wp_get_image_mime

wp_get_image_mime: 该函数用于根据文件扩展名确定图像文件的MIME类型。它接受一个文件路径作为其唯一的参数，并返回图像的MIME类型。

返回一个图像文件的真实mime类型。

这取决于 exif_imagetype() 或 getimagesize() 来确定真正的 mime 类型。

function wp_get_image_mime( $file ) {
	/*
	 * Use exif_imagetype() to check the mimetype if available or fall back to
	 * getimagesize() if exif isn't available. If either function throws an Exception
	 * we assume the file could not be validated.
	 */
	try {
		if ( is_callable( 'exif_imagetype' ) ) {
			$imagetype = exif_imagetype( $file );
			$mime      = ( $imagetype ) ? image_type_to_mime_type( $imagetype ) : false;
		} elseif ( function_exists( 'getimagesize' ) ) {
			// Don't silence errors when in debug mode, unless running unit tests.
			if ( defined( 'WP_DEBUG' ) && WP_DEBUG
				&& ! defined( 'WP_RUN_CORE_TESTS' )
			) {
				// Not using wp_getimagesize() here to avoid an infinite loop.
				$imagesize = getimagesize( $file );
			} else {
				// phpcs:ignore WordPress.PHP.NoSilencedErrors
				$imagesize = @getimagesize( $file );
			}

			$mime = ( isset( $imagesize['mime'] ) ) ? $imagesize['mime'] : false;
		} else {
			$mime = false;
		}

		if ( false !== $mime ) {
			return $mime;
		}

		$magic = file_get_contents( $file, false, null, 0, 12 );

		if ( false === $magic ) {
			return false;
		}

		/*
		 * Add WebP fallback detection when image library doesn't support WebP.
		 * Note: detection values come from LibWebP, see
		 * https://github.com/webmproject/libwebp/blob/master/imageio/image_dec.c#L30
		 */
		$magic = bin2hex( $magic );
		if (
			// RIFF.
			( 0 === strpos( $magic, '52494646' ) ) &&
			// WEBP.
			( 16 === strpos( $magic, '57454250' ) )
		) {
			$mime = 'image/webp';
		}
	} catch ( Exception $e ) {
		$mime = false;
	}

	return $mime;
}