Make the sync server client an optional feature

.github/workflows/rust-tests.yml

@@ -1,5 +1,3 @@
-## Run the TaskChampion tests, using both the minimum supported rust version
-## and the latest stable Rust.
 
 name: tests - rust
 
@@ -11,6 +9,42 @@ on:
     types: [opened, reopened, synchronize]
 
 jobs:
+  ## Run the `taskchampion` crate's tests with various combinations of features.
+  features:
+    strategy:
+      matrix:
+        features:
+          - ""
+          - "server-sync"
+
+    name: "taskchampion ${{ matrix.features == '' && 'with no features' || format('with features {0}', matrix.features) }}"
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Cache cargo registry
+        uses: actions/cache@v3
+        with:
+          path: ~/.cargo/registry
+          key: ubuntu-latest-stable-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
+
+      - name: Cache cargo build
+        uses: actions/cache@v3
+        with:
+          path: target
+          key: ubuntu-latest-stable-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
+
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+
+      - name: test
+        run: cargo test -p taskchampion --no-default-features --features "${{ matrix.features }}"
+
+  ## Run all TaskChampion crate tests, using both the minimum supported rust version
+  ## and the latest stable Rust.
   test:
     strategy:
       matrix:

taskchampion/integration-tests/Cargo.toml

@@ -7,7 +7,7 @@ publish = false
 build = "build.rs"
 
 [dependencies]
-taskchampion = { path = "../taskchampion" }
+taskchampion = { path = "../taskchampion", features = ["server-sync"] }
 taskchampion-lib = { path = "../lib" }
 taskchampion-sync-server = { path = "../sync-server" }
 

taskchampion/taskchampion/Cargo.toml

@@ -10,6 +10,14 @@ readme = "../README.md"
 license = "MIT"
 edition = "2018"
 
+[features]
+default = ["server-sync" ]
+server-sync = ["crypto", "dep:ureq"]
+crypto = ["dep:ring"]
+
+[package.metadata.docs.rs]
+all-features = true
+
 [dependencies]
 uuid.workspace = true
 serde.workspace = true
@@ -26,6 +34,9 @@ flate2.workspace = true
 byteorder.workspace = true
 ring.workspace = true
 
+ureq.optional = true
+ring.optional = true
+
 [dev-dependencies]
 proptest.workspace = true
 tempfile.workspace = true

taskchampion/taskchampion/src/errors.rs

@@ -34,6 +34,7 @@ macro_rules! other_error {
         }
     };
 }
+#[cfg(feature = "server-sync")]
 other_error!(ureq::Error);
 other_error!(io::Error);
 other_error!(serde_json::Error);

taskchampion/taskchampion/src/lib.rs

@@ -34,6 +34,14 @@ Create a server with [`ServerConfig`](crate::ServerConfig).
 The [`server`](crate::server) module defines the interface a server must meet.
 Users can define their own server impelementations.
 
+# Feature Flags
+
+Support for some optional functionality is controlled by feature flags.
+
+Sync server client support:
+
+ * `server-sync` - sync to the taskchampion-sync-server
+
 # See Also
 
 See the [TaskChampion Book](http://taskchampion.github.com/taskchampion)

taskchampion/taskchampion/src/server/config.rs

@@ -1,7 +1,10 @@
 use super::types::Server;
-use super::{LocalServer, RemoteServer};
 use crate::errors::Result;
+use crate::server::local::LocalServer;
+#[cfg(feature = "server-sync")]
+use crate::server::sync::SyncServer;
 use std::path::PathBuf;
+#[cfg(feature = "server-sync")]
 use uuid::Uuid;
 
 /// The configuration for a replica's access to a sync server.
@@ -12,6 +15,7 @@ pub enum ServerConfig {
         server_dir: PathBuf,
     },
     /// A remote taskchampion-sync-server instance
+    #[cfg(feature = "server-sync")]
     Remote {
         /// Sync server "origin"; a URL with schema and hostname but no path or trailing `/`
         origin: String,
@@ -30,11 +34,12 @@ impl ServerConfig {
     pub fn into_server(self) -> Result<Box<dyn Server>> {
         Ok(match self {
             ServerConfig::Local { server_dir } => Box::new(LocalServer::new(server_dir)?),
+            #[cfg(feature = "server-sync")]
             ServerConfig::Remote {
                 origin,
                 client_id,
                 encryption_secret,
-            } => Box::new(RemoteServer::new(origin, client_id, encryption_secret)?),
+            } => Box::new(SyncServer::new(origin, client_id, encryption_secret)?),
         })
     }
 }

taskchampion/taskchampion/src/server/crypto.rs

@@ -1,8 +1,8 @@
+#![allow(dead_code)] // temporary
 /// This module implements the encryption specified in the sync-protocol
 /// document.
 use crate::errors::{Error, Result};
 use ring::{aead, digest, pbkdf2, rand, rand::SecureRandom};
-use std::io::Read;
 use uuid::Uuid;
 
 const PBKDF2_ITERATIONS: u32 = 100000;
@@ -177,11 +177,13 @@ pub(super) struct Sealed {
 }
 
 impl Sealed {
+    #[cfg(feature = "server-sync")]
     pub(super) fn from_resp(
         resp: ureq::Response,
         version_id: Uuid,
         content_type: &str,
     ) -> Result<Sealed> {
+        use std::io::Read;
         if resp.header("Content-Type") == Some(content_type) {
             let mut reader = resp.into_reader();
             let mut payload = vec![];

taskchampion/taskchampion/src/server/mod.rs

@@ -12,15 +12,17 @@ However, users who wish to implement their own server interfaces can implement t
 pub(crate) mod test;
 
 mod config;
-mod crypto;
 mod local;
 mod op;
-mod remote;
 mod types;
 
+#[cfg(feature = "crypto")]
+mod crypto;
+
+#[cfg(feature = "server-sync")]
+mod sync;
+
 pub use config::ServerConfig;
-pub use local::LocalServer;
-pub use remote::RemoteServer;
 pub use types::*;
 
 pub(crate) use op::SyncOp;

taskchampion/taskchampion/src/server/remote/mod.rs → taskchampion/taskchampion/src/server/sync/mod.rs

@@ -8,7 +8,7 @@ use uuid::Uuid;
 
 use super::crypto::{Cryptor, Sealed, Secret, Unsealed};
 
-pub struct RemoteServer {
+pub struct SyncServer {
     origin: String,
     client_id: Uuid,
     cryptor: Cryptor,
@@ -21,19 +21,18 @@ const HISTORY_SEGMENT_CONTENT_TYPE: &str = "application/vnd.taskchampion.history
 /// The content-type for snapshots (opaque blobs of bytes)
 const SNAPSHOT_CONTENT_TYPE: &str = "application/vnd.taskchampion.snapshot";
 
-/// A RemoeServer communicates with a remote server over HTTP (such as with
-/// taskchampion-sync-server).
-impl RemoteServer {
-    /// Construct a new RemoteServer.  The `origin` is the sync server's protocol and hostname
+/// A RemoeServer communicates with a taskchampion-sync-server over HTTP .
+impl SyncServer {
+    /// Construct a new SyncServer.  The `origin` is the sync server's protocol and hostname
     /// without a trailing slash, such as `https://tcsync.example.com`.  Pass a client_id to
     /// identify this client to the server.  Multiple replicas synchronizing the same task history
     /// should use the same client_id.
     pub fn new(
         origin: String,
         client_id: Uuid,
         encryption_secret: Vec<u8>,
-    ) -> Result<RemoteServer> {
-        Ok(RemoteServer {
+    ) -> Result<SyncServer> {
+        Ok(SyncServer {
             origin,
             client_id,
             cryptor: Cryptor::new(client_id, &Secret(encryption_secret.to_vec()))?,
@@ -67,7 +66,7 @@ fn get_snapshot_urgency(resp: &ureq::Response) -> SnapshotUrgency {
     }
 }
 
-impl Server for RemoteServer {
+impl Server for SyncServer {
     fn add_version(
         &mut self,
         parent_version_id: VersionId,

taskchampion/taskchampion/src/server/types.rs

@@ -1,7 +1,7 @@
 use crate::errors::Result;
 use uuid::Uuid;
 
-/// Versions are referred to with sha2 hashes.
+/// Versions are referred to with UUIDs.
 pub type VersionId = Uuid;
 
 /// The distinguished value for "no version"
@@ -52,6 +52,11 @@ pub enum GetVersionResult {
 /// A value implementing this trait can act as a server against which a replica can sync.
 pub trait Server {
     /// Add a new version.
+    ///
+    /// This must ensure that the new version is the only version with the given
+    /// `parent_version_id`, and that all versions form a single parent-child chain. Inductively,
+    /// this means that if there are any versions on the server, then `parent_version_id` must be
+    /// the only version that does not already have a child.
     fn add_version(
         &mut self,
         parent_version_id: VersionId,