use EngineService over process.Runner

Author: asmyasnikov

docs/guides/engine-plugins.md

@@ -63,7 +63,7 @@ sql:
 | Field | Description |
 |-------|-------------|
 | `name` | Engine name used in `sql[].engine` |
-| `process.cmd` | Command to run: executable path and optional arguments (e.g. `sqlc-engine-external-db --dont-open-wildcard-star`). First token is the executable; remaining tokens are passed as arguments before the RPC method. |
+| `process.cmd` | Command to run: executable path and optional arguments (e.g. `sqlc-engine-external-db --dont-open-wildcard-star`). First token is the executable; remaining tokens are passed as arguments **before** the full RPC method name `/engine.EngineService/Parse`. |
 | `env` | Environment variable names passed to the plugin |
 
 Each engine must define either `process` (with `cmd`) or `wasm` (with `url` and `sha256`). See [Configuration reference](../reference/config.md) for the full `engines` schema.
@@ -72,7 +72,7 @@ Each engine must define either `process` (with `cmd`) or `wasm` (with `url` and
 
 For an engine with `process.cmd`, sqlc resolves and runs the plugin as follows:
 
-1. **Command parsing** — `process.cmd` is split on whitespace. The first token is the executable; any further tokens are passed as arguments, and sqlc appends the RPC method name (`parse`) when invoking the plugin.
+1. **Command parsing** — `process.cmd` is split on whitespace. The first token is the executable; any further tokens are passed as arguments, and sqlc appends the **gRPC full method name** for Parse — the same pattern as for [codegen plugins](plugins.md): `/engine.EngineService/Parse` (the generated client passes this string as the last argv token to the child process).
 
 2. **Executable lookup** — The first token is resolved the same way as in the shell:
    - If it contains a path separator (e.g. `/usr/bin/sqlc-engine-external-db` or `./bin/sqlc-engine-external-db`), it is treated as a path. Absolute paths are used as-is; relative paths are taken relative to the **current working directory of the process running sqlc**.
@@ -178,19 +178,22 @@ go build -o sqlc-engine-external-db .
 
 ## Protocol
 
-Process plugins use Protocol Buffers on stdin/stdout:
+Process plugins use Protocol Buffers on stdin/stdout — **no TCP gRPC**, but the same **unary RPC shape** as codegen plugins: sqlc uses the generated `EngineServiceClient` with `process.Runner` implementing `grpc.ClientConnInterface`, so the child receives the **full gRPC method path** as the last command-line argument (like `/plugin.CodegenService/Generate` for codegen).
 
 ```
 sqlc  →  stdin (protobuf)  →  plugin  →  stdout (protobuf)  →  sqlc
 ```
 
-Invocation:
+Invocation (method name is one argv token, often quoted in shell examples):
 
 ```bash
-sqlc-engine-external-db parse   # stdin: ParseRequest, stdout: ParseResponse
+sqlc-engine-external-db --flag /engine.EngineService/Parse
+# stdin: ParseRequest, stdout: ParseResponse
 ```
 
-The definition lives in `protos/engine/engine.proto` (generated Go in `pkg/engine`). After editing the proto, run `make proto-engine-plugin` to regenerate the Go code.
+The Go SDK `engine.Run` dispatches **Parse** when `os.Args[1]` is `/engine.EngineService/Parse` or the legacy shorthand `parse` (for older tooling).
+
+The definition lives in `protos/engine/engine.proto` (messages **and** `service EngineService`; generated Go in `pkg/engine`, including `engine_grpc.pb.go` for the client stub). After editing the proto, run `make proto-engine-plugin` to regenerate the Go code.
 
 ## Example
 
@@ -210,7 +213,7 @@ For each `sql[]` block, `sqlc generate` branches on the configured engine: built
 └─────────────────────────────────────────────────────────────────┘
 
     sqlc                          sqlc-engine-external-db
-      │──── spawn, args: ["parse"] ──────────────────────────────► │
+      │──── spawn, argv ends with /engine.EngineService/Parse ─────► │
       │──── stdin: ParseRequest{sql=full query.sql, schema_sql|…}  ► │
       │◄─── stdout: ParseResponse{statements: [stmt1, stmt2, …]} ── │
 ```

internal/cmd/plugin_engine.go

@@ -1,92 +1,30 @@
-// This file runs a database-engine plugin as an external process (parse RPC over stdin/stdout).
+// This file runs a database-engine plugin as an external process (EngineService/Parse over stdin/stdout).
+// Like codegen plugins, sqlc uses the generated EngineServiceClient with process.Runner implementing
+// grpc.ClientConnInterface (full method name /engine.EngineService/Parse as the subprocess argv tail).
 // It is used only by the plugin-engine generate path (runPluginQuerySet). Vet does not support plugin engines.
 
 package cmd
 
 import (
-	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"strings"
 
 	"github.com/sqlc-dev/sqlc/internal/compiler"
 	"github.com/sqlc-dev/sqlc/internal/config"
+	"github.com/sqlc-dev/sqlc/internal/ext/process"
 	"github.com/sqlc-dev/sqlc/internal/metadata"
 	"github.com/sqlc-dev/sqlc/internal/multierr"
 	"github.com/sqlc-dev/sqlc/internal/plugin"
 	"github.com/sqlc-dev/sqlc/internal/sql/ast"
 	"github.com/sqlc-dev/sqlc/internal/sql/catalog"
 	"github.com/sqlc-dev/sqlc/internal/sql/sqlpath"
-	"google.golang.org/protobuf/proto"
 
-	"github.com/sqlc-dev/sqlc/internal/info"
 	pb "github.com/sqlc-dev/sqlc/pkg/engine"
 )
 
-// engineProcessRunner runs an engine plugin as an external process.
-type engineProcessRunner struct {
-	Cmd string
-	Dir string // Working directory for the plugin (config file directory)
-	Env []string
-}
-
-func newEngineProcessRunner(cmd, dir string, env []string) *engineProcessRunner {
-	return &engineProcessRunner{Cmd: cmd, Dir: dir, Env: env}
-}
-
-func (r *engineProcessRunner) invoke(ctx context.Context, method string, req, resp proto.Message) error {
-	stdin, err := proto.Marshal(req)
-	if err != nil {
-		return fmt.Errorf("failed to encode request: %w", err)
-	}
-
-	cmdParts := strings.Fields(r.Cmd)
-	if len(cmdParts) == 0 {
-		return fmt.Errorf("engine plugin not found: %s\n\nSee the engine plugins documentation: https://docs.sqlc.dev/en/latest/guides/engine-plugins.html", r.Cmd)
-	}
-
-	path, err := exec.LookPath(cmdParts[0])
-	if err != nil {
-		return fmt.Errorf("engine plugin not found: %s\n\nSee the engine plugins documentation: https://docs.sqlc.dev/en/latest/guides/engine-plugins.html", r.Cmd)
-	}
-
-	args := append(cmdParts[1:], method)
-	cmd := exec.CommandContext(ctx, path, args...)
-	cmd.Stdin = bytes.NewReader(stdin)
-	if r.Dir != "" {
-		cmd.Dir = r.Dir
-	}
-	cmd.Env = append(os.Environ(), fmt.Sprintf("SQLC_VERSION=%s", info.Version))
-
-	out, err := cmd.Output()
-	if err != nil {
-		stderr := err.Error()
-		var exit *exec.ExitError
-		if errors.As(err, &exit) {
-			stderr = string(exit.Stderr)
-		}
-		return fmt.Errorf("engine plugin error: %s", stderr)
-	}
-
-	if err := proto.Unmarshal(out, resp); err != nil {
-		return fmt.Errorf("failed to decode response: %w", err)
-	}
-	return nil
-}
-
-// parseRequest invokes the plugin's Parse RPC. Used by runPluginQuerySet.
-func (r *engineProcessRunner) parseRequest(ctx context.Context, req *pb.ParseRequest) (*pb.ParseResponse, error) {
-	resp := &pb.ParseResponse{}
-	if err := r.invoke(ctx, "parse", req, resp); err != nil {
-		return nil, err
-	}
-	return resp, nil
-}
-
 // runPluginQuerySet runs the plugin-engine path: schema and queries are sent to the
 // engine plugin via ParseRequest; the responses are turned into compiler.Result and
 // passed to ProcessResult. No AST or compiler parsing is used.
@@ -139,7 +77,13 @@ func runPluginQuerySet(ctx context.Context, rp resultProcessor, name, dir string
 			return o.PluginParseFunc(schemaStr, querySQL)
 		}
 	} else {
-		r := newEngineProcessRunner(enginePlugin.Process.Cmd, combo.Dir, enginePlugin.Env)
+		runner := &process.Runner{
+			Cmd:              enginePlugin.Process.Cmd,
+			Env:              enginePlugin.Env,
+			Dir:              combo.Dir,
+			InheritParentEnv: true,
+		}
+		engineClient := pb.NewEngineServiceClient(runner)
 		parseFn = func(querySQL string) (*pb.ParseResponse, error) {
 			req := &pb.ParseRequest{Sql: querySQL}
 			if databaseOnly {
@@ -149,7 +93,7 @@ func runPluginQuerySet(ctx context.Context, rp resultProcessor, name, dir string
 			} else {
 				req.SchemaSource = &pb.ParseRequest_SchemaSql{SchemaSql: schemaSQL}
 			}
-			return r.parseRequest(ctx, req)
+			return engineClient.Parse(ctx, req)
 		}
 	}
 

internal/cmd/plugin_engine_test.go

@@ -232,12 +232,11 @@ func TestPluginPipeline_FullPipeline(t *testing.T) {
 }
 
 // TestPluginPipeline_WithoutOverride_UsesPluginPackage proves that when PluginParseFunc
-// is not set, the pipeline calls the engine process runner (newEngineProcessRunner + parseRequest).
+// is not set, the pipeline calls process.Runner + NewEngineServiceClient(...).Parse (real subprocess).
 // It runs generate with a plugin engine and nil PluginParseFunc; we expect failure
 // (e.g. from running "echo" as the engine binary), but the error must NOT be
 // "unknown engine" — so we know we went past config lookup and into the plugin path.
-// If you add panic("azaza") at the start of newEngineProcessRunner or parseRequest,
-// this test will panic, confirming that the plugin package is actually invoked.
+// If you add panic at the start of that path, this test will panic, confirming the runner is invoked.
 func TestPluginPipeline_WithoutOverride_UsesPluginPackage(t *testing.T) {
 	ctx := context.Background()
 	conf, err := config.ParseConfig(strings.NewReader(testPluginPipelineConfig))

internal/ext/process/gen.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"strings"
 
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
@@ -22,6 +23,12 @@ type Runner struct {
 	Cmd    string
 	Format string
 	Env    []string
+	// Dir, if set, is the working directory for the child process (e.g. directory of sqlc.yaml).
+	Dir string
+	// InheritParentEnv, if true, starts the child with os.Environ() and appends SQLC_VERSION and
+	// variables listed in Env (same names as codegen). Use for database engine plugins that need
+	// a normal shell-like environment (e.g. PATH). Default false matches historical codegen behavior.
+	InheritParentEnv bool
 }
 
 func (r *Runner) Invoke(ctx context.Context, method string, args any, reply any, opts ...grpc.CallOption) error {
@@ -53,16 +60,25 @@ func (r *Runner) Invoke(ctx context.Context, method string, args any, reply any,
 		return fmt.Errorf("unknown plugin format: %s", r.Format)
 	}
 
-	// Check if the output plugin exists
-	path, err := exec.LookPath(r.Cmd)
+	cmdFields := strings.Fields(strings.TrimSpace(r.Cmd))
+	if len(cmdFields) == 0 {
+		return fmt.Errorf("process: empty command")
+	}
+	exePath, err := exec.LookPath(cmdFields[0])
 	if err != nil {
 		return fmt.Errorf("process: %s not found", r.Cmd)
 	}
 
-	cmd := exec.CommandContext(ctx, path, method)
+	argv := append(append([]string(nil), cmdFields[1:]...), method)
+	cmd := exec.CommandContext(ctx, exePath, argv...)
 	cmd.Stdin = bytes.NewReader(stdin)
-	cmd.Env = []string{
-		fmt.Sprintf("SQLC_VERSION=%s", info.Version),
+	if r.Dir != "" {
+		cmd.Dir = r.Dir
+	}
+	if r.InheritParentEnv {
+		cmd.Env = append(append([]string(nil), os.Environ()...), fmt.Sprintf("SQLC_VERSION=%s", info.Version))
+	} else {
+		cmd.Env = []string{fmt.Sprintf("SQLC_VERSION=%s", info.Version)}
 	}
 	for _, key := range r.Env {
 		if key == "SQLC_AUTH_TOKEN" {

pkg/engine/sdk.go

@@ -70,7 +70,7 @@ func Run(h Handler) {
 
 func run(h Handler, args []string, stdin io.Reader, stdout, stderr io.Writer) error {
 	if len(args) < 2 {
-		return fmt.Errorf("usage: %s <method>", args[0])
+		return fmt.Errorf("usage: %s <%s|parse>", args[0], EngineService_Parse_FullMethodName)
 	}
 
 	method := args[1]
@@ -81,8 +81,12 @@ func run(h Handler, args []string, stdin io.Reader, stdout, stderr io.Writer) er
 
 	var output proto.Message
 
-	switch method {
-	case "parse":
+	switch {
+	// Full gRPC method name (same argv tail as codegen plugins use for CodegenService/Generate).
+	case method == EngineService_Parse_FullMethodName:
+		fallthrough
+	// Legacy shorthand for manual invocation and older sqlc versions.
+	case method == "parse":
 		var req ParseRequest
 		if err := proto.Unmarshal(input, &req); err != nil {
 			return fmt.Errorf("parsing request: %w", err)
@@ -93,7 +97,7 @@ func run(h Handler, args []string, stdin io.Reader, stdout, stderr io.Writer) er
 		output, err = h.Parse(&req)
 
 	default:
-		return fmt.Errorf("unknown method: %s", method)
+		return fmt.Errorf("unknown method: %q (expected %q or legacy \"parse\")", method, EngineService_Parse_FullMethodName)
 	}
 
 	if err != nil {

pkg/engine/sdk_test.go

@@ -0,0 +1,57 @@
+package engine
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"google.golang.org/protobuf/proto"
+)
+
+func TestRun_acceptsFullGRPCMethodName(t *testing.T) {
+	called := false
+	h := Handler{
+		Parse: func(req *ParseRequest) (*ParseResponse, error) {
+			called = true
+			return &ParseResponse{}, nil
+		},
+	}
+	in, err := proto.Marshal(&ParseRequest{Sql: "SELECT 1"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	var stdout bytes.Buffer
+	err = run(h, []string{"plugin", EngineService_Parse_FullMethodName}, bytes.NewReader(in), &stdout, io.Discard)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !called {
+		t.Fatal("Parse not invoked for full gRPC method argv")
+	}
+	var resp ParseResponse
+	if err := proto.Unmarshal(stdout.Bytes(), &resp); err != nil {
+		t.Fatalf("stdout protobuf: %v", err)
+	}
+}
+
+func TestRun_acceptsLegacyParseArgv(t *testing.T) {
+	called := false
+	h := Handler{
+		Parse: func(req *ParseRequest) (*ParseResponse, error) {
+			called = true
+			return &ParseResponse{}, nil
+		},
+	}
+	in, err := proto.Marshal(&ParseRequest{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	var stdout bytes.Buffer
+	err = run(h, []string{"plugin", "parse"}, bytes.NewReader(in), &stdout, io.Discard)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !called {
+		t.Fatal("Parse not invoked for legacy parse argv")
+	}
+}