Add API to change database passphrase

New API is:
- dc_context_is_encrypted()
- dc_context_change_passphrase()

deltachat-ffi/deltachat.h

@@ -241,6 +241,32 @@ int             dc_context_open              (dc_context_t *context, const char*
 int             dc_context_is_open           (dc_context_t *context);
 
 
+/**
+ * Return 1 if database is encrypted. Can only be checked on open database.
+ * Use this method to decide whether to present an option to change passphrase
+ * to the user.
+ *
+ * @member dc_context_t
+ * @param context The context object.
+ * @return 1 if database is encrypted, 0 if database is not encrypted or on
+ * error.
+ */
+int             dc_context_is_encrypted      (dc_context_t *context);
+
+
+/**
+ * Changes passphrase for the open database. The database must be encrypted
+ * already, i.e. have a non-empty password. Unencrypted databases can only be
+ * encrypted during import/export.
+ * @memberof dc_context_t
+ * @param context The context object.
+ * @param passpharse New passphrase.
+ * @return 1 if database was reencrypted with the new passphrase, 0 on error
+ * (database is closed, database is not encrypted, other SQLCipher error).
+ */
+int             dc_context_change_passphrase (dc_context_t *context, char *passphrase);
+
+
 /**
  * Free a context object.
  *

deltachat-ffi/src/lib.rs

@@ -144,6 +144,34 @@ pub unsafe extern "C" fn dc_context_is_open(context: *mut dc_context_t) -> libc:
     block_on(ctx.is_open()) as libc::c_int
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn dc_context_is_encrypted(context: *mut dc_context_t) -> libc::c_int {
+    if context.is_null() {
+        eprintln!("ignoring careless call to dc_context_is_encrypted()");
+        return 0;
+    }
+
+    let ctx = &*context;
+    block_on(ctx.is_encrypted()) as libc::c_int
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn dc_context_change_passphrase(
+    context: *mut dc_context_t,
+    passphrase: *const libc::c_char,
+) -> libc::c_int {
+    if context.is_null() {
+        eprintln!("ignoring careless call to dc_context_change_passphrase()");
+        return 0;
+    }
+
+    let ctx = &*context;
+    let passphrase = to_string_lossy(passphrase);
+    block_on(ctx.change_passphrase(passphrase))
+        .log_err(ctx, "change_passphrase failed")
+        .is_ok() as libc::c_int
+}
+
 /// Release the context structure.
 ///
 /// This function releases the memory of the `dc_context_t` structure.