move decimal fn to common and reuse it with client and server

common/Cargo.toml

@@ -6,6 +6,7 @@ license.workspace = true
 
 [dependencies]
 prost-types = { workspace = true }
+rust_decimal = { workspace = true }
 
 tonic = "0.14.6"
 prost = "0.14.4"

common/src/decimal.rs

@@ -0,0 +1,112 @@
+// common/src/decimal.rs
+//!
+//! The one canonical decimal spelling shared by the client and the server.
+//!
+//! Every `NUMERIC` column travels the wire as a string so no value passes
+//! through `f64`. Both ends parse that string with [`parse_decimal_exact`], so
+//! the client rejects exactly what the server would reject and a value that
+//! parses locally is guaranteed to be accepted.
+
+use rust_decimal::Decimal;
+
+/// Parses a decimal written in canonical base-10 notation.
+///
+/// Rejects anything ambiguous or non-finite: exponents (`1e2`), grouping
+/// (`1,00`), a leading `+`, surrounding whitespace, `NaN`/`inf`, and values
+/// outside [`Decimal`]'s range.
+pub fn parse_decimal_exact(value: &str) -> Result<Decimal, String> {
+    if value.is_empty() || value.len() > 128 {
+        return Err("Decimal must contain between 1 and 128 characters".to_string());
+    }
+    let unsigned = value.strip_prefix('-').unwrap_or(value);
+    if unsigned.is_empty() {
+        return Err("Decimal must contain digits".to_string());
+    }
+    let mut parts = unsigned.split('.');
+    let integer = parts.next().unwrap_or_default();
+    let fraction = parts.next();
+    if parts.next().is_some()
+        || integer.is_empty()
+        || !integer.bytes().all(|byte| byte.is_ascii_digit())
+        || fraction.is_some_and(|fraction| {
+            fraction.is_empty() || !fraction.bytes().all(|byte| byte.is_ascii_digit())
+        })
+    {
+        return Err("Decimal must use canonical base-10 notation".to_string());
+    }
+    Decimal::from_str_exact(value).map_err(|error| error.to_string())
+}
+
+/// True for the `data_type` spellings `GetTableStructure` reports for a decimal
+/// column: `NUMERIC` (from `numeric` and `money`), `NUMERIC(p)` and
+/// `NUMERIC(p,s)` (from `decimal(p,s)`).
+pub fn is_decimal_data_type(data_type: &str) -> bool {
+    data_type
+        .trim()
+        .to_ascii_uppercase()
+        .starts_with(DECIMAL_DATA_TYPE_PREFIX)
+}
+
+const DECIMAL_DATA_TYPE_PREFIX: &str = "NUMERIC";
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn canonical_parser_rejects_ambiguous_or_non_finite_input() {
+        for value in [
+            "",
+            " 1",
+            "1 ",
+            "1,00",
+            "1_000",
+            "+1",
+            "1e2",
+            "NaN",
+            "inf",
+            "+inf",
+            "--1",
+            "-",
+            ".5",
+            "1.",
+            "1.2.3",
+            "79228162514264337593543950336",
+            "8000000000000000000000000000.1",
+            "0.00000000000000000000000000001",
+        ] {
+            assert!(
+                parse_decimal_exact(value).is_err(),
+                "unexpectedly accepted {value:?}"
+            );
+        }
+    }
+
+    #[test]
+    fn canonical_parser_preserves_the_written_scale() {
+        for value in [
+            "0",
+            "-0.01",
+            "12.50",
+            "12.500",
+            "123456789012345678901.25",
+            "-79228162514264337593543950335",
+        ] {
+            assert_eq!(
+                parse_decimal_exact(value).unwrap().to_string(),
+                value,
+                "round trip changed {value:?}"
+            );
+        }
+    }
+
+    #[test]
+    fn decimal_data_type_covers_every_numeric_spelling() {
+        for data_type in ["NUMERIC", "NUMERIC(12)", "NUMERIC(12,3)", "numeric(12,3)"] {
+            assert!(is_decimal_data_type(data_type), "missed {data_type}");
+        }
+        for data_type in ["TEXT", "INT8", "TIMESTAMPTZ", "VARCHAR(255)", ""] {
+            assert!(!is_decimal_data_type(data_type), "matched {data_type}");
+        }
+    }
+}

common/src/lib.rs

@@ -1,6 +1,7 @@
 // common/src/lib.rs
 
 pub mod search;
+pub mod decimal;
 pub mod grpc_error;
 pub mod relationship;