HTTP/2 client preface string missing or corrupt for C client gRPC using HTTPClient - protocol-buffers

Question

I am getting "HTTP/2 client preface string missing or corrupt."
My thoughts are that it has to do with the headers not being set correctly. It is likely the implementation of WifiClient/WifiSecureClient. I've been thinking about this for over several weeks and I'm stuck. Any advice?
[Updated: Answer below]
The client was generated using the nanopb protocol buffer compiler:
protoc --plugin=protoc-gen-nanopb=~/grpc/nanopb/generator/protoc-gen-nanopb --nanopb_out=. helloworld.proto
Arduino client:
DHT dht(DHTPIN, DHTTYPE);
WiFiClient client;
//WiFiClientSecure client;
void setup() {
Serial.setDebugOutput(true);
Serial.begin(115200);
delay(10);
WiFi.begin("<SSID>", "<My Password>");
delay(3000);
while (WiFi.status() != WL_CONNECTED) {
Serial.println("WIFI connection failed, reconnecting...");
delay(2000);
}
Serial.print("WiFi connected, ");
Serial.print("IP address: ");
Serial.println(WiFi.localIP());
Serial.println("Starting DHT11 sensor...");
dht.begin();
}
void loop() {
Serial.print("connecting to ");
Serial.println(addr);
// client.setInsecure();
if (!client.connect(addr, port)) {
Serial.println(addr);
Serial.println(port);
Serial.println("connection failed");
Serial.println("wait 5 sec to reconnect...");
delay(5000);
return;
}
Serial.println("reading humidity/temp...");
float hum = dht.readHumidity();
float tmp = dht.readTemperature(true);
Serial.println(hum);
Serial.println(tmp);
if (isnan(hum) || isnan(tmp)) {
Serial.println("failed to read sensor data");
delay(2000);
return;
}
float hiCel = dht.computeHeatIndex(tmp, hum, true);
helloworld_TempEvent temp = helloworld_TempEvent_init_zero;
temp.deviceId = 1;
temp.eventId = 0;
temp.humidity = hum;
temp.tempCel = tmp;
temp.heatIdxCel = hiCel;
sendTemp(temp);
delay(1000);
}
void sendTemp(helloworld_TempEvent e) {
uint8_t buffer[128];
pb_ostream_t stream = pb_ostream_from_buffer(buffer, sizeof(buffer));
if (!pb_encode(&stream, helloworld_TempEvent_fields, &e)) {
Serial.println("failed to encode temp proto");
Serial.println(PB_GET_ERROR(&stream));
return;
}
Serial.print("sending temp... ");
Serial.println(e.tempCel);
client.write(buffer, stream.bytes_written);
}
The server was generated using the standard java protocol buffer compiler. The only thing I changed was adding a TempEvent (below).
... (helloworld template stuff) ...
// The request message containing temperatures
message TempEvent {
int32 deviceId = 1;
int32 eventId = 2;
float humidity = 3;
float tempCel = 4;
float heatIdxCel = 5;
}
The sample java client works without any issues. Where my problem lies is the simple client using nanopb on an ESP8266-01 wifi module which is sending the data using gRPC.
public class Server {
// Doesn't work
public static void main(String[] args) throws IOException, InterruptedException {
io.grpc.Server server = ServerBuilder
.forPort(8080)
.addService(new HelloServiceImpl()).build();
server.start();
server.awaitTermination();
}
// Works just fine
public static void main(String[] args) throws IOException, InterruptedException {
try (ServerSocket server = new ServerSocket(8080)) {
System.out.println("Server accepting connections on port " + server.getLocalPort());
TemperatureClient tempClient = new TemperatureClient();
while(true) {
Socket client = server.accept();
System.out.println("Client connected using remote port " + client.getPort());
final Thread t = new Thread(() -> {
try {
TempEvent p = TempEvent.parseFrom(client.getInputStream());
float i = p.getTempCel();
System.out.println("TEMP " + i);
} catch (IOException ioe) {
ioe.printStackTrace();
}
});
t.start();
}
}
}
The client is able to hit the server:
Nov 29, 2021 5:49:30 PM io.grpc.netty.shaded.io.grpc.netty.NettyServerTransport notifyTerminated
INFO: Transport failed
io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2Exception: HTTP/2 client preface string missing or corrupt. Hex dump for received bytes: 080c10641d0000d84125e17aa0422de4459e42
at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2Exception.connectionError(Http2Exception.java:108)
at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler$PrefaceDecoder.readClientPrefaceString(Http2ConnectionHandler.java:306)
at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler$PrefaceDecoder.decode(Http2ConnectionHandler.java:239)
at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler.decode(Http2ConnectionHandler.java:438)
at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:508)
at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:447)
at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:276)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
at io.grpc.netty.shaded.io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
at io.grpc.netty.shaded.io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)
at io.grpc.netty.shaded.io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:719)
at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655)
at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581)
at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)
at io.grpc.netty.shaded.io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
at io.grpc.netty.shaded.io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.grpc.netty.shaded.io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:831)
To debug this, I wanted to first see if I could use grpcurl, but I get this:
localhost#pro ~ % grpcurl -plaintext localhost:50051 list
Failed to list services: server does not support the reflection API
localhost#pro ~ % grpcurl -insecure localhost:50051 list
Failed to dial target host "localhost:50051": tls: first record does not look like a TLS handshake
I started looking into the implementation for WifiClient.h used in my implementation code, but does anyone have any ideas on a simple way to test this without digging into everything? I was thinking this should be super simple... but it is turning out to be much more entailed to generate a simple client than I thought. I feel like I am missing something here.
From other forums on here: "The client and server aren't agreeing. Typically this is because one is plaintext and the other using TLS. But it can also be due to HTTP/1 vs HTTP/2 in certain environments."
After looking at the Go Lang implementation, I just tried using WiFiClientSecure client.setInsecure(); // didn't work and the hex dump is below.
17:36:33.030 [grpc-nio-worker-ELG-3-1] DEBUG io.grpc.netty.shaded.io.grpc.netty.NettyServerHandler - [id: 0x41b96938, L:/192.168.0.23:8080 - R:/192.168.0.24:61587] OUTBOUND SETTINGS: ack=false settings={MAX_CONCURRENT_STREAMS=2147483647, INITIAL_WINDOW_SIZE=1048576, MAX_HEADER_LIST_SIZE=8192}
17:36:33.031 [grpc-nio-worker-ELG-3-1] DEBUG io.grpc.netty.shaded.io.grpc.netty.NettyServerHandler - [id: 0x41b96938, L:/192.168.0.23:8080 - R:/192.168.0.24:61587] OUTBOUND WINDOW_UPDATE: streamId=0 windowSizeIncrement=983041
17:36:33.063 [grpc-nio-worker-ELG-3-1] DEBUG io.grpc.netty.shaded.io.grpc.netty.NettyServerHandler - [id: 0x41b96938, L:/192.168.0.23:8080 - R:/192.168.0.24:61587] OUTBOUND GO_AWAY: lastStreamId=2147483647 errorCode=1 length=126 bytes=485454502f3220636c69656e74207072656661636520737472696e67206d697373696e67206f7220636f72727570742e204865782064756d7020666f72207265...
17:36:33.064 [grpc-nio-worker-ELG-3-1] DEBUG io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler - [id: 0x41b96938, L:/192.168.0.23:8080 - R:/192.168.0.24:61587] Sent GOAWAY: lastStreamId '2147483647', errorCode '1', debugData 'HTTP/2 client preface string missing or corrupt. Hex dump for received bytes: 16030100d4010000d00303000000005c2f03aae7147c5f36'. Forcing shutdown of the connection.
Dec 10, 2021 5:36:33 PM io.grpc.netty.shaded.io.grpc.netty.NettyServerTransport notifyTerminated
INFO: Transport failed
io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2Exception: HTTP/2 client preface string missing or corrupt. Hex dump for received bytes: 16030100d4010000d00303000000005c2f03aae7147c5f36
at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2Exception.connectionError(Http2Exception.java:108)
at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler$PrefaceDecoder.readClientPrefaceString(Http2ConnectionHandler.java:306)
at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler$PrefaceDecoder.decode(Http2ConnectionHandler.java:239)
at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler.decode(Http2ConnectionHandler.java:438)
at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:508)
at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:447)
at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:276)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
at io.grpc.netty.shaded.io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
at io.grpc.netty.shaded.io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)
at io.grpc.netty.shaded.io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:719)
at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655)
at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581)
at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)
at io.grpc.netty.shaded.io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
at io.grpc.netty.shaded.io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.grpc.netty.shaded.io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:831)

Answer 1

WiFiClient client;
if (!client.connect(addr, port)) {
This forms a basic TCP connection. However, gRPC is a complex protocol based on HTTP/2. Currently you are just writing raw protobuf messages to a TCP socket, which can work for communication but is certainly not what a gRPC server is expecting.
Nanopb does not have gRPC support in itself. There is a third-party project adding it, but it is currently unmaintained.