windows/storage.c: factor out low-level Registry access.

All the fiddly business where you have to check that a thing exists,
make sure of its type, find its size, allocate some memory, and then
read it again properly (or, alternatively, loop round dealing with
ERROR_MORE_DATA) just doesn't belong at every call site. It's crying
out to be moved out into some separate utility functions that present
a more ergonomic API, so that the code that decides _which_ Registry
entries to read and what to do with them can concentrate on that.

So I've written a fresh set of registry API wrappers in windows/utils,
and simplified windows/storage.c as a result. The jump-list handling
code in particular is almost legible now!

windows/utils/registry.c

@@ -0,0 +1,184 @@
+/*
+ * Implement convenience wrappers on the awkward low-level functions
+ * for accessing the Windows registry.
+ */
+
+#include "putty.h"
+
+HKEY open_regkey_fn(bool create, HKEY hk, const char *path, ...)
+{
+    HKEY toret = NULL;
+    bool hk_needs_close = false;
+    va_list ap;
+    va_start(ap, path);
+
+    for (; path; path = va_arg(ap, const char *)) {
+        HKEY hk_sub = NULL;
+
+        LONG status;
+        if (create)
+            status = RegCreateKeyEx(
+                hk, path, 0, NULL, REG_OPTION_NON_VOLATILE,
+                KEY_READ | KEY_WRITE, NULL, &hk_sub, NULL);
+        else
+            status = RegOpenKeyEx(
+                hk, path, 0, KEY_READ | KEY_WRITE, &hk_sub);
+
+        if (status != ERROR_SUCCESS)
+            goto out;
+
+        if (hk_needs_close)
+            RegCloseKey(hk);
+        hk = hk_sub;
+        hk_needs_close = true;
+    }
+
+    toret = hk;
+    hk = NULL;
+    hk_needs_close = false;
+
+  out:
+    va_end(ap);
+    if (hk_needs_close)
+        RegCloseKey(hk);
+    return toret;
+}
+
+void close_regkey(HKEY key)
+{
+    RegCloseKey(key);
+}
+
+void del_regkey(HKEY key, const char *name)
+{
+    RegDeleteKey(key, name);
+}
+
+char *enum_regkey(HKEY key, int index)
+{
+    size_t regbuf_size = MAX_PATH + 1;
+    char *regbuf = snewn(regbuf_size, char);
+
+    while (1) {
+        LONG status = RegEnumKey(key, index, regbuf, regbuf_size);
+        if (status == ERROR_SUCCESS)
+            return regbuf;
+        if (status != ERROR_MORE_DATA) {
+            sfree(regbuf);
+            return NULL;
+        }
+        sgrowarray(regbuf, regbuf_size, regbuf_size);
+    }
+}
+
+bool get_reg_dword(HKEY key, const char *name, DWORD *out)
+{
+    DWORD type, size;
+    size = sizeof(*out);
+
+    if (RegQueryValueEx(key, name, 0, &type,
+                        (BYTE *)out, &size) != ERROR_SUCCESS ||
+        size != sizeof(*out) || type != REG_DWORD)
+        return false;
+    else
+        return true;
+}
+
+bool put_reg_dword(HKEY key, const char *name, DWORD value)
+{
+    return RegSetValueEx(key, name, 0, REG_DWORD, (CONST BYTE *) &value,
+                         sizeof(value)) == ERROR_SUCCESS;
+}
+
+char *get_reg_sz(HKEY key, const char *name)
+{
+    DWORD type, size;
+
+    if (RegQueryValueEx(key, name, 0, &type, NULL,
+                        &size) != ERROR_SUCCESS || type != REG_SZ)
+        return NULL;                   /* not a string */
+
+    size_t allocsize = size+1;         /* allow for an extra NUL if needed */
+    char *toret = snewn(allocsize, char);
+    if (RegQueryValueEx(key, name, 0, &type, (BYTE *)toret,
+                        &size) != ERROR_SUCCESS || type != REG_SZ) {
+        sfree(toret);
+        return NULL;
+    }
+    assert(size < allocsize);
+    toret[size] = '\0'; /* add an extra NUL in case RegQueryValueEx
+                         * didn't supply one */
+
+    return toret;
+}
+
+bool put_reg_sz(HKEY key, const char *name, const char *str)
+{
+    /* You have to store the trailing NUL as well */
+    return RegSetValueEx(key, name, 0, REG_SZ, (CONST BYTE *)str,
+                         1 + strlen(str)) == ERROR_SUCCESS;
+}
+
+/*
+ * REG_MULTI_SZ items are stored as a concatenation of NUL-terminated
+ * strings, terminated in turn with an empty string, i.e. a second
+ * consecutive NUL.
+ *
+ * We represent these in their storage format, as a strbuf - but
+ * *without* the second consecutive NUL.
+ *
+ * So you can build up a new MULTI_SZ value in a strbuf by calling
+ * put_asciz once per output string and then put_reg_multi_sz; and you
+ * can consume one by initialising a BinarySource to the result of
+ * get_reg_multi_sz, and then calling get_asciz on it and assuming
+ * that !get_err(src) means you have a real output string.
+ *
+ * Also, calling strbuf_to_str on one of these will give you back a
+ * bare 'char *' with the same double-NUL termination, to pass back to
+ * a caller.
+ */
+strbuf *get_reg_multi_sz(HKEY key, const char *name)
+{
+    DWORD type, size;
+
+    if (RegQueryValueEx(key, name, 0, &type, NULL,
+                        &size) != ERROR_SUCCESS || type != REG_MULTI_SZ)
+        return NULL;                   /* not a string */
+
+    strbuf *toret = strbuf_new();
+    void *ptr = strbuf_append(toret, (size_t)size + 2);
+    if (RegQueryValueEx(key, name, 0, &type, (BYTE *)ptr,
+                        &size) != ERROR_SUCCESS || type != REG_MULTI_SZ) {
+        strbuf_free(toret);
+        return NULL;
+    }
+    strbuf_shrink_to(toret, size);
+    /* Ensure we end with exactly one \0 */
+    while (strbuf_chomp(toret, '\0'));
+    put_byte(toret, '\0');
+    return toret;
+}
+
+bool put_reg_multi_sz(HKEY key, const char *name, strbuf *str)
+{
+    /*
+     * Of course, to write our string list into the registry, we _do_
+     * have to include both trailing NULs. But this is easy, because a
+     * strbuf is also designed to hold a single string and make it
+     * conveniently accessible in NUL-terminated form, so it stores a
+     * NUL in its buffer just beyond its formal length. So we just
+     * include that extra byte in the data we write.
+     */
+    return RegSetValueEx(key, name, 0, REG_MULTI_SZ, (CONST BYTE *)str->s,
+                         str->len + 1) == ERROR_SUCCESS;
+}
+
+char *get_reg_sz_simple(HKEY key, const char *name, const char *leaf)
+{
+    HKEY subkey = open_regkey(false, key, name);
+    if (!subkey)
+        return NULL;
+    char *toret = get_reg_sz(subkey, leaf);
+    RegCloseKey(subkey);
+    return toret;
+}

windows/utils/registry_get_string.c

@@ -1,43 +0,0 @@
-/*
- * Self-contained function to try to fetch a single string value from
- * the Registry, and return it as a dynamically allocated C string.
- */
-
-#include "putty.h"
-
-char *registry_get_string(HKEY root, const char *path, const char *leaf)
-{
-    HKEY key = root;
-    bool need_close_key = false;
-    char *toret = NULL, *str = NULL;
-
-    if (path) {
-        if (RegCreateKey(key, path, &key) != ERROR_SUCCESS)
-            goto out;
-        need_close_key = true;
-    }
-
-    DWORD type, size;
-    if (RegQueryValueEx(key, leaf, 0, &type, NULL, &size) != ERROR_SUCCESS)
-        goto out;
-    if (type != REG_SZ)
-        goto out;
-
-    str = snewn(size + 1, char);
-    DWORD size_got = size;
-    if (RegQueryValueEx(key, leaf, 0, &type, (LPBYTE)str,
-                        &size_got) != ERROR_SUCCESS)
-        goto out;
-    if (type != REG_SZ || size_got > size)
-        goto out;
-    str[size_got] = '\0';
-
-    toret = str;
-    str = NULL;
-
-  out:
-    if (need_close_key)
-        RegCloseKey(key);
-    sfree(str);
-    return toret;
-}