fix(windows): quote command-line tokens, drop duplicated argv[0]

src/flutter_pty_win.c

@@ -7,22 +7,76 @@
 #include "include/dart_api_dl.h"
 #include "include/dart_native_api.h"
 
+// Windows' CreateProcessW takes the whole command line as one string, so any
+// token containing a space or tab must be quoted or it splits into several
+// argv entries for the child (and, worse, can throw off CreateProcessW's own
+// search for where the executable name ends when lpApplicationName is NULL -
+// e.g. "C:\Program Files\Git\bin\bash.exe" without quotes). Windows filenames
+// cannot contain a double quote, so a token that needs quoting here never
+// contains one that would itself need escaping.
+static int needs_quoting(const char *token)
+{
+    if (token == NULL || token[0] == 0)
+    {
+        return 1;
+    }
+
+    for (int i = 0; token[i] != 0; i++)
+    {
+        if (token[i] == ' ' || token[i] == '\t')
+        {
+            return 1;
+        }
+    }
+
+    return 0;
+}
+
+static int quoted_length(char *token)
+{
+    int length = (int)strlen(token);
+    return needs_quoting(token) ? length + 2 : length;
+}
+
+static void append_token(LPWSTR command, int *pos, char *token)
+{
+    int quote = needs_quoting(token);
+
+    if (quote)
+    {
+        command[(*pos)++] = L'"';
+    }
+
+    for (int j = 0; token[j] != 0; j++)
+    {
+        command[(*pos)++] = (WCHAR)token[j];
+    }
+
+    if (quote)
+    {
+        command[(*pos)++] = L'"';
+    }
+}
+
 static LPWSTR build_command(char *executable, char **arguments)
 {
     int command_length = 0;
 
     if (executable != NULL)
     {
-        command_length += (int)strlen(executable);
+        command_length += quoted_length(executable);
     }
 
-    if (arguments != NULL)
+    // arguments[0] duplicates executable - flutter_pty's Dart side always
+    // prepends it so Unix's execvp() gets a conventional argv[0], but here
+    // it would otherwise be written out a second time. Start at index 1.
+    if (arguments != NULL && arguments[0] != NULL)
     {
-        int i = 0;
+        int i = 1;
 
         while (arguments[i] != NULL)
         {
-            command_length += (int)strlen(arguments[i]) + 1;
+            command_length += quoted_length(arguments[i]) + 1;
             i++;
         }
     }
@@ -31,42 +85,26 @@ static LPWSTR build_command(char *executable, char **arguments)
 
     if (command != NULL)
     {
-        int i = 0;
+        int pos = 0;
 
         if (executable != NULL)
         {
-            int j = 0;
-
-            while (executable[j] != 0)
-            {
-                command[i] = (WCHAR)executable[j];
-                i++;
-                j++;
-            }
+            append_token(command, &pos, executable);
         }
 
-        if (arguments != NULL)
+        if (arguments != NULL && arguments[0] != NULL)
         {
-            int j = 0;
+            int i = 1;
 
-            while (arguments[j] != NULL)
+            while (arguments[i] != NULL)
             {
-                command[i++] = ' ';
-
-                int k = 0;
-
-                while (arguments[j][k] != 0)
-                {
-                    command[i] = (WCHAR)arguments[j][k];
-                    i++;
-                    k++;
-                }
-
-                j++;
+                command[pos++] = L' ';
+                append_token(command, &pos, arguments[i]);
+                i++;
             }
         }
 
-        command[i] = 0;
+        command[pos] = 0;
     }
 
     return command;
@@ -467,4 +505,4 @@ FFI_PLUGIN_EXPORT int pty_getpid(PtyHandle *handle)
 FFI_PLUGIN_EXPORT char *pty_error()
 {
     return error_message;
-}
+}