feat(cli): --allow-private-network for localhost development (#33) (#203)

Picks up @Timtech4u's PR #33, which has been waiting since April. The
  design (CLI flag + threading through BrowserContext + http client) is
  theirs and is correct; this is a clean rewrite on top of current main
  because repeated rebase rounds had been reverting unrelated work that
  landed in the meantime.

  Issue #4 blocked all loopback / RFC1918 / link-local fetches to prevent
  SSRF. The only escape was OBSCURA_ALLOW_PRIVATE_NETWORK=1, which is
  process-wide and clunky in pipelines. Multiple users (@Timtech4u in
  the original PR, then @duartemvix and @necrogami in the comment
  thread) reported they cannot use obscura for development against
  http://localhost:N without it.

  Adds --allow-private-network as a global CLI flag, works on fetch,
  serve, and scrape. Threads through BrowserContext::with_storage_and_network
  and the http client's validate_url. CdpContext gets a new_full
  builder and obscura_cdp::start_with_full_serve_options entry point so
  'obscura serve --allow-private-network' lets Puppeteer/Playwright
  navigate to localhost too. Default remains blocked.

  Backward compat: the env var still works (OR'd with the flag inside
  validate_url). All existing constructors and entry points unchanged.

  Verified end-to-end against a local http.server on 127.0.0.1: fetch
  and CDP Page.navigate both blocked by default, both succeed with the
  flag. Public URLs unaffected. Integration suite 28/28, full workspace
  cargo test all green.

crates/obscura-net/src/client.rs

@@ -72,8 +72,24 @@ pub enum ResourceType {
 pub type RequestCallback = Arc<dyn Fn(&RequestInfo) + Send + Sync>;
 pub type ResponseCallback = Arc<dyn Fn(&RequestInfo, &Response) + Send + Sync>;
 
-fn validate_url(url: &Url) -> Result<(), ObscuraNetError> {
-    let allow_private_network = std::env::var_os("OBSCURA_ALLOW_PRIVATE_NETWORK").is_some();
+/// Process-wide opt-in via env var. Older flow that issue #4 introduced. The
+/// new `--allow-private-network` CLI flag (issue #33) sets a per-client field
+/// that is OR'd with this so existing scripts and Docker setups that pin the
+/// env var keep working unchanged.
+pub fn env_allows_private_network() -> bool {
+    matches!(
+        std::env::var("OBSCURA_ALLOW_PRIVATE_NETWORK")
+            .ok()
+            .as_deref()
+            .map(str::trim)
+            .map(str::to_ascii_lowercase)
+            .as_deref(),
+        Some("1") | Some("true") | Some("yes") | Some("on")
+    )
+}
+
+fn validate_url(url: &Url, allow_private_network: bool) -> Result<(), ObscuraNetError> {
+    let allow_private_network = allow_private_network || env_allows_private_network();
     let scheme = url.scheme();
     if scheme != "http" && scheme != "https" && scheme != "file" {
         return Err(ObscuraNetError::Network(format!(
@@ -175,6 +191,10 @@ pub struct ObscuraHttpClient {
     pub timeout: Duration,
     pub in_flight: Arc<std::sync::atomic::AtomicU32>,
     pub block_trackers: bool,
+    /// When true, `validate_url` lets localhost / RFC1918 / link-local addresses
+    /// through in addition to the `OBSCURA_ALLOW_PRIVATE_NETWORK` env var.
+    /// Set via `--allow-private-network` on the CLI (issue #33).
+    pub allow_private_network: bool,
 }
 
 impl ObscuraHttpClient {
@@ -187,6 +207,14 @@ impl ObscuraHttpClient {
     }
 
     pub fn with_options(cookie_jar: Arc<CookieJar>, proxy_url: Option<&str>) -> Self {
+        Self::with_full_options(cookie_jar, proxy_url, false)
+    }
+
+    pub fn with_full_options(
+        cookie_jar: Arc<CookieJar>,
+        proxy_url: Option<&str>,
+        allow_private_network: bool,
+    ) -> Self {
         ObscuraHttpClient {
             client: tokio::sync::OnceCell::new(),
             proxy_url: proxy_url.map(|s| s.to_string()),
@@ -201,6 +229,7 @@ impl ObscuraHttpClient {
             in_flight: Arc::new(std::sync::atomic::AtomicU32::new(0)),
             timeout: Duration::from_secs(30),
             block_trackers: false,
+            allow_private_network,
         }
     }
 
@@ -244,7 +273,7 @@ impl ObscuraHttpClient {
         url: &Url,
         initial_body: Option<Vec<u8>>,
     ) -> Result<Response, ObscuraNetError> {
-        validate_url(url)?;
+        validate_url(url, self.allow_private_network)?;
 
         if url.scheme() == "file" {
             return fetch_file_url(url).await;
@@ -427,7 +456,7 @@ impl ObscuraHttpClient {
                     let next_url = current_url.join(location_str).map_err(|e| {
                         ObscuraNetError::Network(format!("Invalid redirect URL: {}", e))
                     })?;
-                    validate_url(&next_url)?;
+                    validate_url(&next_url, self.allow_private_network)?;
                     redirects.push(current_url.clone());
                     current_url = next_url;
                     if status == reqwest::StatusCode::MOVED_PERMANENTLY

crates/obscura-net/src/lib.rs

@@ -7,7 +7,10 @@ pub mod blocklist;
 #[cfg(feature = "stealth")]
 pub mod wreq_client;
 
-pub use client::{ObscuraHttpClient, ObscuraNetError, RequestInfo, ResourceType, Response};
+pub use client::{
+    env_allows_private_network, ObscuraHttpClient, ObscuraNetError, RequestInfo, ResourceType,
+    Response,
+};
 pub use cookies::{CookieInfo, CookieJar};
 pub use encoding::{decode_non_html, decode_response};
 pub use robots::RobotsCache;