feat(libstore/s3): add toHttpsUrl

This is extracted from the work in #13752

src/libstore/include/nix/store/s3.hh

@@ -75,6 +75,12 @@ struct ParsedS3URL
     }
 
     static ParsedS3URL parse(const ParsedURL & uri);
+
+    /**
+     * Convert this ParsedS3URL to HTTPS ParsedURL for use with curl's AWS SigV4 authentication
+     */
+    ParsedURL toHttpsUrl() const;
+
     auto operator<=>(const ParsedS3URL & other) const = default;
 };
 

src/libstore/s3.cc

@@ -1,6 +1,8 @@
 #include "nix/store/s3.hh"
 #include "nix/util/split.hh"
 #include "nix/util/url.hh"
+#include "nix/util/util.hh"
+#include "nix/util/canon-path.hh"
 
 namespace nix {
 
@@ -64,6 +66,42 @@ try {
     throw;
 }
 
+ParsedURL ParsedS3URL::toHttpsUrl() const
+{
+    std::string regionStr = region.value_or("us-east-1");
+    std::string schemeStr = scheme.value_or("https");
+
+    // Handle endpoint configuration using std::visit
+    return std::visit(
+        overloaded{
+            [&](const std::monostate &) {
+                // No custom endpoint, use standard AWS S3 endpoint
+                return ParsedURL{
+                    .scheme = schemeStr,
+                    .authority = ParsedURL::Authority{.host = "s3." + regionStr + ".amazonaws.com"},
+                    .path = (CanonPath::root / bucket / CanonPath(key)).abs(),
+                };
+            },
+            [&](const ParsedURL::Authority & auth) {
+                // Endpoint is just an authority (hostname/port)
+                return ParsedURL{
+                    .scheme = schemeStr,
+                    .authority = auth,
+                    .path = (CanonPath::root / bucket / CanonPath(key)).abs(),
+                };
+            },
+            [&](const ParsedURL & endpointUrl) {
+                // Endpoint is already a ParsedURL (e.g., http://server:9000)
+                return ParsedURL{
+                    .scheme = endpointUrl.scheme,
+                    .authority = endpointUrl.authority,
+                    .path = (CanonPath(endpointUrl.path) / bucket / CanonPath(key)).abs(),
+                };
+            },
+        },
+        endpoint);
+}
+
 #endif
 
 } // namespace nix