Add support for oversize text messages sent as attachments.

// FREEBIE

src/Util/MIMETypeUtil.h

@@ -4,6 +4,7 @@
 
 extern NSString *const OWSMimeTypeApplicationOctetStream;
 extern NSString *const OWSMimeTypeImagePng;
+extern NSString *const OWSMimeTypeOversizeTextMessage;
 
 @interface MIMETypeUtil : NSObject
 

src/Util/MIMETypeUtil.m

@@ -12,6 +12,7 @@
 
 NSString *const OWSMimeTypeApplicationOctetStream = @"application/octet-stream";
 NSString *const OWSMimeTypeImagePng = @"image/png";
+NSString *const OWSMimeTypeOversizeTextMessage = @"text/x-signal-plain";
 
 @implementation MIMETypeUtil
 
@@ -291,6 +292,8 @@ NSString *const OWSMimeTypeImagePng = @"image/png";
         return [MIMETypeUtil filePathForAnimated:uniqueId ofMIMEType:contentType inFolder:folder];
     } else if ([self isBinaryData:contentType]) {
         return [MIMETypeUtil filePathForBinaryData:uniqueId ofMIMEType:contentType inFolder:folder];
+    } else if ([contentType isEqualToString:OWSMimeTypeOversizeTextMessage]) {
+        return [MIMETypeUtil filePathForOversizeTextMessage:uniqueId inFolder:folder];
     }
 
     DDLogError(@"Got asked for path of file %@ which is unsupported", contentType);
@@ -344,6 +347,13 @@ NSString *const OWSMimeTypeImagePng = @"image/png";
         stringByAppendingPathExtension:[self getSupportedExtensionFromBinaryDataMIMEType:contentType]];
 }
 
++ (NSString *)filePathForOversizeTextMessage:(NSString *)uniqueId inFolder:(NSString *)folder {
+    // This file extension is arbitrary - it should never be exposed to the user or
+    // be used outside the app.
+    return [[folder stringByAppendingFormat:@"/%@", uniqueId]
+            stringByAppendingPathExtension:@"signal-text-message"];
+}
+
 #if TARGET_OS_IPHONE
 
 + (NSString *)getSupportedImageMIMETypeFromImage:(UIImage *)image {