Extract libnitrokey version from crate version

This patch uses the nitrokey-sys-rs crate version to extract the version
of the contained libnitrokey and to deduce the name of the libnitrokey
directory.

The implementation uses these assumptions:
1. The crate major and minor version match the libnitrokey major and
   minor version.
2. If the crate has a pre-release version, it is assumed that this
   version has the format pre.<d>, where <d> is the output of `git
   describe` with all dashes replaced by dots.
3. The name of the libnitrokey directory is libnitrokey-<tag>, where
   <tag> is the corresponding Git version tag.
4. libnitrokey uses version tags of the format v<maj>.<min>, where <maj>
   the major version and <min> is the minor version.

1 files changed, 46 insertions, 4 deletions

diff --git a/build.rs b/build.rs
index 47d2e19..e44b3c0 100644
--- a/build.rs
+++ b/build.rs
@@ -1,8 +1,49 @@
 extern crate cc;
 
-use std::path::Path;
+use std::env;
+use std::path;
+
+struct Version {
+    major: String,
+    minor: String,
+    git: String,
+}
+
+fn stringify(err: env::VarError) -> String {
+    format!("{}", err)
+}
+
+fn extract_git_version(pre: &str) -> Result<String, String> {
+    // If a pre-release version is set, it is expected to have the format
+    // pre.v<maj>.<min>.<n>.g<hash>, where <maj> and <min> are the last major and minor version,
+    // <n> is the number of commits since this version and <hash> is the hash of the last commit.
+    let parts: Vec<&str> = pre.split('.').collect();
+    if parts.len() != 5 {
+        return Err(format!("'{}' is not a valid pre-release version", pre));
+    }
+    Ok(format!("{}.{}-{}-{}", parts[1], parts[2], parts[3], parts[4]))
+}
+
+fn get_version() -> Result<Version, String> {
+    let major = env::var("CARGO_PKG_VERSION_MAJOR").map_err(stringify)?;
+    let minor = env::var("CARGO_PKG_VERSION_MINOR").map_err(stringify)?;
+    let pre = env::var("CARGO_PKG_VERSION_PRE").map_err(stringify)?;
+
+    let git = match pre.is_empty() {
+        true => format!("v{}.{}", major, minor),
+        false => extract_git_version(&pre)?,
+    };
+
+    Ok(Version {
+        major,
+        minor,
+        git,
+    })
+}
 
 fn main() {
+    let version = get_version().expect("Could not extract library version");
+
     let sources = [
         "DeviceCommunicationExceptions.cpp",
         "NK_C_API.cc",
@@ -12,12 +53,13 @@ fn main() {
         "log.cc",
         "misc.cc",
     ];
-    let library_dir = Path::new("libnitrokey-v3.3");
+    let library_dir = format!("libnitrokey-{}", version.git);
+    let library_path = path::Path::new(&library_dir);
 
     cc::Build::new()
         .cpp(true)
-        .include(library_dir.join("libnitrokey"))
-        .files(sources.iter().map(|s| library_dir.join(s)))
+        .include(library_path.join("libnitrokey"))
+        .files(sources.iter().map(|s| library_path.join(s)))
         .compile("libnitrokey.a");
 
     println!("cargo:rustc-link-lib=hidapi-libusb");