file: allow changing the sample rate when throttle=true

this is dangerous from signal processing perspective and should be used
with caution.

lib/file/file_source_c.cc

@@ -26,7 +26,6 @@
 
 #include <gnuradio/io_signature.h>
 #include <gnuradio/blocks/file_source.h>
-#include <gnuradio/blocks/throttle.h>
 
 #include "file_source_c.h"
 
@@ -73,19 +72,21 @@ file_source_c::file_source_c(const std::string &args) :
   if (_freq < 0)
     throw std::runtime_error("Parameter 'freq' may not be negative.");
 
-  if (0 == _rate)
+  if (0 == _rate && throttle)
     throw std::runtime_error("Parameter 'rate' is missing in arguments.");
 
+  _file_rate = _rate;
+
   gr::blocks::file_source::sptr src = \
       gr::blocks::file_source::make( sizeof(gr_complex),
                                      filename.c_str(),
                                      repeat );
 
-  if (throttle) {
-    gr::blocks::throttle::sptr throttle = gr::blocks::throttle::make( sizeof(gr_complex), _rate );
+  _throttle = gr::blocks::throttle::make( sizeof(gr_complex), _file_rate );
 
-    connect( src, 0, throttle, 0 );
-    connect( throttle, 0, self(), 0 );
+  if (throttle) {
+    connect( src, 0, _throttle, 0 );
+    connect( _throttle, 0, self(), 0 );
   } else {
     connect( src, 0, self(), 0 );
   }
@@ -104,7 +105,8 @@ std::vector<std::string> file_source_c::get_devices()
 {
   std::vector<std::string> devices;
 
-  std::string args = "file='/path/to/your/file',rate=1e6,freq=100e6,repeat=true,throttle=true";
+  std::string args = "file='/path/to/your/file'";
+  args += ",rate=1e6,freq=100e6,repeat=true,throttle=true";
   args += ",label='Complex Sampled (IQ) File'";
   devices.push_back( args );
 
@@ -120,13 +122,24 @@ osmosdr::meta_range_t file_source_c::get_sample_rates( void )
 {
   osmosdr::meta_range_t range;
 
-  range += osmosdr::range_t( get_sample_rate() );
+  range += osmosdr::range_t( _file_rate ); /* always return file's original rate */
 
   return range;
 }
 
 double file_source_c::set_sample_rate( double rate )
 {
+  if ( _file_rate != rate )
+  {
+    std::cerr << boost::format("WARNING: Overriding original sample rate of %g with %g")
+                 % _file_rate % rate
+              << std::endl;
+  }
+
+  _throttle->set_sample_rate( rate );
+
+  _rate = rate;
+
   return get_sample_rate();
 }
 

lib/file/file_source_c.h

@@ -21,6 +21,7 @@
 #define FILE_SOURCE_C_H
 
 #include <gnuradio/hier_block2.h>
+#include <gnuradio/blocks/throttle.h>
 
 #include "source_iface.h"
 
@@ -71,6 +72,8 @@ public:
   std::string get_antenna( size_t chan = 0 );
 
 private:
+  gr::blocks::throttle::sptr _throttle;
+  double _file_rate;
   double _freq, _rate;
 };