skip download if ELECTRSD_SKIP_DOWNLOAD is set

Author: RCasatta

README.md

@@ -46,6 +46,10 @@ if let Ok(exe_path) = electrsd::exe_path() {
 
 Startup options could be configured via the `Conf` struct using `electrsD::with_conf` or `electrsD::from_downloaded_with_conf`.
 
+## Nix
+
+For determinisim, in nix you cannot hit the internet within the `build.rs`. Moreover, some downstream crates cannot remove the auto-download feature from their dev-deps. In this case you can set the `ELECTRSD_SKIP_DOWNLOAD` env var and provide the electrs executable in the `PATH` (or skip the test execution).
+
 ## Issues with traditional approach
 
 I used integration testing based on external bash script launching needed external processes, there are many issues with this approach like:

build.rs

@@ -32,6 +32,10 @@ mod download {
     }
 
     pub fn download() {
+        if std::env::var_os("ELECTRSD_SKIP_DOWNLOAD").is_some() {
+            return;
+        }
+
         if !HAS_FEATURE {
             return;
         }

src/lib.rs

@@ -346,9 +346,9 @@ impl Drop for ElectrsD {
     }
 }
 
-/// Provide the electrs executable path if a version feature has been specified
+/// Provide the electrs executable path if a version feature has been specified and `ELECTRSD_SKIP_DOWNLOAD` is not set.
 pub fn downloaded_exe_path() -> Option<String> {
-    if versions::HAS_FEATURE {
+    if versions::HAS_FEATURE && std::env::var_os("ELECTRSD_SKIP_DOWNLOAD").is_none() {
         Some(format!(
             "{}/electrs/{}/electrs",
             env!("OUT_DIR"),