From: P. F. Chimento <philip.chimento@gmail.com>
Date: Sat, 18 Jun 2011 19:16:57 +0000 (+0200)
Subject: C stdio trickery for read/write mode
X-Git-Tag: v0.9~73^2~1^2~4
X-Git-Url: https://git.stderr.nl/gitweb?p=projects%2Fchimara%2Fchimara.git;a=commitdiff_plain;h=83b722ae4670ad289fedc0967d72c71cc5e2bab8

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 a161a4b..b9d56cd 100644
--- 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) {