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Merged
malpou merged 1 commit into from
Oct 19, 2026
Merged

feat(natsclient): the shared NATS client, with private inboxes, micro endpoints, requests and metrics (ENG-443) #3

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76 changes: 75 additions & 1 deletion README.md
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Expand Up @@ -2,7 +2,8 @@

Shared Go module for services on the platform. The `runtime` package
implements the runtime contract once, so a service's `main` is: load the
runtime, register readiness checks, serve.
runtime, register readiness checks, serve. The `natsclient` package is the
NATS client every service shares.

```go
ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
Expand Down Expand Up @@ -67,6 +68,79 @@ curl -i localhost:8081/readyz # 503 for two seconds, then 200
curl localhost:9464/metrics
```

## natsclient

The `natsclient` package is the one NATS client every Go service uses: it
connects with the projected token and the service's identity, serves
request/reply endpoints and makes requests with deadlines, tracing and
metrics. Events and commands (JetStream) come from the service's AsyncAPI
contract, not from this package.

```go
nc, err := natsclient.Connect(ctx, natsclient.FromRuntime(rt.Config), rt.Logger)
if err != nil { ... }
rt.Ready("nats", nc.Connected())

svc, err := nc.Service("orders", version) // $SRV discovery for free
err = svc.AddEndpoint("get", func(ctx context.Context, req natsclient.Request) error {
return req.Respond(data) // orders.svc.get, queue group "orders"
})

ctx, cancel := context.WithTimeout(ctx, 2*time.Second) // a deadline is required
reply, err := nc.Request(ctx, natsclient.EndpointSubject("orders", "get"), body, nil)
```

Subjects follow ADR 0006: `<service>.svc.<endpoint>` for synchronous calls on
core NATS, `<service>.evt.<event>` and `<service>.cmd.<command>` on JetStream.
Endpoints join a queue group named after the service, so replicas share the
load; `WithQueueGroup` picks another group for an endpoint that must see every
request. The connection re-reads the token on every (re)connect, reconnects
forever, is named after the service, and logs every connection event: the
hourly credential expiry at Info, a closed connection at Error.

Replies arrive on a private inbox, `_INBOX_<ns>_<sa>` from `SERVICE_IDENTITY`
with dots turned into `_`, which the auth callout grants to that identity
alone. Until the grant is issued (ENG-447) an identity requests with
`WithSharedInbox()`, which keeps nats.go's `_INBOX` prefix.

`Request` tells failures apart, so a caller can act on them:

| Error | Meaning |
|---|---|
| `ErrNoDeadline` | the context has no deadline; a request without one would hang on a lost reply |
| `ErrNoResponders` | nobody serves the subject: the target is down or not deployed (wraps `nats.ErrNoResponders`) |
| `ErrTimeout` | the deadline passed with no reply: the target is slow (wraps `context.DeadlineExceeded`) |
| `*ServiceError` | the endpoint answered with an error response; a handler returns one to pick the code, any other error is 500 |

Every request is counted in `nats_requests_total{service,endpoint,outcome}`
(`ok`, `no_responders`, `timeout`, `error`) and timed in
`nats_request_duration_seconds` with the same labels. The caller's trace
goes along as a W3C `traceparent` header, and the handler's context carries
it, so logs and spans on both sides share one trace.

### Conventions for Rust and .NET

The other languages follow the same conventions with their own clients;
nothing is wrapped.

- Connect as the user `SERVICE_IDENTITY` with the projected token at
`NATS_TOKEN_FILE` as the password, read on every connect attempt, never
once at start (async-nats: `ConnectOptions::auth_callback`; NATS.Net:
`NatsAuthOpts.AuthCredCallback`), reconnect without limit, and name the
connection after the service.
- Set the private inbox prefix `_INBOX_<ns>_<sa>` (async-nats:
`ConnectOptions::custom_inbox_prefix`; NATS.Net: `NatsOpts.InboxPrefix`).
- Subjects are `<service>.svc.<endpoint>`, `<service>.evt.<event>` and
`<service>.cmd.<command>`; endpoints join the queue group named after the
service.
- Every request has a deadline, and "no responders" is handled apart from a
timeout (async-nats: `RequestErrorKind::NoResponders` vs `TimedOut`;
NATS.Net: `NatsNoRespondersException` vs `NatsNoReplyException`).
- The W3C `traceparent` header carries the trace; the handler continues it in
a server span.
- Metrics are `nats_requests_total{service,endpoint,outcome}` and
`nats_request_duration_seconds` with the same labels.

## Working here

```
Expand Down
19 changes: 15 additions & 4 deletions go.mod
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Expand Up @@ -4,12 +4,15 @@ go 1.26.0

require (
github.com/caarlos0/env/v11 v11.4.1
github.com/nats-io/nats-server/v2 v2.15.1
github.com/nats-io/nats.go v1.54.0
github.com/prometheus/client_golang v1.23.2
github.com/stretchr/testify v1.11.1
go.opentelemetry.io/contrib/instrumentation/runtime v0.68.0
go.opentelemetry.io/otel v1.44.0
go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.44.0
go.opentelemetry.io/otel/exporters/prometheus v0.66.0
go.opentelemetry.io/otel/metric v1.44.0
go.opentelemetry.io/otel/sdk v1.44.0
go.opentelemetry.io/otel/sdk/metric v1.44.0
go.opentelemetry.io/otel/trace v1.44.0
Expand All @@ -18,27 +21,35 @@ require (
)

require (
github.com/antithesishq/antithesis-sdk-go v0.8.0-default-no-op // indirect
github.com/beorn7/perks v1.0.1 // indirect
github.com/cenkalti/backoff/v5 v5.0.3 // indirect
github.com/cespare/xxhash/v2 v2.3.0 // indirect
github.com/davecgh/go-spew v1.1.1 // indirect
github.com/go-logr/logr v1.4.3 // indirect
github.com/go-logr/stdr v1.2.2 // indirect
github.com/google/go-tpm v0.9.8 // indirect
github.com/google/uuid v1.6.0 // indirect
github.com/grpc-ecosystem/grpc-gateway/v2 v2.29.0 // indirect
github.com/klauspost/compress v1.20.1 // indirect
github.com/minio/highwayhash v1.0.4 // indirect
github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
github.com/nats-io/jwt/v2 v2.8.2 // indirect
github.com/nats-io/nkeys v0.4.16 // indirect
github.com/nats-io/nuid v1.0.1 // indirect
github.com/pmezard/go-difflib v1.0.0 // indirect
github.com/prometheus/client_model v0.6.2 // indirect
github.com/prometheus/common v0.67.5 // indirect
github.com/prometheus/otlptranslator v1.0.0 // indirect
github.com/prometheus/procfs v0.20.1 // indirect
go.opentelemetry.io/auto/sdk v1.2.1 // indirect
go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.44.0 // indirect
go.opentelemetry.io/otel/metric v1.44.0 // indirect
go.yaml.in/yaml/v2 v2.4.4 // indirect
golang.org/x/net v0.55.0 // indirect
golang.org/x/sys v0.45.0 // indirect
golang.org/x/text v0.37.0 // indirect
golang.org/x/crypto v0.57.0 // indirect
golang.org/x/net v0.58.0 // indirect
golang.org/x/sys v0.48.0 // indirect
golang.org/x/text v0.42.0 // indirect
golang.org/x/time v0.16.0 // indirect
google.golang.org/genproto/googleapis/api v0.0.0-20260526163538-3dc84a4a5aaa // indirect
google.golang.org/genproto/googleapis/rpc v0.0.0-20260526163538-3dc84a4a5aaa // indirect
google.golang.org/protobuf v1.36.11 // indirect
Expand Down
37 changes: 29 additions & 8 deletions go.sum
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Open in desktop
Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
github.com/antithesishq/antithesis-sdk-go v0.8.0-default-no-op h1:1BOWQJweNyvZMlpAHXGLiZQn9S+QXGcz3xh94lC0w6E=
github.com/antithesishq/antithesis-sdk-go v0.8.0-default-no-op/go.mod h1:FQyySiasQQM8735Ddel3MRojmy4dA1IqCeyJ5jmPMbI=
github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
github.com/caarlos0/env/v11 v11.4.1 h1:fYwH0sWEsBSMPG7t4e/PEfTFzrWrpjyygXyUnWiSwEw=
Expand All @@ -17,20 +19,34 @@ github.com/golang/protobuf v1.5.4 h1:i7eJL8qZTpSEXOPTxNKhASYpMn+8e5Q6AdndVa1dWek
github.com/golang/protobuf v1.5.4/go.mod h1:lnTiLA8Wa4RWRcIUkrtSVa5nRhsEGBg48fD6rSs7xps=
github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
github.com/google/go-tpm v0.9.8 h1:slArAR9Ft+1ybZu0lBwpSmpwhRXaa85hWtMinMyRAWo=
github.com/google/go-tpm v0.9.8/go.mod h1:h9jEsEECg7gtLis0upRBQU+GhYVH6jMjrFxI8u6bVUY=
github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
github.com/grpc-ecosystem/grpc-gateway/v2 v2.29.0 h1:5VipnvEpbqr2gA2VbM+nYVbkIF28c5ZQfqCBQ5g2xfk=
github.com/grpc-ecosystem/grpc-gateway/v2 v2.29.0/go.mod h1:Hyl3n6Twe1hvtd9XUXDec4pTvgMSEixRuQKPTMH2bNs=
github.com/klauspost/compress v1.18.0 h1:c/Cqfb0r+Yi+JtIEq73FWXVkRonBlf0CRNYc8Zttxdo=
github.com/klauspost/compress v1.18.0/go.mod h1:2Pp+KzxcywXVXMr50+X0Q/Lsb43OQHYWRCY2AiWywWQ=
github.com/klauspost/compress v1.20.1 h1:T7kKElXUMXrUJ2E9QhQhxFtcK5rPyLdsGZvdbLMPdiQ=
github.com/klauspost/compress v1.20.1/go.mod h1:LUdAzn7YLVvxLpc7y3V1m40wESHTgc1422pwwBSKYuI=
github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=
github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
github.com/minio/highwayhash v1.0.4 h1:asJizugGgchQod2ja9NJlGOWq4s7KsAWr5XUc9Clgl4=
github.com/minio/highwayhash v1.0.4/go.mod h1:GGYsuwP/fPD6Y9hMiXuapVvlIUEhFhMTh0rxU3ik1LQ=
github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
github.com/nats-io/jwt/v2 v2.8.2 h1:XXRgB60MSTnqsRwejQurVDs/hcv2dkt+86GjI+I/bMc=
github.com/nats-io/jwt/v2 v2.8.2/go.mod h1:Ag/56sq9OblL4JgdYufDd16Egb17Kr/8WwwuO/forVc=
github.com/nats-io/nats-server/v2 v2.15.1 h1:fK3AeYFIji1Smng60jB0hVoAPZezA/UzsaI3BqXFNEI=
github.com/nats-io/nats-server/v2 v2.15.1/go.mod h1:yeuYRtKVKIFtmMz2/YPk+6hvmNBnk+WwTUzErBdH6IE=
github.com/nats-io/nats.go v1.54.0 h1:vsXoOxjHp/GmPUN+EcI7uOf/uB+iAP+kEsAFNQN0yzA=
github.com/nats-io/nats.go v1.54.0/go.mod h1:y+DZoD1oBOYfZTU681eTUiUjI0vbqYGixNVFHcjHJ0k=
github.com/nats-io/nkeys v0.4.16 h1:rd5oAuLOb8mnAycB0xleuEBNS1pVVnN0fv/FF34Eypg=
github.com/nats-io/nkeys v0.4.16/go.mod h1:llLgWoI0o4z/Q57q2R1kHfmocyhGV6VG/U18Glg1Afs=
github.com/nats-io/nuid v1.0.1 h1:5iA8DT8V7q8WK2EScv2padNa/rTESc1KdnPw4TC2paw=
github.com/nats-io/nuid v1.0.1/go.mod h1:19wcPz3Ph3q0Jbyiqsd0kePYG7A95tJPxeL+1OSON2c=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/prometheus/client_golang v1.23.2 h1:Je96obch5RDVy3FDMndoUsjAhG5Edi49h0RJWRi/o0o=
Expand Down Expand Up @@ -75,12 +91,17 @@ go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
go.yaml.in/yaml/v2 v2.4.4 h1:tuyd0P+2Ont/d6e2rl3be67goVK4R6deVxCUX5vyPaQ=
go.yaml.in/yaml/v2 v2.4.4/go.mod h1:gMZqIpDtDqOfM0uNfy0SkpRhvUryYH0Z6wdMYcacYXQ=
golang.org/x/net v0.55.0 h1:bcvxaJn3e1U6InsFWt1JUq1aSjnRxLzT2rtD2KfkDF8=
golang.org/x/net v0.55.0/go.mod h1:L5U2KuzuOe1lY7Z+aWVIKK6qEeJXnXV9yzGA+WCHJww=
golang.org/x/sys v0.45.0 h1:dO4czNzziLiiXplLQgBCEpCvXQ3dnkn0SdaZSYdQ+FY=
golang.org/x/sys v0.45.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
golang.org/x/text v0.37.0 h1:Cqjiwd9eSg8e0QAkyCaQTNHFIIzWtidPahFWR83rTrc=
golang.org/x/text v0.37.0/go.mod h1:a5sjxXGs9hsn/AJVwuElvCAo9v8QYLzvavO5z2PiM38=
golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
golang.org/x/net v0.58.0 h1:ynWG7rqYi4ccpTEuPZ2QGWHktVEM9DMCj9yzDE0Q7To=
golang.org/x/net v0.58.0/go.mod h1:YwCddHnFlT7eLQqVprV19OnhLGtc5xOKgE0RyqgfWAU=
golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
golang.org/x/text v0.42.0 h1:JbOZXgfeCPU9gacVtYliJqOhD+zhrEqK4LfdpmlUZqI=
golang.org/x/text v0.42.0/go.mod h1:ojzP1Z+2QtioaF8DTtO8K5q7JWVVYwZKenzujK0Zd0E=
golang.org/x/time v0.16.0 h1:vMb6ptszcQMkcwiRTAuNNU50gom6++Q/6gY2hDM6VDE=
golang.org/x/time v0.16.0/go.mod h1:rVKOqvZeKvrDKTQiAHJ7wmwP0RzleSphoEA9RcdLA0s=
gonum.org/v1/gonum v0.17.0 h1:VbpOemQlsSMrYmn7T2OUvQ4dqxQXU+ouZFQsZOx50z4=
gonum.org/v1/gonum v0.17.0/go.mod h1:El3tOrEuMpv2UdMrbNlKEh9vd86bmQ6vqIcDwxEOc1E=
google.golang.org/genproto/googleapis/api v0.0.0-20260526163538-3dc84a4a5aaa h1:Kjn0N0tCrDgiAFW+lGO4JZ3ck44CehvJQMAwj9QF0G8=
Expand Down
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