# Need help with digest p4runtime
**URL:** https://forum.p4.org/t/need-help-with-digest-p4runtime/366
**Category:** Getting Started with P4
**Created:** [June 7, 2022, 12:28pm UTC](https://forum.p4.org/t/need-help-with-digest-p4runtime/366 "2022-06-07T12:28:33Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@doraeric](https://forum.p4.org/u/doraeric)
#### Post date: [June 7, 2022, 12:28pm UTC](https://forum.p4.org/t/need-help-with-digest-p4runtime/366/1 "2022-06-07T12:28:33Z")
Hello,
I want to send digest message from bmv2 to controller through p4runtime, but I can’t make it work.
I tried different environments, but none of them will work. Maybe I missed something.
To my understanding, I have to send WriteRequest to insert a DigestEntry, so the switch will start to send digest messages to controller through StreamChannel.
With `stratum_bmv2`, I can insert the entry, but I didn’t receive any digest message. I can still get PacketIn messages meanwhile.
With `simple_switch_grpc`, I can’t insert the entry. I received a helpless message as below
```auto
Traceback (most recent call last):
File "./p4runtime_test.py", line 152, in
main2(stub)
File "./p4runtime_test.py", line 141, in main2
insert_digest(stub, 401776493)
File "./p4runtime_test.py", line 117, in insert_digest
response = stub.Write(req)
File "/home/doraeric/venv/lib/python3.8/site-packages/grpc/_channel.py", line 946, in __call__
return _end_unary_response_blocking(state, call, False, None)
File "/home/doraeric/venv/lib/python3.8/site-packages/grpc/_channel.py", line 849, in _end_unary_response_blocking
raise _InactiveRpcError(state)
grpc._channel._InactiveRpcError: <_InactiveRpcError of RPC that terminated with:
status = StatusCode.UNKNOWN
details = ""
debug_error_string = "{"created":"@1654597469.924974618","description":"Error received from peer ipv6:[::1]:50051","file":"src/core/lib/surface/call.cc"
,"file_line":952,"grpc_message":"","grpc_status":2}"
```
The server didn’t response any details about the error. I can receive PacketIn in the setup, too.
I tried both using [p4runtime-shell](https://github.com/p4lang/p4runtime-shell) and writing grpc client by myself, neither of them have received digest messages.
The P4 program with digest call can be compiled and upload to switch through `SetForwardingPipelineConfig` without error, but it didn’t send any digest message.
How can I send digest messages?
Did I miss some steps?
Is there any working example or tool I can try?
This is the python I used to insert digest entry:
```python
def insert_digest(stub, digest_id):
req = p4runtime_pb2.WriteRequest()
req.device_id = device_id
req.election_id.high = 0
req.election_id.low = 1
req.role_id = 0
update = req.updates.add()
update.type = p4runtime_pb2.Update.INSERT
digest_entry = update.entity.digest_entry
digest_entry.digest_id = digest_id
digest_entry.config.max_timeout_ns = 0
response = stub.Write(req)
print('digest added')
```
Here are some environment information. I truncated some less important output.
```auto
# stratum
$ stratum_bmv2 --version
stratum_bmv2 version e00eac942a877e22e3927ef8ec0818685622039d
$ ps aux | grep '[s]tratum_bmv2'
root 73 1.6 0.2 1089148 53272 ? Ssl 09:37 2:41 stratum_bmv2 -device_id=1 -chassis_config_file=/tmp/s1/chassis-config.txt -forwarding_pipeline_configs_file=/tmp/s1/pipe.txt -persistent_config_dir=/tmp/s1 -initial_pipeline=/root/dummy.json -cpu_port=255 -external_stratum_urls=0.0.0.0:50001 -local_stratum_url=localhost:55361 -max_num_controllers_per_node=10 -write_req_log_file=/tmp/s1/write-reqs.txt -bmv2_log_level=warn
# simple_switch_grpc
$ simple_switch_grpc --version
1.14.0-2de095c7
$ ps aux | grep '[s]imple_switch'
root 57014 0.7 1.1 1267316 45252 pts/7 Sl+ 16:48 1:34 simple_switch_grpc -i 1@s1-eth1 -i 2@s1-eth2 -i 3@s1-eth3 -i 4@s1-eth4 --pcap /home/doraeric/tutorials/exercises/basic/pcaps --nanolog ipc:///tmp/bm-0-log.ipc --device-id 0 build/basic.json --log-console --thrift-port 9090 -- --grpc-server-addr 0.0.0.0:50051 --cpu-port 255
```
---
### Author:  [@doraeric](https://forum.p4.org/u/doraeric)
#### Post date: [June 8, 2022, 7:54am UTC](https://forum.p4.org/t/need-help-with-digest-p4runtime/366/2 "2022-06-08T07:54:01Z")
I found a [working example](https://github.com/ebiken/p4labs/tree/master/digest) finally.
I think the problem is at the P4 source code.
The following code does **NOT** work on `simple_switch_grpc`.
```auto
digest(1, meta.test_digest);
digest(1, hdr.ethernet.srcAddr);
```
The code is found from [here](https://github.com/nsg-ethz/p4-learning/wiki/BMv2-Simple-Switch#packet-digests) and [p4c testdata](https://github.com/p4lang/p4c/blob/a1f21cb979/testdata/p4_16_samples/v1model-digest-custom-type.p4#L156).
Here is a **working** example from the first link:
```auto
struct mac_learn_digest_t {
EthernetAddress srcAddr;
PortId_t ingress_port;
}
digest(1, {hdr.ether.srcAddr, st_md.ingress_port});
```
I also set the digest list size to 1 as he does.
```python
digest_entry.config.max_list_size = 1
```
With the original not working p4 code, there is no warning or error when compiling and calling `SetForwardingPipelineConfig`.
The p4runtime server by `simple_switch_grpc` will only give you an unknown status code when you try to enable digest by inserting a digest entry. After updating p4 code, it works now.
`stratum_bmv2` doesn’t seem to support digest function. There is a [closed issue](https://github.com/stratum/stratum/issues/528) on github without clarifying its functionality. And I can’t make it work even with fixed p4 code.
---
### Author:  [@andyfingerhut](https://forum.p4.org/u/andyfingerhut)
#### Post date: [June 10, 2022, 4:23am UTC](https://forum.p4.org/t/need-help-with-digest-p4runtime/366/3 "2022-06-10T04:23:56Z")
If you are able to publish your working example, and also the smallest modification you can find to it related to the `digest` call that makes it no longer work (e.g. make it “one step closer” to the non-working examples you found), and also publish that, someone else may be able to reproduce your situation more easily, and perhaps determine if there is a bug in the compiler related to this. Would you be willing to do so?
---
### Author:  [@doraeric](https://forum.p4.org/u/doraeric)
#### Post date: [June 12, 2022, 3:00pm UTC](https://forum.p4.org/t/need-help-with-digest-p4runtime/366/4 "2022-06-12T15:00:47Z")
Here is my code. I tried to make it as minimal as I can.
P4 code. Check line 46 and 49 and choose one to use.
The argument for second digest is not a struct. Maybe that’s the reason it failed.
```auto
// main.p4
#include
#include
header ethernet_t {
bit<48> dst_addr;
bit<48> src_addr;
bit<16> ether_type;
}
struct headers_t {
ethernet_t ethernet;
}
struct mac_learn_digest_t {
bit<48> src_addr;
bit<9> ingress_port;
}
struct local_metadata_t { }
parser parser_impl(
packet_in pkt,
out headers_t hdr,
inout local_metadata_t user_md,
inout standard_metadata_t st_md) {
state start { transition parse_ethernet; }
state parse_ethernet {
pkt.extract(hdr.ethernet);
transition accept;
}
}
control deparser(
packet_out pkt,
in headers_t hdr) {
apply {
pkt.emit(hdr.ethernet);
}
}
control ingress(
inout headers_t hdr,
inout local_metadata_t user_md,
inout standard_metadata_t st_md) {
apply {
// passed
digest(1, {hdr.ethernet.src_addr, st_md.ingress_port});
// failed
// digest(1, hdr.ethernet.src_addr);
}
}
control egress(
inout headers_t hdr,
inout local_metadata_t user_md,
inout standard_metadata_t st_md) {
apply { }
}
control no_verify_checksum(
inout headers_t hdr,
inout local_metadata_t user_md) {
apply { }
}
control no_compute_checksum(
inout headers_t hdr,
inout local_metadata_t user_md) {
apply { }
}
V1Switch(parser_impl(),
no_verify_checksum(),
ingress(),
egress(),
no_compute_checksum(),
deparser()
) main;
```
python controller. Check which digest\_id to use before running.
```auto
#!/usr/bin/env python3
"""
mininet >
h1 route add default gw 10.0.0.254 dev h1-eth0
h1 arp -i h1-eth0 -s 10.0.0.254 00:00:0a:00:00:fe
"""
import logging
import os
import queue
import sys
import threading
import traceback
import google.protobuf.text_format
from google.rpc import status_pb2, code_pb2
import grpc
from p4.v1 import p4runtime_pb2
from p4.v1 import p4runtime_pb2_grpc
# parameters
device_id = 1
P4INFO = os.getenv('P4INFO', 'build/p4info.txt')
P4BIN = os.getenv('P4BIN', 'build/main.json')
passed_digest_id = 402184575
failed_digest_id = 401776493
digest_id = passed_digest_id
logging.basicConfig(
format='%(asctime)s.%(msecs)03d: %(process)d: %(levelname).1s/%(name)s: %(filename)s:%(lineno)d: %(message)s',
datefmt='%Y-%m-%d %H:%M:%S',
level=logging.INFO)
send_queue = queue.Queue()
recv_queue = queue.Queue()
def gen_handshake(election_id):
req = p4runtime_pb2.StreamMessageRequest()
arbitration = req.arbitration
arbitration.device_id = device_id
eid = arbitration.election_id
eid.high = election_id[0]
eid.low = election_id[1]
return req
def check_handshake():
rep = recv_queue.get(timeout=2)
if rep is None:
logging.critical("Failed to establish session with server")
sys.exit(1)
is_primary = (rep.arbitration.status.code == code_pb2.OK)
logging.debug("Session established, client is '%s'", 'primary' if is_primary else 'backup')
if not is_primary:
logging.info("You are not the primary client, you only have read access to the server")
else:
logging.info('You are primary')
def stream(stub):
def recv_handler(responses):
for response in responses:
logging.info('Receive response')
logging.info(response)
recv_queue.put(response)
responses = stub.StreamChannel(iter(send_queue.get, None))
logging.info('created channel')
recv_thread = threading.Thread(target=recv_handler, args=(responses,))
recv_thread.start()
send_queue.put(gen_handshake(election_id=(0, 1)))
check_handshake()
logging.info('handshaked')
return recv_thread
def insert_digest(stub, digest_id):
req = p4runtime_pb2.WriteRequest()
req.device_id = device_id
req.election_id.high = 0
req.election_id.low = 1
req.role_id = 0
update = req.updates.add()
update.type = p4runtime_pb2.Update.INSERT
digest_entry = update.entity.digest_entry
digest_entry.digest_id = digest_id
digest_entry.config.max_timeout_ns = 0
digest_entry.config.max_list_size = 1
digest_entry.config.ack_timeout_ns = 0
response = stub.Write(req)
def set_fwd_pipe_config(stub, p4info_path, bin_path):
req = p4runtime_pb2.SetForwardingPipelineConfigRequest()
req.device_id = device_id
election_id = req.election_id
election_id.high = 0
election_id.low = 1
req.action = p4runtime_pb2.SetForwardingPipelineConfigRequest.VERIFY_AND_COMMIT
with open(p4info_path, 'r') as f1:
with open(bin_path, 'rb') as f2:
try:
google.protobuf.text_format.Merge(f1.read(), req.config.p4info)
except google.protobuf.text_format.ParseError:
logging.error("Error when parsing P4Info")
raise
req.config.p4_device_config = f2.read()
return stub.SetForwardingPipelineConfig(req)
def client_main(stub):
logging.info('SetForwardingPipelineConfig...')
set_fwd_pipe_config(stub, P4INFO, P4BIN)
logging.info('SetForwardingPipelineConfig passed')
logging.info('insert_digest...')
insert_digest(stub, digest_id)
logging.info('insert_digest passed')
with grpc.insecure_channel('localhost:50001') as channel:
stub = p4runtime_pb2_grpc.P4RuntimeStub(channel)
recv_t = stream(stub)
try:
client_main(stub)
while True:
cmd = input('> ')
if cmd.lower() == 'exit': break
if cmd.lower() == 'quit': break
except (KeyboardInterrupt, EOFError):
pass
except:
traceback.print_exc()
send_queue.put(None)
recv_t.join()
```
Here are the steps to reproduce:
1. Start bmv2 switch from docker, so the environment is consistent for everyone.
There are two types of switches as I mentioned earlier: `stratum_bmv2` and `simple_switch_grpc`. Choose the one you want to use.
- stratum\_bmv2: `docker run --privileged --rm -it --net=host opennetworking/mn-stratum --topo single,1`
- simple\_switch\_grpc: `docker run --privileged --rm -it --net=host opennetworking/p4mn --topo single,1`
1. Make mininet host usable. Type in the following commands in mininet shell.
```auto
h1 route add default gw 10.0.0.254 dev h1-eth0
h1 arp -i h1-eth0 -s 10.0.0.254 00:00:0a:00:00:fe
```
1. Compile p4. Check ingress to use the digest you want.
```auto
p4c --std p4-16 -b bmv2 --p4runtime-files build/p4info.txt -o build src/main.p4
```
1. Start python controller. Save the python code to a file. Check line 26 to change digest\_id before running.
## Results
With passed\_digest and simple\_switch\_grpc, everything works.
You can verify by entering the command `h1 ping 1.1.1.1` in mininet shell and seeing the digest messages in python controller.
With passed\_digest and stratum\_bmv2, there is no error message. No digest message is received on controller while there should be messages.
With failed\_digest and any bmv2, there is only a warning message complaining about name:
```auto
src/main.p4(49): [--Wwarn=mismatch] warning: Cannot find a good name for digest method call, using auto-generated name 'digest_0'
digest(1, hdr.ethernet.src_addr);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
There is no other error message during compiling or setting forwarding pipeline. It only gives an error when inserting digest entry:
```auto
grpc._channel._InactiveRpcError: <_InactiveRpcError of RPC that terminated with:
status = StatusCode.UNKNOWN
details = ""
debug_error_string = "{"created":"@1655044976.054394098","description":"Error received from peer ipv6:[::1]:50001","file":"src/core/lib/surface/call.cc","file_line":1074,"grpc_message":"","grpc_status":2}"
>
```
If the second digest is not a valid p4 statement, I think it should give me error messages during compiling or during setting forwarding pipeline.