fetchedMavenDeps: honor HTTP[S]_PROXY, NO_PROXY env vars

Maven doesn't honor HTTP[S]_PROXY and NO_PROXY env vars out of the box.
Instead, it expects the user to configure a settings.xml file.
We however impurely pass only these env vars in FODs.
This creates the XML file on demand, if one or more env vars is set.

pkgs/by-name/ma/maven/build-maven-package.nix

···
   stdenv,
   jdk,
   maven,
+  writers,
 }:
 
 {
···
 
 let
   mvnSkipTests = lib.optionalString (!doCheck) "-DskipTests";
+
+  writeProxySettings = writers.writePython3 "write-proxy-settings" { } ./maven-proxy.py;
+
   fetchedMavenDeps = stdenv.mkDerivation (
     {
       name = "${pname}-${version}-maven-deps";
···
       buildPhase =
         ''
           runHook preBuild
+
+          MAVEN_EXTRA_ARGS=""
+
+          # handle proxy
+          if [[ -n "''${HTTP_PROXY-}" ]] || [[ -n "''${HTTPS_PROXY-}" ]] || [[ -n "''${NO_PROXY-}" ]];then
+            mvnSettingsFile="$(mktemp -d)/settings.xml"
+            ${writeProxySettings} $mvnSettingsFile
+            MAVEN_EXTRA_ARGS="-s=$mvnSettingsFile"
+          fi
         ''
         + lib.optionalString buildOffline ''
-          mvn de.qaware.maven:go-offline-maven-plugin:1.2.8:resolve-dependencies -Dmaven.repo.local=$out/.m2 ${mvnDepsParameters}
+          mvn $MAVEN_EXTRA_ARGS de.qaware.maven:go-offline-maven-plugin:1.2.8:resolve-dependencies -Dmaven.repo.local=$out/.m2 ${mvnDepsParameters}
 
           for artifactId in ${builtins.toString manualMvnArtifacts}
           do
             echo "downloading manual $artifactId"
-            mvn dependency:get -Dartifact="$artifactId" -Dmaven.repo.local=$out/.m2
+            mvn $MAVEN_EXTRA_ARGS dependency:get -Dartifact="$artifactId" -Dmaven.repo.local=$out/.m2
           done
 
           for artifactId in ${builtins.toString manualMvnSources}
···
             group=$(echo $artifactId | cut -d':' -f1)
             artifact=$(echo $artifactId | cut -d':' -f2)
             echo "downloading manual sources $artifactId"
-            mvn dependency:sources -DincludeGroupIds="$group" -DincludeArtifactIds="$artifact" -Dmaven.repo.local=$out/.m2
+            mvn $MAVEN_EXTRA_ARGS dependency:sources -DincludeGroupIds="$group" -DincludeArtifactIds="$artifact" -Dmaven.repo.local=$out/.m2
           done
         ''
         + lib.optionalString (!buildOffline) ''
-          mvn package -Dmaven.repo.local=$out/.m2 ${mvnSkipTests} ${mvnParameters}
+          mvn $MAVEN_EXTRA_ARGS package -Dmaven.repo.local=$out/.m2 ${mvnSkipTests} ${mvnParameters}
         ''
         + ''
           runHook postBuild

pkgs/by-name/ma/maven/maven-proxy.py

···
+"""
+Maven doesn't honor HTTP[S]_PROXY and NO_PROXY env vars out of the box.
+Instead, it expects the user to configure a settings.xml file.
+We however impurely pass only these env vars in FODs.
+This creates the XML file on demand, if one or more env vars is set.
+"""
+
+import os
+import sys
+from urllib.parse import urlparse
+
+
+def parse_proxy_url(url):
+    if url is None:
+        return None
+    parsed = urlparse(url)
+
+    if parsed.hostname is None:
+        print(f"Failed to parse proxy URL {url}, ignoring", file=sys.stderr)
+        return None
+
+    return {
+        'protocol': parsed.scheme or 'http',
+        'host': parsed.hostname,
+        'port': parsed.port or (443 if parsed.scheme == 'https' else 80),
+        'username': parsed.username,
+        'password': parsed.password
+    }
+
+
+def format_proxy_block(proxy, id_suffix, non_proxy_hosts):
+    auth = ""
+    if proxy.get("username"):
+        auth += f"    <username>{proxy['username']}</username>\n"
+    if proxy.get("password"):
+        auth += f"    <password>{proxy['password']}</password>\n"
+
+    np_hosts = ""
+    if non_proxy_hosts:
+        np_hosts = f"    <nonProxyHosts>{non_proxy_hosts}</nonProxyHosts>\n"
+
+    return f"""  <proxy>
+    <id>{id_suffix}-proxy</id>
+    <active>true</active>
+    <protocol>{proxy['protocol']}</protocol>
+    <host>{proxy['host']}</host>
+    <port>{proxy['port']}</port>
+{auth}{np_hosts}  </proxy>"""
+
+
+def main(output_path):
+    http_proxy = parse_proxy_url(os.environ.get("HTTP_PROXY"))
+    https_proxy = parse_proxy_url(os.environ.get("HTTPS_PROXY"))
+    non_proxy_hosts = os.environ.get("NO_PROXY", "").replace(",", "|")
+
+    proxy_blocks = []
+
+    if http_proxy:
+        proxy_blocks.append(
+          format_proxy_block(http_proxy, "http", non_proxy_hosts)
+        )
+    if https_proxy and https_proxy != http_proxy:
+        proxy_blocks.append(
+          format_proxy_block(https_proxy, "https", non_proxy_hosts)
+        )
+
+    settings_xml = f"""<?xml version="1.0" encoding="UTF-8"?>
+<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
+                  http://maven.apache.org/xsd/settings-1.0.0.xsd">
+  <proxies>
+{'\n'.join(proxy_blocks)}
+  </proxies>
+</settings>
+"""
+
+    with open(output_path, "w") as f:
+        f.write(settings_xml)
+
+    print(f"Generated Maven settings.xml at {output_path}")
+
+
+if __name__ == "__main__":
+    output_file = sys.argv[1] if len(sys.argv) > 1 else "settings.xml"
+    main(output_file)