Add Support for Google Cloud Speech-To-Text V2 library in mod_google_transcribe (#23)

* Introduce Google Speech-To-Text V2 library

* Add sign-off to previous commit

Signed-off-by: Andrew Golledge <andreas.golledge@gmail.com>

---------

Signed-off-by: Andrew Golledge <andreas.golledge@gmail.com>

mod_google_transcribe/gstreamer.h

@@ -0,0 +1,147 @@
+#include <cstdlib>
+#include <algorithm>
+#include <future>
+
+#include <switch.h>
+#include <switch_json.h>
+#include <grpc++/grpc++.h>
+#include <grpcpp/impl/codegen/sync_stream.h>
+
+#include "mod_google_transcribe.h"
+#include "simple_buffer.h"
+
+#define CHUNKSIZE (320)
+
+namespace {
+  int case_insensitive_match(std::string s1, std::string s2) {
+   std::transform(s1.begin(), s1.end(), s1.begin(), ::tolower);
+   std::transform(s2.begin(), s2.end(), s2.begin(), ::tolower);
+   if(s1.compare(s2) == 0)
+      return 1; //The strings are same
+   return 0; //not matched
+  }
+}
+
+template <typename Request, typename Response, typename Stub>
+class GStreamer {
+public:
+	GStreamer(
+    switch_core_session_t *session, 
+    uint32_t channels, 
+    char* lang, 
+    int interim, 
+    uint32_t config_sample_rate,
+		uint32_t samples_per_second,
+    int single_utterance, 
+    int separate_recognition,
+		int max_alternatives, 
+    int profanity_filter, 
+    int word_time_offset, 
+    int punctuation, 
+    const char* model, 
+    int enhanced, 
+	const char* hints);
+
+	~GStreamer() {
+		//switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(m_session), SWITCH_LOG_INFO, "GStreamer::~GStreamer - deleting channel and stub: %p\n", (void*)this);
+	}
+
+	bool write(void* data, uint32_t datalen);
+
+	void connect() {
+		assert(!m_connected);
+		// Begin a stream.
+		m_streamer = m_stub->StreamingRecognize(&m_context);
+		m_connected = true;
+
+		// read thread is waiting on this
+		m_promise.set_value();
+
+		// Write the first request, containing the config only.
+		m_streamer->Write(m_request);
+
+		// send any buffered audio
+		int nFrames = m_audioBuffer.getNumItems();
+		switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "GStreamer %p got stream ready, %d buffered frames\n", this, nFrames);	
+		if (nFrames) {
+			char *p;
+			do {
+				p = m_audioBuffer.getNextChunk();
+				if (p) {
+					write(p, CHUNKSIZE);
+				}
+			} while (p);
+		}
+	}
+
+	uint32_t nextMessageSize(void) {
+		uint32_t size = 0;
+		m_streamer->NextMessageSize(&size);
+		return size;
+	}
+
+	bool read(Response* response) {
+		return m_streamer->Read(response);
+	}
+
+	grpc::Status finish() {
+		return m_streamer->Finish();
+	}
+
+	void writesDone() {
+		// grpc crashes if we call this twice on a stream
+		if (!m_connected) {
+			cancelConnect();
+		}
+		else if (!m_writesDone) {
+			m_streamer->WritesDone();
+			m_writesDone = true;
+		}
+	}
+
+	bool waitForConnect() {
+		std::shared_future<void> sf(m_promise.get_future());
+		sf.wait();
+		return m_connected;
+	}
+
+	void cancelConnect() {
+		assert(!m_connected);
+		m_promise.set_value();
+	}
+
+	bool isConnected() {
+		return m_connected;
+	}
+
+private:
+	std::shared_ptr<grpc::Channel> create_grpc_channel(switch_channel_t *channel) {
+	    const char* google_uri;
+		if (!(google_uri = switch_channel_get_variable(channel, "GOOGLE_SPEECH_TO_TEXT_URI"))) {
+			google_uri = "speech.googleapis.com";
+		}
+
+	    const char* var;
+		if (var = switch_channel_get_variable(channel, "GOOGLE_APPLICATION_CREDENTIALS")) {
+			auto channelCreds = grpc::SslCredentials(grpc::SslCredentialsOptions());
+			auto callCreds = grpc::ServiceAccountJWTAccessCredentials(var);
+			auto creds = grpc::CompositeChannelCredentials(channelCreds, callCreds);
+			return grpc::CreateChannel(google_uri, creds);
+		}
+		else {
+			auto creds = grpc::GoogleDefaultCredentials();
+			return grpc::CreateChannel(google_uri, creds);
+		}
+	}
+
+	switch_core_session_t* m_session;
+	grpc::ClientContext m_context;
+	std::shared_ptr<grpc::Channel> m_channel;
+	std::unique_ptr<Stub> 	m_stub;
+	std::unique_ptr< grpc::ClientReaderWriterInterface<Request, Response> > m_streamer;
+	Request m_request;
+	bool m_writesDone;
+	bool m_connected;
+	std::promise<void> m_promise;
+	SimpleBuffer m_audioBuffer;
+};