# Data Model: KME Article Content Fetch (003)

**Phase 1 output for `003-kme-content-fetch`**

---

## Entities

### 1. KME Article Content

Represents a single article fetched from the KME Content Service.

| Field | Type | Source | Notes |
|-------|------|--------|-------|
| `vkm:url` | `string` | KME Content Service JSON-LD | Identifies the article; used as the fetch target (`kmeURL` param) |
| `vkm:articleBody` | `string \| null` | KME Content Service JSON-LD | HTML body of the article; may be absent, null, or empty |

**Validation rules**:
- `vkm:articleBody` must be a non-empty, non-whitespace string to constitute a valid article body.
- Absent, null, empty string, and whitespace-only string are all treated as "article body not present" → 404.

**State transitions**: None. This is a read-only fetch — no mutations, no lifecycle.

---

### 2. OIDC Token

Short-lived bearer credential used to authenticate upstream requests to the KME Content Service.

| Field | Type | Storage | Notes |
|-------|------|---------|-------|
| `id_token` | `string` | Redis hash `authorization:token` | The OIDC id_token value |
| `expiry` | `number` (Unix epoch, seconds) | Redis hash `authorization:expiry` | Expiry timestamp; compared to `Date.now() / 1000` |

**Validation rules**:
- Token is valid if `cachedToken !== null && Date.now() / 1000 < expiry`.
- Managed exclusively by `getValidToken()` in `kmeContentSourceAdapterHelpers.js`. Not modified by `contentFetchFlow()`.

**Managed by**: `getValidToken()` (existing helper — unmodified).

---

### 3. Proxy Request

Incoming HTTP request received by the adapter, carrying routing signals and parameters.

| Field | Type | Source | Notes |
|-------|------|--------|-------|
| `req.url` | `string` | Node.js `http.IncomingMessage` | Relative path + query string, e.g. `/?kmeURL=https://...` |
| `req.method` | `string` | Node.js `http.IncomingMessage` | Always `GET` for content-fetch flow |
| `kmeURL` (extracted) | `string` | `new URL(req.url, 'http://localhost').searchParams.get('kmeURL')` | The verbatim target URL for upstream fetch |

**Validation rules for `kmeURL`**:
1. **Absent or empty**: `!kmeURL.trim()` → 400 Bad Request (FR-007)
2. **Malformed or non-absolute**: `new URL(kmeURL)` throws, or protocol is not `http:`/`https:` → 400 Bad Request (FR-008)
3. **Valid**: passes both guards → proceed to token acquisition + upstream fetch

---

## Data Flow

```
Incoming request (req.url contains ?kmeURL=...)
          │
          ▼
  Extract kmeURL from query string
  (new URL(req.url, 'http://localhost').searchParams.get('kmeURL'))
          │
          ▼
  ┌── Validate kmeURL ──────────────────────────────────────┐
  │  absent/empty?  ──────────────────────────────► 400     │
  │  malformed/non-https? ────────────────────────► 400     │
  └─────────────────────────────────────────────────────────┘
          │ valid
          ▼
  getValidToken() → OIDC token (from Redis cache or fresh fetch)
          │
          │  token fetch failed? ──────────────────► 502
          ▼
  axios.get(kmeURL, { Authorization: OIDC_id_token {token}, timeout: 10000 })
          │
          │  timeout?           ──────────────────► 502
          │  upstream 4xx?      ──────────────────► 404
          │  upstream 5xx?      ──────────────────► 502
          │  network error?     ──────────────────► 502
          ▼
  Parse response.data as JSON-LD object
          │
          │  unparseable?       ──────────────────► 502
          │  non-object?        ──────────────────► 502
          ▼
  extractArticleBody(data) → vkm:articleBody string or null
          │
          │  null (absent/empty/whitespace)? ─────► 404
          ▼
  res.writeHead(200, { 'Content-Type': 'text/html' })
  res.end(articleBody)
```

---

## Helper: `extractArticleBody(data)`

**Location**: `src/globalVariables/kmeContentSourceAdapterHelpers.js`  
**Type**: Pure function — no side effects, no state, no injected globals required  
**Added to exports**: `return { ..., extractArticleBody }`

**Signature**:
```javascript
function extractArticleBody(data) → string | null
```

**Input/output contract**:

| Input | Output |
|-------|--------|
| `{ 'vkm:articleBody': '<p>Hello</p>' }` | `'<p>Hello</p>'` |
| `{ 'vkm:articleBody': '' }` | `null` |
| `{ 'vkm:articleBody': '   ' }` | `null` |
| `{ 'vkm:articleBody': null }` | `null` |
| `{}` (field absent) | `null` |
| `null` | `null` |
| `'a string'` (non-object) | `null` |

**Implementation**:
```javascript
function extractArticleBody(data) {
  if (!data || typeof data !== 'object') return null;
  const body = data['vkm:articleBody'];
  if (body == null || typeof body !== 'string' || body.trim() === '') return null;
  return body;
}
```

---

## KME Content Service Response Shape

The KME Content Service returns a JSON-LD document. Only `vkm:articleBody` is consumed by this
feature. Example:

```json
{
  "@context": "https://vocabs.kme.example/context.jsonld",
  "@type": "vkm:Article",
  "vkm:url": "https://content.kme.example/articles/123",
  "vkm:articleBody": "<p>Article content here...</p>",
  "vkm:title": "Example Article"
}
```

All other fields are ignored by `extractArticleBody`. The proxy passes the raw HTML string of
`vkm:articleBody` directly as the response body — no transformation, sanitisation, or re-encoding.

---

## Settings Used (from `kme_CSA_settings`)

The content-fetch flow reads the same OIDC settings as `oidcAuthFlow` and `sitemapFlow`:

| Field | Purpose |
|-------|---------|
| `tokenUrl` | OIDC token endpoint |
| `username` | OIDC username credential |
| `password` | OIDC password credential |
| `clientId` | OIDC client identifier |
| `scope` | OIDC requested scope |

These are validated via `kmeContentSourceAdapterHelpers.validateSettings()` before calling
`getValidToken()`. Missing fields produce a 500 Configuration Error response.