Safer endpoint Uri construction (#1553)

Make endpoint Uri construction less fragile by stripping out duplicate slashes.

Fixes #997

The functionality to append the signal path to a user-supplied tracing endpoint is already in place. However, it does so in a way that is likely to break for any user who's passing the string value of a Uri or Url, which will have a trailing slash appended to them. This attempts to fix that issue.

There were other possible changes discussed but ever implemented/merged in #1056. This PR attempts to keep it simple by just changing existing behavior to not break in a common use case.

opentelemetry-otlp/src/exporter/http/mod.rs

@@ -270,6 +270,15 @@ impl OtlpHttpClient {
     }
 }
 
+fn build_endpoint_uri(endpoint: &str, path: &str) -> Result<Uri, crate::Error> {
+    let path = if endpoint.ends_with('/') && path.starts_with('/') {
+        path.strip_prefix('/').unwrap()
+    } else {
+        path
+    };
+    format!("{endpoint}{path}").parse().map_err(From::from)
+}
+
 // see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/exporter.md#endpoint-urls-for-otlphttp
 fn resolve_endpoint(
     signal_endpoint_var: &str,
@@ -287,15 +296,13 @@ fn resolve_endpoint(
     // if signal env var is not set, then we check if the OTEL_EXPORTER_OTLP_ENDPOINT is set
     if let Some(endpoint) = env::var(OTEL_EXPORTER_OTLP_ENDPOINT)
         .ok()
-        .and_then(|s| format!("{s}{signal_endpoint_path}").parse().ok())
+        .and_then(|s| build_endpoint_uri(&s, signal_endpoint_path).ok())
     {
         return Ok(endpoint);
     }
 
-    // if neither works, we use the one provided in pipeline. If user never provide one, we will use the default one
-    format!("{provided_or_default_endpoint}{signal_endpoint_path}")
-        .parse()
-        .map_err(From::from)
+    // if neither works, we use the one provided in pipeline. If user never provides one, we will use the default one
+    build_endpoint_uri(provided_or_default_endpoint, signal_endpoint_path)
 }
 
 #[allow(clippy::mutable_key_type)] // http headers are not mutated
@@ -313,6 +320,8 @@ mod tests {
     use crate::exporter::tests::run_env_test;
     use crate::{OTEL_EXPORTER_OTLP_ENDPOINT, OTEL_EXPORTER_OTLP_TRACES_ENDPOINT};
 
+    use super::build_endpoint_uri;
+
     #[test]
     fn test_append_signal_path_to_generic_env() {
         run_env_test(
@@ -374,6 +383,20 @@ mod tests {
         });
     }
 
+    #[test]
+    fn test_build_endpoint_uri() {
+        let uri = build_endpoint_uri("https://example.com", "/v1/traces").unwrap();
+        assert_eq!(uri, "https://example.com/v1/traces");
+
+        // Should be no duplicate slahes:
+        let uri = build_endpoint_uri("https://example.com/", "/v1/traces").unwrap();
+        assert_eq!(uri, "https://example.com/v1/traces");
+
+        // Append paths properly:
+        let uri = build_endpoint_uri("https://example.com/additional/path/", "/v1/traces").unwrap();
+        assert_eq!(uri, "https://example.com/additional/path/v1/traces");
+    }
+
     #[test]
     fn test_invalid_uri_in_signal_env_falls_back_to_generic_env() {
         run_env_test(