Update README, monkey patch generator.rs

README.md

@@ -12,6 +12,14 @@ And building protos? You use a builder. We don't make some fancy
 structure and give you a marshal function, nah. You give us a blob
 to write data into, and we write what you tell us, no questions asked.
 
+### Design
+
+The `protoc` command generates a CodeGeneratorRequest message; `protoc-gen-roto` (from src/bin/protoc-gen-roto.rs)
+reads this message from stdin, and generated a CodeGeneratorResponse, which it sends to stdout.
+
+The generated files get written to disk by protoc; these should be included in the Rust code being developed to
+use the protobuffers in question.
+
 ### Sample usage
 
 ```rust

src/generator.rs

@@ -32,7 +32,7 @@ fn map_type_to_rust_accessor(field_type: i32, label: i32) -> (String, String) {
         ), // TYPE_STRING
         1 => (
             "f64".to_string(),
-            "f64::from_le_bytes(bytes.try_into().map_err(|_| RotoError::WireFormatViolation)?)".to_string(),
+            "Ok(f64::from_le_bytes(bytes.try_into().map_err(|_| RotoError::WireFormatViolation)?))".to_string(),
         ), // TYPE_DOUBLE
         2 => (
             "f32".to_string(),
@@ -77,7 +77,7 @@ fn map_type_to_rust_builder(field_type: i32) -> (String, String) {
 
 pub fn generate_rust_code(set: &FileDescriptorSet) -> String {
     let mut output = String::new();
-    output.push_str("use crate::{ProtoAccessor, ProtoBuilder, Result, RotoError};\n");
+    output.push_str("use crate::{ProtoAccessor, ProtoBuilder, Result, RotoError, read_varint, RepeatedFieldIterator};\n");
     output.push_str("use std::str;\n\n");
 
     for file_res in set.file() {