Add a node.js script to test webhook delivery locally

With this script, developers can copy/paste the headers and the payload
from https://github.com/settings/apps/gitforwindowshelper/advanced, save
the result in a file, and then simulate the re-delivery by running this
script with the file as command-line argument.

If anything interesting needs to be tested (such as sending GitHub API
requests using the installation token of the GitHub App), the
`local.settings.json` file needs to be set up like it would have to be
for running the Azure Function locally, as described in the `README.md`.

Signed-off-by: Johannes Schindelin <[email protected]>

test-pr-comment-delivery.js

@@ -0,0 +1,56 @@
+(async () => {
+    const fs = require('fs')
+
+    // Expect a path as command-line parameter that points to a file containing
+    // an event copy/pasted from
+    // https://github.com/settings/apps/gitforwindowshelper/advanced in the form:
+    //
+    // Headers
+    //
+    // Request method: POST
+    // [...]
+    //
+    // Payload
+    //
+    // {
+    //    [...]
+    // }
+
+    const path = process.argv[2]
+    const contents = fs.readFileSync(path).toString('utf-8')
+
+    const req = {
+        headers: {}
+    }
+
+    const payloadOffset = contents.indexOf('\n{')
+    if (payloadOffset < 0) throw new Error(`Could not find start of payload in ${path}`)
+    contents.substring(0, payloadOffset).split(/\r?\n/).forEach(line => {
+        const colon = line.indexOf(':')
+        if (colon < 0) return
+
+        const key = line.substring(0, colon).toLowerCase()
+        const value = line.substring(colon + 1).replace(/^\s+/, '')
+
+        if (key === 'request method') req.method = value
+        else req.headers[key] = value
+    })
+    req.rawBody = contents.substring(payloadOffset + 1)
+        // In https://github.com/settings/apps/gitforwindowshelper/advanced, the
+        // JSON is pretty-printed, but the actual webhook event avoids any
+        // unnecessary white-space in the body
+        .replace(/\r?\n\s*("[^"]*":)\s*/g, '$1')
+        .replace(/\r?\n\s*/g, '')
+    req.body = JSON.parse(req.rawBody)
+
+    const context = {
+        log: console.log,
+        req,
+    }
+
+    const localSettings = JSON.parse(fs.readFileSync('local.settings.json'))
+    Object.entries(localSettings.Values).forEach(([key, value]) => process.env[key] = value)
+
+    const index = require('./GitForWindowsHelper/index')
+    console.log(await index(context, req) || context.res)
+})().catch(console.log)