Use 'application/txt' when sending text files

app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt

@@ -901,7 +901,11 @@ class ThreadActivity : SimpleActivity() {
         }
 
         thread_attachments_recyclerview.beVisible()
-        val mimeType = contentResolver.getType(uri).orEmpty()
+        val mimeType = contentResolver.getType(uri)
+        if (mimeType == null) {
+            toast(R.string.unknown_error_occurred)
+            return
+        }
         val attachment = AttachmentSelection(
             id = id,
             uri = uri,

app/src/main/kotlin/com/simplemobiletools/smsmessenger/extensions/String.kt

@@ -43,3 +43,7 @@ fun String.isPdfMimeType(): Boolean {
 fun String.isZipMimeType(): Boolean {
     return lowercase().endsWith("zip")
 }
+
+fun String.isPlainTextMimeType(): Boolean {
+    return lowercase().startsWith("text")
+}

app/src/main/kotlin/com/simplemobiletools/smsmessenger/helpers/Messaging.kt

@@ -14,6 +14,7 @@ import com.simplemobiletools.commons.extensions.showErrorToast
 import com.simplemobiletools.commons.helpers.isMarshmallowPlus
 import com.simplemobiletools.smsmessenger.R
 import com.simplemobiletools.smsmessenger.extensions.config
+import com.simplemobiletools.smsmessenger.extensions.isPlainTextMimeType
 import com.simplemobiletools.smsmessenger.models.Attachment
 import com.simplemobiletools.smsmessenger.models.Message
 import com.simplemobiletools.smsmessenger.receivers.ScheduledMessageReceiver
@@ -49,7 +50,11 @@ fun Context.sendMessage(text: String, addresses: List<String>, subscriptionId: I
                 val uri = attachment.getUri()
                 contentResolver.openInputStream(uri)?.use {
                     val bytes = it.readBytes()
-                    val mimeType = contentResolver.getType(uri) ?: return@use
+                    val mimeType = if (attachment.mimetype.isPlainTextMimeType()) {
+                        "application/txt"
+                    } else {
+                        attachment.mimetype
+                    }
                     val name = attachment.filename
                     message.addMedia(bytes, mimeType, name, name)
                 }