent
diff --git a/lib/setopt.c b/lib/setopt.c
index 69f98a64d..f03e6d5fa 100644
--- a/lib/setopt.c
+++ b/lib/setopt.c
@@ -2533,6 +2533,12 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option,
   case CURLOPT_SSH_COMPRESSION:
     data->set.ssh_compression = (0 != va_arg(param, long))?TRUE:FALSE;
     break;
+  case CURLOPT_HAPPY_EYEBALLS_TIMEOUT:
+    arg = va_arg(param, long);
+    if(arg < 0)
+      return CURLE_BAD_FUNCTION_ARGUMENT;
+    data->set.happy_eyeballs_timeout = arg;
+    break;
   default:
     /* unknown tag and its companion, just ignore: */
     result = CURLE_UNKNOWN_OPTION;
diff --git a/lib/url.c b/lib/url.c
index 74813e874..90afd03a6 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -527,6 +527,7 @@ CURLcode Curl_init_userdefined(struct Curl_easy *data)
   set->expect_100_timeout = 1000L; /* Wait for a second by default. */
   set->sep_headers = TRUE; /* separated header lists by default */
   set->buffer_size = READBUFFER_SIZE;
+  set->happy_eyeballs_timeout = CURL_HET_DEFAULT;
 
   Curl_http2_init_userset(set);
   return result;
diff --git a/lib/urldata.h b/lib/urldata.h
index 6c594fe8d..35014c232 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1520,6 +1520,7 @@ struct UserDefined {
   long timeout;         /* in milliseconds, 0 means no timeout */
   long connecttimeout;  /* in milliseconds, 0 means no timeout */
   long accepttimeout;   /* in milliseconds, 0 means no timeout */
+  long happy_eyeballs_timeout; /* in milliseconds, 0 is a valid value */
   long server_response_timeout; /* in milliseconds, 0 means no timeout */
   long tftp_blksize;    /* in bytes, 0 means use default */
   bool tftp_no_options; /* do not send TFTP options requests */
diff --git a/packages/OS400/curl.inc.in b/packages/OS400/curl.inc.in
index 03603e290..1b2996894 100644
--- a/packages/OS400/curl.inc.in
+++ b/packages/OS400/curl.inc.in
@@ -1322,6 +1322,10 @@
      d                 c                   00268
      d  CURLOPT_MIMEPOST...
      d                 c                   10269
+     d  CURLOPT_TIMEVALUE_LARGE...
+     d                 c                   30270
+     d  CURLOPT_HAPPY_EYEBALLS_TIMEOUT...
+     d                 c                   00271
       *
       /if not defined(CURL_NO_OLDIES)
      d  CURLOPT_FILE   c                   10001
diff --git a/src/tool_cfgable.c b/src/tool_cfgable.c
index d77488166..81e16c1c8 100644
--- a/src/tool_cfgable.c
+++ b/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)
diff --git a/src/tool_cfgable.h b/src/tool_cfgable.h
index 0f316775d..743ce725d 100644
--- a/src/tool_cfgable.h
+++ b/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 */
diff --git a/src/tool_getparam.c b/src/tool_getparam.c
index 46e7dd3cd..c6b1a0d6f 100644
--- a/src/tool_getparam.c
+++ b/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 */
diff --git a/src/tool_help.c b/src/tool_help.c
index 751b43aca..9796b7e87 100644
--- a/src/tool_help.c
+++ b/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>",
diff --git a/src/tool_operate.c b/src/tool_operate.c
index f326a0d0c..c8e9c6901 100644
--- a/src/tool_operate.c
+++ b/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 */