GenerateTemplate RPC

docs/brainstorms/2026-02-16-generate-template-api-brainstorm.md

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+# Tech Design: YAML Generation — Imperative Functions vs. GenerateTemplate API
+
+**Date:** 2026-02-16
+**Status:** Brainstorm
+**Author:** Cyrus Goh
+
+---
+
+## Problem Statement
+
+The frontend has two imperative YAML builder functions — `compileSourceYAML()` and `compileConnectorYAML()` — that share overlapping logic but diverge in subtle ways. This creates:
+
+1. **Duplication:** Both functions handle secret extraction (`{{ .env.* }}` placeholders), string quoting, empty-value filtering, and property ordering — but with separate, slightly different implementations.
+2. **Maintenance burden:** Adding a new connector or field type requires touching complex conditional logic with many special cases (ClickHouse `managed: false` exclusion, DuckDB SQL rewriting, HTTP header formatting, etc.).
+3. **Frontend owns YAML format:** The frontend knows too much about what valid YAML looks like for each resource type. This knowledge should live closer to the backend, which actually parses and validates these files.
+
+### Current Architecture
+
+```
+Form Data → compileSourceYAML() / compileConnectorYAML() → YAML string → PutFile RPC → Backend
+                  (imperative string builder)
+```
+
+**Key files:**
+- `web-common/src/features/sources/sourceUtils.ts` — `compileSourceYAML()` (~90 lines)
+- `web-common/src/features/connectors/code-utils.ts` — `compileConnectorYAML()` (~100 lines)
+- `web-common/src/features/sources/modal/submitAddDataForm.ts` — primary caller
+- `web-common/src/features/sources/modal/AddDataFormManager.ts` — YAML preview caller
+
+### Shared Logic (duplicated between the two functions)
+
+| Concern | compileSourceYAML | compileConnectorYAML |
+|---------|-------------------|----------------------|
+| YAML header with doc link | Yes | Yes |
+| Secret → `{{ .env.VAR }}` | Yes | Yes |
+| String property quoting | Yes | Yes |
+| Empty value filtering | Yes | Yes |
+| Env var name generation | Via `makeEnvVarKey()` | Via `makeEnvVarKey()` |
+| SQL multi-line formatting | Yes | No |
+| Headers map formatting | No | Yes |
+| Property ordering | Implicit (object key order) | Explicit (orderedProperties) |
+| Field filtering | Implicit (step-based) | Explicit (fieldFilter function) |
+| Dev section | Yes (with Redshift exception) | No |
+
+---
+
+## Approach A: Consolidate Imperative Functions (Frontend-Only Refactor)
+
+Merge `compileConnectorYAML` and `compileSourceYAML` into a unified `compileResourceYAML()` function that handles all resource types through configuration.
+
+### Design
+
+```typescript
+interface ResourceYAMLOptions {
+  resourceType: "connector" | "source" | "model";
+  driver: string;
+  formValues: Record<string, unknown>;
+  orderedProperties?: ConnectorDriverProperty[];
+  fieldFilter?: (property: ConnectorDriverProperty) => boolean;
+  secretKeys?: string[];
+  stringKeys?: string[];
+  connectorInstanceName?: string;
+  schema?: { properties?: Record<string, { "x-env-var-name"?: string }> };
+  existingEnvBlob?: string;
+  includeDevSection?: boolean;
+  originalDriverName?: string;
+}
+
+function compileResourceYAML(opts: ResourceYAMLOptions): string {
+  // Unified logic:
+  // 1. Generate header (type + driver + doc link)
+  // 2. Filter properties (by step, field filter, empty values)
+  // 3. Order properties (explicit or implicit)
+  // 4. Format each property:
+  //    - Secrets → {{ .env.VAR }}
+  //    - Strings → quoted
+  //    - SQL → multi-line
+  //    - Headers → YAML map
+  //    - Default → raw value
+  // 5. Optional dev section
+  // 6. Return assembled YAML
+}
+```
+
+### Migration Path
+
+1. Create `compileResourceYAML()` with all shared logic
+2. Re-implement `compileSourceYAML()` and `compileConnectorYAML()` as thin wrappers
+3. Gradually migrate callers to the unified function
+4. Remove wrappers once all callers are migrated
+
+### Pros
+
+- No backend changes required
+- Incremental, low-risk refactor
+- Eliminates duplication between the two functions
+- Can be done in a single PR
+
+### Cons
+
+- Frontend still owns YAML format knowledge — can drift from backend expectations
+- Special cases keep accumulating as connectors are added
+- Doesn't extend to other resource types (explores, dashboards, etc.) without growing the function
+- YAML string building is inherently fragile (indentation, quoting, escaping)
+
+### Effort Estimate
+
+Small — 1-2 days of frontend work.
+
+---
+
+## Approach B: Backend `GenerateTemplate` RPC (Recommended)
+
+New backend endpoint that accepts structured data and returns rendered YAML. The frontend becomes a thin form layer.
+
+### Design
+
+#### New RPC
+
+```protobuf
+// GenerateTemplate renders a YAML file from structured input.
+// Supports all resource types: connector, source, model, explore, dashboard, etc.
+rpc GenerateTemplate(GenerateTemplateRequest) returns (GenerateTemplateResponse) {
+  option (google.api.http) = {
+    post: "/v1/instances/{instance_id}/generate/template",
+    body: "*"
+  };
+}
+
+message GenerateTemplateRequest {
+  string instance_id = 1;
+  // Resource type: "connector", "source", "model", "explore", "metrics_view", etc.
+  string resource_type = 2;
+  // Driver name (for connectors/sources): "clickhouse", "s3", "duckdb", etc.
+  string driver = 3;
+  // Structured key-value properties from the form
+  google.protobuf.Struct properties = 4;
+  // Optional: connector instance name (for sources that reference a connector)
+  string connector_name = 5;
+  // Optional: fields that should be treated as secrets (extracted to .env)
+  repeated string secret_keys = 6;
+}
+
+message GenerateTemplateResponse {
+  // Rendered YAML blob, ready to write via PutFile
+  string blob = 1;
+  // Environment variables to write to .env (key → value)
+  map<string, string> env_vars = 2;
+}
+```
+
+#### New Architecture
+
+```
+Form Data → GenerateTemplate RPC → { blob, env_vars } → PutFile RPC (blob) + update .env (env_vars)
+                (backend)
+```
+
+#### Backend Implementation
+
+The backend would:
+1. Look up a Go template for the given `resource_type` + `driver` combination
+2. Apply structured properties to the template
+3. Handle secret extraction: replace secret values with `{{ .env.VAR }}` and return the real values in `env_vars`
+4. Return the rendered YAML blob
+
+Templates could be Go `text/template` files or a simple struct-to-YAML mapper using the `gopkg.in/yaml.v3` library.
+
+#### Frontend Changes
+
+```typescript
+// Before (imperative)
+const blob = compileConnectorYAML(connector, formValues, { ...options });
+await runtimeServicePutFile(instanceId, { path, blob, create: true });
+await updateDotEnvWithSecrets(instanceId, connector, formValues, options);
+
+// After (declarative)
+const { blob, envVars } = await runtimeServiceGenerateTemplate(instanceId, {
+  resourceType: "connector",
+  driver: connector.name,
+  properties: formValues,
+  secretKeys: schemaSecretKeys,
+});
+await runtimeServicePutFile(instanceId, { path, blob, create: true });
+await writeDotEnv(instanceId, envVars);
+```
+
+### Migration Path
+
+1. **Phase 1:** Implement `GenerateTemplate` RPC for connectors
+2. **Phase 2:** Migrate `compileConnectorYAML()` callers to use the RPC
+3. **Phase 3:** Add source/model support, migrate `compileSourceYAML()` callers
+4. **Phase 4:** Extend to other resource types (explores, dashboards, etc.)
+5. **Phase 5:** Remove frontend compile functions
+
+Each phase can be a separate PR. Old and new paths can coexist during migration.
+
+### Pros
+
+- Backend owns the canonical YAML format — single source of truth
+- Frontend complexity drops dramatically — no YAML string building, quoting, or escaping
+- Generalizes to all resource types (connectors, sources, models, explores, dashboards, APIs, canvases, themes, reports, alerts)
+- Aligns with existing backend generation patterns (`GenerateMetricsViewFile`, `GenerateCanvas`, `GenerateResolver`)
+- Secret handling can be co-located with template logic
+- Backend can validate property completeness before rendering
+
+### Cons
+
+- Requires backend work (new RPC, template registry, tests)
+- Larger scope — multi-phase migration across frontend and backend
+- YAML preview in the form is lost (acceptable per discussion — not critical)
+- Network round-trip for template rendering (acceptable — only on submit)
+- Need to decide where templates live (Go code, embedded files, or database)
+
+### Effort Estimate
+
+Medium — 1-2 weeks across backend + frontend.
+
+---
+
+## Open Questions
+
+1. **Secret handling ownership:** Should the backend fully own env var naming and `.env` file writes? Or should it just return `env_vars` and let the frontend write them?
+   - Option A: Backend returns `env_vars` map, frontend writes to `.env` (simpler, frontend already has this code)
+   - Option B: Backend writes `.env` directly as part of `GenerateTemplate` (cleaner, but couples template rendering with file I/O)
+
+2. **Template storage:** Where do the YAML templates live?
+   - Go struct-to-YAML mapping (type-safe, no template files)
+   - Embedded Go `text/template` files (flexible, easy to edit)
+   - Hardcoded strings in Go (simple, like current frontend approach but server-side)
+
+3. **DuckDB rewriting:** Currently `maybeRewriteToDuckDb()` transforms S3/GCS/HTTPS sources into DuckDB SQL. Should this logic move to the backend too, or stay as a frontend preprocessing step?
+
+4. **Connector property metadata:** The frontend schemas define `x-secret`, `x-string`, `x-env-var-name` extensions. Should the backend be the source of truth for these, or should the frontend continue to pass `secretKeys`/`stringKeys` in the request?
+
+5. **Backward compatibility:** Do we need to support both old (imperative) and new (RPC) paths simultaneously during migration? Or can we cut over all at once?
+
+---
+
+## Recommendation
+
+**Approach B (Backend `GenerateTemplate` RPC)** is recommended because:
+
+- It addresses the root cause: the frontend shouldn't own YAML format knowledge
+- It's a natural extension of existing backend patterns (`GenerateMetricsViewFile`, etc.)
+- It generalizes to all resource types, not just connectors/sources
+- The migration can be incremental (phase by phase)
+- Loss of YAML preview is acceptable
+
+Approach A is a valid stopgap if backend bandwidth is limited, but it doesn't solve the fundamental problem of frontend-owned YAML format.
+
+---
+
+## Key Decisions Made
+
+- **Motivation:** Duplication and maintenance burden in `compileSourceYAML`/`compileConnectorYAML`
+- **Direction:** Backend RPC over frontend-only refactor
+- **Scope:** All resource types (design wide), implement connectors/sources first
+- **YAML Preview:** Can be dropped — not critical for users
+- **Secret handling:** Open question to resolve during planning