Introduce CURLOPT_PROXY_TRANSFER_MODE option. See the manpage patch for info.
---
 docs/libcurl/curl_easy_setopt.3 |    7 +++++++
 include/curl/curl.h             |    3 +++
 lib/http.c                      |   34 ++++++++++++++++++----------------
 lib/url.c                       |   17 +++++++++++++++++
 lib/urldata.h                   |    2 ++
 5 files changed, 47 insertions(+), 16 deletions(-)

--- include/curl/curl.h.orig
+++ include/curl/curl.h
@@ -1182,6 +1182,9 @@ typedef enum {
   /* POST volatile input fields. */
   CINIT(COPYPOSTFIELDS, OBJECTPOINT, 165),
 
+  /* set transfer mode (;type=<a|i>) when doing FTP via an HTTP proxy */
+  CINIT(PROXY_TRANSFER_MODE, LONG, 166),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;
 
--- lib/http.c.orig
+++ lib/http.c
@@ -2122,22 +2122,24 @@ CURLcode Curl_http(struct connectdata *c
       }
     }
     ppath = data->change.url;
-    /* when doing ftp, append ;type=<a|i> if not present */
-    if(checkprefix("ftp://", ppath) || checkprefix("ftps://", ppath)) {
-      char *p = strstr(ppath, ";type=");
-      if(p && p[6] && p[7] == 0) {
-        switch (toupper((int)((unsigned char)p[6]))) {
-        case 'A':
-        case 'D':
-        case 'I':
-          break;
-        default:
-          p = NULL;
-        }
-      }
-      if(!p)
-        snprintf(ftp_typecode, sizeof(ftp_typecode), ";type=%c",
-                 data->set.prefer_ascii ? 'a' : 'i');
+    if (data->set.proxy_transfer_mode) {
+      /* when doing ftp, append ;type=<a|i> if not present */
+      if(checkprefix("ftp://", ppath) || checkprefix("ftps://", ppath)) {
+        char *p = strstr(ppath, ";type=");
+        if(p && p[6] && p[7] == 0) {
+          switch (toupper((int)((unsigned char)p[6]))) {
+          case 'A':
+          case 'D':
+          case 'I':
+            break;
+          default:
+            p = NULL;
+          }
+        }
+        if(!p)
+          snprintf(ftp_typecode, sizeof(ftp_typecode), ";type=%c",
+                   data->set.prefer_ascii ? 'a' : 'i');
+      }
     }
   }
   if(HTTPREQ_POST_FORM == httpreq) {
--- lib/url.c.orig
+++ lib/url.c
@@ -2036,6 +2036,23 @@ CURLcode Curl_setopt(struct SessionHandl
      */
     data->set.new_directory_perms = va_arg(param, long);
     break;
+  case CURLOPT_PROXY_TRANSFER_MODE:
+    /*
+     * set transfer mode (;type=<a|i>) when doing FTP via an HTTP proxy
+     */
+    switch (va_arg(param, long)) {
+      case 0:
+        data->set.proxy_transfer_mode = 0;
+        break;
+      case 1:
+        data->set.proxy_transfer_mode = 1;
+        break;
+      default:
+        /* reserve other values for future use */
+        result = CURLE_FAILED_INIT;
+        break;
+    }
+    break;
 
   default:
     /* unknown tag and its companion, just ignore: */
--- lib/urldata.h.orig
+++ lib/urldata.h
@@ -1439,6 +1439,8 @@ struct UserDefined {
                             content-encoded (chunked, compressed) */
   long new_file_perms;    /* Permissions to use when creating remote files */
   long new_directory_perms; /* Permissions to use when creating remote dirs */
+  bool proxy_transfer_mode; /* set transfer mode (;type=<a|i>) when doing FTP
+                               via an HTTP proxy */
 
   char *str[STRING_LAST]; /* array of strings, pointing to allocated memory */
 };
--- docs/libcurl/curl_easy_setopt.3.orig
+++ docs/libcurl/curl_easy_setopt.3
@@ -1064,6 +1064,13 @@ or similar.
 libcurl does not do a complete ASCII conversion when doing ASCII transfers
 over FTP. This is a known limitation/flaw that nobody has rectified. libcurl
 simply sets the mode to ascii and performs a standard transfer.
+.IP CURLOPT_PROXY_TRANSFER_MODE
+Pass a long. If the value is set to 1 (one), it tells libcurl to set the
+transfer mode (binary or ASCII) for FTP transfers done via an HTTP proxy, by
+appending ;type=a or ;type=i to the URL. Without this setting, or it being
+set to 0 (zero, the default), \fICURLOPT_TRANSFERTEXT\fP has no effect when
+doing FTP via a proxy. Beware that not all proxies support this feature.
+(Added in 7.17.2)
 .IP CURLOPT_CRLF
 Convert Unix newlines to CRLF newlines on transfers.
 .IP CURLOPT_RANGE