Replace std::env::home_dir with working implementation on Unix

Cargo.toml

@@ -8,5 +8,8 @@ repository  = "https://github.com/soc/dirs-rs"
 maintenance = { status = "actively-developed" }
 keywords    = ["xdg", "basedir", "app_dirs", "path", "folder"]
 
-[dependencies]
+[target.'cfg(unix)'.dependencies]
+libc = "0.2"
+
+[target.'cfg(windows)'.dependencies]
 winapi = { version = "0.3", features = ["knownfolders", "objbase", "shlobj"] }

src/lib.rs

@@ -19,6 +19,7 @@ use std::path::PathBuf;
 #[cfg(target_os = "linux")]   mod lin;
 #[cfg(target_os = "windows")] mod win;
 #[cfg(target_os = "macos")]   mod mac;
+#[cfg(unix)]                  mod unix;
 
 #[cfg(target_os = "linux")]   use lin as sys;
 #[cfg(target_os = "windows")] use win as sys;

src/lin.rs

@@ -5,7 +5,9 @@ use std::ffi::OsString;
 use std::path::PathBuf;
 use std::process::Command;
 
-pub fn home_dir()       -> Option<PathBuf> { env::home_dir() }
+use unix;
+
+pub fn home_dir()       -> Option<PathBuf> { unix::home_dir() }
 pub fn cache_dir()      -> Option<PathBuf> { env::var_os("XDG_CACHE_HOME") .and_then(is_absolute_path).or_else(|| home_dir().map(|h| h.join(".cache"))) }
 pub fn config_dir()     -> Option<PathBuf> { env::var_os("XDG_CONFIG_HOME").and_then(is_absolute_path).or_else(|| home_dir().map(|h| h.join(".config"))) }
 pub fn data_dir()       -> Option<PathBuf> { env::var_os("XDG_DATA_HOME")  .and_then(is_absolute_path).or_else(|| home_dir().map(|h| h.join(".local/share"))) }

src/mac.rs

@@ -1,9 +1,10 @@
 #![cfg(target_os = "macos")]
 
-use std::env;
 use std::path::PathBuf;
 
-pub fn home_dir()       -> Option<PathBuf> { env::home_dir() }
+use unix;
+
+pub fn home_dir()       -> Option<PathBuf> { unix::home_dir() }
 pub fn cache_dir()      -> Option<PathBuf> { home_dir().map(|h| h.join("Library/Caches")) }
 pub fn config_dir()     -> Option<PathBuf> { home_dir().map(|h| h.join("Library/Preferences")) }
 pub fn data_dir()       -> Option<PathBuf> { home_dir().map(|h| h.join("Library/Application Support")) }

src/unix.rs

@@ -0,0 +1,48 @@
+#![cfg(unix)]
+
+use std::env;
+use std::path::PathBuf;
+use std::mem;
+use std::ptr;
+use std::ffi::CStr;
+use std::ffi::OsString;
+use std::os::unix::ffi::OsStringExt;
+
+extern crate libc;
+
+// https://github.com/rust-lang/rust/blob/master/src/libstd/sys/unix/os.rs#L498
+pub fn home_dir() -> Option<PathBuf> {
+    return env::var_os("HOME").filter(|h| !h.is_empty()).or_else(|| unsafe {
+        fallback()
+    }).map(PathBuf::from);
+
+    #[cfg(any(target_os = "android",
+              target_os = "ios",
+              target_os = "emscripten"))]
+    unsafe fn fallback() -> Option<OsString> { None }
+    #[cfg(not(any(target_os = "android",
+                  target_os = "ios",
+                  target_os = "emscripten")))]
+    unsafe fn fallback() -> Option<OsString> {
+        let amt = match libc::sysconf(libc::_SC_GETPW_R_SIZE_MAX) {
+            n if n < 0 => 512 as usize,
+            n => n as usize,
+        };
+        let mut buf = Vec::with_capacity(amt);
+        let mut passwd: libc::passwd = mem::zeroed();
+        let mut result = ptr::null_mut();
+        match libc::getpwuid_r(libc::getuid(), &mut passwd, buf.as_mut_ptr(),
+                               buf.capacity(), &mut result) {
+            0 if !result.is_null() => {
+                let ptr = passwd.pw_dir as *const _;
+                let bytes = CStr::from_ptr(ptr).to_bytes();
+                if bytes.is_empty() {
+                    None
+                } else {
+                    Some(OsStringExt::from_vec(bytes.to_vec()))
+                }
+            },
+            _ => None,
+        }
+    }
+}