C stdio trickery for read/write mode

As pointed out in the new version of the Glk spec, when opening a file
for appending, you cannot seek in it. We must open the file for
appending, to make sure it is created, then close it and reopen it
for read/writing.

Fixes part of #34.

diff --git a/libchimara/stream.c b/libchimara/stream.c
index a161a4b83437da93a84fc24d5489ec1f5ef1cfbd..b9d56cd03d4c055444a4198bfdfa067f7b3de7cd 100644 (file)
--- a/libchimara/stream.c
+++ b/libchimara/stream.c
@@ -358,14 +358,17 @@ file_stream_new(frefid_t fileref, glui32 fmode, glui32 rock, gboolean unicode)
                        modestr = g_strdup(binary? "wb" : "w");
                        break;
                case filemode_WriteAppend:
-                       modestr = g_strdup(binary? "ab" : "a");
-                       break;
                case filemode_ReadWrite:
-                       if( g_file_test(fileref->filename, G_FILE_TEST_EXISTS) ) {
-                               modestr = g_strdup(binary? "r+b" : "r+");
-                       } else {
-                               modestr = g_strdup(binary? "w+b" : "w+");
+               {
+                       /* We have to open the file first and then close it, in order to
+                        both make sure it exists and be able to seek in it later */
+                       FILE *fp = g_fopen(fileref->filename, binary? "ab" : "a");
+                       if(fclose(fp) != 0) {
+                               IO_WARNING( "Error opening file", fileref->filename, g_strerror(errno) );
+                               return NULL;
                        }
+                       modestr = g_strdup(binary? "r+b" : "r+");
+               }
                        break;
                default:
                        ILLEGAL_PARAM("Invalid file mode: %u", fmode);
@@ -379,6 +382,12 @@ file_stream_new(frefid_t fileref, glui32 fmode, glui32 rock, gboolean unicode)
                return NULL;
        }
        
+       /* Fast-forward to the end if we are appending */
+       if(fmode == filemode_WriteAppend && fseek(fp, 0, SEEK_END) != 0) {
+               IO_WARNING("Error fast-forwarding file to end", fileref->filename, g_strerror(errno));
+               return NULL;
+       }
+
        /* If they opened a file in write mode but didn't specifically get
        permission to do so, complain if the file already exists */
        if(fileref->orig_filemode == filemode_Read && fmode != filemode_Read) {