2 files changed, 156 insertions, 0 deletions
diff --git a/src/posix/environment_posix.c b/src/posix/environment_posix.c
new file mode 100644
index 0000000..58b8fd2
--- /dev/null
+++ b/src/posix/environment_posix.c
@@ -0,0 +1,134 @@
+// Copyright 2012-2024 David Robillard <d@drobilla.net>
+// SPDX-License-Identifier: ISC
+
+#include <zix/environment.h>
+
+#include <zix/allocator.h>
+#include <zix/string_view.h>
+
+#include <stdbool.h>
+#include <string.h>
+
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+extern char** environ;
+
+static bool
+is_path_delim(const char c)
+{
+  return c == '/' || c == ':' || c == '\0';
+}
+
+static bool
+is_var_name_char(const char c)
+{
+  return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c == '_');
+}
+
+static const char*
+find_env(const ZixStringView name)
+{
+  if (environ) {
+    for (size_t i = 0U; environ[i]; ++i) {
+      // Find the first character in this entry that doesn't match the name
+      const char* const entry = environ[i];
+      size_t            j     = 0U;
+      while (j < name.length && entry[j] == name.data[j]) {
+        ++j;
+      }
+
+      if (j == name.length && entry[j] == '=') {
+        return entry + j + 1U;
+      }
+    }
+  }
+
+  return NULL;
+}
+
+// Append suffix to dst, update dst_len, and return the realloc'd result
+static char*
+append_str(ZixAllocator* const allocator,
+           size_t* const       dst_len,
+           char* const         dst,
+           const size_t        suffix_len,
+           const char* const   suffix)
+{
+  const size_t out_len = *dst_len + suffix_len;
+  char* const  out     = (char*)zix_realloc(allocator, dst, out_len + 1U);
+  if (!out) {
+    zix_free(allocator, dst);
+    return NULL;
+  }
+
+  memcpy(out + *dst_len, suffix, suffix_len);
+  out[(*dst_len += suffix_len)] = '\0';
+  return out;
+}
+
+// Append the value of the environment variable var to dst if one is set
+static char*
+append_var(ZixAllocator* const allocator,
+           size_t* const       dst_len,
+           char* const         dst,
+           const size_t        ref_len,
+           const char* const   ref)
+{
+  // Get value from environment
+  const ZixStringView var = zix_substring(ref + 1U, ref_len - 1U);
+  const char*         val = find_env(var);
+  if (val) {
+    return append_str(allocator, dst_len, dst, strlen(val), val);
+  }
+
+  // No value found, append variable reference as-is
+  return append_str(allocator, dst_len, dst, ref_len, ref);
+}
+
+char*
+zix_expand_environment_strings(ZixAllocator* const allocator,
+                               const char* const   string)
+{
+  char*  out = NULL;
+  size_t len = 0U;
+
+  size_t start = 0U; // Start of current chunk to copy
+  for (size_t s = 0U; string[s];) {
+    const char c = string[s];
+    if (c == '$' && is_var_name_char(string[s + 1U])) {
+      // Hit $ (variable reference like $VAR_NAME)
+      for (size_t t = 1U;; ++t) {
+        if (!is_var_name_char(string[s + t])) {
+          const char* const prefix     = string + start;
+          const size_t      prefix_len = s - start;
+          if ((prefix_len &&
+               !(out = append_str(allocator, &len, out, prefix_len, prefix))) ||
+              !(out = append_var(allocator, &len, out, t, string + s))) {
+            return NULL;
+          }
+          start = s = t;
+          break;
+        }
+      }
+    } else if (c == '~' && is_path_delim(string[s + 1U])) {
+      // Hit ~ before delimiter or end of string (home directory reference)
+      const char* const prefix     = string + start;
+      const size_t      prefix_len = s - start;
+      if ((prefix_len &&
+           !(out = append_str(allocator, &len, out, prefix_len, prefix))) ||
+          !(out = append_var(allocator, &len, out, 5U, "$HOME"))) {
+        return NULL;
+      }
+      start = ++s;
+    } else {
+      ++s;
+    }
+  }
+
+  if (string[start]) {
+    const char* const tail     = string + start;
+    const size_t      tail_len = strlen(tail);
+    out = append_str(allocator, &len, out, tail_len, tail);
+  }
+
+  return out;
+}
diff --git a/src/win32/environment_win32.c b/src/win32/environment_win32.c
new file mode 100644
index 0000000..e7a0ee3
--- /dev/null
+++ b/src/win32/environment_win32.c
@@ -0,0 +1,22 @@
+// Copyright 2012-2024 David Robillard <d@drobilla.net>
+// SPDX-License-Identifier: ISC
+
+#include <zix/environment.h>
+
+#include <windows.h>
+
+char*
+zix_expand_environment_strings(ZixAllocator* const allocator,
+                               const char* const   string)
+{
+  const DWORD size = ExpandEnvironmentStrings(string, NULL, 0U);
+  if (!size) {
+    return NULL;
+  }
+
+  char* const out = (char*)zix_calloc(allocator, 1U, size + 1U);
+  if (out) {
+    ExpandEnvironmentStrings(string, out, size + 1U);
+  }
+  return out;
+}