Add variant of stringWithContentsOfFile that produces an error

It turns out that the [NSString stringWithContentsOfFile:] family of
methods do not have a way of reporting why a file could not be read;
[NSString stringWithContentsOfFile:usedEncoding:error:] will only set
the error object if there was a problem with decoding.

So, we cook our own variant that tries to figure out why opening the
file failed.

User-visible effect: in the GTK+ port, if you try to open a file from
the "open recent" menu that no longer exists, you will get a more
helpful error message.

5 files changed, 96 insertions, 3 deletions

diff --git a/tikzit/src/Makefile.am b/tikzit/src/Makefile.am
index e869686..c679afa 100644
--- a/tikzit/src/Makefile.am
+++ b/tikzit/src/Makefile.am
@@ -90,6 +90,7 @@ tikzit_SOURCES = gtk/Application.m \
                  common/NSFileManager+Utils.m \
                  common/NSString+LatexConstants.m \
                  common/NSString+Tikz.m \
+                 common/NSString+Util.m \
                  common/PickSupport.m \
                  common/PropertyHolder.m \
                  common/GraphElementProperty.m \
diff --git a/tikzit/src/common/NSString+Util.h b/tikzit/src/common/NSString+Util.h
new file mode 100644
index 0000000..548edb3
--- /dev/null
+++ b/tikzit/src/common/NSString+Util.h
@@ -0,0 +1,27 @@
+/*
+ * Copyright 2013  Alex Merry <alex.merry@kdemail.net>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#import <Foundation/Foundation.h>
+
+@interface NSString (Util)
+	+ (NSString*) stringWithContentsOfFile:(NSString*)path
+									 error:(NSError**)error;
+	- (id) initWithContentsOfFile:(NSString*)path
+							error:(NSError**)error;
+@end
+
+// vi:ft=objc:noet:ts=4:sts=4:sw=4
diff --git a/tikzit/src/common/NSString+Util.m b/tikzit/src/common/NSString+Util.m
new file mode 100644
index 0000000..b18f397
--- /dev/null
+++ b/tikzit/src/common/NSString+Util.m
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2013  Alex Merry <alex.merry@kdemail.net>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#import <Foundation/Foundation.h>
+#import "NSString+Util.h"
+#import "NSError+Tikzit.h"
+
+@implementation NSString (Util)
++ (NSString*) stringWithContentsOfFile:(NSString*)path
+								 error:(NSError**)error
+{
+	return [[[self alloc] initWithContentsOfFile:path error:error] autorelease];
+}
+- (id) initWithContentsOfFile:(NSString*)path
+						error:(NSError**)error
+{
+	// Fun fact: on GNUstep, at least,
+	// [stringWithContentsOfFile:usedEncoding:error:] only
+	// sets error objects if the decoding fails, not if file
+	// access fails.
+	// Fun fact 2: on GNUstep, trying to read a directory using
+	// [stringWithContentsOfFile:] causes an out-of-memory error;
+	// hence we do these checks *before* trying to read the file.
+	NSFileManager *fm = [NSFileManager defaultManager];
+	BOOL isDir = NO;
+	NSString *msg = nil;
+	if (![fm fileExistsAtPath:path isDirectory:&isDir]) {
+		msg = [NSString stringWithFormat:@"\"%@\" does not exist", path];
+	} else if (isDir) {
+		msg = [NSString stringWithFormat:@"\"%@\" is a directory", path];
+	} else if (![fm isReadableFileAtPath:path]) {
+		msg = [NSString stringWithFormat:@"\"%@\" is not readable", path];
+	}
+	if (msg != nil) {
+		if (error) {
+			*error = [NSError errorWithMessage:msg
+										  code:TZ_ERR_IO];
+		}
+		return nil;
+	}
+	self = [self initWithContentsOfFile:path];
+	if (self == nil) {
+		if (error) {
+			*error = [NSError errorWithMessage:@"unknown error"
+										  code:TZ_ERR_IO];
+		}
+	}
+	return self;
+}
+@end
+
+// vi:ft=objc:noet:ts=4:sts=4:sw=4
diff --git a/tikzit/src/gtk/TZFoundation.h b/tikzit/src/gtk/TZFoundation.h
index f275004..2ff20ca 100644
--- a/tikzit/src/gtk/TZFoundation.h
+++ b/tikzit/src/gtk/TZFoundation.h
@@ -25,5 +25,6 @@
 #import "NSString+Glib.h"
 #import "NSString+LatexConstants.h"
 #import "NSString+Tikz.h"
+#import "NSString+Util.h"
 
 // vim:ft=objc:ts=8:et:sts=4:sw=4
diff --git a/tikzit/src/gtk/TikzDocument.m b/tikzit/src/gtk/TikzDocument.m
index 6e013b1..bff5a2e 100644
--- a/tikzit/src/gtk/TikzDocument.m
+++ b/tikzit/src/gtk/TikzDocument.m
@@ -139,9 +139,7 @@
        styleManager:(StyleManager*)manager
               error:(NSError**)error
 {
-    NSStringEncoding enc; // we can't pass in NULL here...
-    NSString *t = [NSString stringWithContentsOfFile:pth
-                            usedEncoding:&enc error:error];
+    NSString *t = [NSString stringWithContentsOfFile:pth error:error];
     if (t == nil) {
         [self release];
         return nil;