make startup file creation fail more explicitly (#7)

* add explicit permission error handling

* create error_helpers as mod to keep main.rs succint

* rename error_helpers -> startup_helpers

lib/src/lib.rs

@@ -1,6 +1,7 @@
 #[macro_use]
 extern crate rust_embed;
 
+pub mod startup_helpers;
 pub mod lightclient;
 pub mod grpcconnector;
 pub mod lightwallet;

lib/src/startup_helpers.rs

@@ -0,0 +1,20 @@
+pub fn report_permission_error() {
+    let user = std::env::var("USER").expect(
+        "Unexpected error reading value of $USER!");
+    let home = std::env::var("HOME").expect(
+        "Unexpected error reading value of $HOME!");
+    let current_executable = std::env::current_exe()
+        .expect("Unexpected error reporting executable path!");
+    eprintln!("USER: {}", user);
+    eprintln!("HOME: {}", home);
+    eprintln!("Executable: {}", current_executable.display());
+    if home == "/" {
+        eprintln!("User {} must have permission to write to '{}.zcash/' .",
+                  user,
+                  home);
+    } else {
+        eprintln!("User {} must have permission to write to '{}/.zcash/' .",
+                  user,
+                  home);
+    }
+}

src/main.rs

@@ -2,7 +2,7 @@ use std::io::{Result, Error, ErrorKind};
 use std::sync::Arc;
 use std::sync::mpsc::{channel, Sender, Receiver};
 
-use zecwalletlitelib::{commands, 
+use zecwalletlitelib::{commands, startup_helpers,
     lightclient::{self, LightClient, LightClientConfig},
 };
 
@@ -111,12 +111,17 @@ pub fn main() {
 
     let dangerous = matches.is_present("dangerous");
     let nosync = matches.is_present("nosync");
-
     let (command_tx, resp_rx) = match startup(server, dangerous, seed, !nosync, command.is_none()) {
         Ok(c) => c,
         Err(e) => {
             eprintln!("Error during startup: {}", e);
             error!("Error during startup: {}", e);
+            match e.raw_os_error() {
+                Some(13) => {
+                    startup_helpers::report_permission_error();
+                },
+                _ => eprintln!("Something else!")
+            }
             return;
         }
     };