[hci] Use dynamically allocated buffers for editable strings

Editable strings currently require a fixed-size buffer, which is
inelegant and limits the potential for creating interactive forms with
a variable number of edit box widgets.

Remove this limitation by switching to using a dynamically allocated
buffer for editable strings and edit box widgets.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/editbox.h

@@ -36,7 +36,7 @@ enum edit_box_flags {
 	EDITBOX_STARS = 0x0001,
 };
 
-extern void init_editbox ( struct edit_box *box, char *buf, size_t len,
+extern void init_editbox ( struct edit_box *box, char **buf,
 			   WINDOW *win, unsigned int row, unsigned int col,
 			   unsigned int width, unsigned int flags )
 			   __attribute__ (( nonnull (1, 2) ));

src/include/ipxe/editstring.h

@@ -11,10 +11,8 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 /** An editable string */
 struct edit_string {
-	/** Buffer for string */
-	char *buf;
-	/** Size of buffer (including terminating NUL) */
-	size_t len;
+	/** Dynamically allocated string buffer */
+	char **buf;
 	/** Cursor position */
 	unsigned int cursor;
 
@@ -32,17 +30,28 @@ struct edit_string {
  * Initialise editable string
  *
  * @v string		Editable string
- * @v buf		Buffer for string
- * @v len		Length of buffer
+ * @v buf		Dynamically allocated string buffer
+ *
+ * The @c buf parameter must be the address of a caller-provided
+ * pointer to a NUL-terminated string allocated using malloc() (or
+ * equivalent, such as strdup()).  Any edits made to the string will
+ * realloc() the string buffer as needed.
+ *
+ * The caller may choose leave the initial string buffer pointer as @c
+ * NULL, in which case it will be allocated upon the first attempt to
+ * insert a character into the buffer.  If the caller does this, then
+ * it must be prepared to find the pointer still @c NULL after
+ * editing, since the user may never attempt to insert any characters.
  */
-static inline void init_editstring ( struct edit_string *string, char *buf,
-				     size_t len ) {
+static inline __nonnull void init_editstring ( struct edit_string *string,
+					       char **buf ) {
+
 	string->buf = buf;
-	string->len = len;
 }
 
-extern void replace_string ( struct edit_string *string,
-			     const char *replacement ) __nonnull;
-extern int edit_string ( struct edit_string *string, int key ) __nonnull;
+extern __attribute__ (( nonnull ( 1 ) )) int
+replace_string ( struct edit_string *string, const char *replacement );
+
+extern __nonnull int edit_string ( struct edit_string *string, int key );
 
 #endif /* _IPXE_EDITSTRING_H */

src/include/ipxe/errfile.h

@@ -416,6 +416,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define ERRFILE_efi_settings	      ( ERRFILE_OTHER | 0x005e0000 )
 #define ERRFILE_x25519		      ( ERRFILE_OTHER | 0x005f0000 )
 #define ERRFILE_des		      ( ERRFILE_OTHER | 0x00600000 )
+#define ERRFILE_editstring	      ( ERRFILE_OTHER | 0x00610000 )
 
 /** @} */