Add a new wxFileName function to resolve symlinks to absolute paths

include/wx/filefn.h

@@ -381,7 +381,10 @@ enum wxPosixPermissions
     #define   wxCRT_Access     access
     #define   wxCRT_Chmod      chmod
 
+    #define   wxCRT_Readlink   readlink
+
     #define wxHAS_NATIVE_LSTAT
+    #define wxHAS_NATIVE_READLINK
 #endif // platforms
 
 // if the platform doesn't have symlinks, define wxCRT_Lstat to be the same as
@@ -406,6 +409,11 @@ inline int wxChmod(const wxString& path, mode_t mode)
 inline int wxOpen(const wxString& path, int flags, mode_t mode)
     { return wxCRT_Open(path.fn_str(), flags, mode); }
 
+#if defined(wxHAS_NATIVE_READLINK)
+inline int wxReadlink(const wxString& path, char* buf, int size)
+    { return wxCRT_Readlink(path.fn_str(), buf, size); }
+#endif
+
 inline int wxStat(const wxString& path, wxStructStat *buf)
     { return wxCRT_Stat(path.fn_str(), buf); }
 inline int wxLstat(const wxString& path, wxStructStat *buf)

include/wx/filename.h

@@ -389,6 +389,9 @@ public:
         return !m_dontFollowLinks;
     }
 
+    // Resolve a wxFileName object representing a link to its target
+    wxFileName ResolveLink();
+
 #if defined(__WIN32__) && wxUSE_OLE
         // if the path is a shortcut, return the target and optionally,
         // the arguments

interface/wx/filename.h

@@ -1138,6 +1138,24 @@ public:
     */
     bool ReplaceHomeDir(wxPathFormat format = wxPATH_NATIVE);
 
+    /**
+        Find the absolute path of the file/directory that is pointed to by this
+        path.
+
+        If this path isn't a symlink, then this function will return the current
+        path. If the path does not exist on disk, An empty wxFileName instance
+        will be returned.
+
+        @note This is only supported on Unix-like platforms (e.g. wxGTK, wxOSX),
+              on other platforms (e.g. wxMSW) this function just returns the
+              current path.
+
+        @since 3.1.5
+
+        @return The absolute path that the current symlink path points to.
+    */
+    wxFileName ResolveLink();
+
 
     /**
         Deletes the specified directory from the file system.

src/common/filename.cpp

@@ -1668,6 +1668,56 @@ bool wxFileName::GetShortcutTarget(const wxString& shortcutPath,
 
 #endif // __WIN32__
 
+// ----------------------------------------------------------------------------
+// Resolve links
+// ----------------------------------------------------------------------------
+
+wxFileName wxFileName::ResolveLink()
+{
+    wxString link = GetFullPath();
+    wxFileName linkTarget( *this );
+
+// Only resolve links on platforms with readlink (e.g. Unix-like platforms)
+#if defined(wxHAS_NATIVE_READLINK)
+    wxStructStat st;
+
+    // This means the link itself doesn't exist, so return an empty filename
+    if ( !StatAny(st, link, wxFILE_EXISTS_NO_FOLLOW) )
+    {
+        linkTarget.Clear();
+        return linkTarget;
+    }
+
+    // If it isn't an actual link, bail out just and return the link as the result
+    if ( !S_ISLNK(st.st_mode) )
+        return linkTarget;
+
+    // Dynamically compute the buffer size from the stat call, but fallback if it isn't valid
+    int bufSize = 4096;
+    if( st.st_size != 0 )
+        bufSize = st.st_size + 1;
+
+    char buf[bufSize];
+    int result = wxReadlink(link, buf, bufSize - 1);
+
+    if ( result != -1 )
+    {
+        buf[result] = '\0'; // readlink() doesn't NULL-terminate the buffer
+        linkTarget.Assign( wxString(buf, wxConvLibc) );
+
+        // Ensure the resulting path is absolute since readlink can return paths relative to the link
+        if ( !linkTarget.IsAbsolute() )
+            linkTarget.MakeAbsolute(GetPath());
+    }
+    else
+    {
+        // This means the lookup failed for some reason
+        linkTarget.Clear();
+    }
+#endif
+
+    return linkTarget;
+}
 
 // ----------------------------------------------------------------------------
 // absolute/relative paths

tests/filename/filenametest.cpp

@@ -842,25 +842,71 @@ void FileNameTestCase::TestSymlinks()
     wxFileName targetfn(wxFileName::CreateTempFileName(tempdir));
     CPPUNIT_ASSERT(targetfn.FileExists());
 
+    // Resolving a non-symlink will just return the same thing
+    CPPUNIT_ASSERT_EQUAL_MESSAGE
+    (
+        "Non-symlink didn't resolve to the same file",
+        targetfn, targetfn.ResolveLink()
+    );
+
     // Create a symlink to that file
     wxFileName linktofile(tempdir, "linktofile");
     CPPUNIT_ASSERT_EQUAL(0, symlink(targetfn.GetFullPath().c_str(),
-                                        linktofile.GetFullPath().c_str()));
+                                    linktofile.GetFullPath().c_str()));
+
+    // Test resolving the filename to the symlink
+    CPPUNIT_ASSERT_EQUAL_MESSAGE
+    (
+        "Failed to resolve symlink to file",
+        targetfn, linktofile.ResolveLink()
+    );
+
+    // Create a relative symlink to that file
+    wxFileName relativelinktofile(tempdir, "relativelinktofile");
+    wxString relativeFileName = "./" + targetfn.GetFullName();
+    CPPUNIT_ASSERT_EQUAL(0, symlink(relativeFileName.c_str(),
+                                    relativelinktofile.GetFullPath().c_str()));
+
+    CPPUNIT_ASSERT_EQUAL_MESSAGE
+    (
+        "Failed to resolve relative symlink to absolute file path",
+        targetfn, relativelinktofile.ResolveLink()
+    );
 
     // ... and another to the temporary directory
     const wxString linktodirName(tempdir + "/linktodir");
+    wxFileName linktodirfn(linktodirName);
     wxFileName linktodir(wxFileName::DirName(linktodirName));
     CPPUNIT_ASSERT_EQUAL(0, symlink(tmpfn.GetFullPath().c_str(),
-                                        linktodirName.c_str()));
+                                    linktodirName.c_str()));
+
+    CPPUNIT_ASSERT_EQUAL_MESSAGE
+    (
+        "Failed to resolve symlink to directory",
+        tmpfn, linktodirfn.ResolveLink()
+    );
 
     // And symlinks to both of those symlinks
     wxFileName linktofilelnk(tempdir, "linktofilelnk");
     CPPUNIT_ASSERT_EQUAL(0, symlink(linktofile.GetFullPath().c_str(),
                                     linktofilelnk.GetFullPath().c_str()));
+
+    CPPUNIT_ASSERT_EQUAL_MESSAGE
+    (
+        "Failed to resolve symlink to file symlink",
+        targetfn, linktofilelnk.ResolveLink()
+    );
+
     wxFileName linktodirlnk(tempdir, "linktodirlnk");
     CPPUNIT_ASSERT_EQUAL(0, symlink(linktodir.GetFullPath().c_str(),
                                     linktodirlnk.GetFullPath().c_str()));
 
+    CPPUNIT_ASSERT_EQUAL_MESSAGE
+    (
+        "Failed to resolve symlink to directory symlink",
+        tmpfn, linktodirlnk.ResolveLink()
+    );
+
     // Run the tests twice: once in the default symlink following mode and the
     // second time without following symlinks.
     bool deref = true;
@@ -969,6 +1015,14 @@ void FileNameTestCase::TestSymlinks()
 
     // Finally test Exists() after removing the file.
     CPPUNIT_ASSERT(wxRemoveFile(targetfn.GetFullPath()));
+
+    // Resolving a file that doesn't exist returns empty
+    CPPUNIT_ASSERT_EQUAL_MESSAGE
+    (
+        "Non-existant file didn't resolve correctly",
+        wxFileName(), targetfn.ResolveLink()
+    );
+
     // This should succeed, as the symlink still exists and
     // the default wxFILE_EXISTS_ANY implies wxFILE_EXISTS_NO_FOLLOW
     CPPUNIT_ASSERT(wxFileName(tempdir, "linktofile").Exists());