Support seekfunction callback

Fixes #307

NEWS

@@ -1,5 +1,6 @@
 5.0.2
  - Fix a unit test for behavioral change in libcurl 8.0.0
+ - Support seekfunction callback
 
 5.0.1
  - Setting verbose=TRUE now prints to R's stderr instead of the process, such that

src/callbacks.c

@@ -57,6 +57,16 @@ size_t R_curl_callback_read(char *buffer, size_t size, size_t nitems, SEXP fun)
   return bytes_read;
 }
 
+/* origin is always SEEK_SET in libcurl, not really useful to pass on */
+int R_curl_callback_seek(SEXP fun, curl_off_t offset, int origin){
+  SEXP soffset = PROTECT(ScalarReal(offset));
+  SEXP call = PROTECT(Rf_lang2(fun, soffset));
+  int ok;
+  R_tryEval(call, R_GlobalEnv, &ok);
+  UNPROTECT(2);
+  return ok ? CURL_SEEKFUNC_FAIL : CURL_SEEKFUNC_OK;
+}
+
 int R_curl_callback_debug(CURL *handle, curl_infotype type_, char *data,
                           size_t size, SEXP fun) {
 

src/callbacks.h

@@ -1,6 +1,7 @@
 int R_curl_callback_progress(SEXP fun, double dltotal, double dlnow,
   double ultotal, double ulnow);
 size_t R_curl_callback_read(char *buffer, size_t size, size_t nitems, SEXP fun);
+int R_curl_callback_seek(SEXP fun, curl_off_t offset, int origin);
 int R_curl_callback_debug(CURL *handle, curl_infotype type_, char *data,
                           size_t size, SEXP fun);
 

src/handle.c

@@ -208,7 +208,7 @@ SEXP R_new_handle(void){
   ref->handle = curl_easy_init();
   total_handles++;
   set_handle_defaults(ref);
-  SEXP prot = PROTECT(allocVector(VECSXP, 6)); //for protecting callback functions
+  SEXP prot = PROTECT(allocVector(VECSXP, 7)); //for protecting callback functions
   SEXP ptr = PROTECT(R_MakeExternalPtr(ref, R_NilValue, prot));
   R_RegisterCFinalizerEx(ptr, fin_handle, TRUE);
   setAttrib(ptr, R_ClassSymbol, mkString("curl_handle"));
@@ -314,6 +314,13 @@ SEXP R_handle_setopt(SEXP ptr, SEXP keys, SEXP values){
                               (curl_ssl_ctx_callback) R_curl_callback_ssl_ctx));
       assert(curl_easy_setopt(handle, CURLOPT_SSL_CTX_DATA, val));
       SET_VECTOR_ELT(prot, 5, val); //protect gc
+    } else if (key == CURLOPT_SEEKFUNCTION) {
+      if (TYPEOF(val) != CLOSXP)
+        error("Value for option %s (%d) must be a function.", optname, key);
+      assert(curl_easy_setopt(handle, CURLOPT_SEEKFUNCTION,
+                              (curl_seek_callback) R_curl_callback_seek));
+      assert(curl_easy_setopt(handle, CURLOPT_SEEKDATA, val));
+      SET_VECTOR_ELT(prot, 6, val); //protect gc
     } else if (key == CURLOPT_URL) {
       /* always use utf-8 for urls */
       const char * url_utf8 = translateCharUTF8(STRING_ELT(val, 0));