Update homedir and pwd to use StringVector and buffer resizing (#32295)

* Use StringVector and fix logic in pwd and homedir

* remove extra whitespace

* Address feedback

Author: musm

base/file.jl

@@ -27,8 +27,6 @@ export
     unlink,
     walkdir
 
-import .Base.RefValue
-
 # get and set current directory
 
 """
@@ -48,12 +46,22 @@ julia> pwd()
 ```
 """
 function pwd()
-    b = Vector{UInt8}(undef, 1024)
-    len = RefValue{Csize_t}(length(b))
-    uv_error(:getcwd, ccall(:uv_cwd, Cint, (Ptr{UInt8}, Ptr{Csize_t}), b, len))
-    String(b[1:len[]])
+    buf = Base.StringVector(AVG_PATH - 1) # space for null-terminator implied by StringVector
+    sz = RefValue{Csize_t}(length(buf) + 1) # total buffer size including null
+    while true
+        rc = ccall(:uv_cwd, Cint, (Ptr{UInt8}, Ptr{Csize_t}), buf, sz)
+        if rc == 0
+            resize!(buf, sz[])
+            return String(buf)
+        elseif rc == Base.UV_ENOBUFS
+            resize!(buf, sz[] - 1) # space for null-terminator implied by StringVector
+        else
+            uv_error(:cwd, rc)
+        end
+    end
 end
 
+
 """
     cd(dir::AbstractString=homedir())
 

base/filesystem.jl

@@ -44,10 +44,16 @@ import .Base:
     skip, stat, unsafe_read, unsafe_write, write, transcode, uv_error,
     rawhandle, OS_HANDLE, INVALID_OS_HANDLE, windowserror
 
+import .Base.RefValue
+
 if Sys.iswindows()
     import .Base: cwstring
 end
 
+# Average buffer size including null terminator for several filesystem operations.
+# On Windows we use the MAX_PATH = 260 value on Win32.
+const AVG_PATH = Sys.iswindows() ? 260 : 512
+
 include("path.jl")
 include("stat.jl")
 include("file.jl")

base/path.jl

@@ -62,18 +62,17 @@ Return the current user's home directory.
     [`uv_os_homedir` documentation](http://docs.libuv.org/en/v1.x/misc.html#c.uv_os_homedir).
 """
 function homedir()
-    path_max = 1024
-    buf = Vector{UInt8}(undef, path_max)
-    sz = RefValue{Csize_t}(path_max + 1)
+    buf = Base.StringVector(AVG_PATH - 1) # space for null-terminator implied by StringVector
+    sz = RefValue{Csize_t}(length(buf) + 1) # total buffer size including null
     while true
         rc = ccall(:uv_os_homedir, Cint, (Ptr{UInt8}, Ptr{Csize_t}), buf, sz)
         if rc == 0
             resize!(buf, sz[])
             return String(buf)
         elseif rc == Base.UV_ENOBUFS
-            resize!(buf, sz[] - 1)
+            resize!(buf, sz[] - 1) # space for null-terminator implied by StringVector
         else
-            error("unable to retrieve home directory")
+            uv_error(:homedir, rc)
         end
     end
 end

test/path.jl

@@ -258,9 +258,9 @@ end
 end
 @testset "homedir" begin
     var = Sys.iswindows() ? "USERPROFILE" : "HOME"
-    MAX_PATH = Sys.iswindows() ? 240 : 1020
+    AVG_PATH = Base.Filesystem.AVG_PATH - 1 # null-termination character
     for i = 0:9
-        local home = " "^MAX_PATH * "123456789"[1:i]
+        local home = " "^AVG_PATH * "123456789"[1:i]
         @test withenv(var => home) do
             homedir()
         end == home