diff --git a/src/gmio_core/transfer.c b/src/gmio_core/transfer.c
index db1af5e..405ddd5 100644
--- a/src/gmio_core/transfer.c
+++ b/src/gmio_core/transfer.c
@@ -23,3 +23,10 @@ gmio_bool_t gmio_transfer_is_stop_requested(const gmio_transfer_t* trsf)
         return trsf->is_stop_requested_func(trsf->cookie);
     return GMIO_FALSE;
 }
+
+gmio_bool_t gmio_transfer_handle_progress(
+        const gmio_transfer_t* trsf, size_t value, size_t max_value)
+{
+    if (trsf != NULL && trsf->handle_progress_func != NULL)
+        trsf->handle_progress_func(trsf->cookie, value, max_value);
+}
diff --git a/src/gmio_core/transfer.h b/src/gmio_core/transfer.h
index 165e52a..35bac92 100644
--- a/src/gmio_core/transfer.h
+++ b/src/gmio_core/transfer.h
@@ -35,11 +35,20 @@ struct gmio_transfer
     /*! Optional pointer on a function that says if the currently running
      *  operation must stop
      *
-     *  If GMIO_TRUE is returned then the current transfer should abort as
+     *  If \c GMIO_TRUE is returned then the current transfer should abort as
      *  soon as possible, otherwise it can continue execution.
      */
     gmio_bool_t (*is_stop_requested_func)(void* cookie);
 
+    /*! Optional pointer on a function that is called anytime some progress
+     *  was done during transfer
+     *
+     *  \param cookie The cookie set inside the gmio_transfer object
+     *  \param value Current value of the transfer progress (<= \p max_value )
+     *  \param max_value Maximum value of the transfer progress
+     */
+    void (*handle_progress_func)(void* cookie, size_t value, size_t max_value);
+
     /*! The stream object to be used for I/O */
     gmio_stream_t stream;
 
@@ -53,9 +62,25 @@ struct gmio_transfer
 
 typedef struct gmio_transfer gmio_transfer_t;
 
+/*! Safe and convenient function for gmio_transfer::is_stop_requested_func()
+ *
+ *  Same as: \code trsf->is_stop_requested_func(trsf->cookie) \endcode
+ *
+ *  TODO: don't export, move to gmio_core/internal
+ */
 GMIO_LIB_EXPORT
 gmio_bool_t gmio_transfer_is_stop_requested(const gmio_transfer_t* trsf);
 
+/*! Safe and convenient function for gmio_transfer::handle_progress_func()
+ *
+ *  Same as: \code trsf->handle_progress_func(trsf->cookie, v, maxv) \endcode
+ *
+ *  TODO: don't export, move to gmio_core/internal
+ */
+GMIO_LIB_EXPORT
+gmio_bool_t gmio_transfer_handle_progress(
+        const gmio_transfer_t* trsf, size_t value, size_t max_value);
+
 GMIO_C_LINKAGE_END
 
 #endif /* GMIO_TRANSFER_H */
diff --git a/src/gmio_stl/stl_io.h b/src/gmio_stl/stl_io.h
index 3cbdb69..74b50b2 100644
--- a/src/gmio_stl/stl_io.h
+++ b/src/gmio_stl/stl_io.h
@@ -34,13 +34,22 @@ GMIO_C_LINKAGE_BEGIN
 
 /*! Options for gmio_stla_read()
  *
- *  No options yet, it just exists for future needs, which could possibly be:
+ *  Possible other options in the future:
  *     - flag to force locale ?
  *     - case sensitive/insensitive ?
  */
 struct gmio_stla_read_options
 {
-    void* dummy; /*!< Structs must have at least one member in strict ISO-C90 */
+    /*! Hint about the total size (in bytes) of the STL ascii data to be read
+     *  from stream
+     *
+     *  \p stream_size is passed to gmio_transfer::handle_progress_func() as
+     *  the \p max_value argument.
+     *
+     *  It's defaulted to \c 0 if options argument is set to NULL (when
+     *  calling gmio_stla_read())
+     */
+    size_t stream_size;
 };
 typedef struct gmio_stla_read_options  gmio_stla_read_options_t;
 
@@ -51,7 +60,7 @@ typedef struct gmio_stla_read_options  gmio_stla_read_options_t;
 GMIO_LIBSTL_EXPORT
 int gmio_stla_read(gmio_stl_mesh_creator_t* creator,
                    gmio_transfer_t* trsf,
-                   const gmio_stla_read_options_t* options /* NULL */);
+                   const gmio_stla_read_options_t* options);
 
 /*! Options for gmio_stla_write() */
 struct gmio_stla_write_options
diff --git a/src/gmio_stl/stla_read.c b/src/gmio_stl/stla_read.c
index 66f6b03..14c6413 100644
--- a/src/gmio_stl/stla_read.c
+++ b/src/gmio_stl/stla_read.c
@@ -78,8 +78,13 @@
 /* gmio_stream_fwd_iterator_stla_cookie */
 typedef struct
 {
+    /* Copy of gmio_stla_read() corresponding argument */
     gmio_transfer_t* transfer;
+    /* Copy of gmio_stla_read_options::stream_size */
+    size_t           stream_size;
+    /* Offset (in bytes) from beginning of stream : current position */
     size_t           stream_offset;
+    /* Cache for gmio_transfer::is_stop_requested_func */
     gmio_bool_t      is_stop_requested;
 } gmio_string_stream_fwd_iterator_cookie_t;
 
@@ -118,10 +123,12 @@ static void gmio_stream_fwd_iterator_stla_read_hook(void* cookie,
     gmio_string_stream_fwd_iterator_cookie_t* tcookie =
             (gmio_string_stream_fwd_iterator_cookie_t*)(cookie);
     const gmio_transfer_t* trsf = tcookie != NULL ? tcookie->transfer : NULL;
-    if (trsf != NULL)
-        tcookie->is_stop_requested = gmio_transfer_is_stop_requested(trsf);
-    if (tcookie != NULL)
+    if (tcookie != NULL) {
         tcookie->stream_offset += buffer->len;
+        tcookie->is_stop_requested = gmio_transfer_is_stop_requested(trsf);
+        gmio_transfer_handle_progress(
+                    trsf, tcookie->stream_offset, tcookie->stream_size);
+    }
 }
 
 GMIO_INLINE static gmio_bool_t parsing_can_continue(const gmio_stla_parse_data_t* data)
@@ -294,8 +301,9 @@ static void parse_beginsolid(gmio_stla_parse_data_t* data)
                 && data->creator != NULL
                 && data->creator->ascii_begin_solid_func != NULL)
         {
-            data->creator->ascii_begin_solid_func(data->creator->cookie,
-                                                  current_token_as_identifier(data));
+            data->creator->ascii_begin_solid_func(
+                        data->creator->cookie,
+                        current_token_as_identifier(data));
         }
         if (data->token == ID_token)
             parsing_eat_token(ID_token, data);
@@ -377,10 +385,12 @@ static void parse_facets(gmio_stla_parse_data_t* data)
 {
     uint32_t i_facet_offset = 0;
     gmio_stl_triangle_t facet;
+    const gmio_bool_t is_add_triangle_available =
+            data->creator != NULL && data->creator->add_triangle_func != NULL;
 
     while (data->token == FACET_token && parsing_can_continue(data)) {
         parse_facet(data, &facet);
-        if (data->creator != NULL && data->creator->add_triangle_func != NULL)
+        if (is_add_triangle_available)
             data->creator->add_triangle_func(data->creator->cookie, i_facet_offset, &facet);
         ++i_facet_offset;
     }
diff --git a/src/gmio_stl/stla_write.c b/src/gmio_stl/stla_write.c
index ab16c7f..81a95c5 100644
--- a/src/gmio_stl/stla_write.c
+++ b/src/gmio_stl/stla_write.c
@@ -167,6 +167,8 @@ int gmio_stla_write(const gmio_stl_mesh_t* mesh,
         gmio_stl_triangle_t tri;
         uint32_t ibuffer_facet;
 
+        gmio_transfer_handle_progress(trsf, ifacet, total_facet_count);
+
         /* Writing of facets is buffered */
         buffer_iterator = trsf->buffer;
         for (ibuffer_facet = ifacet; ibuffer_facet < clamped_facet_count; ++ibuffer_facet) {
diff --git a/src/gmio_stl/stlb_read.c b/src/gmio_stl/stlb_read.c
index cd07986..f709e5e 100644
--- a/src/gmio_stl/stlb_read.c
+++ b/src/gmio_stl/stlb_read.c
@@ -107,6 +107,9 @@ int gmio_stlb_read(gmio_stl_mesh_creator_t *creator,
     while (gmio_no_error(error)
            && rparams.i_facet_offset < total_facet_count)
     {
+        gmio_transfer_handle_progress(
+                    trsf, rparams.i_facet_offset, total_facet_count);
+
         rparams.facet_count =
                 gmio_size_to_uint32(
                     gmio_stream_read(
diff --git a/src/gmio_stl/stlb_write.c b/src/gmio_stl/stlb_write.c
index bd2e10f..c03ac39 100644
--- a/src/gmio_stl/stlb_write.c
+++ b/src/gmio_stl/stlb_write.c
@@ -106,6 +106,8 @@ int gmio_stlb_write(const gmio_stl_mesh_t* mesh,
          i_facet < facet_count && gmio_no_error(error);
          i_facet += wparams.facet_count)
     {
+        gmio_transfer_handle_progress(trsf, i_facet, facet_count);
+
         /* Write to buffer */
         wparams.facet_count = GMIO_MIN(wparams.facet_count,
                                        facet_count - wparams.i_facet_offset);