Honor HTTP proxy environment variables in package downloads

src/unbundle/download.zig

@@ -70,6 +70,7 @@ pub const DownloadError = error{
     NoHashInUrl,
     NetworkError,
     FileError,
+    InvalidProxyUrl,
 } || unbundle.UnbundleError || std.mem.Allocator.Error;
 
 pub const Version = base.url.Version;
@@ -189,10 +190,18 @@ fn downloadToFile(
     filename_prefix: []const u8,
     filename_out: []u8,
 ) DownloadError![]const u8 {
+    // Proxy configuration must outlive the client, so its arena is declared first.
+    var proxy_arena = std.heap.ArenaAllocator.init(allocator.*);
+    defer proxy_arena.deinit();
+
     // Create HTTP client
     var client = std.http.Client{ .allocator = allocator.*, .io = io };
     defer client.deinit();
 
+    // Honor the standard proxy environment variables so downloads work in
+    // proxied/network-restricted environments (same variables `zig fetch` uses).
+    try initProxiesFromEnv(&client, proxy_arena.allocator());
+
     // Parse the URL
     const uri = std.Uri.parse(url) catch return error.InvalidUrl;
 
@@ -262,6 +271,27 @@ fn downloadToFile(
     return error.FileError;
 }
 
+/// Populate the client's proxy configuration from the standard proxy
+/// environment variables (http_proxy/HTTP_PROXY, https_proxy/HTTPS_PROXY,
+/// all_proxy/ALL_PROXY). `arena` owns the proxy allocations and must outlive
+/// `client`.
+fn initProxiesFromEnv(client: *std.http.Client, arena: Allocator) DownloadError!void {
+    var environ_map = std.process.Environ.Map.init(arena);
+    const proxy_env_vars = [_][:0]const u8{
+        "http_proxy", "HTTP_PROXY", "https_proxy", "HTTPS_PROXY", "all_proxy", "ALL_PROXY",
+    };
+    for (proxy_env_vars) |name| {
+        const value = std.c.getenv(name.ptr) orelse continue;
+        const value_slice = std.mem.span(value);
+        if (value_slice.len == 0) continue;
+        environ_map.put(name, value_slice) catch return error.OutOfMemory;
+    }
+    client.initDefaultProxies(arena, &environ_map) catch |err| switch (err) {
+        error.OutOfMemory => return error.OutOfMemory,
+        else => return error.InvalidProxyUrl,
+    };
+}
+
 /// Download and extract a bundled tar.zst file to memory buffers.
 ///
 /// Returns a BufferExtractWriter containing all extracted files and directories.