Failed to "modifyAckDeadline": Metadata key contains illegal characters

Environment details

• OS: linux
• Node.js version: 10.15.3
• yarn version: 1.15.2
• @google-cloud/pubsub version: 0.30.1

Steps to reproduce

We use code similar to the sample https://github.com/googleapis/nodejs-pubsub/blob/ede57841e391680f4d8875d60eb17b62389cd7d8/samples/subscriptions.js#L225 to receive messages, but use the following subscription config:

    const options = {
      flowControl: {
        allowExcessMessages: false,
        maxMessages: 20,
        maxExtension: 10,
      },
    }
    pubSub.subscription(subscriptionName, options)

We see the following error messages in our logs:

Error: Failed to "modifyAckDeadline" for 9 message(s). Reason: Metadata key "a" contains illegal characters
    at Object.keys.map (/base/node_modules/@google-cloud/pubsub/src/message-queues.ts:238:15)

We haven’t seen this message before we updated to version 0.30.0 and this error is still reported after updating to version 0.30.1.

[katmatt]

@bcoe We updated to version 1.1.5 of google-gax and it didn’t fix this issue. We now see a different, but somehow related error in our logs:

(node:1) Error: Failed to add metadata entry  §NÜ: Thu, 18 Jul 2019 10:39:54 GMT. Metadata key " §nü" contains illegal characters

[bcoe]

@katmatt 👍 awesome. Going to go ahead and close this issue, please let us know if you bump into any related issues.