Allow to set the user-agent on wasm target

[FirelightFlagboy]

Currently reqwest provide the method ClientBuilder::user_agent(..) to set the User-Agent header.

But this method does not exist when targeting wasm32-unknown-unknown.

Steps to reproduce

I've the following src/lib.rs:

use reqwest::ClientBuilder;

pub async fn test() {
    let client = ClientBuilder::default()
        .user_agent("FooBar/1.2.3")
        .build()
        .unwrap();

    let _rep = client.get("https://www.google.com").send().await.unwrap();
}

and the following Cargo.toml:

[package]
name = "request-user-agent-wasm"
version = "0.1.0"
edition = "2021"

[dependencies]
reqwest = "0.11.22"

When I execute cargo check --target wasm32-unknown-unknown, I get the following error:

    Checking request-user-agent-wasm v0.1.0 (/tmp/request-user-agent-wasm)
error[E0599]: no method named `user_agent` found for struct `ClientBuilder` in the current scope
 --> src/lib.rs:5:10
  |
4 |       let client = ClientBuilder::default()
  |  __________________-
5 | |         .user_agent("FooBar/1.2.3")
  | |         -^^^^^^^^^^ method not found in `ClientBuilder`
  | |_________|
  | 

For more information about this error, try `rustc --explain E0599`.
error: could not compile `request-user-agent-wasm` (lib) due to previous error

What I'm expecting

I would like that reqwest::wasm::ClientBuilder provide the method user_agent(..) to set the User-Agent header

Current workaround

reqwest::wasm::ClientBuilder provide default_headers(..) so I can use it to set User-Agent

--- src/lib.rs.back	2023-10-30 15:59:03.729542547 +0100
+++ src/lib.rs	2023-10-30 16:01:03.162871429 +0100
@@ -1,11 +1,14 @@
-use reqwest::ClientBuilder;
+use reqwest::{header, ClientBuilder};
 
 pub async fn test() {
+    let headers = header::HeaderMap::from_iter([(
+        header::HeaderName::from_static("User-Agent"),
+        header::HeaderValue::from_static("FooBar/1.2.3"),
+    )]);
     let client = ClientBuilder::default()
-        .user_agent("FooBar/1.2.3")
+        .default_headers(headers)
         .build()
         .unwrap();
 
     let _rep = client.get("https://www.google.com").send().await.unwrap();
 }
-

[seanmonstar]

It should be a small addition to make this available. Would you like to submit a PR?

[FirelightFlagboy]

Yes, I'm already working on a fix