Cyrill Osterwalder posted a detailed analysis about a bug that occurs when

using a custom Host: header and curl fails to send a request on a re-used
persistent connection and thus creates a new connection and resends it. It
then sent two Host: headers. Cyrill's analysis was posted here:
http://curl.haxx.se/mail/archive-2005-01/0022.html

CHANGES

@@ -8,6 +8,12 @@
 
 
 Daniel (11 January 2005)
+- Cyrill Osterwalder posted a detailed analysis about a bug that occurs when
+  using a custom Host: header and curl fails to send a request on a re-used
+  persistent connection and thus creates a new connection and resends it. It
+  then sent two Host: headers. Cyrill's analysis was posted here:
+  http://curl.haxx.se/mail/archive-2005-01/0022.html
+
 - Bruce Mitchener identified (bug report #1099640) the never-ending SOCKS5
   problem with the version byte and the check for bad versions. Bruce has lots
   of clues on this, and based on his suggestion I've now removed the check of

RELEASE-NOTES

@@ -16,6 +16,7 @@ This release includes the following changes:
 
 This release includes the following bugfixes:
 
+ o duplicate Host: when failed connection re-use
  o SOCKS5 version check
  o memory problem with cleaning up multi interface
  o SSL certificate name memory leak
@@ -35,6 +36,6 @@ advice from friends like these:
 
  Dan Fandrich, Peter Pentchev, Marcin Konicki, Rune Kleveland, David Shaw,
  Werner Koch, Gisle Vanem, Alex Neblett, Kai Sommerfeld, Marty Kuhrt,
- Hzhijun, Pavel Orehov, Bruce Mitchener
+ Hzhijun, Pavel Orehov, Bruce Mitchener, Cyrill Osterwalder
 
         Thanks! (and sorry if I forgot to mention someone)

lib/multi.c

@@ -342,7 +342,7 @@ CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles)
           gotourl = strdup(easy->easy_handle->change.url);
           if(gotourl) {
             easy->easy_handle->change.url_changed = FALSE;
-            easy->result = Curl_follow(easy->easy_handle, gotourl);
+            easy->result = Curl_follow(easy->easy_handle, gotourl, FALSE);
             if(CURLE_OK == easy->result)
               easy->state = CURLM_STATE_CONNECT;
             else
@@ -518,7 +518,7 @@ CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles)
             easy->easy_conn->newurl = NULL;
             easy->result = Curl_done(&easy->easy_conn, CURLE_OK);
             if(easy->result == CURLE_OK)
-              easy->result = Curl_follow(easy->easy_handle, newurl);
+              easy->result = Curl_follow(easy->easy_handle, newurl, FALSE);
             if(CURLE_OK == easy->result) {
               easy->state = CURLM_STATE_CONNECT;
               result = CURLM_CALL_MULTI_PERFORM;

lib/transfer.c

@@ -1742,9 +1742,11 @@ static void strcpy_url(char *output, char *url)
  * as given by the remote server and set up the new URL to request.
  */
 CURLcode Curl_follow(struct SessionHandle *data,
-                     char *newurl) /* this 'newurl' is the Location: string,
+                     char *newurl, /* this 'newurl' is the Location: string,
                                       and it must be malloc()ed before passed
                                       here */
+                     bool retry) /* set TRUE if this is a request retry as
+                                    opposed to a real redirect following */
 {
   /* Location: redirect */
   char prot[16]; /* URL protocol string storage */
@@ -1758,6 +1760,7 @@ CURLcode Curl_follow(struct SessionHandle *data,
     return CURLE_TOO_MANY_REDIRECTS;
   }
 
+  if(!retry)
     /* mark the next request as a followed location: */
     data->state.this_is_a_follow = TRUE;
 
@@ -2063,7 +2066,7 @@ Curl_connect_host(struct SessionHandle *data,
       res = Curl_done(conn, res);
       if(CURLE_OK == res) {
         char *gotourl = strdup(data->change.url);
-        res = Curl_follow(data, gotourl);
+        res = Curl_follow(data, gotourl, FALSE);
         if(res)
           free(gotourl);
       }
@@ -2086,6 +2089,7 @@ CURLcode Curl_perform(struct SessionHandle *data)
   CURLcode res2;
   struct connectdata *conn=NULL;
   char *newurl = NULL; /* possibly a new URL to follow to! */
+  bool retry = FALSE;
 
   data->state.used_interface = Curl_if_easy;
 
@@ -2119,6 +2123,8 @@ CURLcode Curl_perform(struct SessionHandle *data)
         res = Transfer(conn); /* now fetch that URL please */
         if(res == CURLE_OK) {
 
+          retry = FALSE;
+
           if((conn->keep.bytecount+conn->headerbytecount == 0) &&
              conn->bits.reuse) {
             /* We got no data and we attempted to re-use a connection. This
@@ -2135,6 +2141,7 @@ CURLcode Curl_perform(struct SessionHandle *data)
                                         prevent i.e HTTP transfers to return
                                         error just because nothing has been
                                         transfered! */
+            retry = TRUE;
           }
           else
             /*
@@ -2174,7 +2181,7 @@ CURLcode Curl_perform(struct SessionHandle *data)
        */
 
       if((res == CURLE_OK) && newurl) {
-        res = Curl_follow(data, newurl);
+        res = Curl_follow(data, newurl, retry);
         if(CURLE_OK == res) {
           newurl = NULL;
           continue;

lib/transfer.h

@@ -26,7 +26,7 @@ CURLcode Curl_perform(struct SessionHandle *data);
 CURLcode Curl_pretransfer(struct SessionHandle *data);
 CURLcode Curl_pretransfersec(struct connectdata *conn);
 CURLcode Curl_posttransfer(struct SessionHandle *data);
-CURLcode Curl_follow(struct SessionHandle *data, char *newurl);
+CURLcode Curl_follow(struct SessionHandle *data, char *newurl, bool retry);
 CURLcode Curl_readwrite(struct connectdata *conn, bool *done);
 void Curl_single_fdset(struct connectdata *conn,
                        fd_set *read_fd_set,