feat: Add TryFrom implementations for MetadataValue (#990)

Co-authored-by: Adam Chalmers <[email protected]>

examples/src/authentication/client.rs

@@ -9,7 +9,7 @@ use tonic::{metadata::MetadataValue, transport::Channel, Request};
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let channel = Channel::from_static("http://[::1]:50051").connect().await?;
 
-    let token = MetadataValue::from_str("Bearer some-auth-token")?;
+    let token: MetadataValue<_> = "Bearer some-auth-token".parse()?;
 
     let mut client = EchoClient::with_interceptor(channel, move |mut req: Request<()>| {
         req.metadata_mut().insert("authorization", token.clone());

examples/src/authentication/server.rs

@@ -59,7 +59,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 }
 
 fn check_auth(req: Request<()>) -> Result<Request<()>, Status> {
-    let token = MetadataValue::from_str("Bearer some-secret-token").unwrap();
+    let token: MetadataValue<_> = "Bearer some-secret-token".parse().unwrap();
 
     match req.metadata().get("authorization") {
         Some(t) if token == t => Ok(req),

examples/src/gcp/client.rs

@@ -22,7 +22,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .ok_or_else(|| "Expected a project name as the first argument.".to_string())?;
 
     let bearer_token = format!("Bearer {}", token);
-    let header_value = MetadataValue::from_str(&bearer_token)?;
+    let header_value: MetadataValue<_> = bearer_token.parse()?;
 
     let certs = tokio::fs::read("examples/data/gcp/roots.pem").await?;