web: Export `text-content-type?'.

* module/web/client.scm (text-type?): Remove.
  (decode-response-body): Use `text-content-type?'.
* module/web/response.scm (text-content-type?): New procedure.
* doc/ref/web.texi (Responses): Document it.

doc/ref/web.texi

@@ -1361,6 +1361,12 @@ headers.
 Return the given response header, or @var{default} if none was present.
 @end deffn
 
+@deffn {Scheme Procedure} text-content-type? @var{type}
+Return @code{#t} if @var{type}, a symbol as returned by
+@code{response-content-type}, represents a textual type such as
+@code{text/plain}.
+@end deffn
+
 
 @node Web Client
 @subsection Web Client

module/web/client.scm

@@ -83,12 +83,6 @@
           (close-port p)
           res))))
 
-(define (text-type? type)
-  (let ((type (symbol->string type)))
-    (or (string-prefix? "text/" type)
-        (string-suffix? "/xml" type)
-        (string-suffix? "+xml" type))))
-
 ;; Logically the inverse of (web server)'s `sanitize-response'.
 ;;
 (define (decode-response-body response body)
@@ -104,7 +98,7 @@
        ((response-content-type response)
         => (lambda (type)
              (cond
-              ((text-type? (car type))
+              ((text-content-type? (car type))
                (decode-string body (or (assq-ref (cdr type) 'charset)
                                        "iso-8859-1")))
               (else body))))

module/web/response.scm

@@ -62,6 +62,7 @@
             response-content-md5
             response-content-range
             response-content-type
+            text-content-type?
             response-expires
             response-last-modified
 
@@ -175,6 +176,14 @@ reason phrase for the response's code."
   (or (%response-reason-phrase response)
       (code->reason-phrase (response-code response))))
 
+(define (text-content-type? type)
+  "Return #t if TYPE, a symbol as returned by `response-content-type',
+represents a textual type such as `text/plain'."
+  (let ((type (symbol->string type)))
+    (or (string-prefix? "text/" type)
+        (string-suffix? "/xml" type)
+        (string-suffix? "+xml" type))))
+
 (define (read-response port)
   "Read an HTTP response from PORT.