fix(proxy): fail fast on unsupported flag

Some flags do not make sense over IPFS proxy so we throw early with
meaningful error message.

add-on/src/lib/ipfs-proxy/pre-command.js

@@ -5,12 +5,19 @@
 const COMMAND_WHITELIST = Object.freeze(require('./command-whitelist.json'))
 
 // Creates a "pre" function that is called prior to calling a real function
-// on the IPFS instance. It will throw if access is denied due to API not being whitelisted
+// on the IPFS instance. It will throw if access is denied
+// due to API not being whitelisted of arguments not being supported
 function createPreCommand (permission) {
   return async (...args) => {
     if (!inCommandWhitelist(permission)) {
       throw createCommandWhitelistError(permission)
     }
+    if (['add', 'files.add'].includes(permission)) {
+      // Fail fast: nocopy does not work over proxy
+      if (args.some(arg => typeof arg === 'object' && arg.nocopy)) {
+        throw new Error(`ipfs.${permission} with 'nocopy' flag is not supported by IPFS Proxy`)
+      }
+    }
     return args
   }
 }

test/functional/lib/ipfs-proxy/pre-command.test.js

@@ -24,6 +24,24 @@ describe('lib/ipfs-proxy/pre-command', () => {
     expect(() => { if (error) throw error }).to.throw(`Access to '${permission}' commands over IPFS Proxy is globally blocked`)
   })
 
+  it('should throw early if flag is not supported', async () => {
+    const permission = 'add'
+    const preApiWhitelist = createPreCommand(permission)
+    const flag = 'nocopy'
+    const opts = {}
+    opts[flag] = true
+
+    let error
+
+    try {
+      await preApiWhitelist('foo', opts)
+    } catch (err) {
+      error = err
+    }
+
+    expect(() => { if (error) throw error }).to.throw(`ipfs.${permission} with '${flag}' flag is not supported by IPFS Proxy`)
+  })
+
   it('should have a well-formed Error if denied', async () => {
     const permission = 'config.show'
     const preApiWhitelist = createPreCommand(permission)