getMimeInfo = function (contentType, response) {
        var normalized,
            detected,
            detectedExtension;


        if (!contentType) {
            detected = fileType(response);
            detected && (contentType = detected.mime) && (detectedExtension = detected.ext);
        }

        // if contentType is not detected set text/plain as default
        if (!contentType) {
            contentType = CONTENT_TYPE_TEXT_PLAIN;
        }

        normalized = mimeFormat.lookup(contentType);

        return {
            contentType: normalized.source,
            mimeType: normalized.type, // sanitized mime type base
            mimeFormat: normalized.format, // format specific to the type returned
            charset: normalized.charset || CHARSET_UTF8,
            extension: detectedExtension || mimeType.extension(normalized.source) || E
        };
    }
Takes the content-type header value and performs the mime sniffing with known mime types.
If content-type header is not present, detects the mime type from the response stream or response body
If content-type is not provided and not able to detect, then text/plain is taken as default

@private
@param {?String} contentType - The value of content type header
@param {Stream|String} response - The response stream or body, for which content-info should be determined
@returns {Object} - mime information from response headers