Accept arbitrary incoming attachments.

// FREEBIE

src/Messages/Attachments/OWSAttachmentsProcessor.m

@@ -79,7 +79,10 @@ NS_ASSUME_NONNULL_BEGIN
 
         [attachmentIds addObject:pointer.uniqueId];
 
-        if ([MIMETypeUtil isSupportedMIMEType:pointer.contentType]) {
+        // TODO: We need to revisit isSupportedMIMEType.
+        if ([MIMETypeUtil isSupportedMIMEType:pointer.contentType] ||
+            [pointer.contentType isEqualToString:OWSMimeTypeOversizeTextMessage] ||
+            [pointer.contentType isEqualToString:OWSMimeTypeUnknownForTests]) {
             [pointer save];
             [supportedAttachmentPointers addObject:pointer];
             [supportedAttachmentIds addObject:pointer.uniqueId];

src/Util/MIMETypeUtil.h

@@ -5,6 +5,7 @@
 extern NSString *const OWSMimeTypeApplicationOctetStream;
 extern NSString *const OWSMimeTypeImagePng;
 extern NSString *const OWSMimeTypeOversizeTextMessage;
+extern NSString *const OWSMimeTypeUnknownForTests;
 
 @interface MIMETypeUtil : NSObject
 
@@ -52,4 +53,8 @@ extern NSString *const OWSMimeTypeOversizeTextMessage;
 + (NSSet<NSString *> *)supportedImageUTITypes;
 + (NSSet<NSString *> *)supportedAnimatedImageUTITypes;
 
++ (NSString *)utiTypeForMIMEType:(NSString *)mimeType;
++ (NSString *)fileExtensionForUTIType:(NSString *)utiType;
++ (NSString *)fileExtensionForMIMEType:(NSString *)mimeType;
+
 @end

src/Util/MIMETypeUtil.m

@@ -13,6 +13,7 @@
 NSString *const OWSMimeTypeApplicationOctetStream = @"application/octet-stream";
 NSString *const OWSMimeTypeImagePng = @"image/png";
 NSString *const OWSMimeTypeOversizeTextMessage = @"text/x-signal-plain";
+NSString *const OWSMimeTypeUnknownForTests = @"unknown/mimetype";
 
 @implementation MIMETypeUtil
 
@@ -294,6 +295,8 @@ NSString *const OWSMimeTypeOversizeTextMessage = @"text/x-signal-plain";
         return [MIMETypeUtil filePathForBinaryData:uniqueId ofMIMEType:contentType inFolder:folder];
     } else if ([contentType isEqualToString:OWSMimeTypeOversizeTextMessage]) {
         return [MIMETypeUtil filePathForOversizeTextMessage:uniqueId inFolder:folder];
+    } else if ([contentType isEqualToString:OWSMimeTypeUnknownForTests]) {
+        return [MIMETypeUtil filePathForUnknownContent:uniqueId inFolder:folder];
     }
 
     DDLogError(@"Got asked for path of file %@ which is unsupported", contentType);
@@ -354,6 +357,13 @@ NSString *const OWSMimeTypeOversizeTextMessage = @"text/x-signal-plain";
             stringByAppendingPathExtension:@"signal-text-message"];
 }
 
++ (NSString *)filePathForUnknownContent:(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:@"unknown"];
+}
+
 #if TARGET_OS_IPHONE
 
 + (NSString *)getSupportedImageMIMETypeFromImage:(UIImage *)image {
@@ -373,6 +383,23 @@ NSString *const OWSMimeTypeOversizeTextMessage = @"text/x-signal-plain";
     return (__bridge_transfer NSString *)utiType;
 }
 
++ (NSString *)fileExtensionForUTIType:(NSString *)utiType
+{
+    CFStringRef fileExtension
+    = UTTypeCopyPreferredTagWithClass((__bridge CFStringRef) utiType, kUTTagClassFilenameExtension);
+    return (__bridge_transfer NSString *)fileExtension;
+}
+
++ (NSString *)fileExtensionForMIMEType:(NSString *)mimeType
+{
+    NSString *utiType = [self utiTypeForMIMEType:mimeType];
+    if (!utiType) {
+        return nil;
+    }
+    NSString *fileExtension = [self fileExtensionForUTIType:utiType];
+    return fileExtension;
+}
+
 + (NSSet<NSString *> *)utiTypesForMIMETypes:(NSArray *)mimeTypes
 {
     NSMutableSet<NSString *> *result = [NSMutableSet new];