Add some missing 'const'.

plug_receive(), sftp_senddata() and handle_gotdata() in particular now
take const pointers. Also fixed 'char *receive_data' in struct
ProxySocket.

logging.c

@@ -31,7 +31,7 @@ static Filename *xlatlognam(Filename *s, char *hostname, int port,
  * isn't open, buffering data if it's in the process of being
  * opened asynchronously, etc.
  */
-static void logwrite(LogContext *ctx, void *data, int len)
+static void logwrite(LogContext *ctx, const void *data, int len)
 {
     /*
      * In state L_CLOSED, we call logfopen, which will set the state

network.h

@@ -70,7 +70,7 @@ struct PlugVtable {
     /* error_msg is NULL iff it is not an error (ie it closed normally) */
     /* calling_back != 0 iff there is a Plug function */
     /* currently running (would cure the fixme in try_send()) */
-    void (*receive) (Plug *p, int urgent, char *data, int len);
+    void (*receive) (Plug *p, int urgent, const char *data, int len);
     /*
      *  - urgent==0. `data' points to `len' bytes of perfectly
      *    ordinary data.

nullplug.c

@@ -17,7 +17,7 @@ static void nullplug_closing(Plug *plug, const char *error_msg, int error_code,
 {
 }
 
-static void nullplug_receive(Plug *plug, int urgent, char *data, int len)
+static void nullplug_receive(Plug *plug, int urgent, const char *data, int len)
 {
 }
 

pageant.c

@@ -755,7 +755,8 @@ static void pageant_conn_log(void *logctx, const char *fmt, va_list ap)
     sfree(formatted);
 }
 
-static void pageant_conn_receive(Plug *plug, int urgent, char *data, int len)
+static void pageant_conn_receive(
+    Plug *plug, int urgent, const char *data, int len)
 {
     struct pageant_conn_state *pc = container_of(
         plug, struct pageant_conn_state, plug);

portfwd.c

@@ -192,7 +192,7 @@ static char *ipv6_to_string(ptrlen ipv6)
                      (unsigned)GET_16BIT_MSB_FIRST(addr + 14));
 }
 
-static void pfd_receive(Plug *plug, int urgent, char *data, int len)
+static void pfd_receive(Plug *plug, int urgent, const char *data, int len)
 {
     struct PortForwarding *pf =
         container_of(plug, struct PortForwarding, plug);

proxy.c

@@ -214,7 +214,7 @@ static void plug_proxy_closing (Plug *p, const char *error_msg,
     }
 }
 
-static void plug_proxy_receive (Plug *p, int urgent, char *data, int len)
+static void plug_proxy_receive (Plug *p, int urgent, const char *data, int len)
 {
     ProxySocket *ps = container_of(p, ProxySocket, plugimpl);
 

proxy.h

@@ -68,7 +68,7 @@ struct ProxySocket {
 
     /* receive */
     bool receive_urgent;
-    char *receive_data;
+    const char *receive_data;
     int receive_len;
 
     /* sent */

pscp.c

@@ -574,7 +574,7 @@ bool sftp_recvdata(char *buf, int len)
 {
     return ssh_scp_recv(buf, len);
 }
-bool sftp_senddata(char *buf, int len)
+bool sftp_senddata(const char *buf, int len)
 {
     backend_send(backend, buf, len);
     return true;

psftp.c

@@ -2493,7 +2493,7 @@ bool sftp_recvdata(char *buf, int len)
 
     return true;
 }
-bool sftp_senddata(char *buf, int len)
+bool sftp_senddata(const char *buf, int len)
 {
     backend_send(backend, buf, len);
     return true;

raw.c

@@ -89,7 +89,7 @@ static void raw_closing(Plug *plug, const char *error_msg, int error_code,
     }
 }
 
-static void raw_receive(Plug *plug, int urgent, char *data, int len)
+static void raw_receive(Plug *plug, int urgent, const char *data, int len)
 {
     Raw *raw = container_of(plug, Raw, plug);
     c_write(raw, data, len);

rlogin.c

@@ -71,9 +71,11 @@ static void rlogin_closing(Plug *plug, const char *error_msg, int error_code,
     }				       /* Otherwise, the remote side closed the connection normally. */
 }
 
-static void rlogin_receive(Plug *plug, int urgent, char *data, int len)
+static void rlogin_receive(Plug *plug, int urgent, const char *data, int len)
 {
     Rlogin *rlogin = container_of(plug, Rlogin, plug);
+    if (len == 0)
+        return;
     if (urgent == 2) {
 	char c;
 

sftp.h

@@ -70,7 +70,7 @@
  * sftp_sendbuffer returns the size of the backlog of data in the
  * transmit queue.
  */
-bool sftp_senddata(char *data, int len);
+bool sftp_senddata(const char *data, int len);
 int sftp_sendbuffer(void);
 bool sftp_recvdata(char *data, int len);
 

ssh.c

@@ -573,7 +573,7 @@ static void ssh_closing(Plug *plug, const char *error_msg, int error_code,
     }
 }
 
-static void ssh_receive(Plug *plug, int urgent, char *data, int len)
+static void ssh_receive(Plug *plug, int urgent, const char *data, int len)
 {
     Ssh *ssh = container_of(plug, Ssh, plug);
 

sshserver.c

@@ -133,7 +133,7 @@ static void server_closing(Plug *plug, const char *error_msg, int error_code,
     }
 }
 
-static void server_receive(Plug *plug, int urgent, char *data, int len)
+static void server_receive(Plug *plug, int urgent, const char *data, int len)
 {
     server *srv = container_of(plug, server, plug);
 

sshshare.c

@@ -1754,7 +1754,7 @@ static void share_got_pkt_from_downstream(struct ssh_sharing_connstate *cs,
         (c) = (unsigned char)*data++;                           \
     } while (0)
 
-static void share_receive(Plug *plug, int urgent, char *data, int len)
+static void share_receive(Plug *plug, int urgent, const char *data, int len)
 {
     ssh_sharing_connstate *cs = container_of(
         plug, ssh_sharing_connstate, plug);

telnet.c

@@ -506,7 +506,7 @@ static void process_subneg(Telnet *telnet)
     }
 }
 
-static void do_telnet_read(Telnet *telnet, char *buf, int len)
+static void do_telnet_read(Telnet *telnet, const char *buf, int len)
 {
     strbuf *outbuf = strbuf_new();
 
@@ -654,7 +654,7 @@ static void telnet_closing(Plug *plug, const char *error_msg, int error_code,
     /* Otherwise, the remote side closed the connection normally. */
 }
 
-static void telnet_receive(Plug *plug, int urgent, char *data, int len)
+static void telnet_receive(Plug *plug, int urgent, const char *data, int len)
 {
     Telnet *telnet = container_of(plug, Telnet, plug);
     if (urgent)

unix/uxpgnt.c

@@ -155,7 +155,7 @@ void chan_no_request_response(Channel *chan, bool success) {}
  */
 static void x11_log(Plug *p, int type, SockAddr *addr, int port,
 		    const char *error_msg, int error_code) {}
-static void x11_receive(Plug *plug, int urgent, char *data, int len) {}
+static void x11_receive(Plug *plug, int urgent, const char *data, int len) {}
 static void x11_sent(Plug *plug, int bufsize) {}
 static void x11_closing(Plug *plug, const char *error_msg, int error_code,
 			bool calling_back)

windows/winhsock.c

@@ -45,7 +45,7 @@ typedef struct HandleSocket {
     Socket sock;
 } HandleSocket;
 
-static int handle_gotdata(struct handle *h, void *data, int len)
+static int handle_gotdata(struct handle *h, const void *data, int len)
 {
     HandleSocket *hs = (HandleSocket *)handle_get_privdata(h);
 
@@ -79,7 +79,7 @@ static int handle_gotdata(struct handle *h, void *data, int len)
     }
 }
 
-static int handle_stderr(struct handle *h, void *data, int len)
+static int handle_stderr(struct handle *h, const void *data, int len)
 {
     HandleSocket *hs = (HandleSocket *)handle_get_privdata(h);
 

windows/winplink.c

@@ -205,7 +205,7 @@ char *do_select(SOCKET skt, bool startup)
     return NULL;
 }
 
-int stdin_gotdata(struct handle *h, void *data, int len)
+int stdin_gotdata(struct handle *h, const void *data, int len)
 {
     if (len < 0) {
 	/*

windows/winser.c

@@ -40,7 +40,7 @@ static void serial_terminate(Serial *serial)
     }
 }
 
-static int serial_gotdata(struct handle *h, void *data, int len)
+static int serial_gotdata(struct handle *h, const void *data, int len)
 {
     Serial *serial = (Serial *)handle_get_privdata(h);
     if (len <= 0) {

windows/winstuff.h

@@ -603,7 +603,7 @@ void init_ucs(Conf *, struct unicode_data *);
 #define HANDLE_FLAG_IGNOREEOF 2
 #define HANDLE_FLAG_UNITBUFFER 4
 struct handle;
-typedef int (*handle_inputfn_t)(struct handle *h, void *data, int len);
+typedef int (*handle_inputfn_t)(struct handle *h, const void *data, int len);
 typedef void (*handle_outputfn_t)(struct handle *h, int new_backlog);
 struct handle *handle_input_new(HANDLE handle, handle_inputfn_t gotdata,
 				void *privdata, int flags);

x11fwd.c

@@ -726,7 +726,7 @@ static void x11_closing(Plug *plug, const char *error_msg, int error_code,
     }
 }
 
-static void x11_receive(Plug *plug, int urgent, char *data, int len)
+static void x11_receive(Plug *plug, int urgent, const char *data, int len)
 {
     struct X11Connection *xconn = container_of(
         plug, struct X11Connection, plug);