parsing headers as integer cause failed to send usage report to apollo studio

[Blankll]

Issue Description

when sending all headers to apollo studio

ApolloServerPluginUsageReporting({
      sendHeaders: { all: true },
      sendVariableValues: { all: true },
    }),

apollo server parse some of the request headers value to integer(I only observed field content-length parsed to an integer, not sure if other fields are also able to convert to non-string value),
headers below are the values we observed in code line during debugging

{
  "requestHeaders": {
    "host": {
      "value": [
        "localhost:4001"
      ]
    },
    "connection": {
      "value": [
        "keep-alive"
      ]
    },
    "content-length": {
      "value": [
        227
      ]
    }
  }
...
}

but usage report's proto-buf defined the header value as string

message Values map<string, Values> request_headers = 4;{
      repeated string value = 1;
    }
...
map<string, Values> request_headers = 4;

so we get the errors as bellow:

2023-01-08T15:19:27.472Z	xxxx 	ERROR	Error: Error encoding trace: http.requestHeaders.value: string[] expected
    at addTrace (/var/task/node_modules/@apollo/server/dist/cjs/plugin/usageReporting/plugin.js:395:35)
    at runNextTicks (node:internal/process/task_queues:61:5)
    at processImmediate (node:internal/timers:437:9)
    at process.callbackTrampoline (node:internal/async_hooks:130:17)

-- | --

Link to Reproduction

https://github.com/Blankll/serverless-event

Reproduction Steps

follow the repo's readme to package & deploy it to aws, checke the cloudwatch you will see the error message

[glasser]

Is it possible to simplify your reproduction? Remove dependencies on things like newrelic and dynamodb, get it to be as small as possible and still reproduce the error? I'd rather not have to set up a New Relic account for an issue that presumably doesn't depend on New Relic. (And ideally if it can be reproduced locally without deploying to AWS that would be great to know as well!)

[glasser]

At a high level: the Apollo Server express middleware expects that the headers it receives should be strings or lists of strings.

I do see a few places where @vendia/serverless-express sets content-length headers to Buffer.byteLength return values, which are numbers. This seems wrong! I see some discussion at CodeGenieApp/serverless-express#563 about this causing problems. (Or well, that seems to be about express.static setting content-length to numbers, not serverless-express itself.) They suggest that serverless-express should stringify all headers but it hasn't been fixed.

I suggest opening a more explicit issue (or PR?) against @vendia/serverless-express adding stringification to the Buffer.byteLength calls?

I also see that this is fixed in serverless-adapter which is a more recent project that started as a fork of serverless-express. serverless-adapter actually has explicit built-in support for AS4 without even going through Express, so you might find that better than the vendia project. (It's definitely a newer and less widely used project though.)