feat: error handling for dot parser

Cargo.toml

@@ -7,6 +7,7 @@ edition = "2021"
 
 [dependencies]
 bimap = "0.6.2"
+thiserror = "1.0.38"
 
 [build-dependencies]
 bindgen = "0.59.1"

src/error.rs

@@ -0,0 +1,9 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum DotGraphError {
+    #[error("`{0}` is not a valid dot graph")]
+    Invalid(String),
+    #[error("`{0}` is not a digraph")]
+    UnDiGraph(String),
+}

src/lib.rs

@@ -3,10 +3,12 @@ pub mod graph;
 pub mod node;
 pub mod edge;
 pub mod parser;
+pub mod error;
 
 pub use node::node::Node;
 pub use edge::edge::Edge;
 pub use graph::{
     graph::Graph,
     subgraph::SubGraph,
 };
+pub use error::DotGraphError;

src/parser.rs

@@ -1,5 +1,6 @@
+use crate::DotGraphError;
 use crate::graphviz::{
-    agfstnode, agfstout, agfstsubg, agget, agnameof, agnxtattr, agnxtnode, agnxtout, agnxtsubg,
+    agfstnode, agfstout, agfstsubg, agget, agisdirected, agnameof, agnxtattr, agnxtnode, agnxtout, agnxtsubg,
     agread, fopen, Agedge_s, Agnode_s, Agraph_s, Agsym_s,
 };
 use crate::{
@@ -18,14 +19,21 @@ unsafe fn c_to_rust_string(ptr: *const i8) -> String {
     String::from_utf8_lossy(CStr::from_ptr(ptr).to_bytes()).to_string()
 }
 
-pub fn parse(path: &str) -> Graph {
-    let path = CString::new(path).unwrap();
-    let option = CString::new("r").unwrap();
+pub fn parse(path: &str) -> Result<Graph, DotGraphError> {
+    let cpath = CString::new(path).unwrap();
+    let coption = CString::new("r").unwrap();
     unsafe {
-        let fp = fopen(path.as_ptr(), option.as_ptr());
+        let fp = fopen(cpath.as_ptr(), coption.as_ptr());
 
         let graph = agread(fp as _, 0 as _);
-        parse_graph(graph)
+        if graph.is_null() {
+            return Err(DotGraphError::Invalid(String::from(path)));
+        }
+        if agisdirected(graph) == 0 {
+            return Err(DotGraphError::UnDiGraph(String::from(path)));
+        }
+
+        Ok(parse_graph(graph))
     }
 }