BUILD.md: document the Rust source edit (custom.txt path is broken for unsigned forks)

BUILD.md

@@ -114,34 +114,44 @@ Dart 3.12 rejects `const Map<FontWeight, String>{...}`. Change `const` to `final
 be wiped by `flutter pub cache clean`.** To make it permanent, copy the patched file into
 `./local_google_fonts/` and use `dependency_overrides: google_fonts: { path: ... }`.
 
-### 2.6. `flutter/macos/Runner/custom.txt` (default settings via Rust's `load_custom_client`)
+### 2.6. `src/common.rs` — hardcode `enable-audio` default to off (NOT via custom.txt)
 
-RustDesk's Rust core reads `Contents/Resources/custom.txt` on startup
-(see `src/common.rs::load_custom_client` + `read_custom_client`). It accepts two
-keys: `default-settings` (fills `DEFAULT_SETTINGS`; user config still wins) and
-`override-settings` (fills `OVERWRITE_SETTINGS`; user can't override).
+**The naive approach (custom.txt) is broken for unsigned forks.** `load_custom_client`
+reads `Contents/Resources/custom.txt` and passes the content to `read_custom_client`,
+but `read_custom_client` (line 2191) immediately calls `decode64()` and then
+`sign::verify()` with a hardcoded ed25519 public key. Plain JSON fails the
+base64 decode and the function returns early — your settings are silently dropped.
+Only **official signed** custom-client builds can use the `custom.txt` path.
 
-**Current contents:**
-```json
+**What we do instead: inject `enable-audio = N` directly into `DEFAULT_SETTINGS` at
+the end of `load_custom_client`**, in [src/common.rs:2104-2114](src/common.rs#L2104):
+
+```rust
+// Custom fork: hardcode enable-audio = N as the default. User can still flip it on in Settings.
+// Reason: RustDesk's official custom.txt path requires ed25519-signed base64 (see
+// read_custom_client at line 2191 — decode64 + sign::verify with key
+// "5Qbwsde3unUcJBtrx9ZkvUmwFNoExHzpryHuPUdqlWM="), which we can't produce without the
+// official signing key. So we bypass custom.txt and inject directly into DEFAULT_SETTINGS.
+// entry().or_insert() preserves the priority chain: OVERWRITE_SETTINGS → CONFIG2 → DEFAULT_SETTINGS.
 {
-  "app-name": "RustDesk",
-  "default-settings": {
-    "enable-audio": "N"
-  }
+    let mut defaults = config::DEFAULT_SETTINGS.write().unwrap();
+    defaults.entry("enable-audio".to_string()).or_insert("N".to_string());
 }
 ```
 
-Effect: the "Enable audio" option in Settings is **off by default** for new
-installs. Users can still flip it on. To add more defaults, follow the
-`KEYS_SETTINGS` whitelist in `libs/hbb_common/src/config.rs:3130`.
+`entry().or_insert()` (not `insert()`) is intentional — it lets users override
+`enable-audio` by writing to their own `RustDesk2.toml`'s `[options]` table
+(CONFIG2 wins in the priority chain).
 
-**Two parts to make this work:**
+**To add more default-off settings**, append more `defaults.entry(...).or_insert(...)`
+lines. Any key from the `KEYS_SETTINGS` whitelist at
+[libs/hbb_common/src/config.rs:3130](libs/hbb_common/src/config.rs#L3130) works.
+Candidates: `enable-clipboard`, `enable-keyboard`, `enable-file-transfer`,
+`enable-tunnel`, `enable-record-session`.
 
-1. The file `flutter/macos/Runner/custom.txt` must exist (it does in git).
-2. `flutter/macos/Runner.xcodeproj/project.pbxproj` must list `custom.txt` in
-   the `PBXResourcesBuildPhase`'s `files` list. We added it under UUIDs
-   `AABBCC000100000000000001` (BuildFile) and `AABBCC000200000000000002`
-   (FileReference). If you regenerate the Xcode project, re-add it.
+**Verified end-to-end:** debug eprintln confirmed `DEFAULT_SETTINGS.get("enable-audio") == Some("N")`
+at startup. UI's "Settings → Permissions" page now shows the audio checkbox unchecked.
+User can still flip it on in Settings.
 
 ---