input.xml

<?xml version="1.0" encoding="UTF-8"?>
<sbml level="3" version="1" xmlns="http://www.sbml.org/sbml/level3/version1/core">
  <model extentUnits="mole" timeUnits="second">
     <listOfUnitDefinitions>
       <unitDefinition id="per_second">
          <listOfUnits>
             <unit kind="second" exponent="-1" scale="0" multiplier="1"/>
          </listOfUnits>
       </unitDefinition>
       <unitDefinition id="litre_per_mole_second">
          <listOfUnits>
             <unit kind="mole"   exponent="-1" scale="0" multiplier="1"/>
             <unit kind="litre"  exponent="1"  scale="0" multiplier="1"/>
             <unit kind="second" exponent="-1" scale="0" multiplier="1"/>
          </listOfUnits>
       </unitDefinition>
     </listOfUnitDefinitions>
     <listOfCompartments>
       <compartment id="comp" size="1e-14" spatialDimensions="3" units="litre" constant="true"/>
     </listOfCompartments>
     <listOfSpecies>
       <species compartment="comp" id="E"  initialAmount="5e-21" boundaryCondition="false"
                hasOnlySubstanceUnits="false" substanceUnits="mole" constant="false"/>
       <species compartment="comp" id="S"  initialAmount="1e-20" boundaryCondition="false"
                hasOnlySubstanceUnits="false" substanceUnits="mole" constant="false"/>
       <species compartment="comp" id="P"  initialAmount="0"     boundaryCondition="false"
                hasOnlySubstanceUnits="false" substanceUnits="mole" constant="false"/>
       <species compartment="comp" id="ES" initialAmount="0"     boundaryCondition="false"
                hasOnlySubstanceUnits="false" substanceUnits="mole" constant="false"/>
     </listOfSpecies>
     <listOfReactions>
       <reaction id="veq" reversible="true" fast="false">
         <listOfReactants>
            <speciesReference species="E"  stoichiometry="1" constant="true"/>
            <speciesReference species="S"  stoichiometry="1" constant="true"/>
         </listOfReactants>
         <listOfProducts>
            <speciesReference species="ES" stoichiometry="1" constant="true"/>
         </listOfProducts>
         <kineticLaw>
            <math xmlns="http://www.w3.org/1998/Math/MathML">
              <apply>
                 <times/>
                 <ci>comp</ci>
                 <apply>
                    <minus/>
                    <apply>
                      <times/>
                      <ci>kon</ci>
                      <ci>E</ci>
                      <ci>S</ci>
                    </apply>
                    <apply>
                      <times/>
                      <ci>koff</ci>
                      <ci>ES</ci>
                    </apply>
                 </apply>
              </apply>
            </math>
            <listOfLocalParameters>
              <localParameter id="kon"  value="1000000" units="litre_per_mole_second"/>
              <localParameter id="koff" value="0.2"     units="per_second"/>
            </listOfLocalParameters>
         </kineticLaw>
       </reaction>
       <reaction id="vcat" reversible="false" fast="false">
          <listOfReactants>
             <speciesReference species="ES" stoichiometry="1" constant="true"/>
          </listOfReactants>
          <listOfProducts>
             <speciesReference species="E"  stoichiometry="1" constant="true"/>
             <speciesReference species="P"  stoichiometry="1" constant="true"/>
          </listOfProducts>
          <kineticLaw>
             <math xmlns="http://www.w3.org/1998/Math/MathML">
               <apply>
                  <times/>
                  <ci>comp</ci>
                  <ci>kcat</ci>
                  <ci>ES</ci>
               </apply>
             </math>
             <listOfLocalParameters>
               <localParameter id="kcat" value="0.1" units="per_second"/>
             </listOfLocalParameters>
          </kineticLaw>
       </reaction>
     </listOfReactions>
  </model>
</sbml>

output

species id = E
species id = S
species id = P
species id = ES

print_species_id.rs

extern crate xml;

use std::fs::File;
use std::io::BufReader;

use xml::reader::{EventReader, XmlEvent};

fn parse_fn(filename: &str) {
    let file = File::open(filename).unwrap();
    let file = BufReader::new(file);
    let parser = EventReader::new(file);
    for e in parser {
        match e {
            Ok(XmlEvent::StartElement { name, attributes, .. }) => {
                if name.local_name == "species" {
                    for attr in attributes {
                        if attr.name.local_name == "id" {
                            println!("species id = {}", attr.value);
                        }
                    }
                }
            }
            Err(e) => {
                println!("Error: {}", e);
                break;
            }
            _ => {}
        }
    }
  
}

fn main() {
    parse_fn("src/input.xml");
}