Fix a couple of bugs with wget

- Provide a friendly message when writing to a file fails.
 - Correctly write empty files

Fixes #832, closes #833

src/main/resources/data/computercraft/lua/rom/programs/http/wget.lua

@@ -51,7 +51,7 @@ local function get(sUrl)
 
     local sResponse = response.readAll()
     response.close()
-    return sResponse
+    return sResponse or ""
 end
 
 if run then
@@ -79,7 +79,12 @@ else
     local res = get(url)
     if not res then return end
 
-    local file = fs.open(sPath, "wb")
+    local file, err = fs.open(sPath, "wb")
+    if not file then
+        printError("Cannot save file: " .. err)
+        return
+    end
+
     file.write(res)
     file.close()
 

src/test/resources/test-rom/spec/programs/http/wget_spec.lua

@@ -1,7 +1,8 @@
 local capture = require "test_helpers".capture_program
 
 describe("The wget program", function()
-    local function setup_request()
+    local default_contents = [[print("Hello", ...)]]
+    local function setup_request(contents)
         stub(_G, "http", {
             checkURL = function()
                 return true
@@ -9,7 +10,7 @@ describe("The wget program", function()
             get = function()
                 return {
                     readAll = function()
-                        return [[print("Hello", ...)]]
+                        return contents
                     end,
                     close = function()
                     end,
@@ -19,28 +20,52 @@ describe("The wget program", function()
     end
 
     it("downloads one file", function()
-        setup_request()
+        fs.delete("/example.com")
+        setup_request(default_contents)
+
         capture(stub, "wget", "https://example.com")
 
         expect(fs.exists("/example.com")):eq(true)
     end)
 
     it("downloads one file with given filename", function()
-        setup_request()
+        fs.delete("/test-files/download")
+        setup_request(default_contents)
+
         capture(stub, "wget", "https://example.com /test-files/download")
 
         expect(fs.exists("/test-files/download")):eq(true)
     end)
 
+    it("downloads empty files", function()
+        fs.delete("/test-files/download")
+        setup_request(nil)
+
+        capture(stub, "wget", "https://example.com", "/test-files/download")
+
+        expect(fs.exists("/test-files/download")):eq(true)
+        expect(fs.getSize("/test-files/download")):eq(0)
+    end)
+
+    it("cannot save to rom", function()
+        setup_request(default_contents)
+
+        expect(capture(stub, "wget", "https://example.com", "/rom/a-file.txt")):matches {
+            ok = true,
+            output = "Connecting to https://example.com... Success.\n",
+            error = "Cannot save file: /rom/a-file.txt: Access denied\n",
+        }
+    end)
+
     it("runs a program from the internet", function()
-        setup_request()
+        setup_request(default_contents)
 
         expect(capture(stub, "wget", "run", "http://test.com", "a", "b", "c"))
             :matches { ok = true, output = "Connecting to http://test.com... Success.\nHello a b c\n", error = "" }
     end)
 
     it("displays its usage when given no arguments", function()
-        setup_request()
+        setup_request(default_contents)
 
         expect(capture(stub, "wget"))
             :matches { ok = true, output = "Usage:\nwget <url> [filename]\nwget run <url>\n", error = "" }