Unable to use third party async libraries due to Sync requirements

[vultix]

Pull Request #284 Introduced the Sync requirement for all http lambdas.

This broke any http lambdas using any of these libraries:

• Rusoto
• Mongodb
• Sqlx

Reproduction

use lambda_http::{
    handler,
    lambda::{self, Context},
    IntoResponse, Request, RequestExt, Response,
};

use serde_json::{json, Value};
use rusoto_core::Region;
use rusoto_dynamodb::{DynamoDb, DynamoDbClient, ListTablesInput};

type Error = Box<dyn std::error::Error + Send + Sync + 'static>;

#[tokio::main]
async fn main() -> Result<(), Error> {
    lambda::run(handler(func)).await?;
    Ok(())
}

async fn func(_: Request, _: Context) -> Result<Value, Error> {
    let client = DynamoDbClient::new(Region::UsEast1);

    let output = client.list_tables(Default::default()).await?;

    dbg!{output};

    Ok(json!({"success": true}))
}

[dependencies]
serde_json = "1.0"
serde = "1.0"
tokio = {version = "1.0", features = ["macros"]}

lambda_http = { git = "https://github.com/awslabs/aws-lambda-rust-runtime/", branch = "master"}
lambda = { git = "https://github.com/awslabs/aws-lambda-rust-runtime/", branch = "master"}
rusoto_dynamodb = "0.46.0"
rusoto_core = "0.46.0"

This is the error I get:

error: future cannot be shared between threads safely
   --> src/main.rs:16:17
    |
16  |     lambda::run(handler(func)).await?;
    |                 ^^^^^^^ future returned by `func` is not `Sync`
    | 
   ::: ~/.cargo/git/checkouts/aws-lambda-rust-runtime-7c865cce90132439/9bd45c1/lambda-http/src/lib.rs:109:19
    |
109 | pub fn handler<H: Handler>(handler: H) -> Adapter<H> {
    |                   ------- required by this bound in `handler`
    |
    = help: the trait `Sync` is not implemented for `dyn Future<Output = std::result::Result<ListTablesOutput, RusotoError<ListTablesError>>> + Send`
note: future is not `Sync` as it awaits another future which is not `Sync`
   --> src/main.rs:23:18
    |
23  |     let output = client.list_tables(Default::default()).await?;
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ await occurs here on type `Pin<Box<dyn Future<Output = std::result::Result<ListTablesOutput, RusotoError<ListTablesError>>> + Send>>`, which is not `Sync`

[bahildebrand]

I'm looking into this. I'll get back to you when I have a solution.

[bahildebrand]

@vultix after looking at this more I think we were a bit aggressive adding the sync trait. Considering the amount of libraries that could not be used if we kept the sync trait, I've removed it. I ran this with the provided example. Let me know if this helps with your other lambdas.

[vultix]

Thank you!!