Merge pull request #108 from wasmx/error-handling

Better error handling in transformation modules

Author: axic

libchisel/src/deployer.rs

@@ -1,4 +1,5 @@
 use super::{ModuleCreator, ModuleError};
+use crate::utils::*;
 use parity_wasm::builder;
 use parity_wasm::elements::{CustomSection, Module};
 
@@ -65,27 +66,26 @@ fn deployer_code() -> Vec<u8> {
 }
 
 /// Returns a module which contains the deployable bytecode as a custom section.
-fn create_custom_deployer(payload: &[u8]) -> Module {
+fn create_custom_deployer(payload: &[u8]) -> Result<Module, ModuleError> {
     // The standard deployer code, which expects a 32 bit little endian as the trailing content
     // immediately following the payload, placed in a custom section.
     let code = deployer_code();
 
     // This is the pre-written deployer code.
-    let mut module: Module = parity_wasm::deserialize_buffer(&code).expect("invalid wasm bytecode");
+    let mut module: Module = parity_wasm::deserialize_buffer(&code)?;
 
     // Re-write memory to pre-allocate enough for code size
     let memory_initial = (payload.len() as u32 / 65536) + 1;
     let mem_type = parity_wasm::elements::MemoryType::new(memory_initial, None, false);
     module
         .memory_section_mut()
+        // This would be an internal error (.e.g the the deployer code above has no memory section)
         .expect("failed to get memory section")
         .entries_mut()[0] = mem_type;
 
     // Prepare payload (append length).
     let mut custom_payload = payload.to_vec();
-    custom_payload
-        .write_i32::<LittleEndian>(payload.len() as i32)
-        .expect("failed to write payload size");
+    custom_payload.write_i32::<LittleEndian>(payload.len() as i32)?;
 
     // Prepare and append custom section.
     let custom = CustomSection::new("deployer".to_string(), custom_payload);
@@ -94,7 +94,7 @@ fn create_custom_deployer(payload: &[u8]) -> Module {
         .sections_mut()
         .push(parity_wasm::elements::Section::Custom(custom));
 
-    module
+    Ok(module)
 }
 
 /// Returns a module which contains the deployable bytecode as a data segment.
@@ -162,7 +162,7 @@ impl<'a> ModuleCreator for Deployer<'a> {
     fn create(&self) -> Result<Module, ModuleError> {
         let output = match self {
             Deployer::Memory(payload) => create_memory_deployer(&payload),
-            Deployer::CustomSection(payload) => create_custom_deployer(&payload),
+            Deployer::CustomSection(payload) => create_custom_deployer(&payload)?,
         };
 
         Ok(output)

libchisel/src/lib.rs

@@ -57,6 +57,13 @@ impl From<String> for ModuleError {
     }
 }
 
+impl From<std::io::Error> for ModuleError {
+    fn from(error: std::io::Error) -> Self {
+        use std::error::Error;
+        ModuleError::Custom(error.description().to_string())
+    }
+}
+
 impl fmt::Display for ModuleError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(