tiberius/tds/codec/token/
token_alt_meta_data.rs

1use std::borrow::Cow;
2
3use crate::{tds::codec::BaseMetaDataColumn, SqlReadBytes};
4
5/// A column produced by a COMPUTE clause, as described by an
6/// [`TokenAltMetaData`] (`ALTMETADATA`, token `0x88`) stream.
7///
8/// In addition to the regular column metadata, each computed column carries the
9/// aggregate operator (`op`) that produced it (for example `SUM`, `AVG`,
10/// `COUNT`) and the operand column number (`operand`) the operator was applied
11/// to. See [MS-TDS] section 2.2.7.1.
12///
13/// [MS-TDS]: https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-tds/
14#[derive(Debug, Clone)]
15pub struct AltMetaDataColumn<'a> {
16    /// The aggregate operator that produced this column (`Op` in [MS-TDS]).
17    pub op: u8,
18    /// The column number in the originating result set that the aggregate
19    /// operator was applied to (`Operand` in [MS-TDS]).
20    pub operand: u16,
21    /// The regular column metadata (flags, type information).
22    pub base: BaseMetaDataColumn,
23    /// The name of the computed column.
24    pub col_name: Cow<'a, str>,
25}
26
27/// The token describing the layout of a COMPUTE (BY) result set
28/// (`ALTMETADATA`, token `0x88`).
29///
30/// A single query can contain more than one COMPUTE clause; each is uniquely
31/// identified by [`id`](Self::id), which the matching [`TokenAltRow`] rows refer
32/// back to. See [MS-TDS] section 2.2.7.1.
33///
34/// [`TokenAltRow`]: crate::tds::codec::TokenAltRow
35/// [MS-TDS]: https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-tds/
36#[derive(Debug, Clone)]
37pub struct TokenAltMetaData<'a> {
38    /// Identifies the COMPUTE clause this metadata describes. The associated
39    /// [`TokenAltRow`](crate::tds::codec::TokenAltRow) rows carry the same id.
40    pub id: u16,
41    /// The column numbers (from the originating result set) listed in the
42    /// COMPUTE `BY` clause, in order.
43    pub by_columns: Vec<u16>,
44    /// The computed columns, one per aggregate operator in the COMPUTE clause.
45    pub columns: Vec<AltMetaDataColumn<'a>>,
46}
47
48impl TokenAltMetaData<'static> {
49    pub(crate) async fn decode<R>(src: &mut R) -> crate::Result<Self>
50    where
51        R: SqlReadBytes + Unpin,
52    {
53        // Number of computed columns, e.g. `COMPUTE SUM(x), AVG(x)` -> 2.
54        let column_count = src.read_u16_le().await?;
55
56        // Identifies the COMPUTE clause; referenced by the ALTROW token.
57        let id = src.read_u16_le().await?;
58
59        // Number of grouping columns in the `BY` list.
60        let by_cols = src.read_u8().await?;
61
62        let mut by_columns = Vec::with_capacity(by_cols as usize);
63        for _ in 0..by_cols {
64            by_columns.push(src.read_u16_le().await?);
65        }
66
67        // `column_count` is an untrusted u16 (up to 65535); cap the up-front
68        // reservation so a hostile ALTMETADATA token can't force a large
69        // transient allocation before the column data has arrived. The Vec
70        // still grows as real columns are decoded.
71        let mut columns = Vec::with_capacity(
72            (column_count as usize).min(crate::tds::codec::column_data::MAX_PREALLOC),
73        );
74        for _ in 0..column_count {
75            let op = src.read_u8().await?;
76            let operand = src.read_u16_le().await?;
77
78            let base = BaseMetaDataColumn::decode(src).await?;
79            let col_name = Cow::from(src.read_b_varchar().await?);
80
81            columns.push(AltMetaDataColumn {
82                op,
83                operand,
84                base,
85                col_name,
86            });
87        }
88
89        Ok(TokenAltMetaData {
90            id,
91            by_columns,
92            columns,
93        })
94    }
95}
96
97#[cfg(test)]
98mod tests {
99    use super::*;
100    use crate::{sql_read_bytes::test_utils::IntoSqlReadBytes, tds::codec::TypeInfo, FixedLenType};
101    use bytes::{BufMut, BytesMut};
102
103    #[tokio::test]
104    async fn decode_alt_meta_data_single_sum_column() {
105        // `SELECT ... COMPUTE SUM(x) BY y` style metadata for one Int4 column.
106        let mut buf = BytesMut::new();
107
108        buf.put_u16_le(1); // column count (one aggregate)
109        buf.put_u16_le(7); // compute id
110        buf.put_u8(1); // by_cols
111        buf.put_u16_le(2); // BY column number
112
113        // ComputeData for the single column:
114        buf.put_u8(0x4f); // Op = SUM
115        buf.put_u16_le(1); // Operand column number
116
117        // BaseMetaDataColumn: user type (u32), flags (u16), TYPE_INFO
118        buf.put_u32_le(0); // user type
119        buf.put_u16_le(0x0001); // flags (Nullable)
120        buf.put_u8(FixedLenType::Int4 as u8); // TYPE_INFO: INT4TYPE
121
122        // ColName as B_VARCHAR (length in chars, then UTF-16LE)
123        let name: Vec<u16> = "sum".encode_utf16().collect();
124        buf.put_u8(name.len() as u8);
125        for c in name {
126            buf.put_u16_le(c);
127        }
128
129        let mut reader = buf.into_sql_read_bytes();
130        let meta = TokenAltMetaData::decode(&mut reader).await.unwrap();
131
132        assert_eq!(7, meta.id);
133        assert_eq!(vec![2], meta.by_columns);
134        assert_eq!(1, meta.columns.len());
135
136        let col = &meta.columns[0];
137        assert_eq!(0x4f, col.op);
138        assert_eq!(1, col.operand);
139        assert_eq!("sum", col.col_name);
140        assert!(matches!(
141            col.base.ty,
142            TypeInfo::FixedLen(FixedLenType::Int4)
143        ));
144    }
145}
tiberius/tds/codec/token/token_alt_meta_data.rs

tiberius/tds/codec/token/
token_alt_meta_data.rs
