1 files changed, 72 insertions, 0 deletions
diff --git a/windows/utils/win_strerror.c b/windows/utils/win_strerror.c
new file mode 100644
index 00000000..5572bc8b
--- /dev/null
+++ b/windows/utils/win_strerror.c
@@ -0,0 +1,72 @@
+/*
+ * Wrapper around the Windows FormatMessage system for retrieving the
+ * text of a system error code, with a simple API similar to strerror.
+ *
+ * Works by keeping a tree234 containing mappings from system error
+ * codes to strings. Entries allocated in this tree are simply never
+ * freed.
+ *
+ * Also, the returned string has its trailing newline removed (so it
+ * can go in places like the Event Log that never want a newline), and
+ * is prefixed with the error number (so that if a user sends an error
+ * report containing a translated error message we can't read, we can
+ * still find out what the error actually was).
+ */
+
+#include "putty.h"
+
+struct errstring {
+    int error;
+    char *text;
+};
+
+static int errstring_find(void *av, void *bv)
+{
+    int *a = (int *)av;
+    struct errstring *b = (struct errstring *)bv;
+    if (*a < b->error)
+        return -1;
+    if (*a > b->error)
+        return +1;
+    return 0;
+}
+static int errstring_compare(void *av, void *bv)
+{
+    struct errstring *a = (struct errstring *)av;
+    return errstring_find(&a->error, bv);
+}
+
+static tree234 *errstrings = NULL;
+
+const char *win_strerror(int error)
+{
+    struct errstring *es;
+
+    if (!errstrings)
+        errstrings = newtree234(errstring_compare);
+
+    es = find234(errstrings, &error, errstring_find);
+
+    if (!es) {
+        char msgtext[65536]; /* maximum size for FormatMessage is 64K */
+
+        es = snew(struct errstring);
+        es->error = error;
+        if (!FormatMessage((FORMAT_MESSAGE_FROM_SYSTEM |
+                            FORMAT_MESSAGE_IGNORE_INSERTS), NULL, error,
+                           MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+                           msgtext, lenof(msgtext)-1, NULL)) {
+            sprintf(msgtext,
+                    "(unable to format: FormatMessage returned %u)",
+                    (unsigned int)GetLastError());
+        } else {
+            int len = strlen(msgtext);
+            if (len > 0 && msgtext[len-1] == '\n')
+                msgtext[len-1] = '\0';
+        }
+        es->text = dupprintf("Error %d: %s", error, msgtext);
+        add234(errstrings, es);
+    }
+
+    return es->text;
+}