Use GetEnvironmentVariableA on Windows

getenv does not see env variables set with SetEnvironmentVariable.

jni/tools/libjvm_stub/libjvm_stub.c

@@ -130,24 +130,18 @@ static int try_load_libjvm_under_basepath(const char* basepath) {
 /* The returned string has to be freed by the caller. */
 static char* find_java_executable() {
   char* java_path_candidate = NULL;
-  const char* path_env;
-  char* path_env_copy = NULL;
+  char* path_env;
   const char* path_env_entry;
   char* res = NULL;
 
-  path_env = getenv("PATH");
+  path_env = get_env_copy("PATH");
   if (path_env == NULL) {
     trace("PATH not set");
     goto cleanup;
   }
   trace("PATH is set: %s", path_env);
-  path_env_copy = our_strdup(path_env);
-  if (path_env_copy == NULL) {
-    perror(MSG_PREFIX "Failed to allocate copy of PATH");
-    exit(EXIT_FAILURE);
-  }
 
-  path_env_entry = strtok(path_env_copy, PATH_ENV_SEPARATOR);
+  path_env_entry = strtok(path_env, PATH_ENV_SEPARATOR);
   while (path_env_entry) {
     java_path_candidate =
         (char*)malloc(strlen(path_env_entry) + strlen(JAVA_EXECUTABLE) + 1);
@@ -179,32 +173,22 @@ static char* find_java_executable() {
   trace("java executable not found in PATH");
 
 cleanup:
-  if (path_env_copy != NULL) {
-    free(path_env_copy);
-  }
-  if (java_path_candidate != NULL) {
-    free(java_path_candidate);
-  }
+  free(path_env);
+  free(java_path_candidate);
   return res;
 }
 
 /* The returned string has to be freed by the caller. */
 static char* find_java_home() {
-  const char* java_home_env;
   char* java_home_fallback = NULL;
   char* java_executable_path = NULL;
   char* pos;
   size_t separator_count_from_end;
   char* res = NULL;
 
-  java_home_env = getenv("JAVA_HOME");
-  if (java_home_env != NULL) {
-    trace("JAVA_HOME is set: %s", java_home_env);
-    res = our_strdup(java_home_env);
-    if (res == NULL) {
-      perror(MSG_PREFIX "Failed to allocate copy of JAVA_HOME");
-      exit(EXIT_FAILURE);
-    }
+  res = get_env_copy("JAVA_HOME");
+  if (res != NULL) {
+    trace("JAVA_HOME is set: %s", res);
     return res;
   }
 

jni/tools/libjvm_stub/unix/utils.h

@@ -45,9 +45,16 @@ static const size_t MAX_CANDIDATE_PATH_LENGTH = 22;
 
 static int executable_exists(const char* path) { return access(path, X_OK); }
 
-#ifdef __APPLE__
 static char* our_strdup(const char* src);
-#endif
+
+/* The returned string has to be freed by the caller. */
+static char* get_env_copy(const char* key) {
+  const char* value = getenv(key);
+  if (value == NULL) {
+    return NULL;
+  }
+  return our_strdup(value);
+}
 
 /* The returned string has to be freed by the caller. */
 static char* get_java_home_fallback() {

jni/tools/libjvm_stub/windows/utils.h

@@ -41,6 +41,28 @@ static int executable_exists(const char* path) {
   return 0;
 }
 
+/* The returned string has to be freed by the caller. */
+static char* get_env_copy(const char* key) {
+  /* On Windows, getenv does not see variables set with SetEnvironmentVariable.
+   * https://curl.se/mail/lib-2020-01/0006.html */
+  DWORD size = GetEnvironmentVariableA(key, NULL, 0);
+  char* value;
+  if (size == 0) {
+    /* We treat any error as indicating that the variable is not set. If it were
+     * empty, the returned size would have been 1 instead to account for the
+     * terminating null character. */
+    return NULL;
+  }
+  value = (char*)malloc(size);
+  if (value == NULL) {
+    return NULL;
+  }
+  if (GetEnvironmentVariableA(key, value, size) == 0) {
+    return NULL;
+  }
+  return value;
+}
+
 static char* get_java_home_fallback() { return NULL; }
 
 static void* load_library(const char* path) { return LoadLibrary(path); }