StripCtrlChars: retarget and reset functions.

stripctrl_retarget() points the StripCtrlChars at a new BinarySink, to
avoid having to pointlessly throw it away and make a new one all the
time.

Since that probably means the same scc is going to be reused for
processing a fresh data stream, we also don't want any character-set
conversion state hanging over from the previous stream, so we also
reset the state in the process. Just in case it's needed,
stripctrl_reset() is also provided to do that operation on its own.

misc.h

@@ -384,6 +384,8 @@ StripCtrlChars *stripctrl_new_term_fn(
         Terminal *, term_utf8_decode *, unsigned char));
 #define stripctrl_new_term(bs, cr, sub, term) \
     stripctrl_new_term_fn(bs, cr, sub, term, term_translate)
+void stripctrl_retarget(StripCtrlChars *sccpub, BinarySink *new_bs_out);
+void stripctrl_reset(StripCtrlChars *sccpub);
 void stripctrl_free(StripCtrlChars *sanpub);
 char *stripctrl_string_ptrlen(ptrlen str);
 static inline char *stripctrl_string(const char *str)

stripctrl.c

@@ -76,6 +76,30 @@ StripCtrlChars *stripctrl_new_term_fn(
     return &scc->public;
 }
 
+void stripctrl_retarget(StripCtrlChars *sccpub, BinarySink *new_bs_out)
+{
+    StripCtrlCharsImpl *scc =
+        container_of(sccpub, StripCtrlCharsImpl, public);
+    scc->bs_out = new_bs_out;
+    stripctrl_reset(sccpub);
+}
+
+void stripctrl_reset(StripCtrlChars *sccpub)
+{
+    StripCtrlCharsImpl *scc =
+        container_of(sccpub, StripCtrlCharsImpl, public);
+
+    /*
+     * Clear all the fields that might have been in the middle of a
+     * multibyte character or non-default shift state, so that we can
+     * start converting a fresh piece of data to send to a channel
+     * that hasn't seen the previous output.
+     */
+    memset(&scc->term_utf8_decode, 0, sizeof(scc->term_utf8_decode));
+    memset(&scc->mbs_in, 0, sizeof(scc->mbs_in));
+    memset(&scc->mbs_out, 0, sizeof(scc->mbs_out));
+}
+
 void stripctrl_free(StripCtrlChars *sccpub)
 {
     StripCtrlCharsImpl *scc =