Add an rpmostree-client sub-crate

This is intended to be published to https://crates.io/crates/rpmostree-client
Part of coreos#2389

This directly imports the code from
https://github.com/ostreedev/ostree/blob/5551c54c6e6eba8145b95bd3b28223f1941a9e8d/tests/inst/src/rpmostree.rs

Once merged and released I'll try converting the ostree test suite
over as well as Zincati.

Internally add a testutils helper to validate it works.

Cargo.toml

@@ -60,6 +60,7 @@ libdnf-sys = { path = "rust/libdnf-sys", version = "0.1.0" }
 memfd = "0.3.0"
 rust-ini = "0.16.1"
 os-release = "0.1.0"
+rpmostree-client = { path = "rust/rpmostree-client", version = "0.1.0" }
 
 [build-dependencies]
 cbindgen = "0.16.0"

rust/rpmostree-client/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "rpmostree-client"
+description = "Client side bindings for rpm-ostree"
+version = "0.1.0"
+edition = "2018"
+license = "Apache-2.0"
+keywords = ["ostree", "rpm-ostree"]
+documentation = "http://docs.rs/rpmostree-client"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+anyhow = "1.0.38"
+serde = { version = "1.0.123", features = ["derive"] }
+serde_derive = "1.0.118"
+serde_json = "1.0.62"

rust/rpmostree-client/src/lib.rs

@@ -0,0 +1,64 @@
+//! APIs for interacting with rpm-ostree client side.
+
+use anyhow::Context;
+use serde_derive::Deserialize;
+use std::process::Command;
+
+/// Our generic catchall fatal error, expected to be converted
+/// to a string to output to a terminal or logs.
+type Result<T> = std::result::Result<T, Box<dyn std::error::Error + Send + Sync + 'static>>;
+
+/// Representation of the rpm-ostree client-side state; this
+/// can be parsed directly from the output of `rpm-ostree status --json`.
+/// Currently not all fields are here, but that is a bug.
+#[derive(Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub struct Status {
+    pub deployments: Vec<Deployment>,
+}
+
+/// A single deployment, i.e. a bootable ostree commit
+#[derive(Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub struct Deployment {
+    pub unlocked: Option<String>,
+    pub osname: String,
+    pub pinned: bool,
+    pub checksum: String,
+    pub staged: Option<bool>,
+    pub booted: bool,
+    pub serial: u32,
+    pub origin: String,
+}
+
+/// Gather a snapshot of the system status.
+pub fn query_status() -> Result<Status> {
+    // Retry on temporary activation failures, see
+    // https://github.com/coreos/rpm-ostree/issues/2531
+    let pause = std::time::Duration::from_secs(1);
+    let max_retries = 10;
+    let mut retries = 0;
+    let cmd_res = loop {
+        retries += 1;
+        let res = Command::new("rpm-ostree")
+            .args(&["status", "--json"])
+            .output()
+            .context("failed to spawn 'rpm-ostree status'")?;
+
+        if res.status.success() || retries >= max_retries {
+            break res;
+        }
+        std::thread::sleep(pause);
+    };
+
+    if !cmd_res.status.success() {
+        return Err(format!(
+            "running 'rpm-ostree status' failed: {}",
+            String::from_utf8_lossy(&cmd_res.stderr)
+        )
+        .into());
+    }
+
+    Ok(serde_json::from_slice(&cmd_res.stdout)
+        .context("failed to parse 'rpm-ostree status' output")?)
+}