postrust-core 2.3.2

//! Conversion of PostgreSQL rows to JSON.
//!
//! Shared by every adapter that returns query results (the HTTP server, the
//! Lambda adapter). Keeping one implementation matters: a per-adapter copy
//! that reads every column as `serde_json::Value` silently yields `null` for
//! anything that is not `json`/`jsonb`, because sqlx cannot decode an `int4`
//! into a JSON value.

/// Convert a sqlx row to a JSON object, decoding each column by its
/// PostgreSQL type.
///
/// A column whose value cannot be decoded becomes `null` rather than failing
/// the whole row.
pub fn row_to_json(row: &sqlx::postgres::PgRow) -> serde_json::Value {
    use sqlx::{Column, Row, TypeInfo};

    let mut map = serde_json::Map::new();

    // By name, not by position: where two columns share a name, both read the
    // *last* one's value -- sqlx's name lookup is a map the later column
    // overwrote -- and the object holds that one value under the name. That
    // is how this has always behaved, and the socket driver matches it.
    for column in row.columns() {
        let name = column.name();
        let value = decode(row, name, column.type_info().name());
        map.insert(name.to_string(), value);
    }

    serde_json::Value::Object(map)
}

/// A row's columns in order, decoded by the rules [`row_to_json`] uses.
pub fn row_to_values(row: &sqlx::postgres::PgRow) -> Vec<serde_json::Value> {
    use sqlx::{Column, Row, TypeInfo};

    row.columns()
        .iter()
        .map(|column| decode(row, column.ordinal(), column.type_info().name()))
        .collect()
}

/// One column, by name or by position, decoded by its PostgreSQL type.
fn decode<I>(row: &sqlx::postgres::PgRow, index: I, type_name: &str) -> serde_json::Value
where
    I: sqlx::ColumnIndex<sqlx::postgres::PgRow> + Copy,
{
    use sqlx::Row;
    // `name` reads as it always has; it may be a position.
    let name = index;

    let value = match type_name {
        "INT2" | "SMALLINT" => row
            .try_get::<i16, _>(name)
            .ok()
            .map(|v| serde_json::Value::Number(v.into())),
        "INT4" | "INT" | "INTEGER" => row
            .try_get::<i32, _>(name)
            .ok()
            .map(|v| serde_json::Value::Number(v.into())),
        "INT8" | "BIGINT" => row
            .try_get::<i64, _>(name)
            .ok()
            .map(|v| serde_json::Value::Number(v.into())),
        "FLOAT4" | "REAL" => row
            .try_get::<f32, _>(name)
            .ok()
            .and_then(|v| serde_json::Number::from_f64(v as f64))
            .map(serde_json::Value::Number),
        "FLOAT8" | "DOUBLE PRECISION" => row
            .try_get::<f64, _>(name)
            .ok()
            .and_then(serde_json::Number::from_f64)
            .map(serde_json::Value::Number),
        // PostgreSQL's own row_to_json emits NUMERIC as a JSON number, and so
        // does PostgREST, so returning a string here made every numeric column
        // arrive at the client quoted.
        //
        // The value is parsed from its exact decimal text rather than through
        // f64, so a NUMERIC(20, 6) keeps the digits it was stored with. NUMERIC
        // also permits NaN, which JSON has no number for; that falls back to a
        // string, which is what row_to_json does as well.
        "NUMERIC" | "DECIMAL" => row
            .try_get::<sqlx::types::BigDecimal, _>(name)
            .ok()
            .map(|v| {
                let text = v.to_string();
                serde_json::from_str::<serde_json::Value>(&text)
                    .ok()
                    .filter(serde_json::Value::is_number)
                    .unwrap_or(serde_json::Value::String(text))
            }),
        "BOOL" | "BOOLEAN" => row
            .try_get::<bool, _>(name)
            .ok()
            .map(serde_json::Value::Bool),
        "JSON" | "JSONB" => row.try_get::<serde_json::Value, _>(name).ok(),
        "UUID" => row
            .try_get::<sqlx::types::Uuid, _>(name)
            .ok()
            .map(|v| serde_json::Value::String(v.to_string())),
        "TIMESTAMPTZ" | "TIMESTAMP WITH TIME ZONE" => row
            .try_get::<chrono::DateTime<chrono::Utc>, _>(name)
            .ok()
            .map(|v| serde_json::Value::String(v.to_rfc3339())),
        // ISO 8601, with `T` between the date and the time. `to_string`
        // puts a space there, which is PostgreSQL's *display* format but
        // not what it writes in JSON -- and a client parsing the result
        // as a timestamp is parsing JSON.
        "TIMESTAMP" | "TIMESTAMP WITHOUT TIME ZONE" => row
            .try_get::<chrono::NaiveDateTime, _>(name)
            .ok()
            .map(|v| serde_json::Value::String(v.format("%Y-%m-%dT%H:%M:%S%.f").to_string())),
        "DATE" => row
            .try_get::<chrono::NaiveDate, _>(name)
            .ok()
            .map(|v| serde_json::Value::String(v.to_string())),
        "TIME" | "TIME WITHOUT TIME ZONE" => row
            .try_get::<chrono::NaiveTime, _>(name)
            .ok()
            .map(|v| serde_json::Value::String(v.to_string())),
        _ => row
            .try_get::<String, _>(name)
            .ok()
            .map(serde_json::Value::String),
    };

    value.unwrap_or(serde_json::Value::Null)
}

#[cfg(test)]
mod tests {
    /// The `T` is not decoration: `to_string` writes a space, which is
    /// PostgreSQL's display format and not what it puts in JSON.
    #[test]
    fn a_timestamp_without_a_zone_is_written_in_iso_8601() {
        let format = "%Y-%m-%dT%H:%M:%S%.f";

        let with_fraction = chrono::NaiveDateTime::parse_from_str(
            "2015-12-08 04:22:57.472738",
            "%Y-%m-%d %H:%M:%S%.f",
        )
        .unwrap();
        assert_eq!(
            with_fraction.format(format).to_string(),
            "2015-12-08T04:22:57.472738"
        );

        let whole_second =
            chrono::NaiveDateTime::parse_from_str("2018-01-02 00:00:00", "%Y-%m-%d %H:%M:%S")
                .unwrap();
        assert_eq!(
            whole_second.format(format).to_string(),
            "2018-01-02T00:00:00"
        );
    }
}