channel: implement ssh_channel_poll_timeout

Resolves bug #57

include/libssh/libssh.h

@@ -341,6 +341,7 @@ LIBSSH_API int ssh_channel_open_forward(ssh_channel channel, const char *remoteh
     int remoteport, const char *sourcehost, int localport);
 LIBSSH_API int ssh_channel_open_session(ssh_channel channel);
 LIBSSH_API int ssh_channel_poll(ssh_channel channel, int is_stderr);
+int ssh_channel_poll_timeout(ssh_channel channel, int timeout, int is_stderr);
 LIBSSH_API int ssh_channel_read(ssh_channel channel, void *dest, uint32_t count, int is_stderr);
 LIBSSH_API int ssh_channel_read_nonblocking(ssh_channel channel, void *dest, uint32_t count,
     int is_stderr);

src/channels.c

@@ -2730,6 +2730,61 @@ int ssh_channel_poll(ssh_channel channel, int is_stderr){
   return buffer_get_rest_len(stdbuf);
 }
 
+/**
+ * @brief Polls a channel for data to read, waiting for a certain timeout.
+ *
+ * @param[in]  channel   The channel to poll.
+ * @param[in]  timeout   Set an upper limit on the time for which this function
+ *                       will block, in milliseconds. Specifying a negative value
+ *                       means an infinite timeout. This parameter is passed to
+ *                       the poll() function.
+ * @param[in]  is_stderr A boolean to select the stderr stream.
+ *
+ * @return              The number of bytes available for reading,
+ *                      0 if nothing is available (timeout elapsed),
+ *                      SSH_EOF on end of file,
+ *                      SSH_ERROR on error.
+ *
+ * @warning When the channel is in EOF state, the function returns SSH_EOF.
+ *
+ * @see channel_is_eof()
+ */
+int ssh_channel_poll_timeout(ssh_channel channel, int timeout, int is_stderr){
+  ssh_session session;
+  ssh_buffer stdbuf;
+  struct ssh_channel_read_termination_struct ctx;
+  int rc;
+
+  if(channel == NULL) {
+      return SSH_ERROR;
+  }
+
+  session = channel->session;
+  stdbuf = channel->stdout_buffer;
+  enter_function();
+
+  if (is_stderr) {
+    stdbuf = channel->stderr_buffer;
+  }
+  ctx.buffer = stdbuf;
+  ctx.channel = channel;
+  ctx.count = 1;
+  rc = ssh_handle_packets_termination(channel->session, timeout,
+      ssh_channel_read_termination, &ctx);
+  if(rc ==SSH_ERROR || session->session_state == SSH_SESSION_STATE_ERROR){
+    rc = SSH_ERROR;
+    goto end;
+  }
+  rc = buffer_get_rest_len(stdbuf);
+  if(rc > 0)
+    goto end;
+  if (channel->remote_eof)
+    rc = SSH_EOF;
+end:
+  leave_function();
+  return rc;
+}
+
 /**
  * @brief Recover the session in which belongs a channel.
  *