upgrade protobuf to v2.0 and gen binding file in the build script

Cargo.toml

@@ -27,13 +27,14 @@ dev = ["clippy"]
 nightly = ["libc", "spin/unstable"]
 push = ["hyper", "libc"]
 process = ["libc", "procinfo"]
+gen = ["protobuf-codegen-pure"]
 
 [[bench]]
 name = "benches"
 path = "benches/benches.rs"
 
 [dependencies]
-protobuf = "=1.4.0"
+protobuf = "2.0"
 quick-error = "0.2"
 clippy = {version = "^0", optional = true}
 fnv = "1.0"
@@ -56,5 +57,8 @@ optional = true
 getopts = "0.2"
 hyper = {version = "0.9", default-features = false}
 
+[build-dependencies]
+protobuf-codegen-pure = {version = "2.0", optional = true}
+
 [workspace]
 members = ["static-metric"]

README.md

@@ -31,6 +31,16 @@ The main Structures and APIs are ported from [Go client](https://github.com/prom
     features = ["nightly"]
     ```
 
+### Note
+
+The crate has a pre-generated protobuf binding file for `protobuf` v2.0, if you need use the latest version of `protobuf`, you can generate the binding file on building with the `gen` feature.
+
+```toml
+[dependencies.prometheus]
+git = "https://github.com/pingcap/rust-prometheus.git"
+features = ["gen"]
+```
+
 ## Example
 
 ```rust

build.rs

@@ -0,0 +1,19 @@
+#[cfg(feature = "gen")]
+extern crate protobuf_codegen_pure;
+
+#[cfg(feature = "gen")]
+fn generate_protobuf_binding_file() {
+    protobuf_codegen_pure::run(protobuf_codegen_pure::Args {
+        out_dir: "proto",
+        input: &["proto/metrics.proto"],
+        includes: &["proto"],
+        ..Default::default()
+    }).unwrap();
+}
+
+#[cfg(not(feature = "gen"))]
+fn generate_protobuf_binding_file() {}
+
+fn main() {
+    generate_protobuf_binding_file()
+}