paths: New module

Path utilities (doh)

2 files changed, 120 insertions, 0 deletions

diff --git a/src/paths.cc b/src/paths.cc
new file mode 100644
index 0000000..091be6e
--- /dev/null
+++ b/src/paths.cc
@@ -0,0 +1,100 @@
+#include "paths.hh"
+
+#include "str.hh"
+
+#include <algorithm>
+#include <cerrno>
+#include <cstddef>
+#include <cstdlib>
+#include <iterator>
+#include <memory>
+#include <pwd.h>
+#include <string_view>
+#include <unistd.h>
+#include <unordered_set>
+#include <vector>
+
+namespace paths {
+
+namespace {
+
+std::vector<std::filesystem::path> xdg_read_dirs(
+    const char* userdir_env_name, std::string_view userdir_home_default,
+    const char* dirs_env_name,
+    std::vector<std::filesystem::path> const& dirs_default_value) {
+  std::vector<std::filesystem::path> ret;
+  std::unordered_set<std::filesystem::path> tmp;
+  auto* env_userdir = getenv(userdir_env_name);
+  if (env_userdir != nullptr && env_userdir[0] != '\0') {
+    ret.emplace_back(env_userdir);
+  } else {
+    ret.emplace_back(home() / userdir_home_default);
+  }
+  tmp.insert(ret.back());
+  auto* env_dirs = getenv(dirs_env_name);
+  if (env_dirs != nullptr && env_dirs[0] != '\0') {
+    for (auto dir : str::split(env_dirs, ':')) {
+      if (tmp.emplace(dir).second) {
+        ret.emplace_back(dir);
+      }
+    }
+  } else {
+    std::ranges::copy_if(
+        dirs_default_value, std::back_inserter(ret),
+        [&tmp](auto const& dir) { return tmp.emplace(dir).second; });
+  }
+  return ret;
+}
+
+}  // namespace
+
+std::filesystem::path home() {
+  {
+    auto* str = getenv("HOME");
+    if (str != nullptr && str[0] != '\0')
+      return str;
+  }
+
+  {
+    auto maybe_size = sysconf(_SC_GETPW_R_SIZE_MAX);
+    size_t size = maybe_size > 0 ? static_cast<size_t>(maybe_size) : 1024;
+    auto buffer = std::make_unique<char[]>(size);
+    struct passwd pwd;
+    struct passwd* ret;
+    int err;
+    while (true) {
+      err = getpwuid_r(geteuid(), &pwd, buffer.get(), size, &ret);
+      if (err == 0)
+        break;
+      if (err != ERANGE)
+        break;
+      auto new_size = size * 2;
+      if (new_size < size)
+        break;
+      buffer = std::make_unique<char[]>(new_size);
+      size = new_size;
+    }
+    if (err == 0 && ret) {
+      if (ret->pw_dir != nullptr && ret->pw_dir[0] != '\0') {
+        return ret->pw_dir;
+      }
+    }
+  }
+
+  return "/";
+}
+
+std::vector<std::filesystem::path> config_dirs() {
+  static const std::vector<std::filesystem::path> fallback{"/etc/xdg"};
+  return xdg_read_dirs("XDG_CONFIG_HOME", ".config", "XDG_CONFIG_DIRS",
+                       fallback);
+}
+
+std::vector<std::filesystem::path> data_dirs() {
+  static const std::vector<std::filesystem::path> fallback{"/usr/local/share/",
+                                                           "/usr/share/"};
+  return xdg_read_dirs("XDG_DATA_HOME", ".local/share", "XDG_DATA_DIRS",
+                       fallback);
+}
+
+}  // namespace paths
diff --git a/src/paths.hh b/src/paths.hh
new file mode 100644
index 0000000..8bd4c75
--- /dev/null
+++ b/src/paths.hh
@@ -0,0 +1,20 @@
+#ifndef PATHS_HH
+#define PATHS_HH
+
+#include <filesystem>  // IWYU pragma: export
+#include <vector>
+
+namespace paths {
+
+// Return home directory, goes HOME, /etc/passwd entry, / in that order.
+std::filesystem::path home();
+
+// Return config directories for reading, in order of priority.
+std::vector<std::filesystem::path> config_dirs();
+
+// Return data directories for reading, in order of priority.
+std::vector<std::filesystem::path> data_dirs();
+
+}  // namespace paths
+
+#endif  // PATHS_HH