Validate DelimFile headers

Cargo.toml

@@ -24,6 +24,7 @@ flate2 = "^1"
 # For auto-serialization of structs to csv/tsv
 csv = "^1"
 serde = { version = "^1.0.123", features = ["derive"] }
+serde-aux = "^4"
 
 [dev-dependencies]
 tempfile = "3.2.0"

src/io/mod.rs

@@ -171,8 +171,16 @@ impl<D: DeserializeOwned> DelimFileReader<D> {
             .has_headers(true)
             .quoting(quote)
             .from_reader(reader);
-        assert!(csv_reader.has_headers(), "Expected input file to have a header row");
+
+        // NB: csv_reader.has_header() does not actually check for existence of a header, but only
+        // checks that the reader is configured to read a header.
+
+        // If the header is not empty (try to parse it)
         let header = csv_reader.headers().map_err(FgError::ConversionError)?.to_owned();
+        if !header.is_empty() {
+            Self::validate_header(&header, delimiter)?
+        }
+
         let record_iter = csv_reader.into_deserialize();
         Ok(Self { record_iter, header })
     }
@@ -186,6 +194,25 @@ impl<D: DeserializeOwned> DelimFileReader<D> {
     pub fn read(&mut self) -> Option<Result<D>> {
         self.record_iter.next().map(|result| result.map_err(FgError::ConversionError))
     }
+
+    fn validate_header(header: &StringRecord, delimiter: u8) -> Result<()> {
+        let delim = String::from_utf8(vec![delimiter]).unwrap();
+        let found_header_parts: Vec<&str> = header.iter().collect();
+        let expected_header_parts = serde_aux::prelude::serde_introspect::<D>();
+
+        // Expected header fields must be a _subset_ of found header fields
+        let ok = expected_header_parts.iter().all(|field| found_header_parts.contains(field));
+
+        if !ok {
+            let expected = expected_header_parts.join(&delim);
+            return Err(FgError::DelimFileHeaderError {
+                expected,
+                found: header.as_slice().to_owned(),
+            });
+        }
+
+        Ok(())
+    }
 }
 
 impl<D: DeserializeOwned> Iterator for DelimFileReader<D> {
@@ -342,6 +369,7 @@ impl DelimFile {
 
 #[cfg(test)]
 mod tests {
+    use super::*;
     use crate::io::{DelimFile, Io};
     use serde::{Deserialize, Serialize};
     use tempfile::TempDir;
@@ -355,6 +383,25 @@ mod tests {
         o: Option<f64>,
     }
 
+    // Trickier record types in which fields are skipped in de/serialization
+    #[derive(Debug, Serialize, Deserialize, PartialEq)]
+    struct RecWithSkipDe {
+        s: String,
+        i: usize,
+        b: bool,
+        #[serde(skip_deserializing)]
+        o: Option<f64>,
+    }
+
+    #[derive(Debug, Serialize, Deserialize, PartialEq)]
+    struct RecWithSkipSe {
+        s: String,
+        i: usize,
+        b: bool,
+        #[serde(skip_serializing)]
+        o: Option<f64>,
+    }
+
     #[test]
     fn test_reading_and_writing_lines_to_file() {
         let lines = vec!["foo", "bar,splat,whee", "baz\twhoopsie"];
@@ -431,4 +478,47 @@ mod tests {
         assert_eq!(from_csv, recs);
         assert_eq!(from_tsv, recs);
     }
+
+    #[test]
+    fn test_header_error() {
+        let recs = vec![
+            RecWithSkipDe { s: "Hello".to_string(), i: 123, b: true, o: None },
+            RecWithSkipDe { s: "A,B,C".to_string(), i: 456, b: false, o: Some(123.45) },
+        ];
+        let tmp = TempDir::new().unwrap();
+        let csv = tmp.path().join("recs.csv");
+        let df = DelimFile::default();
+        df.write_csv(&csv, recs).unwrap();
+
+        let result: Result<Vec<RecWithSkipDe>> = df.read_tsv(&csv);
+        let err = result.unwrap_err();
+
+        // Serialized CSV should contain all fields, deserializing should skip "o"
+        if let FgError::DelimFileHeaderError { expected, found } = err {
+            assert_eq!(expected, "s\ti\tb");
+            assert_eq!(found, "s,i,b,o");
+        } else {
+            panic!()
+        }
+
+        let recs = vec![
+            RecWithSkipSe { s: "Hello".to_string(), i: 123, b: true, o: None },
+            RecWithSkipSe { s: "A,B,C".to_string(), i: 456, b: false, o: Some(123.45) },
+        ];
+        let tmp = TempDir::new().unwrap();
+        let csv = tmp.path().join("recs.csv");
+        let df = DelimFile::default();
+        df.write_csv(&csv, recs).unwrap();
+
+        let result: Result<Vec<RecWithSkipSe>> = df.read_tsv(&csv);
+        let err = result.unwrap_err();
+
+        // Serialized CSV should contain should skip "o", deserailize should expect all fields
+        if let FgError::DelimFileHeaderError { expected, found } = err {
+            assert_eq!(expected, "s\ti\tb\to");
+            assert_eq!(found, "s,i,b");
+        } else {
+            panic!()
+        }
+    }
 }

src/lib.rs

@@ -16,6 +16,9 @@ pub enum FgError {
 
     #[error("Error parsing/formatting delimited data.")]
     ConversionError(#[from] csv::Error),
+
+    #[error("Error parsing delimited data file header.")]
+    DelimFileHeaderError { expected: String, found: String },
 }
 
 /// Result type that should be used everywhere