wip(ssr): initial work on server-renderer

packages/server-renderer/src/index.ts

@@ -1,3 +1,84 @@
-export function renderToString() {
-  // TODO
+import {
+  App,
+  Component,
+  ComponentInternalInstance,
+  SuspenseBoundary
+} from '@vue/runtime-dom'
+import { isString } from '@vue/shared'
+
+type SSRBuffer = SSRBufferItem[]
+type SSRBufferItem = string | Promise<SSRBuffer>
+type ResolvedSSRBuffer = (string | ResolvedSSRBuffer)[]
+
+function createSSRBuffer() {
+  let appendable = false
+  const buffer: SSRBuffer = []
+  return {
+    buffer,
+    push(item: SSRBufferItem) {
+      const isStringItem = isString(item)
+      if (appendable && isStringItem) {
+        buffer[buffer.length - 1] += item as string
+      } else {
+        buffer.push(item)
+      }
+      appendable = isStringItem
+    }
+  }
+}
+
+export async function renderToString(app: App): Promise<string> {
+  const resolvedBuffer = (await renderComponent(
+    app._component,
+    app._props,
+    null,
+    null
+  )) as ResolvedSSRBuffer
+  return unrollBuffer(resolvedBuffer)
+}
+
+function unrollBuffer(buffer: ResolvedSSRBuffer): string {
+  let ret = ''
+  for (let i = 0; i < buffer.length; i++) {
+    const item = buffer[i]
+    if (isString(item)) {
+      ret += item
+    } else {
+      ret += unrollBuffer(item)
+    }
+  }
+  return ret
+}
+
+export async function renderComponent(
+  comp: Component,
+  props: Record<string, any> | null,
+  parentComponent: ComponentInternalInstance | null,
+  parentSuspense: SuspenseBoundary | null
+): Promise<SSRBuffer> {
+  // 1. create component buffer
+  const { buffer, push } = createSSRBuffer()
+
+  // 2. TODO create actual instance
+  const instance = {
+    proxy: {
+      msg: 'hello'
+    }
+  }
+
+  if (typeof comp === 'function') {
+    // TODO FunctionalComponent
+  } else {
+    if (comp.ssrRender) {
+      // optimized
+      comp.ssrRender(push, instance.proxy)
+    } else if (comp.render) {
+      // TODO fallback to vdom serialization
+    } else {
+      // TODO warn component missing render function
+    }
+  }
+  // TS can't figure this out due to recursive occurance of Promise in type
+  // @ts-ignore
+  return Promise.all(buffer)
 }