[RUST][FRONTEND] Fix resnet example (apache#3000)

Due to the previous changes the frontend resnet example failed to build.  So this patch 

1) fixes it 
2) adds ~~a local `run_tests.sh` to remedy non-existence of MXNet CI (used in python build example)~~ the example build to CI with random weights and a flag for pretrained resnet weights

Please review: @tqchen @nhynes @kazimuth

rust/common/src/packed_func.rs

@@ -155,7 +155,7 @@ TVMPODValue! {
         Bytes(val) => {
             (TVMValue { v_handle: val.clone() as *const _ as *mut c_void }, TVMTypeCode_kBytes)
         }
-        Str(val) => { (TVMValue { v_handle: val.as_ptr() as *mut c_void }, TVMTypeCode_kStr)}
+        Str(val) => { (TVMValue { v_handle: val.as_ptr() as *mut c_void }, TVMTypeCode_kStr) }
     }
 }
 
@@ -260,12 +260,24 @@ impl<'a> From<&'a str> for TVMArgValue<'a> {
     }
 }
 
+impl<'a> From<String> for TVMArgValue<'a> {
+    fn from(s: String) -> Self {
+        Self::String(CString::new(s).unwrap())
+    }
+}
+
 impl<'a> From<&'a CStr> for TVMArgValue<'a> {
     fn from(s: &'a CStr) -> Self {
         Self::Str(s)
     }
 }
 
+impl<'a> From<&'a TVMByteArray> for TVMArgValue<'a> {
+    fn from(s: &'a TVMByteArray) -> Self {
+        Self::Bytes(s)
+    }
+}
+
 impl<'a> TryFrom<TVMArgValue<'a>> for &'a str {
     type Error = ValueDowncastError;
     fn try_from(val: TVMArgValue<'a>) -> Result<Self, Self::Error> {

rust/common/src/value.rs

@@ -17,7 +17,7 @@
  * under the License.
  */
 
-use std::str::FromStr;
+use std::{os::raw::c_char, str::FromStr};
 
 use failure::Error;
 
@@ -157,17 +157,57 @@ impl_tvm_context!(
     DLDeviceType_kDLExtDev: [ext_dev]
 );
 
+/// A struct holding TVM byte-array.
+///
+/// ## Example
+///
+/// ```
+/// let v = b"hello";
+/// let barr = TVMByteArray::from(&v);
+/// assert_eq!(barr.len(), v.len());
+/// assert_eq!(barr.data(), &[104u8, 101, 108, 108, 111]);
+/// ```
 impl TVMByteArray {
+    /// Gets the underlying byte-array
     pub fn data(&self) -> &'static [u8] {
         unsafe { std::slice::from_raw_parts(self.data as *const u8, self.size) }
     }
+
+    /// Gets the length of the underlying byte-array
+    pub fn len(&self) -> usize {
+        self.size
+    }
+
+    /// Converts the underlying byte-array to `Vec<u8>`
+    pub fn to_vec(&self) -> Vec<u8> {
+        self.data().to_vec()
+    }
 }
 
-impl<'a> From<&'a [u8]> for TVMByteArray {
-    fn from(bytes: &[u8]) -> Self {
-        Self {
-            data: bytes.as_ptr() as *const i8,
-            size: bytes.len(),
+// Needs AsRef for Vec
+impl<T: AsRef<[u8]>> From<T> for TVMByteArray {
+    fn from(arg: T) -> Self {
+        let arg = arg.as_ref();
+        TVMByteArray {
+            data: arg.as_ptr() as *const c_char,
+            size: arg.len(),
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn convert() {
+        let v = vec![1u8, 2, 3];
+        let barr = TVMByteArray::from(&v);
+        assert_eq!(barr.len(), v.len());
+        assert_eq!(barr.to_vec(), vec![1u8, 2, 3]);
+        let v = b"hello";
+        let barr = TVMByteArray::from(&v);
+        assert_eq!(barr.len(), v.len());
+        assert_eq!(barr.data(), &[104u8, 101, 108, 108, 111]);
+    }
+}

rust/frontend/examples/resnet/README.md

@@ -21,12 +21,25 @@ This end-to-end example shows how to:
 * build `Resnet 18` with `tvm` and `nnvm` from Python
 * use the provided Rust frontend API to test for an input image
 
-To run the example, first `tvm`, `nnvm` and `mxnet` must be installed for the python build. To install mxnet for cpu, run `pip install mxnet`
+To run the example with pretrained resnet weights, first `tvm`, `nnvm` and `mxnet` must be installed for the python build. To install mxnet for cpu, run `pip install mxnet`
 and to install `tvm` and `nnvm` with `llvm` follow the [TVM installation guide](https://docs.tvm.ai/install/index.html).
 
-* **Build the example**: `cargo build`
+* **Build the example**: `cargo build
 
 To have a successful build, note that it is required to instruct Rust compiler to link to the compiled shared library, for example with
 `println!("cargo:rustc-link-search=native={}", build_path)`. See the `build.rs` for more details.
 
 * **Run the example**: `cargo run`
+
+Note: To use pretrained weights, one can enable `--pretrained` in `build.rs` with
+
+```
+let output = Command::new("python")
+        .arg(concat!(env!("CARGO_MANIFEST_DIR"), "/src/build_resnet.py"))
+        .arg(&format!("--build-dir={}", env!("CARGO_MANIFEST_DIR")))
+        .arg(&format!("--pretrained"))
+        .output()
+        .expect("Failed to execute command");
+```
+
+Otherwise, *random weights* are used, therefore, the prediction will be `limpkin, Aramus pictus`!

rust/frontend/examples/resnet/build.rs

@@ -17,16 +17,23 @@
  * under the License.
  */
 
-use std::process::Command;
+use std::{path::Path, process::Command};
 
 fn main() {
-    let output = Command::new(concat!(env!("CARGO_MANIFEST_DIR"), "/src/build_resnet.py"))
+    let output = Command::new("python3")
+        .arg(concat!(env!("CARGO_MANIFEST_DIR"), "/src/build_resnet.py"))
+        .arg(&format!("--build-dir={}", env!("CARGO_MANIFEST_DIR")))
         .output()
         .expect("Failed to execute command");
     assert!(
-        std::path::Path::new(concat!(env!("CARGO_MANIFEST_DIR"), "/deploy_lib.o")).exists(),
+        Path::new(&format!("{}/deploy_lib.o", env!("CARGO_MANIFEST_DIR"))).exists(),
         "Could not prepare demo: {}",
-        String::from_utf8(output.stderr).unwrap().trim()
+        String::from_utf8(output.stderr)
+            .unwrap()
+            .trim()
+            .split("\n")
+            .last()
+            .unwrap_or("")
     );
     println!(
         "cargo:rustc-link-search=native={}",

rust/frontend/examples/resnet/src/build_resnet.py

@@ -24,19 +24,18 @@
 
 import numpy as np
 
-import mxnet as mx
-from mxnet.gluon.model_zoo.vision import get_model
-from mxnet.gluon.utils import download
-
 import tvm
+from tvm import relay
+from tvm.relay import testing
 from tvm.contrib import graph_runtime, cc
-import nnvm
 
 logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(name)s - %(levelname)s - %(message)s')
 logger = logging.getLogger(__name__)
 
 parser = argparse.ArgumentParser(description='Resnet build example')
 aa = parser.add_argument
+aa('--build-dir', type=str, required=True, help='directory to put the build artifacts')
+aa('--pretrained', action='store_true', help='use a pretrained resnet')
 aa('--batch-size', type=int, default=1, help='input image batch size')
 aa('--opt-level', type=int, default=3,
    help='level of optimization. 0 is unoptimized and 3 is the highest level')
@@ -45,7 +44,7 @@
 aa('--image-name', type=str, default='cat.png', help='name of input image to download')
 args = parser.parse_args()
 
-target_dir = osp.dirname(osp.dirname(osp.realpath(__file__)))
+build_dir = args.build_dir
 batch_size = args.batch_size
 opt_level = args.opt_level
 target = tvm.target.create(args.target)
@@ -57,30 +56,42 @@ def build(target_dir):
     deploy_lib = osp.join(target_dir, 'deploy_lib.o')
     if osp.exists(deploy_lib):
         return
-    # download the pretrained resnet18 trained on imagenet1k dataset for
-    # image classification task
-    block = get_model('resnet18_v1', pretrained=True)
 
-    sym, params = nnvm.frontend.from_mxnet(block)
-    # add the softmax layer for prediction
-    net = nnvm.sym.softmax(sym)
+    if args.pretrained:
+        # needs mxnet installed
+        from mxnet.gluon.model_zoo.vision import get_model
+
+        # if `--pretrained` is enabled, it downloads a pretrained
+        # resnet18 trained on imagenet1k dataset for image classification task
+        block = get_model('resnet18_v1', pretrained=True)
+        net, params = relay.frontend.from_mxnet(block, {"data": data_shape})
+        # we want a probability so add a softmax operator
+        net = relay.Function(net.params, relay.nn.softmax(net.body),
+            None, net.type_params, net.attrs)
+    else:
+        # use random weights from relay.testing
+        net, params = relay.testing.resnet.get_workload(
+            num_layers=18, batch_size=batch_size, image_shape=image_shape)
+
     # compile the model
-    with nnvm.compiler.build_config(opt_level=opt_level):
-        graph, lib, params = nnvm.compiler.build(
-            net, target, shape={"data": data_shape}, params=params)
+    with relay.build_config(opt_level=opt_level):
+            graph, lib, params = relay.build_module.build(net, target, params=params)
+
     # save the model artifacts
     lib.save(deploy_lib)
     cc.create_shared(osp.join(target_dir, "deploy_lib.so"),
                     [osp.join(target_dir, "deploy_lib.o")])
 
     with open(osp.join(target_dir, "deploy_graph.json"), "w") as fo:
-        fo.write(graph.json())
+        fo.write(graph)
 
     with open(osp.join(target_dir,"deploy_param.params"), "wb") as fo:
-        fo.write(nnvm.compiler.save_param_dict(params))
+        fo.write(relay.save_param_dict(params))
 
 def download_img_labels():
     """ Download an image and imagenet1k class labels for test"""
+    from mxnet.gluon.utils import download
+
     img_name = 'cat.png'
     synset_url = ''.join(['https://gist.githubusercontent.com/zhreshold/',
                       '4d0b62f3d01426887599d4f7ede23ee5/raw/',
@@ -97,11 +108,11 @@ def download_img_labels():
         w = csv.writer(fout)
         w.writerows(synset.items())
 
-def test_build(target_dir):
+def test_build(build_dir):
     """ Sanity check with random input"""
-    graph = open(osp.join(target_dir, "deploy_graph.json")).read()
-    lib = tvm.module.load(osp.join(target_dir, "deploy_lib.so"))
-    params = bytearray(open(osp.join(target_dir,"deploy_param.params"), "rb").read())
+    graph = open(osp.join(build_dir, "deploy_graph.json")).read()
+    lib = tvm.module.load(osp.join(build_dir, "deploy_lib.so"))
+    params = bytearray(open(osp.join(build_dir,"deploy_param.params"), "rb").read())
     input_data = tvm.nd.array(np.random.uniform(size=data_shape).astype("float32"))
     ctx = tvm.cpu()
     module = graph_runtime.create(graph, lib, ctx)
@@ -112,10 +123,11 @@ def test_build(target_dir):
 
 if __name__ == '__main__':
     logger.info("building the model")
-    build(target_dir)
+    build(build_dir)
     logger.info("build was successful")
     logger.info("test the build artifacts")
-    test_build(target_dir)
+    test_build(build_dir)
     logger.info("test was successful")
-    download_img_labels()
-    logger.info("image and synset downloads are successful")
+    if args.pretrained:
+        download_img_labels()
+        logger.info("image and synset downloads are successful")

rust/frontend/examples/resnet/src/main.rs

@@ -84,7 +84,7 @@ fn main() {
     let runtime_create_fn = Function::get("tvm.graph_runtime.create").unwrap();
     let runtime_create_fn_ret = call_packed!(
         runtime_create_fn,
-        &graph,
+        graph,
         &lib,
         &ctx.device_type,
         &ctx.device_id
@@ -107,8 +107,7 @@ fn main() {
         .get_function("set_input", false)
         .unwrap();
 
-    let data_str = "data".to_string();
-    call_packed!(set_input_fn, &data_str, &input).unwrap();
+    call_packed!(set_input_fn, "data".to_string(), &input).unwrap();
     // get `run` function from runtime module
     let ref run_fn = graph_runtime_module.get_function("run", false).unwrap();
     // execute the run function. Note that it has no argument