Add rcutils_expand_user() to expand user directory in path

include/rcutils/filesystem.h

@@ -144,6 +144,24 @@ rcutils_to_native_path(
   const char * path,
   rcutils_allocator_t allocator);
 
+/// Expand user directory in path.
+/**
+ * This function expands an initial '~' to the current user's home directory.
+ * The home directory is fetched using `rcutils_get_home_dir()`.
+ * This function returns a newly allocated string on success.
+ * It is up to the caller to release the memory once it is done with it by
+ * calling `deallocate` on the same allocator passed here.
+ *
+ * \param[in] path A null-terminated C string representing a path.
+ * \param[in] allocator
+ * \return path with expanded home directory on success, or
+ * \return `NULL` on invalid arguments, or
+ * \return `NULL` on failure.
+ */
+RCUTILS_PUBLIC
+char *
+rcutils_expand_user(const char * path, rcutils_allocator_t allocator);
+
 /// Create the specified directory.
 /**
  * This function creates an absolutely-specified directory.

src/filesystem.c

@@ -33,7 +33,9 @@ extern "C"
 
 #include "rcutils/error_handling.h"
 #include "rcutils/format_string.h"
+#include "rcutils/get_env.h"
 #include "rcutils/repl_str.h"
+#include "rcutils/strdup.h"
 
 #ifdef _WIN32
 # define RCUTILS_PATH_DELIMITER "\\"
@@ -181,6 +183,29 @@ rcutils_to_native_path(
   return rcutils_repl_str(path, "/", RCUTILS_PATH_DELIMITER, &allocator);
 }
 
+char *
+rcutils_expand_user(const char * path, rcutils_allocator_t allocator)
+{
+  if (NULL == path) {
+    return NULL;
+  }
+
+  if ('~' != path[0]) {
+    return rcutils_strdup(path, allocator);
+  }
+
+  const char * homedir = rcutils_get_home_dir();
+  if (NULL == homedir) {
+    return NULL;
+  }
+  return rcutils_format_string_limit(
+    allocator,
+    strlen(homedir) + strlen(path),
+    "%s%s",
+    homedir,
+    path + 1);
+}
+
 bool
 rcutils_mkdir(const char * abs_path)
 {

test/test_filesystem.cpp

@@ -16,6 +16,7 @@
 #include <string>
 
 #include "rcutils/filesystem.h"
+#include "rcutils/get_env.h"
 
 #include "osrf_testing_tools_cpp/scope_exit.hpp"
 
@@ -307,6 +308,62 @@ TEST_F(TestFilesystemFixture, is_readable_and_writable) {
   }
 }
 
+TEST_F(TestFilesystemFixture, expand_user) {
+  const char * homedir = rcutils_get_home_dir();
+  ASSERT_STRNE(NULL, homedir);
+  const std::string homedir_str(homedir);
+
+  {
+    // Invalid path arg
+    EXPECT_EQ(NULL, rcutils_expand_user(NULL, g_allocator));
+  }
+  {
+    // No ~
+    const char * path = "/this/path/has/no/tilde";
+    char * ret_path = rcutils_expand_user(path, g_allocator);
+    EXPECT_STREQ(ret_path, path);
+    ASSERT_NE(ret_path, path);
+    g_allocator.deallocate(ret_path, g_allocator.state);
+  }
+  {
+    // No ~ and empty path
+    const char * path = "";
+    char * ret_path = rcutils_expand_user(path, g_allocator);
+    EXPECT_STREQ(ret_path, path);
+    ASSERT_NE(ret_path, path);
+    g_allocator.deallocate(ret_path, g_allocator.state);
+  }
+  {
+    // With ~ but not leading
+    const char * path = "/prefix/~/my/dir";
+    char * ret_path = rcutils_expand_user(path, g_allocator);
+    EXPECT_STREQ(ret_path, path);
+    ASSERT_NE(ret_path, path);
+    g_allocator.deallocate(ret_path, g_allocator.state);
+  }
+  {
+    // With ~ only
+    const char * path = "~";
+    char * ret_path = rcutils_expand_user(path, g_allocator);
+    EXPECT_STREQ(ret_path, homedir);
+    g_allocator.deallocate(ret_path, g_allocator.state);
+  }
+  {
+    // With ~/ only
+    const char * path = "~/";
+    char * ret_path = rcutils_expand_user(path, g_allocator);
+    EXPECT_STREQ(ret_path, (homedir_str + "/").c_str());
+    g_allocator.deallocate(ret_path, g_allocator.state);
+  }
+  {
+    // Normal use-case
+    const char * path = "~/my/directory";
+    char * ret_path = rcutils_expand_user(path, g_allocator);
+    EXPECT_STREQ(ret_path, (homedir_str + "/my/directory").c_str());
+    g_allocator.deallocate(ret_path, g_allocator.state);
+  }
+}
+
 TEST_F(TestFilesystemFixture, mkdir) {
   {
     // Make a new directory