mime: relax easy/mime structures binding

Deprecation and removal of codeset conversion support from the library
have released the strict need for an early binding of mime structures to
an easy handle (https://github.com/curl/curl/commit/2610142).

This constraint currently forces to create the handle before the mime
structure and the latter cannot be attached to another handle once
created (see https://curl.se/mail/lib-2022-08/0027.html).

This commit removes the handle pointers from the mime structures
allowing more flexibility on their use.

When an easy handle is duplicated, bound mime structures must however
still be duplicated too as their components hold send-time dynamic
information.

Closes #9927

1 files changed, 14 insertions, 18 deletions

diff --git a/lib/mime.c b/lib/mime.c
index 117c66f4d..e3f2821db 100644
--- a/lib/mime.c
+++ b/lib/mime.c
@@ -1175,7 +1175,7 @@ void Curl_mime_cleanpart(curl_mimepart *part)
   Curl_safefree(part->mimetype);
   Curl_safefree(part->name);
   Curl_safefree(part->filename);
-  Curl_mime_initpart(part, part->easy);
+  Curl_mime_initpart(part);
 }
 
 /* Recursively delete a mime handle and its parts. */
@@ -1195,7 +1195,8 @@ void curl_mime_free(curl_mime *mime)
   }
 }
 
-CURLcode Curl_mime_duppart(curl_mimepart *dst, const curl_mimepart *src)
+CURLcode Curl_mime_duppart(struct Curl_easy *data,
+                           curl_mimepart *dst, const curl_mimepart *src)
 {
   curl_mime *mime;
   curl_mimepart *d;
@@ -1224,13 +1225,13 @@ CURLcode Curl_mime_duppart(curl_mimepart *dst, const curl_mimepart *src)
   case MIMEKIND_MULTIPART:
     /* No one knows about the cloned subparts, thus always attach ownership
        to the part. */
-    mime = curl_mime_init(dst->easy);
+    mime = curl_mime_init(data);
     res = mime? curl_mime_subparts(dst, mime): CURLE_OUT_OF_MEMORY;
 
     /* Duplicate subparts. */
     for(s = ((curl_mime *) src->arg)->firstpart; !res && s; s = s->nextpart) {
       d = curl_mime_addpart(mime);
-      res = d? Curl_mime_duppart(d, s): CURLE_OUT_OF_MEMORY;
+      res = d? Curl_mime_duppart(data, d, s): CURLE_OUT_OF_MEMORY;
     }
     break;
   default:  /* Invalid kind: should not occur. */
@@ -1282,7 +1283,6 @@ curl_mime *curl_mime_init(struct Curl_easy *easy)
   mime = (curl_mime *) malloc(sizeof(*mime));
 
   if(mime) {
-    mime->easy = easy;
     mime->parent = NULL;
     mime->firstpart = NULL;
     mime->lastpart = NULL;
@@ -1302,10 +1302,9 @@ curl_mime *curl_mime_init(struct Curl_easy *easy)
 }
 
 /* Initialize a mime part. */
-void Curl_mime_initpart(curl_mimepart *part, struct Curl_easy *easy)
+void Curl_mime_initpart(curl_mimepart *part)
 {
   memset((char *) part, 0, sizeof(*part));
-  part->easy = easy;
   part->lastreadstatus = 1; /* Successful read status. */
   mimesetstate(&part->state, MIMESTATE_BEGIN, NULL);
 }
@@ -1321,7 +1320,7 @@ curl_mimepart *curl_mime_addpart(curl_mime *mime)
   part = (curl_mimepart *) malloc(sizeof(*part));
 
   if(part) {
-    Curl_mime_initpart(part, mime->easy);
+    Curl_mime_initpart(part);
     part->parent = mime;
 
     if(mime->lastpart)
@@ -1551,10 +1550,6 @@ CURLcode Curl_mime_set_subparts(curl_mimepart *part,
   cleanup_part_content(part);
 
   if(subparts) {
-    /* Must belong to the same data handle. */
-    if(part->easy && subparts->easy && part->easy != subparts->easy)
-      return CURLE_BAD_FUNCTION_ARGUMENT;
-
     /* Should not have been attached already. */
     if(subparts->parent)
       return CURLE_BAD_FUNCTION_ARGUMENT;
@@ -1565,8 +1560,7 @@ CURLcode Curl_mime_set_subparts(curl_mimepart *part,
       while(root->parent && root->parent->parent)
         root = root->parent->parent;
       if(subparts == root) {
-        if(part->easy)
-          failf(part->easy, "Can't add itself as a subpart");
+        /* Can't add as a subpart of itself. */
         return CURLE_BAD_FUNCTION_ARGUMENT;
       }
     }
@@ -1766,7 +1760,8 @@ static bool content_type_match(const char *contenttype,
   return FALSE;
 }
 
-CURLcode Curl_mime_prepare_headers(curl_mimepart *part,
+CURLcode Curl_mime_prepare_headers(struct Curl_easy *data,
+                                   curl_mimepart *part,
                                    const char *contenttype,
                                    const char *disposition,
                                    enum mimestrategy strategy)
@@ -1835,12 +1830,12 @@ CURLcode Curl_mime_prepare_headers(curl_mimepart *part,
       char *filename = NULL;
 
       if(part->name) {
-        name = escape_string(part->easy, part->name, strategy);
+        name = escape_string(data, part->name, strategy);
         if(!name)
           ret = CURLE_OUT_OF_MEMORY;
       }
       if(!ret && part->filename) {
-        filename = escape_string(part->easy, part->filename, strategy);
+        filename = escape_string(data, part->filename, strategy);
         if(!filename)
           ret = CURLE_OUT_OF_MEMORY;
       }
@@ -1897,7 +1892,8 @@ CURLcode Curl_mime_prepare_headers(curl_mimepart *part,
     if(content_type_match(contenttype, STRCONST("multipart/form-data")))
       disposition = "form-data";
     for(subpart = mime->firstpart; subpart; subpart = subpart->nextpart) {
-      ret = Curl_mime_prepare_headers(subpart, NULL, disposition, strategy);
+      ret = Curl_mime_prepare_headers(data, subpart, NULL,
+                                      disposition, strategy);
       if(ret)
         return ret;
     }