diff --git a/core/basethemelet.php b/core/basethemelet.php
index cc493bb8..bcae8d9f 100644
--- a/core/basethemelet.php
+++ b/core/basethemelet.php
@@ -53,7 +53,7 @@ class BaseThemelet
         $h_tip = html_escape($image->get_tooltip());
         $h_tags = html_escape(strtolower($image->get_tag_list()));
 
-        $extArr = array_flip(['swf', 'svg', 'mp3']); //List of thumbless filetypes
+        $extArr = array_flip([EXTENSION_FLASH, EXTENSION_SVG, EXTENSION_MP3]); //List of thumbless filetypes
         if (!isset($extArr[$image->ext])) {
             $tsize = get_thumbnail_size($image->width, $image->height);
         } else {
diff --git a/core/extension.php b/core/extension.php
index a0060fb0..37d6cad9 100644
--- a/core/extension.php
+++ b/core/extension.php
@@ -275,7 +275,7 @@ abstract class FormatterExtension extends Extension
  */
 abstract class DataHandlerExtension extends Extension
 {
-    protected $SUPPORTED_EXT = [];
+    protected $SUPPORTED_MIME = [];
 
     protected function move_upload_to_archive(DataUploadEvent $event)
     {
@@ -403,7 +403,7 @@ abstract class DataHandlerExtension extends Extension
         $image->hash = $metadata['hash'];
         $image->filename = (($pos = strpos($metadata['filename'], '?')) !== false) ? substr($metadata['filename'], 0, $pos) : $metadata['filename'];
         if ($config->get_bool("upload_use_mime")) {
-            $image->ext = get_extension(getMimeType($filename));
+            $image->ext = get_extension_for_file($filename);
         } else {
             $image->ext = (($pos = strpos($metadata['extension'], '?')) !== false) ? substr($metadata['extension'], 0, $pos) : $metadata['extension'];
         }
@@ -419,15 +419,20 @@ abstract class DataHandlerExtension extends Extension
 
     protected function supported_ext(string $ext): bool
     {
-        return in_array(strtolower($ext), $this->SUPPORTED_EXT);
+        return in_array(get_mime_for_extension($ext), $this->SUPPORTED_MIME);
     }
 
     public static function get_all_supported_exts(): array
     {
         $arr = [];
         foreach (getSubclassesOf("DataHandlerExtension") as $handler) {
-            $arr = array_merge($arr, (new $handler())->SUPPORTED_EXT);
+            $handler = (new $handler());
+
+            foreach($handler->SUPPORTED_MIME as $mime) {
+                $arr = array_merge($arr, get_all_extension_for_mime($mime));
+            }
         }
+        $arr = array_unique($arr);
         return $arr;
     }
 }
diff --git a/core/filetypes.php b/core/filetypes.php
new file mode 100644
index 00000000..169ba58e
--- /dev/null
+++ b/core/filetypes.php
@@ -0,0 +1,409 @@
+<?php
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *\
+* MIME types and extension information and resolvers                        *
+\* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+class MimeTypeMap {
+
+}
+
+const EXTENSION_ANI = 'ani';
+const EXTENSION_ASC = 'asc';
+const EXTENSION_ASF = 'asf';
+const EXTENSION_AVI = 'avi';
+const EXTENSION_BMP = 'bmp';
+const EXTENSION_BZIP = 'bz';
+const EXTENSION_BZIP2 = 'bz2';
+const EXTENSION_CBR = 'cbr';
+const EXTENSION_CBZ = 'cbz';
+const EXTENSION_CBT = 'cbt';
+const EXTENSION_CBA = 'cbA';
+const EXTENSION_CB7 = 'cb7';
+const EXTENSION_CSS = 'css';
+const EXTENSION_CSV = 'csv';
+const EXTENSION_CUR = 'cur';
+const EXTENSION_FLASH = 'swf';
+const EXTENSION_FLASH_VIDEO = 'flv';
+const EXTENSION_GIF = 'gif';
+const EXTENSION_GZIP = 'gz';
+const EXTENSION_HTML = 'html';
+const EXTENSION_HTM = 'htm';
+const EXTENSION_ICO = 'ico';
+const EXTENSION_JFIF = 'jfif';
+const EXTENSION_JFI = 'jfi';
+const EXTENSION_JPEG = 'jpeg';
+const EXTENSION_JPG = 'jpg';
+const EXTENSION_JS = 'js';
+const EXTENSION_JSON = 'json';
+const EXTENSION_MKV = 'mkv';
+const EXTENSION_MP3 = 'mp3';
+const EXTENSION_MP4 = 'mp4';
+const EXTENSION_M4V = 'm4v';
+const EXTENSION_M4A = 'm4a';
+const EXTENSION_MPEG = 'mpeg';
+const EXTENSION_MPG = 'mpg';
+const EXTENSION_OGG = 'ogg';
+const EXTENSION_OGG_VIDEO = 'ogv';
+const EXTENSION_OGG_AUDIO = 'oga';
+const EXTENSION_PDF = 'pdf';
+const EXTENSION_PHP = 'php';
+const EXTENSION_PHP5 = 'php5';
+const EXTENSION_PNG = 'png';
+const EXTENSION_PSD = 'psd';
+const EXTENSION_MOV = 'mov';
+const EXTENSION_RSS = 'rss';
+const EXTENSION_SVG = 'svg';
+const EXTENSION_TAR = 'tar';
+const EXTENSION_TEXT = 'txt';
+const EXTENSION_TIFF = 'tiff';
+const EXTENSION_TIF = 'tif';
+const EXTENSION_WAV = 'wav';
+const EXTENSION_WEBM = 'webm';
+const EXTENSION_WEBP = 'webp';
+const EXTENSION_WMA = 'wma';
+const EXTENSION_WMV = 'wmv';
+const EXTENSION_XML = 'xml';
+const EXTENSION_XSL = 'xsl';
+const EXTENSION_ZIP = 'zip';
+
+
+// Couldn't find a mimetype for ani, so made one up based on it being a riff container
+const MIME_TYPE_ANI = 'application/riff+ani';
+const MIME_TYPE_ASF = 'video/x-ms-asf';
+const MIME_TYPE_AVI = 'video/x-msvideo';
+// Went with mime types from http://fileformats.archiveteam.org/wiki/Comic_Book_Archive
+const MIME_TYPE_COMIC_ZIP = 'application/vnd.comicbook+zip';
+const MIME_TYPE_COMIC_RAR = 'application/vnd.comicbook-rar';
+const MIME_TYPE_BMP = 'image/x-ms-bmp';
+const MIME_TYPE_BZIP = 'application/x-bzip';
+const MIME_TYPE_BZIP2 = 'application/x-bzip2';
+const MIME_TYPE_CSS = 'text/css';
+const MIME_TYPE_CSV = 'text/csv';
+const MIME_TYPE_FLASH = 'application/x-shockwave-flash';
+const MIME_TYPE_FLASH_VIDEO = 'video/x-flv';
+const MIME_TYPE_GIF = 'image/gif';
+const MIME_TYPE_GZIP = 'application/x-gzip';
+const MIME_TYPE_HTML = 'text/html';
+const MIME_TYPE_ICO = 'image/x-icon';
+const MIME_TYPE_JPEG = 'image/jpeg';
+const MIME_TYPE_JS = 'text/javascript';
+const MIME_TYPE_JSON = 'application/json';
+const MIME_TYPE_MKV = 'video/x-matroska';
+const MIME_TYPE_MP3 = 'audio/mpeg';
+const MIME_TYPE_MP4_AUDIO = 'audio/mp4';
+const MIME_TYPE_MP4_VIDEO = 'video/mp4';
+const MIME_TYPE_MPEG = 'video/mpeg';
+const MIME_TYPE_OCTET_STREAM = 'application/octet-stream';
+const MIME_TYPE_OGG = 'application/ogg';
+const MIME_TYPE_OGG_VIDEO = 'video/ogg';
+const MIME_TYPE_OGG_AUDIO = 'audio/ogg';
+const MIME_TYPE_PDF = 'application/pdf';
+const MIME_TYPE_PHP = 'text/x-php';
+const MIME_TYPE_PNG = 'image/png';
+const MIME_TYPE_PSD = 'image/vnd.adobe.photoshop';
+const MIME_TYPE_QUICKTIME = 'video/quicktime';
+const MIME_TYPE_RSS = 'application/rss+xml';
+const MIME_TYPE_SVG = 'image/svg+xml';
+const MIME_TYPE_TAR = 'application/x-tar';
+const MIME_TYPE_TEXT = 'text/plain';
+const MIME_TYPE_TIFF = 'image/tiff';
+const MIME_TYPE_WAV = 'audio/x-wav';
+const MIME_TYPE_WEBM = 'video/webm';
+const MIME_TYPE_WEBP = 'image/webp';
+const MIME_TYPE_WIN_BITMAP = 'image/x-win-bitmap';
+const MIME_TYPE_XML = 'text/xml';
+const MIME_TYPE_XML_APPLICATION = 'application/xml';
+const MIME_TYPE_XSL = 'application/xsl+xml';
+const MIME_TYPE_ZIP = 'application/zip';
+
+const MIME_TYPE_MAP_EXT = 'ext';
+const MIME_TYPE_MAP_MIME = 'mime';
+
+// Mime type map. Each entry in the MIME_TYPE_ARRAY represents a kind of file, identified by the "correct" mimetype as the key.
+// The value for each entry is a map of twokeys, ext and mime.
+// ext's value is an array of all of the extensions that the file type can use, with the "correct" one being first.
+// mime's value is an array of all mime types that the file type is known to use, with the current "correct" one being first.
+
+const MIME_TYPE_MAP = [
+    MIME_TYPE_ANI => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_ANI],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_ANI],
+    ],
+    MIME_TYPE_AVI => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_AVI],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_AVI,'video/avi','video/msvideo'],
+    ],
+    MIME_TYPE_ASF => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_ASF,EXTENSION_WMA,EXTENSION_WMV],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_ASF,'audio/x-ms-wma','video/x-ms-wmv'],
+    ],
+    MIME_TYPE_BMP => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_BMP],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_BMP],
+    ],
+    MIME_TYPE_BZIP => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_BZIP],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_BZIP],
+    ],
+    MIME_TYPE_BZIP2 => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_BZIP2],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_BZIP2],
+    ],
+    MIME_TYPE_COMIC_ZIP => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_CBZ],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_COMIC_ZIP],
+    ],
+    MIME_TYPE_CSS => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_CSS],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_CSS],
+    ],
+    MIME_TYPE_CSV => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_CSV],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_CSV],
+    ],
+    MIME_TYPE_FLASH => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_FLASH],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_FLASH],
+    ],
+    MIME_TYPE_FLASH_VIDEO => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_FLASH_VIDEO],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_FLASH_VIDEO,'video/flv'],
+    ],
+    MIME_TYPE_GIF => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_GIF],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_GIF],
+    ],
+    MIME_TYPE_GZIP => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_GZIP],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_TAR],
+    ],
+    MIME_TYPE_HTML => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_HTM, EXTENSION_HTML],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_HTML],
+    ],
+    MIME_TYPE_ICO => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_ICO, EXTENSION_CUR],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_ICO, MIME_TYPE_WIN_BITMAP],
+    ],
+    MIME_TYPE_JPEG => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_JPG, EXTENSION_JPEG, EXTENSION_JFIF, EXTENSION_JFI],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_JPEG],
+    ],
+    MIME_TYPE_JS => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_JS],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_JS],
+    ],
+    MIME_TYPE_JSON => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_JSON],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_JSON],
+    ],
+    MIME_TYPE_MKV => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_MKV],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_MKV],
+    ],
+    MIME_TYPE_MP3 => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_MP3],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_MP3],
+    ],
+    MIME_TYPE_MP4_AUDIO => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_M4A],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_MP4_AUDIO,"audio/m4a"],
+    ],
+    MIME_TYPE_MP4_VIDEO => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_MP4,EXTENSION_M4V],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_MP4_VIDEO,'video/x-m4v'],
+    ],
+    MIME_TYPE_MPEG => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_MPG,EXTENSION_MPEG],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_MPEG],
+    ],
+    MIME_TYPE_PDF => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_PDF],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_PDF],
+    ],
+    MIME_TYPE_PHP => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_PHP,EXTENSION_PHP5],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_PHP],
+    ],
+    MIME_TYPE_PNG => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_PNG],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_PNG],
+    ],
+    MIME_TYPE_PSD => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_PSD],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_PSD],
+    ],
+    MIME_TYPE_OGG_AUDIO => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_OGG_AUDIO,EXTENSION_OGG],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_OGG_AUDIO,MIME_TYPE_OGG],
+    ],
+    MIME_TYPE_OGG_VIDEO => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_OGG_VIDEO],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_OGG_VIDEO],
+    ],
+    MIME_TYPE_QUICKTIME => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_MOV],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_QUICKTIME],
+    ],
+    MIME_TYPE_RSS => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_RSS],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_RSS],
+    ],
+    MIME_TYPE_SVG => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_SVG],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_SVG],
+    ],
+    MIME_TYPE_TAR => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_TAR],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_TAR],
+    ],
+    MIME_TYPE_TEXT => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_TEXT, EXTENSION_ASC],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_TEXT],
+    ],
+    MIME_TYPE_TIFF => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_TIF,EXTENSION_TIFF],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_TIFF],
+    ],
+    MIME_TYPE_WAV => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_WAV],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_WAV],
+    ],
+    MIME_TYPE_WEBM => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_WEBM],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_WEBM],
+    ],
+    MIME_TYPE_WEBP => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_WEBP],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_WEBP],
+    ],
+    MIME_TYPE_XML => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_XML],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_XML,MIME_TYPE_XML_APPLICATION],
+    ],
+    MIME_TYPE_XSL => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_XSL],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_XSL],
+    ],
+    MIME_TYPE_ZIP => [
+        MIME_TYPE_MAP_EXT => [EXTENSION_ZIP],
+        MIME_TYPE_MAP_MIME => [MIME_TYPE_ZIP],
+    ],
+];
+
+/**
+ * Returns the mimetype that matches the provided extension.
+ */
+function get_mime_for_extension(string $ext): ?string
+{
+    $ext = strtolower($ext);
+
+    foreach (MIME_TYPE_MAP as $key=>$value) {
+        if(in_array($ext,$value[MIME_TYPE_MAP_EXT])) {
+            return $key;
+        }
+    }
+    return null;
+}
+
+/**
+ * Returns the mimetype for the specified file, trying file inspection methods before falling back on extension-based detection.
+ * @param String $file
+ * @param String $ext The files extension, for if the current filename somehow lacks the extension
+ * @return String The extension that was found.
+ */
+function get_mime(string $file, string $ext=""): string
+{
+    if(!file_exists($file)) {
+        throw new SCoreException("File not found: ".$file);
+    }
+
+    $type = false;
+
+    if (extension_loaded('fileinfo')) {
+        $finfo = finfo_open(FILEINFO_MIME_TYPE);
+        try {
+            $type = finfo_file($finfo, $file);
+        } finally {
+            finfo_close($finfo);
+        }
+    } elseif (function_exists('mime_content_type')) {
+        // If anyone is still using mime_content_type()
+        $type = trim(mime_content_type($file));
+    }
+
+    if($type===false || empty($type)) {
+        // Checking by extension is our last resort
+        if($ext==null||strlen($ext) == 0)
+            $ext = pathinfo($file, PATHINFO_EXTENSION);
+
+        $type = get_mime_for_extension($ext);
+    }
+
+    if ($type !== false && strlen($type) > 0) {
+        return $type;
+    }
+
+    return MIME_TYPE_OCTET_STREAM;
+}
+
+/**
+ * Returns the file extension associated with the specified mimetype.
+ */
+function get_extension(?string $mime_type): ?string
+{
+    if (empty($mime_type)) {
+        return null;
+    }
+
+    if($mime_type==MIME_TYPE_OCTET_STREAM) {
+        return null;
+    }
+
+    foreach (MIME_TYPE_MAP as $key=>$value) {
+        if(in_array($mime_type,$value[MIME_TYPE_MAP_MIME])) {
+            return $value[MIME_TYPE_MAP_EXT][0];
+        }
+    }
+    return null;
+}
+
+/**
+ * Returns all of the file extensions associated with the specified mimetype.
+ */
+function get_all_extension_for_mime(?string $mime_type): array
+{
+    $output = [];
+    if (empty($mime_type)) {
+        return $output;
+    }
+
+    foreach (MIME_TYPE_MAP as $key=>$value) {
+        if(in_array($mime_type,$value[MIME_TYPE_MAP_MIME])) {
+            $output = array_merge($output, $value[MIME_TYPE_MAP_EXT]);
+        }
+    }
+    return $output;
+}
+
+/**
+ * Gets an the extension defined in MIME_TYPE_MAP for a file.
+ *
+ * @param String $file_path
+ * @return String The extension that was found, or null if one can not be found.
+ */
+function get_extension_for_file(String $file_path): ?String
+{
+    $mime = get_mime($file_path);
+    if (!empty($mime)) {
+        if($mime==MIME_TYPE_OCTET_STREAM) {
+            return null;
+        } else {
+            $ext = get_extension($mime);
+        }
+        if (!empty($ext)) {
+            return $ext;
+        }
+    }
+    return null;
+}
diff --git a/core/imageboard/image.php b/core/imageboard/image.php
index 513ddbc1..6b786472 100644
--- a/core/imageboard/image.php
+++ b/core/imageboard/image.php
@@ -570,7 +570,7 @@ class Image
      */
     public function get_mime_type(): string
     {
-        return getMimeType($this->get_image_filename(), $this->get_ext());
+        return get_mime($this->get_image_filename(), $this->get_ext());
     }
 
     /**
diff --git a/core/imageboard/misc.php b/core/imageboard/misc.php
index 393e0f94..2fe18795 100644
--- a/core/imageboard/misc.php
+++ b/core/imageboard/misc.php
@@ -142,7 +142,7 @@ function create_scaled_image(string $inname, string $outname, array $tsize, stri
     }
 
     $output_format = $config->get_string(ImageConfig::THUMB_TYPE);
-    if ($output_format=="webp") {
+    if ($output_format==EXTENSION_WEBP) {
         $output_format = Media::WEBP_LOSSY;
     }
 
diff --git a/core/imageboard/tag.php b/core/imageboard/tag.php
index 6b10de46..129bdc39 100644
--- a/core/imageboard/tag.php
+++ b/core/imageboard/tag.php
@@ -116,8 +116,6 @@ class Tag
 
         for ($i = 0; $i < count($tags1); $i++) {
             if ($tags1[$i]!==$tags2[$i]) {
-                var_dump($tags1);
-                var_dump($tags2);
                 return false;
             }
         }
diff --git a/core/polyfills.php b/core/polyfills.php
index 0b733987..38c82baf 100644
--- a/core/polyfills.php
+++ b/core/polyfills.php
@@ -3,6 +3,9 @@
 * Things which should be in the core API                                    *
 \* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 
+require_once "filetypes.php";
+
+
 /**
  * Return the unique elements of an array, case insensitively
  */
@@ -253,99 +256,6 @@ if (!function_exists('mb_strlen')) {
     }
 }
 
-const MIME_TYPE_MAP = [
-    'jpg' => 'image/jpeg',
-    'gif' => 'image/gif',
-    'png' => 'image/png',
-    'tif' => 'image/tiff',
-    'tiff' => 'image/tiff',
-    'ico' => 'image/x-icon',
-    'swf' => 'application/x-shockwave-flash',
-    'flv' => 'video/x-flv',
-    'svg' => 'image/svg+xml',
-    'pdf' => 'application/pdf',
-    'zip' => 'application/zip',
-    'gz' => 'application/x-gzip',
-    'tar' => 'application/x-tar',
-    'bz' => 'application/x-bzip',
-    'bz2' => 'application/x-bzip2',
-    'txt' => 'text/plain',
-    'asc' => 'text/plain',
-    'htm' => 'text/html',
-    'html' => 'text/html',
-    'css' => 'text/css',
-    'js' => 'text/javascript',
-    'xml' => 'text/xml',
-    'xsl' => 'application/xsl+xml',
-    'ogg' => 'application/ogg',
-    'mp3' => 'audio/mpeg',
-    'wav' => 'audio/x-wav',
-    'avi' => 'video/x-msvideo',
-    'mpg' => 'video/mpeg',
-    'mpeg' => 'video/mpeg',
-    'mov' => 'video/quicktime',
-    'php' => 'text/x-php',
-    'mp4' => 'video/mp4',
-    'ogv' => 'video/ogg',
-    'webm' => 'video/webm',
-    'webp' => 'image/webp',
-    'bmp' =>'image/x-ms-bmp',
-    'psd' => 'image/vnd.adobe.photoshop',
-    'mkv' => 'video/x-matroska'
-];
-
-/**
- * Get MIME type for file
- *
- * The contents of this function are taken from the __getMimeType() function
- * from the "Amazon S3 PHP class" which is Copyright (c) 2008, Donovan Schönknecht
- * and released under the 'Simplified BSD License'.
- */
-function getMimeType(string $file, string $ext=""): string
-{
-    // Static extension lookup
-    $ext = strtolower($ext);
-
-    if (array_key_exists($ext, MIME_TYPE_MAP)) {
-        return MIME_TYPE_MAP[$ext];
-    }
-
-    $type = false;
-    // Fileinfo documentation says fileinfo_open() will use the
-    // MAGIC env var for the magic file
-    if (extension_loaded('fileinfo') && isset($_ENV['MAGIC']) &&
-        ($finfo = finfo_open(FILEINFO_MIME, $_ENV['MAGIC'])) !== false) {
-        if (($type = finfo_file($finfo, $file)) !== false) {
-            // Remove the charset and grab the last content-type
-            $type = explode(' ', str_replace('; charset=', ';charset=', $type));
-            $type = array_pop($type);
-            $type = explode(';', $type);
-            $type = trim(array_shift($type));
-        }
-        finfo_close($finfo);
-
-    // If anyone is still using mime_content_type()
-    } elseif (function_exists('mime_content_type')) {
-        $type = trim(mime_content_type($file));
-    }
-
-    if ($type !== false && strlen($type) > 0) {
-        return $type;
-    }
-
-    return 'application/octet-stream';
-}
-
-function get_extension(?string $mime_type): ?string
-{
-    if (empty($mime_type)) {
-        return null;
-    }
-
-    $ext = array_search($mime_type, MIME_TYPE_MAP);
-    return ($ext ? $ext : null);
-}
-
 /** @noinspection PhpUnhandledExceptionInspection */
 function getSubclassesOf(string $parent)
 {
@@ -860,3 +770,4 @@ function stringer($s)
     }
     return (string)$s;
 }
+
diff --git a/ext/alias_editor/main.php b/ext/alias_editor/main.php
index e8a3a678..f3d4f979 100644
--- a/ext/alias_editor/main.php
+++ b/ext/alias_editor/main.php
@@ -96,7 +96,7 @@ class AliasEditor extends Extension
                 $this->theme->display_aliases($t->table($t->query()), $t->paginator());
             } elseif ($event->get_arg(0) == "export") {
                 $page->set_mode(PageMode::DATA);
-                $page->set_type("text/csv");
+                $page->set_type(MIME_TYPE_CSV);
                 $page->set_filename("aliases.csv");
                 $page->set_data($this->get_alias_csv($database));
             } elseif ($event->get_arg(0) == "import") {
diff --git a/ext/auto_tagger/main.php b/ext/auto_tagger/main.php
index da32789a..8f8d16b9 100644
--- a/ext/auto_tagger/main.php
+++ b/ext/auto_tagger/main.php
@@ -98,7 +98,7 @@ class AutoTagger extends Extension
                 $this->theme->display_auto_tagtable($t->table($t->query()), $t->paginator());
             } elseif ($event->get_arg(0) == "export") {
                 $page->set_mode(PageMode::DATA);
-                $page->set_type("text/csv");
+                $page->set_type(MIME_TYPE_CSV);
                 $page->set_filename("auto_tag.csv");
                 $page->set_data($this->get_auto_tag_csv($database));
             } elseif ($event->get_arg(0) == "import") {
diff --git a/ext/autocomplete/main.php b/ext/autocomplete/main.php
index 843c8536..4d459651 100644
--- a/ext/autocomplete/main.php
+++ b/ext/autocomplete/main.php
@@ -20,7 +20,7 @@ class AutoComplete extends Extension
             }
 
             $page->set_mode(PageMode::DATA);
-            $page->set_type("application/json");
+            $page->set_type(MIME_TYPE_JSON);
 
             $s = strtolower($_GET["s"]);
             if (
diff --git a/ext/browser_search/main.php b/ext/browser_search/main.php
index d29326e0..c3965896 100644
--- a/ext/browser_search/main.php
+++ b/ext/browser_search/main.php
@@ -42,7 +42,7 @@ class BrowserSearch extends Extension
 
             // And now to send it to the browser
             $page->set_mode(PageMode::DATA);
-            $page->set_type("text/xml");
+            $page->set_type(MIME_TYPE_XML);
             $page->set_data($xml);
         } elseif ($event->page_matches("browser_search")) {
             $suggestions = $config->get_string("search_suggestions_results_order");
diff --git a/ext/danbooru_api/main.php b/ext/danbooru_api/main.php
index 4eadd66c..0892e3fd 100644
--- a/ext/danbooru_api/main.php
+++ b/ext/danbooru_api/main.php
@@ -10,13 +10,13 @@ class DanbooruApi extends Extension
 
             if ($event->page_matches("api/danbooru/add_post") || $event->page_matches("api/danbooru/post/create.xml")) {
                 // No XML data is returned from this function
-                $page->set_type("text/plain");
+                $page->set_type(MIME_TYPE_TEXT);
                 $this->api_add_post();
             } elseif ($event->page_matches("api/danbooru/find_posts") || $event->page_matches("api/danbooru/post/index.xml")) {
-                $page->set_type("application/xml");
+                $page->set_type(MIME_TYPE_XML_APPLICATION);
                 $page->set_data($this->api_find_posts());
             } elseif ($event->page_matches("api/danbooru/find_tags")) {
-                $page->set_type("application/xml");
+                $page->set_type(MIME_TYPE_XML_APPLICATION);
                 $page->set_data($this->api_find_tags());
             }
 
diff --git a/ext/handle_archive/main.php b/ext/handle_archive/main.php
index 04937c90..d493d354 100644
--- a/ext/handle_archive/main.php
+++ b/ext/handle_archive/main.php
@@ -2,7 +2,7 @@
 
 class ArchiveFileHandler extends DataHandlerExtension
 {
-    protected $SUPPORTED_EXT = ["zip"];
+    protected $SUPPORTED_MIME = [MIME_TYPE_ZIP];
 
     public function onInitExt(InitExtEvent $event)
     {
diff --git a/ext/handle_cbz/main.php b/ext/handle_cbz/main.php
index b9011c52..c6ce429e 100644
--- a/ext/handle_cbz/main.php
+++ b/ext/handle_cbz/main.php
@@ -2,7 +2,7 @@
 
 class CBZFileHandler extends DataHandlerExtension
 {
-    public $SUPPORTED_EXT = ["cbz"];
+    public $SUPPORTED_MIME = [MIME_TYPE_COMIC_ZIP];
 
     protected function media_check_properties(MediaCheckPropertiesEvent $event): void
     {
@@ -27,7 +27,7 @@ class CBZFileHandler extends DataHandlerExtension
             $cover,
             warehouse_path(Image::THUMBNAIL_DIR, $hash),
             get_thumbnail_max_size_scaled(),
-            get_extension(getMimeType($cover)),
+            get_extension(get_mime($cover)),
             null
         );
         return true;
diff --git a/ext/handle_flash/main.php b/ext/handle_flash/main.php
index 2f8fd1aa..2bad8e3e 100644
--- a/ext/handle_flash/main.php
+++ b/ext/handle_flash/main.php
@@ -2,7 +2,7 @@
 
 class FlashFileHandler extends DataHandlerExtension
 {
-    protected $SUPPORTED_EXT = ["swf"];
+    protected $SUPPORTED_MIME = [MIME_TYPE_FLASH];
 
     protected function media_check_properties(MediaCheckPropertiesEvent $event): void
     {
diff --git a/ext/handle_ico/main.php b/ext/handle_ico/main.php
index f80555d3..50e570fd 100644
--- a/ext/handle_ico/main.php
+++ b/ext/handle_ico/main.php
@@ -2,7 +2,7 @@
 
 class IcoFileHandler extends DataHandlerExtension
 {
-    protected $SUPPORTED_EXT = ["ico", "ani", "cur"];
+    protected $SUPPORTED_MIME = [MIME_TYPE_ICO, MIME_TYPE_ANI];
 
     protected function media_check_properties(MediaCheckPropertiesEvent $event): void
     {
diff --git a/ext/handle_mp3/main.php b/ext/handle_mp3/main.php
index 1d943b62..17123bff 100644
--- a/ext/handle_mp3/main.php
+++ b/ext/handle_mp3/main.php
@@ -2,7 +2,7 @@
 
 class MP3FileHandler extends DataHandlerExtension
 {
-    protected $SUPPORTED_EXT = ["mp3"];
+    protected $SUPPORTED_MIME = [MIME_TYPE_MP3];
 
     protected function media_check_properties(MediaCheckPropertiesEvent $event): void
     {
@@ -23,6 +23,6 @@ class MP3FileHandler extends DataHandlerExtension
 
     protected function check_contents(string $tmpname): bool
     {
-        return getMimeType($tmpname) == 'audio/mpeg';
+        return get_mime($tmpname) === MIME_TYPE_MP3;
     }
 }
diff --git a/ext/handle_pixel/main.php b/ext/handle_pixel/main.php
index c44f7bd0..0ba5c73e 100644
--- a/ext/handle_pixel/main.php
+++ b/ext/handle_pixel/main.php
@@ -2,13 +2,13 @@
 
 class PixelFileHandler extends DataHandlerExtension
 {
-    protected $SUPPORTED_EXT = ["jpg", "jpeg", "gif", "png", "webp"];
+    protected $SUPPORTED_MIME = [MIME_TYPE_JPEG, MIME_TYPE_GIF, MIME_TYPE_PNG, MIME_TYPE_WEBP];
 
     protected function media_check_properties(MediaCheckPropertiesEvent $event): void
     {
         if (in_array($event->ext, Media::LOSSLESS_FORMATS)) {
             $event->image->lossless = true;
-        } elseif ($event->ext=="webp") {
+        } elseif ($event->ext==EXTENSION_WEBP) {
             $event->image->lossless = Media::is_lossless_webp($event->file_name);
         }
 
@@ -17,10 +17,10 @@ class PixelFileHandler extends DataHandlerExtension
         }
         $event->image->audio = false;
         switch ($event->ext) {
-            case "gif":
+            case EXTENSION_GIF:
                 $event->image->video = Media::is_animated_gif($event->file_name);
                 break;
-            case "webp":
+            case EXTENSION_WEBP:
                 $event->image->video = Media::is_animated_webp($event->file_name);
                 break;
             default:
diff --git a/ext/handle_svg/main.php b/ext/handle_svg/main.php
index 84eb19a6..7b366a4a 100644
--- a/ext/handle_svg/main.php
+++ b/ext/handle_svg/main.php
@@ -3,7 +3,7 @@ use enshrined\svgSanitize\Sanitizer;
 
 class SVGFileHandler extends DataHandlerExtension
 {
-    protected $SUPPORTED_EXT = ["svg"];
+    protected $SUPPORTED_MIME = [MIME_TYPE_SVG];
 
     /** @var SVGFileHandlerTheme */
     protected $theme;
@@ -16,7 +16,7 @@ class SVGFileHandler extends DataHandlerExtension
             $image = Image::by_id($id);
             $hash = $image->hash;
 
-            $page->set_type("image/svg+xml");
+            $page->set_type(MIME_TYPE_SVG);
             $page->set_mode(PageMode::DATA);
 
             $sanitizer = new Sanitizer();
@@ -67,7 +67,7 @@ class SVGFileHandler extends DataHandlerExtension
 
     protected function check_contents(string $file): bool
     {
-        if (getMimeType($file)!="image/svg+xml") {
+        if (get_mime($file)!==MIME_TYPE_SVG) {
             return false;
         }
 
diff --git a/ext/handle_video/main.php b/ext/handle_video/main.php
index 5b5b3beb..cd3d5453 100644
--- a/ext/handle_video/main.php
+++ b/ext/handle_video/main.php
@@ -3,13 +3,12 @@
 class VideoFileHandler extends DataHandlerExtension
 {
     protected $SUPPORTED_MIME = [
-        'video/webm',
-        'video/mp4',
-        'video/ogg',
-        'video/flv',
-        'video/x-flv'
+        MIME_TYPE_WEBM,
+        MIME_TYPE_MP4_VIDEO,
+        MIME_TYPE_OGG_VIDEO,
+        MIME_TYPE_FLASH_VIDEO,
     ];
-    protected $SUPPORTED_EXT = ["flv", "mp4", "m4v", "ogv", "webm"];
+    protected $SUPPORTED_EXT = [EXTENSION_FLASH_VIDEO, EXTENSION_MP4, EXTENSION_M4V, EXTENSION_OGG_VIDEO, EXTENSION_WEBM];
 
     public function onInitExt(InitExtEvent $event)
     {
@@ -87,6 +86,6 @@ class VideoFileHandler extends DataHandlerExtension
 
     protected function check_contents(string $tmpname): bool
     {
-        return in_array(getMimeType($tmpname), $this->SUPPORTED_MIME);
+        return in_array(get_mime($tmpname), $this->SUPPORTED_MIME);
     }
 }
diff --git a/ext/handle_video/theme.php b/ext/handle_video/theme.php
index 24619e0c..f0e7b71e 100644
--- a/ext/handle_video/theme.php
+++ b/ext/handle_video/theme.php
@@ -2,6 +2,9 @@
 
 class VideoFileHandlerTheme extends Themelet
 {
+
+    const SUPPORTED_TYPES = [MIME_TYPE_MP4_VIDEO, MIME_TYPE_OGG_VIDEO, MIME_TYPE_WEBM, MIME_TYPE_FLASH_VIDEO];
+
     public function display_image(Page $page, Image $image)
     {
         global $config;
@@ -16,10 +19,11 @@ class VideoFileHandlerTheme extends Themelet
         $html = "Video not playing? <a href='$ilink'>Click here</a> to download the file.<br/>";
 
         //Browser media format support: https://developer.mozilla.org/en-US/docs/Web/HTML/Supported_media_formats
-        $supportedExts = ['mp4' => 'video/mp4', 'm4v' => 'video/mp4', 'ogv' => 'video/ogg', 'webm' => 'video/webm', 'flv' => 'video/flv'];
-        if (array_key_exists($ext, $supportedExts)) {
+        $mime = get_mime_for_extension($ext);
+
+        if (in_array($mime, self::SUPPORTED_TYPES)) {
             //FLV isn't supported by <video>, but it should always fallback to the flash-based method.
-            if ($ext == "webm") {
+            if ($mime == MIME_TYPE_WEBM) {
                 //Several browsers still lack WebM support sadly: https://caniuse.com/#feat=webm
                 $html .= "<!--[if IE]><p>To view webm files with IE, please <a href='https://tools.google.com/dlpage/webmmf/' target='_blank'>download this plugin</a>.</p><![endif]-->";
             }
@@ -40,7 +44,7 @@ class VideoFileHandlerTheme extends Themelet
 							<img alt='thumb' src=\"{$thumb_url}\" />
 						</object>";
 
-            if ($ext == "flv") {
+            if ($mime == MIME_TYPE_FLASH_VIDEO) {
                 //FLV doesn't support <video>.
                 $html .= $html_fallback;
             } else {
@@ -50,7 +54,7 @@ class VideoFileHandlerTheme extends Themelet
                 $html .= "
 					<video controls class='shm-main-image' id='main_image' alt='main image' poster='$thumb_url' {$autoplay} {$loop}
 					style='max-width: 100%'>
-						<source src='{$ilink}' type='{$supportedExts[$ext]}'>
+						<source src='{$ilink}' type='{$mime}'>
 
 						<!-- If browser doesn't support filetype, fallback to flash -->
 						{$html_fallback}
@@ -60,7 +64,7 @@ class VideoFileHandlerTheme extends Themelet
             }
         } else {
             //This should never happen, but just in case let's have a fallback..
-            $html = "Video type '$ext' not recognised";
+            $html = "Video type '$mime' not recognised";
         }
         $page->add_block(new Block("Video", $html, "main", 10));
     }
diff --git a/ext/image/main.php b/ext/image/main.php
index e4091141..197b7444 100644
--- a/ext/image/main.php
+++ b/ext/image/main.php
@@ -21,8 +21,8 @@ class ImageIO extends Extension
     ];
 
     const THUMBNAIL_TYPES = [
-        'JPEG' => "jpg",
-        'WEBP (Not IE/Safari compatible)' => "webp"
+        'JPEG' => EXTENSION_JPG,
+        'WEBP (Not IE/Safari compatible)' => EXTENSION_WEBP
     ];
 
     public function onInitExt(InitExtEvent $event)
@@ -32,7 +32,7 @@ class ImageIO extends Extension
         $config->set_default_int(ImageConfig::THUMB_HEIGHT, 192);
         $config->set_default_int(ImageConfig::THUMB_SCALING, 100);
         $config->set_default_int(ImageConfig::THUMB_QUALITY, 75);
-        $config->set_default_string(ImageConfig::THUMB_TYPE, 'jpg');
+        $config->set_default_string(ImageConfig::THUMB_TYPE, EXTENSION_JPG);
 
         if (function_exists(self::EXIF_READ_FUNCTION)) {
             $config->set_default_bool(ImageConfig::SHOW_META, false);
@@ -271,11 +271,7 @@ class ImageIO extends Extension
         if (!is_null($image)) {
             if ($type == "thumb") {
                 $ext = $config->get_string(ImageConfig::THUMB_TYPE);
-                if (array_key_exists($ext, MIME_TYPE_MAP)) {
-                    $page->set_type(MIME_TYPE_MAP[$ext]);
-                } else {
-                    $page->set_type("image/jpeg");
-                }
+                $page->set_type(get_mime_for_extension($ext));
 
                 $file = $image->get_thumb_filename();
             } else {
diff --git a/ext/media/main.php b/ext/media/main.php
index e98da9b0..81e3b24b 100644
--- a/ext/media/main.php
+++ b/ext/media/main.php
@@ -26,26 +26,26 @@ class Media extends Extension
 
     const LOSSLESS_FORMATS = [
         self::WEBP_LOSSLESS,
-        "png",
-        "psd",
-        "bmp",
-        "ico",
-        "cur",
-        "ani",
-        "gif"
+        EXTENSION_PNG,
+        EXTENSION_PSD,
+        EXTENSION_BMP,
+        EXTENSION_ICO,
+        EXTENSION_CUR,
+        EXTENSION_ANI,
+        EXTENSION_GIF
 
     ];
 
     const ALPHA_FORMATS = [
         self::WEBP_LOSSLESS,
         self::WEBP_LOSSY,
-        "webp",
-        "png",
+        EXTENSION_WEBP,
+        EXTENSION_PNG,
     ];
 
     const FORMAT_ALIASES = [
-        "tif" => "tiff",
-        "jpeg" => "jpg",
+        EXTENSION_TIF => EXTENSION_TIFF,
+        EXTENSION_JPEG => EXTENSION_JPG,
     ];
 
 
@@ -363,7 +363,7 @@ class Media extends Extension
 
         $codec = "mjpeg";
         $quality = $config->get_int(ImageConfig::THUMB_QUALITY);
-        if ($config->get_string(ImageConfig::THUMB_TYPE) == "webp") {
+        if ($config->get_string(ImageConfig::THUMB_TYPE) == EXTENSION_WEBP) {
             $codec = "libwebp";
         } else {
             // mjpeg quality ranges from 2-31, with 2 being the best quality.
@@ -436,7 +436,7 @@ class Media extends Extension
         switch ($format) {
             case self::WEBP_LOSSLESS:
             case self::WEBP_LOSSY:
-                return "webp";
+                return EXTENSION_WEBP;
             default:
                 return $format;
         }
@@ -445,7 +445,7 @@ class Media extends Extension
 //    private static function image_save_imagick(Imagick $image, string $path, string $format, int $output_quality = 80, bool $minimize)
 //    {
 //        switch ($format) {
-//            case "png":
+//            case EXTENSION_PNG:
 //                $result = $image->setOption('png:compression-level', 9);
 //                if ($result !== true) {
 //                    throw new GraphicsException("Could not set png compression option");
@@ -555,7 +555,7 @@ class Media extends Extension
             return true;
         }
         switch ($format) {
-            case "webp":
+            case EXTENSION_WEBP:
                 return self::is_lossless_webp($filename);
                 break;
         }
@@ -586,7 +586,7 @@ class Media extends Extension
             $output_type = $input_type;
         }
 
-        if ($output_type=="webp" && self::is_lossless($input_path, $input_type)) {
+        if ($output_type==EXTENSION_WEBP && self::is_lossless($input_path, $input_type)) {
             $output_type = self::WEBP_LOSSLESS;
         }
 
@@ -612,7 +612,7 @@ class Media extends Extension
             case Media::WEBP_LOSSLESS:
                 $args .= '-define webp:lossless=true';
                 break;
-            case "png":
+            case EXTENSION_PNG:
                 $args .= '-define png:compression-level=9';
                 break;
         }
@@ -668,19 +668,19 @@ class Media extends Extension
             /* If not specified, output to the same format as the original image */
             switch ($info[2]) {
                 case IMAGETYPE_GIF:
-                    $output_type = "gif";
+                    $output_type = EXTENSION_GIF;
                     break;
                 case IMAGETYPE_JPEG:
-                    $output_type = "jpeg";
+                    $output_type = EXTENSION_JPEG;
                     break;
                 case IMAGETYPE_PNG:
-                    $output_type = "png";
+                    $output_type = EXTENSION_PNG;
                     break;
                 case IMAGETYPE_WEBP:
-                    $output_type = "webp";
+                    $output_type = EXTENSION_WEBP;
                     break;
                 case IMAGETYPE_BMP:
-                    $output_type = "bmp";
+                    $output_type = EXTENSION_BMP;
                     break;
                 default:
                     throw new MediaException("Failed to save the new image - Unsupported image type.");
@@ -776,21 +776,21 @@ class Media extends Extension
             }
 
             switch ($output_type) {
-                case "bmp":
+                case EXTENSION_BMP:
                     $result = imagebmp($image_resized, $output_filename, true);
                     break;
-                case "webp":
+                case EXTENSION_WEBP:
                 case Media::WEBP_LOSSY:
                     $result = imagewebp($image_resized, $output_filename, $output_quality);
                     break;
-                case "jpg":
-                case "jpeg":
+                case EXTENSION_JPG:
+                case EXTENSION_JPEG:
                     $result = imagejpeg($image_resized, $output_filename, $output_quality);
                     break;
-                case "png":
+                case EXTENSION_PNG:
                     $result = imagepng($image_resized, $output_filename, 9);
                     break;
-                case "gif":
+                case EXTENSION_GIF:
                     $result = imagegif($image_resized, $output_filename);
                     break;
                 default:
@@ -904,7 +904,7 @@ class Media extends Extension
      */
     public static function normalize_format(string $format, ?bool $lossless = null): ?string
     {
-        if ($format == "webp") {
+        if ($format == EXTENSION_WEBP) {
             if ($lossless === true) {
                 $format = Media::WEBP_LOSSLESS;
             } else {
diff --git a/ext/media/media_engine.php b/ext/media/media_engine.php
index 62e56e05..43dc74f4 100644
--- a/ext/media/media_engine.php
+++ b/ext/media/media_engine.php
@@ -15,63 +15,63 @@ abstract class MediaEngine
     ];
     public const OUTPUT_SUPPORT = [
         MediaEngine::GD => [
-            "gif",
-            "jpg",
-            "png",
-            "webp",
+            EXTENSION_GIF,
+            EXTENSION_JPG,
+            EXTENSION_PNG,
+            EXTENSION_WEBP,
             Media::WEBP_LOSSY,
         ],
         MediaEngine::IMAGICK => [
-            "gif",
-            "jpg",
-            "png",
-            "webp",
+            EXTENSION_GIF,
+            EXTENSION_JPG,
+            EXTENSION_PNG,
+            EXTENSION_WEBP,
             Media::WEBP_LOSSY,
             Media::WEBP_LOSSLESS,
         ],
         MediaEngine::FFMPEG => [
-            "jpg",
-            "webp",
-            "png",
+            EXTENSION_JPG,
+            EXTENSION_WEBP,
+            EXTENSION_PNG,
         ],
         MediaEngine::STATIC => [
-            "jpg",
+            EXTENSION_JPG,
         ],
     ];
     public const INPUT_SUPPORT = [
         MediaEngine::GD => [
-            "bmp",
-            "gif",
-            "jpg",
-            "png",
-            "webp",
+            EXTENSION_BMP,
+            EXTENSION_GIF,
+            EXTENSION_JPG,
+            EXTENSION_PNG,
+            EXTENSION_WEBP,
             Media::WEBP_LOSSY,
             Media::WEBP_LOSSLESS,
         ],
         MediaEngine::IMAGICK => [
-            "bmp",
-            "gif",
-            "jpg",
-            "png",
-            "psd",
-            "tiff",
-            "webp",
+            EXTENSION_BMP,
+            EXTENSION_GIF,
+            EXTENSION_JPG,
+            EXTENSION_PNG,
+            EXTENSION_PSD,
+            EXTENSION_TIFF,
+            EXTENSION_WEBP,
             Media::WEBP_LOSSY,
             Media::WEBP_LOSSLESS,
-            "ico",
+            EXTENSION_ICO,
         ],
         MediaEngine::FFMPEG => [
-            "avi",
-            "mkv",
-            "webm",
-            "mp4",
-            "mov",
-            "flv",
+            EXTENSION_AVI,
+            EXTENSION_MKV,
+            EXTENSION_WEBM,
+            EXTENSION_MP4,
+            EXTENSION_MOV,
+            EXTENSION_FLASH_VIDEO,
         ],
         MediaEngine::STATIC => [
-            "jpg",
-            "gif",
-            "png",
+            EXTENSION_JPG,
+            EXTENSION_GIF,
+            EXTENSION_PNG,
         ],
     ];
 }
diff --git a/ext/random_image/main.php b/ext/random_image/main.php
index b33fe4b8..fee4f418 100644
--- a/ext/random_image/main.php
+++ b/ext/random_image/main.php
@@ -35,7 +35,7 @@ class RandomImage extends Extension
                 send_event(new DisplayingImageEvent($image));
             } elseif ($action === "widget") {
                 $page->set_mode(PageMode::DATA);
-                $page->set_type("text/html");
+                $page->set_type(MIME_TYPE_HTML);
                 $page->set_data($this->theme->build_thumb_html($image));
             }
         }
diff --git a/ext/resize/main.php b/ext/resize/main.php
index b43d9ee8..ea03abe4 100644
--- a/ext/resize/main.php
+++ b/ext/resize/main.php
@@ -84,7 +84,7 @@ class ResizeImage extends Extension
                 $height = $config->get_int(ResizeConfig::DEFAULT_HEIGHT);
             }
             $isanigif = 0;
-            if ($image_obj->ext == "gif") {
+            if ($image_obj->ext == EXTENSION_GIF) {
                 $image_filename = warehouse_path(Image::IMAGE_DIR, $image_obj->hash);
                 if (($fh = @fopen($image_filename, 'rb'))) {
                     //check if gif is animated (via https://www.php.net/manual/en/function.imagecreatefromgif.php#104473)
diff --git a/ext/rotate/main.php b/ext/rotate/main.php
index 42ce6304..9b1bfbfa 100644
--- a/ext/rotate/main.php
+++ b/ext/rotate/main.php
@@ -15,7 +15,7 @@ class RotateImage extends Extension
     /** @var RotateImageTheme */
     protected $theme;
 
-    const SUPPORTED_EXT = ["jpg","jpeg","png","gif","webp"];
+    const SUPPORTED_MIME = [MIME_TYPE_JPEG, MIME_TYPE_PNG, MIME_TYPE_GIF, MIME_TYPE_WEBP];
 
     public function onInitExt(InitExtEvent $event)
     {
@@ -28,7 +28,7 @@ class RotateImage extends Extension
     {
         global $user, $config;
         if ($user->can(Permissions::EDIT_FILES) && $config->get_bool("rotate_enabled")
-                && in_array($event->image->ext, self::SUPPORTED_EXT)) {
+                && in_array(get_mime_for_extension($event->image->ext), self::SUPPORTED_MIME)) {
             /* Add a link to rotate the image */
             $event->add_part($this->theme->get_rotate_html($event->image->id));
         }
diff --git a/ext/rss_comments/main.php b/ext/rss_comments/main.php
index cb9f4ab7..77dfb08a 100644
--- a/ext/rss_comments/main.php
+++ b/ext/rss_comments/main.php
@@ -16,7 +16,7 @@ class RSSComments extends Extension
         global $config, $database, $page;
         if ($event->page_matches("rss/comments")) {
             $page->set_mode(PageMode::DATA);
-            $page->set_type("application/rss+xml");
+            $page->set_type(MIME_TYPE_RSS);
 
             $comments = $database->get_all("
 				SELECT
diff --git a/ext/rss_comments/test.php b/ext/rss_comments/test.php
index 2d812f8f..83936ca6 100644
--- a/ext/rss_comments/test.php
+++ b/ext/rss_comments/test.php
@@ -9,7 +9,7 @@ class RSSCommentsTest extends ShimmiePHPUnitTestCase
         send_event(new CommentPostingEvent($image_id, $user, "ASDFASDF"));
 
         $this->get_page('rss/comments');
-        //$this->assert_mime("application/rss+xml");
+        //$this->assert_mime(MIME_TYPE_RSS);
         $this->assert_no_content("Exception");
         $this->assert_content("ASDFASDF");
     }
diff --git a/ext/rss_images/main.php b/ext/rss_images/main.php
index f72b54d3..e0ca5d48 100644
--- a/ext/rss_images/main.php
+++ b/ext/rss_images/main.php
@@ -43,7 +43,7 @@ class RSSImages extends Extension
         global $page;
         global $config;
         $page->set_mode(PageMode::DATA);
-        $page->set_type("application/rss+xml");
+        $page->set_type(MIME_TYPE_RSS);
 
         $data = "";
         foreach ($images as $image) {
diff --git a/ext/rss_images/test.php b/ext/rss_images/test.php
index 00021b77..a3aa9323 100644
--- a/ext/rss_images/test.php
+++ b/ext/rss_images/test.php
@@ -8,26 +8,26 @@ class RSSImagesTest extends ShimmiePHPUnitTestCase
         $this->log_out();
 
         $this->get_page('rss/images');
-        //$this->assert_mime("application/rss+xml");
+        //$this->assert_mime(MIME_TYPE_RSS);
         $this->assert_no_content("Exception");
 
         $this->get_page('rss/images/1');
-        //$this->assert_mime("application/rss+xml");
+        //$this->assert_mime(MIME_TYPE_RSS);
         $this->assert_no_content("Exception");
 
         # FIXME: test that the image is actually found
         $this->get_page('rss/images/computer/1');
-        //$this->assert_mime("application/rss+xml");
+        //$this->assert_mime(MIME_TYPE_RSS);
         $this->assert_no_content("Exception");
 
         # valid tag, invalid page
         $this->get_page('rss/images/computer/2');
-        //$this->assert_mime("application/rss+xml");
+        //$this->assert_mime(MIME_TYPE_RSS);
         $this->assert_no_content("Exception");
 
         # not found
         $this->get_page('rss/images/waffle/2');
-        //$this->assert_mime("application/rss+xml");
+        //$this->assert_mime(MIME_TYPE_RSS);
         $this->assert_no_content("Exception");
     }
 }
diff --git a/ext/shimmie_api/main.php b/ext/shimmie_api/main.php
index 31923d46..ecada937 100644
--- a/ext/shimmie_api/main.php
+++ b/ext/shimmie_api/main.php
@@ -36,7 +36,7 @@ class ShimmieApi extends Extension
 
         if ($event->page_matches("api/shimmie")) {
             $page->set_mode(PageMode::DATA);
-            $page->set_type("text/plain");
+            $page->set_type(MIME_TYPE_TEXT);
 
             if ($event->page_matches("api/shimmie/get_tags")) {
                 if ($event->count_args() > 0) {
diff --git a/ext/sitemap/main.php b/ext/sitemap/main.php
index afa60714..02ef3ccc 100644
--- a/ext/sitemap/main.php
+++ b/ext/sitemap/main.php
@@ -155,7 +155,7 @@ class XMLSitemap extends Extension
         // Generate new sitemap
         file_put_contents($this->sitemap_filepath, $xml);
         $page->set_mode(PageMode::DATA);
-        $page->set_type("application/xml");
+        $page->set_type(MIME_TYPE_XML_APPLICATION);
         $page->set_data($xml);
     }
 
@@ -191,7 +191,7 @@ class XMLSitemap extends Extension
         $xml = file_get_contents($this->sitemap_filepath);
 
         $page->set_mode(PageMode::DATA);
-        $page->set_type("application/xml");
+        $page->set_type(MIME_TYPE_XML_APPLICATION);
         $page->set_data($xml);
     }
 }
diff --git a/ext/static_files/main.php b/ext/static_files/main.php
index 5715f9d4..fd541e37 100644
--- a/ext/static_files/main.php
+++ b/ext/static_files/main.php
@@ -21,15 +21,8 @@ class StaticFiles extends Extension
                 $page->add_http_header('Expires: ' . gmdate('D, d M Y H:i:s', time() + 600) . ' GMT');
                 $page->set_mode(PageMode::DATA);
                 $page->set_data(file_get_contents($filename));
-                if (endsWith($filename, ".ico")) {
-                    $page->set_type("image/x-icon");
-                }
-                if (endsWith($filename, ".png")) {
-                    $page->set_type("image/png");
-                }
-                if (endsWith($filename, ".txt")) {
-                    $page->set_type("text/plain");
-                }
+
+                $page->set_type(get_mime($filename));
             }
         }
     }
diff --git a/ext/tag_list/main.php b/ext/tag_list/main.php
index f7c4f537..9071ded7 100644
--- a/ext/tag_list/main.php
+++ b/ext/tag_list/main.php
@@ -77,7 +77,7 @@ class TagList extends Extension
             }
 
             $page->set_mode(PageMode::DATA);
-            $page->set_type("text/plain");
+            $page->set_type(MIME_TYPE_TEXT);
             $page->set_data(implode("\n", $res));
         }
     }
diff --git a/ext/tagger_xml/main.php b/ext/tagger_xml/main.php
index 8a8165dd..32fc62be 100644
--- a/ext/tagger_xml/main.php
+++ b/ext/tagger_xml/main.php
@@ -30,7 +30,7 @@ class TaggerXML extends Extension
             "</tags>";
 
             $page->set_mode(PageMode::DATA);
-            $page->set_type("text/xml");
+            $page->set_type(MIME_TYPE_XML);
             $page->set_data($xml);
         }
     }
diff --git a/ext/transcode/main.php b/ext/transcode/main.php
index 44062aaf..27c1eb8c 100644
--- a/ext/transcode/main.php
+++ b/ext/transcode/main.php
@@ -17,20 +17,20 @@ class TranscodeImage extends Extension
     const ACTION_BULK_TRANSCODE = "bulk_transcode";
 
     const INPUT_FORMATS = [
-        "BMP" => "bmp",
-        "GIF" => "gif",
-        "ICO" => "ico",
-        "JPG" => "jpg",
-        "PNG" => "png",
-        "PSD" => "psd",
-        "TIFF" => "tiff",
-        "WEBP" => "webp",
+        "BMP" => EXTENSION_BMP,
+        "GIF" => EXTENSION_GIF,
+        "ICO" => EXTENSION_ICO,
+        "JPG" => EXTENSION_JPG,
+        "PNG" => EXTENSION_PNG,
+        "PSD" => EXTENSION_PSD,
+        "TIFF" => EXTENSION_TIFF,
+        "WEBP" => EXTENSION_WEBP,
     ];
 
     const OUTPUT_FORMATS = [
         "" => "",
-        "JPEG (lossy)" => "jpg",
-        "PNG (lossless)" => "png",
+        "JPEG (lossy)" => EXTENSION_JPG,
+        "PNG (lossless)" => EXTENSION_PNG,
         "WEBP (lossy)" => Media::WEBP_LOSSY,
         "WEBP (lossless)" => Media::WEBP_LOSSLESS,
     ];
@@ -102,7 +102,7 @@ class TranscodeImage extends Extension
 
             $ext = Media::normalize_format($ext);
 
-            if ($event->type=="gif"&&Media::is_animated_gif($event->tmpname)) {
+            if ($event->type==EXTENSION_GIF&&Media::is_animated_gif($event->tmpname)) {
                 return;
             }
 
@@ -314,14 +314,14 @@ class TranscodeImage extends Extension
         try {
             $result = false;
             switch ($target_format) {
-                case "webp":
+                case EXTENSION_WEBP:
                 case Media::WEBP_LOSSY:
                     $result = imagewebp($image, $tmp_name, $q);
                     break;
-                case "png":
+                case EXTENSION_PNG:
                     $result = imagepng($image, $tmp_name, 9);
                     break;
-                case "jpg":
+                case EXTENSION_JPG:
                     // In case of alpha channels
                     $width = imagesx($image);
                     $height = imagesy($image);
@@ -376,7 +376,7 @@ class TranscodeImage extends Extension
             case Media::WEBP_LOSSY:
                 $args .= '';
                 break;
-            case "png":
+            case EXTENSION_PNG:
                 $args .= '-define png:compression-level=9';
                 break;
             default:
@@ -387,7 +387,7 @@ class TranscodeImage extends Extension
 
         $source_type = "";
         switch ($source_format) {
-            case "ico":
+            case EXTENSION_ICO:
                 $source_type = "ico:";
         }
 
diff --git a/ext/update/main.php b/ext/update/main.php
index 15ea9434..bd562bb8 100644
--- a/ext/update/main.php
+++ b/ext/update/main.php
@@ -67,7 +67,7 @@ class Update extends Extension
 
         log_info("update", "Attempting to download Shimmie commit:  ".$commitSHA);
         if ($headers = transload($url, $filename)) {
-            if (($headers['Content-Type'] !== "application/zip") || ((int) $headers['Content-Length'] !== filesize($filename))) {
+            if (($headers['Content-Type'] !== MIME_TYPE_ZIP) || ((int) $headers['Content-Length'] !== filesize($filename))) {
                 unlink("./data/update_{$commitSHA}.zip");
                 log_warning("update", "Download failed: not zip / not same size as remote file.");
                 return false;
diff --git a/ext/upload/main.php b/ext/upload/main.php
index 9616dd90..8581d225 100644
--- a/ext/upload/main.php
+++ b/ext/upload/main.php
@@ -45,14 +45,18 @@ class DataUploadEvent extends Event
         $this->set_tmpname($tmpname);
 
         if ($config->get_bool("upload_use_mime")) {
-            $this->set_type(get_extension(getMimeType($tmpname)));
-        } else {
+            $filetype = get_extension_for_file($tmpname);
+        }
+
+        if(empty($filetype)) {
             if (array_key_exists('extension', $metadata) && !empty($metadata['extension'])) {
-                $this->type = strtolower($metadata['extension']);
+                $filetype = strtolower($metadata['extension']);
             } else {
                 throw new UploadException("Could not determine extension for file " . $metadata["filename"]);
             }
         }
+
+        $this->set_type($filetype);
     }
 
     public function set_type(String $type)
diff --git a/ext/upload/theme.php b/ext/upload/theme.php
index f8e74712..a512b744 100644
--- a/ext/upload/theme.php
+++ b/ext/upload/theme.php
@@ -123,22 +123,8 @@ class UploadTheme extends Themelet
         $html .= ' (Drag &amp; drop onto your bookmarks toolbar, then click when looking at an image)';
 
         // Bookmarklet checks if shimmie supports ext. If not, won't upload to site/shows alert saying not supported.
-        $supported_ext = "jpg jpeg gif png webp";
-        if (class_exists("FlashFileHandler")) {
-            $supported_ext .= " swf";
-        }
-        if (class_exists("ICOFileHandler")) {
-            $supported_ext .= " ico ani cur";
-        }
-        if (class_exists("MP3FileHandler")) {
-            $supported_ext .= " mp3";
-        }
-        if (class_exists("SVGFileHandler")) {
-            $supported_ext .= " svg";
-        }
-        if (class_exists("VideoFileHandler")) {
-            $supported_ext .= " flv mp4 ogv webm m4v";
-        }
+        $supported_ext = join(" ", DataHandlerExtension::get_all_supported_exts());
+
         $title = "Booru to " . $config->get_string(SetupConfig::TITLE);
         // CA=0: Ask to use current or new tags | CA=1: Always use current tags | CA=2: Always use new tags
         $html .= '<p><a href="javascript:
diff --git a/themes/rule34v2/themelet.class.php b/themes/rule34v2/themelet.class.php
index 6f2b7aeb..54556b1b 100644
--- a/themes/rule34v2/themelet.class.php
+++ b/themes/rule34v2/themelet.class.php
@@ -19,7 +19,7 @@ class Themelet extends BaseThemelet
         $h_ext = strtolower($image->ext);
 
         // If file is flash or svg then sets thumbnail to max size.
-        if ($image->ext === 'swf' || $image->ext === 'svg') {
+        if ($image->ext === EXTENSION_FLASH || $image->ext === EXTENSION_SVG) {
             $tsize = get_thumbnail_size($config->get_int('thumb_width'), $config->get_int('thumb_height'));
         } else {
             $tsize = get_thumbnail_size($image->width, $image->height);