Fix Windows argument quoting for backslash runs before quotes

subprocess.h

@@ -653,6 +653,7 @@ int subprocess_create_ex(const char *const commandLine[], int options,
   int wide_len;
   int i, j;
   int need_quoting;
+  subprocess_size_t bs_run;
   unsigned long flags = 0;
   unsigned long last_error = 0;
   int result = subprocess_error_unknown;
@@ -906,25 +907,29 @@ int subprocess_create_ex(const char *const commandLine[], int options,
     len++;
 
     // Quote the argument if it has a space in it
-    if (strpbrk(commandLine[i], "\t\v ") != SUBPROCESS_NULL ||
-        commandLine[i][0] == SUBPROCESS_NULL)
+    need_quoting = strpbrk(commandLine[i], "\t\v ") != SUBPROCESS_NULL ||
+                   commandLine[i][0] == SUBPROCESS_NULL;
+    if (need_quoting)
       len += 2;
 
+    bs_run = 0;
     for (j = 0; '\0' != commandLine[i][j]; j++) {
-      switch (commandLine[i][j]) {
-      default:
-        break;
-      case '\\':
-        if (commandLine[i][j + 1] == '"') {
-          len++;
-        }
+      len++;
 
-        break;
-      case '"':
-        len++;
-        break;
+      if ('\\' == commandLine[i][j]) {
+        bs_run++;
+      } else {
+        if ('"' == commandLine[i][j]) {
+          // Duplicate the preceding run and escape the quote.
+          len += bs_run + 1;
+        }
+        bs_run = 0;
       }
-      len++;
+    }
+
+    if (need_quoting) {
+      // Duplicate trailing slashes before the generated closing quote.
+      len += bs_run;
     }
   }
 
@@ -949,22 +954,29 @@ int subprocess_create_ex(const char *const commandLine[], int options,
       commandLineCombined[len++] = '"';
     }
 
-    for (j = 0; '\0' != commandLine[i][j]; j++) {
-      switch (commandLine[i][j]) {
-      default:
-        break;
-      case '\\':
-        if (commandLine[i][j + 1] == '"') {
-          commandLineCombined[len++] = '\\';
-        }
+    for (j = 0; '\0' != commandLine[i][j];) {
+      bs_run = 0;
+      while ('\\' == commandLine[i][j]) {
+        bs_run++;
+        j++;
+      }
+
+      if ('"' == commandLine[i][j]) {
+        // 2n + 1 slashes preserve n slashes and escape the quote.
+        bs_run = (bs_run * 2) + 1;
+      } else if ('\0' == commandLine[i][j] && need_quoting) {
+        // 2n slashes preserve n slashes before the closing quote.
+        bs_run *= 2;
+      }
 
-        break;
-      case '"':
+      while (bs_run > 0) {
         commandLineCombined[len++] = '\\';
-        break;
+        bs_run--;
       }
 
-      commandLineCombined[len++] = commandLine[i][j];
+      if ('\0' != commandLine[i][j]) {
+        commandLineCombined[len++] = commandLine[i][j++];
+      }
     }
     if (need_quoting) {
       commandLineCombined[len++] = '"';

test/process_return_special_argv.c

@@ -26,8 +26,16 @@
 #include <string.h>
 int main(int argc, const char *const argv[]) {
   unsigned int res = 0;
+  if (argc != 9) {
+    return 0;
+  }
   res |= ((strcmp(argv[1], "foo\nbar") == 0) << 0);
   res |= ((strcmp(argv[2], "\"baz\"") == 0) << 1);
   res |= ((strcmp(argv[3], "faz\\\"faz") == 0) << 2);
+  res |= ((strcmp(argv[4], "a b\\") == 0) << 3);
+  res |= ((strcmp(argv[5], "foo\\\\\"bar") == 0) << 4);
+  res |= ((strcmp(argv[6], "a b\\\\") == 0) << 5);
+  res |= ((strcmp(argv[7], "a \\\\\"b") == 0) << 6);
+  res |= ((strcmp(argv[8], "after") == 0) << 7);
   return (int)res;
-}
+}

test/test_shared.h

@@ -411,14 +411,22 @@ SUBPROCESS_TEST(create, subprocess_stderr_argv) {
 
 SUBPROCESS_TEST(create, subprocess_return_special_argv) {
   const char *const commandLine[] = {"./process_return_special_argv",
-                                     "foo\nbar", "\"baz\"", "faz\\\"faz", 0};
+                                     "foo\nbar",
+                                     "\"baz\"",
+                                     "faz\\\"faz",
+                                     "a b\\",
+                                     "foo\\\\\"bar",
+                                     "a b\\\\",
+                                     "a \\\\\"b",
+                                     "after",
+                                     0};
   struct subprocess_s process;
   int ret = -1;
 
   ASSERT_EQ(0, subprocess_create(commandLine, 0, &process));
   ASSERT_EQ(0, subprocess_join(&process, &ret));
 
-  ASSERT_EQ(7, ret); // 0b111
+  ASSERT_EQ(255, ret); // 0b11111111
 
   ASSERT_EQ(0, subprocess_destroy(&process));
 }