testing and fixing json handling for errors of fetch api

source/api/_tests/fetch.test.ts

@@ -0,0 +1,90 @@
+// import * as jest from 'jest';
+import * as http from "http"
+
+import { api } from "../fetch"
+
+interface ResponseMock {
+  body?: any
+  statusCode?: number
+  contentType?: string
+}
+
+class TestServer {
+  private port = 30001
+  private hostname = "localhost"
+  private response: ResponseMock = null
+  private router = (req, res) => {
+    res.statusCode = this.response && this.response.statusCode ? this.response.statusCode : 200
+    res.setHeader(
+      "Content-Type",
+      this.response && this.response.contentType ? this.response.contentType : "application/json"
+    )
+    res.end(this.response ? this.response.body : null)
+  }
+  private server = http.createServer(this.router)
+
+  start = async (response: ResponseMock): Promise<void> => {
+    this.response = response
+    return new Promise<void>((resolve, reject) => {
+      this.server.listen(this.port, this.hostname, err => (err ? reject(err) : resolve()))
+    })
+  }
+  stop = async (): Promise<void> => {
+    this.response = null
+    return new Promise<void>((resolve, reject) => {
+      this.server.close(err => (err ? reject(err) : resolve()))
+    })
+  }
+}
+
+describe("fetch", () => {
+  let url: string
+  let server = new TestServer()
+
+  beforeEach(() => {
+    url = "http://localhost:30001/"
+  })
+
+  afterEach(async () => {
+    await server.stop()
+  })
+
+  it("handles json success", async () => {
+    let body = { key: "valid json" }
+    await server.start({
+      body: JSON.stringify(body),
+    })
+
+    let response = await api(url, {})
+    expect(response.ok).toBe(true)
+    expect(response.status).toBe(200)
+    expect(await response.json()).toMatchObject(body)
+  })
+
+  it("handles json error", async () => {
+    let body = { key: "valid json" }
+    await server.start({
+      body: JSON.stringify(body),
+      statusCode: 500,
+    })
+
+    let response = await api(url, {})
+    expect(response.ok).toBe(false)
+    expect(response.status).toBe(500)
+    expect(await response.json()).toMatchObject(body)
+  })
+
+  it("handles plain text error", async () => {
+    let body = "any plain text response"
+    await server.start({
+      body: body,
+      statusCode: 500,
+      contentType: "text/plain",
+    })
+
+    let response = await api(url, {})
+    expect(response.ok).toBe(false)
+    expect(response.status).toBe(500)
+    expect(await response.text()).toBe(body)
+  })
+})

source/api/fetch.ts

@@ -49,9 +49,17 @@ export function api(url: string | node_fetch.Request, init: node_fetch.RequestIn
   return originalFetch(url, init).then(async (response: node_fetch.Response) => {
     // Handle failing errors
     if (!response.ok) {
-      const responseJSON = await response.json()
-      console.warn(`Request failed [${response.status}]: ${response.url}`)
-      console.warn(`Response: ${JSON.stringify(responseJSON, null, "  ")}`)
+      // we should not modify the response when an error occur to allow body stream to be read again if needed
+      let clonedResponse = response.clone()
+      console.warn(`Request failed [${clonedResponse.status}]: ${clonedResponse.url}`)
+      let responseBody = await clonedResponse.text()
+      try {
+        // tries to pretty print the JSON response when possible
+        const responseJSON = await JSON.parse(responseBody.toString())
+        console.warn(`Response: ${JSON.stringify(responseJSON, null, "  ")}`)
+      } catch (e) {
+        console.warn(`Response: ${responseBody}`)
+      }
     }
 
     return response