a6-plugin-grpc-transcode

Overview

The grpc-transcode plugin converts HTTP/JSON requests into gRPC calls and returns gRPC responses as JSON. Clients send standard HTTP requests; APISIX transcodes them to gRPC using a pre-uploaded protobuf definition, forwards to the gRPC upstream, and returns the response as JSON. The gRPC service needs no modification.

When to Use

• Expose gRPC services via RESTful HTTP endpoints
• Allow browser/mobile clients to call gRPC services without gRPC client libraries
• Add HTTP API gateway features (auth, rate limiting, logging) to gRPC services
• Migrate from REST to gRPC incrementally
• Decode gRPC error details into human-readable JSON

Plugin Configuration Reference (Route/Service)

Field	Type	Required	Default	Description
proto_id	string/integer	Yes	—	ID of the proto resource (uploaded via a6 proto create).
service	string	Yes	—	Fully qualified gRPC service name (e.g., helloworld.Greeter).
method	string	Yes	—	gRPC method name (e.g., SayHello).
deadline	number	No	0	Deadline for the gRPC call in milliseconds. 0 = no deadline.
pb_option	array[string]	No	—	Protobuf serialization options (see table below).
show_status_in_body	boolean	No	false	Include parsed grpc-status-details-bin in the JSON response body on errors.
status_detail_type	string	No	—	Message type for the details field in gRPC error status. Required to decode error details.

pb_option Values

Option	Description
enum_as_name	Return enum fields as string names (e.g., "PENDING")
enum_as_value	Return enum fields as integer values (e.g., 1)
int64_as_number	Return int64 as JSON number (may lose precision in JavaScript)
int64_as_string	Return int64 as string (safe for JavaScript clients)
int64_as_hexstring	Return int64 as hexadecimal string
auto_default_values	Auto-populate default values for unset fields
no_default_values	Do not add default values for unset fields
use_default_values	Use proto-defined default values
use_default_metatable	Use metatable for default values
enable_hooks	Enable protobuf hooks
disable_hooks	Disable protobuf hooks

Multiple options can be combined: ["int64_as_string", "enum_as_name"]

Step-by-Step: Set Up gRPC Transcoding

1. Upload the proto definition

Given a proto file:

syntax = "proto3";
package helloworld;

service Greeter {
    rpc SayHello (HelloRequest) returns (HelloReply) {}
}

message HelloRequest {
    string name = 1;
}

message HelloReply {
    string message = 1;
}

Upload it:

a6 proto create -f - <<'EOF'
{
  "id": "1",
  "content": "syntax = \"proto3\";\npackage helloworld;\nservice Greeter {\n    rpc SayHello (HelloRequest) returns (HelloReply) {}\n}\nmessage HelloRequest {\n    string name = 1;\n}\nmessage HelloReply {\n    string message = 1;\n}"
}
EOF

2. Create a route with grpc-transcode

a6 route create -f - <<'EOF'
{
  "id": "grpc-hello",
  "methods": ["GET", "POST"],
  "uri": "/grpc/hello",
  "plugins": {
    "grpc-transcode": {
      "proto_id": "1",
      "service": "helloworld.Greeter",
      "method": "SayHello"
    }
  },
  "upstream": {
    "scheme": "grpc",
    "type": "roundrobin",
    "nodes": {
      "grpc-server:50051": 1
    }
  }
}
EOF

Critical: The upstream scheme must be "grpc" (or "grpcs" for TLS).

3. Test the endpoint

# Pass parameters via query string
curl "http://localhost:9080/grpc/hello?name=world"
# Response: {"message":"Hello world"}

# Or via POST body
curl -X POST http://localhost:9080/grpc/hello \
  -H "Content-Type: application/json" \
  -d '{"name": "world"}'
# Response: {"message":"Hello world"}

Common Patterns

Proto with imports (use compiled .pb file)

When your proto has import statements, compile to a .pb file first:

protoc --include_imports --descriptor_set_out=service.pb proto/service.proto

Then upload the base64-encoded .pb:

a6 proto create -f - <<EOF
{
  "id": "2",
  "content": "$(base64 -i service.pb)"
}
EOF

Safe int64 handling for JavaScript clients

{
  "plugins": {
    "grpc-transcode": {
      "proto_id": "1",
      "service": "order.OrderService",
      "method": "GetOrder",
      "pb_option": ["int64_as_string"]
    }
  }
}

Returns {"order_id": "9223372036854775807"} instead of {"order_id": 9223372036854775807} (which JavaScript would corrupt).

Human-readable enums

{
  "plugins": {
    "grpc-transcode": {
      "proto_id": "1",
      "service": "order.OrderService",
      "method": "GetOrder",
      "pb_option": ["enum_as_name", "int64_as_string"]
    }
  }
}

Returns {"status": "PENDING"} instead of {"status": 1}.

gRPC error detail decoding

{
  "plugins": {
    "grpc-transcode": {
      "proto_id": "1",
      "service": "helloworld.Greeter",
      "method": "SayHello",
      "show_status_in_body": true,
      "status_detail_type": "helloworld.ErrorDetail"
    }
  }
}

Error response body:

{
  "error": {
    "code": 14,
    "message": "Out of service",
    "details": [
      {
        "type": "service",
        "message": "The server is out of service",
        "code": 1
      }
    ]
  }
}

Timeout control with deadline

{
  "plugins": {
    "grpc-transcode": {
      "proto_id": "1",
      "service": "slow.SlowService",
      "method": "LongRunning",
      "deadline": 5000
    }
  }
}

Request fails if the gRPC service doesn't respond within 5 seconds.

Multiple gRPC methods on different routes

// Route 1: GET /api/users/:id → user.UserService/GetUser
{
  "id": "grpc-get-user",
  "uri": "/api/users/*",
  "methods": ["GET"],
  "plugins": {
    "grpc-transcode": {
      "proto_id": "3",
      "service": "user.UserService",
      "method": "GetUser"
    }
  },
  "upstream": {"scheme": "grpc", "type": "roundrobin", "nodes": {"user-svc:50051": 1}}
}

// Route 2: POST /api/users → user.UserService/CreateUser
{
  "id": "grpc-create-user",
  "uri": "/api/users",
  "methods": ["POST"],
  "plugins": {
    "grpc-transcode": {
      "proto_id": "3",
      "service": "user.UserService",
      "method": "CreateUser"
    }
  },
  "upstream": {"scheme": "grpc", "type": "roundrobin", "nodes": {"user-svc:50051": 1}}
}

Troubleshooting

Symptom	Cause	Fix
"can not find proto"	Proto ID doesn't exist	Verify with a6 proto get <id>
"method not found"	Service or method name mismatch	Use fully qualified name: package.Service, case-sensitive
Connection refused to upstream	Wrong scheme or port	Set upstream scheme to grpc, verify port is gRPC port
Import errors in proto	Proto has imports but raw content uploaded	Compile to .pb with protoc --include_imports
int64 values corrupted	JavaScript precision loss	Use pb_option: ["int64_as_string"]
Enum shows numbers instead of names	Default behavior	Use pb_option: ["enum_as_name"]
Error details not decoded	show_status_in_body not set	Set show_status_in_body: true and status_detail_type
gRPC call times out silently	No deadline set	Set deadline in milliseconds
502 Bad Gateway	gRPC service not running or not reachable	Check gRPC service is up and port is accessible from APISIX

Config Sync Example

version: "1"
protos:
  - id: helloworld-proto
    content: |
      syntax = "proto3";
      package helloworld;
      service Greeter {
          rpc SayHello (HelloRequest) returns (HelloReply) {}
      }
      message HelloRequest {
          string name = 1;
      }
      message HelloReply {
          string message = 1;
      }
routes:
  - id: grpc-hello
    methods:
      - GET
      - POST
    uri: /grpc/hello
    plugins:
      grpc-transcode:
        proto_id: helloworld-proto
        service: helloworld.Greeter
        method: SayHello
        pb_option:
          - int64_as_string
          - enum_as_name
    upstream_id: grpc-backend
upstreams:
  - id: grpc-backend
    scheme: grpc
    type: roundrobin
    nodes:
      "grpc-server:50051": 1