RUST-1592 Support decimal128 to/from human-readable strings (#404)

Author: abr-egn

.evergreen/config.yml

@@ -181,9 +181,9 @@ axes:
   - id: "extra-rust-versions"
     values:
       - id: "min"
-        display_name: "1.53 (minimum supported version)"
+        display_name: "1.56 (minimum supported version)"
         variables:
-          RUST_VERSION: "1.53.0"
+          RUST_VERSION: "1.56.0"
           MSRV: "true"
       - id: "nightly"
         display_name: "nightly"

Cargo.toml

@@ -67,6 +67,7 @@ uuid = { version = "1.1.2", features = ["serde", "v4"] }
 serde_bytes = "0.11.5"
 serde_with = { version = "1", optional = true }
 time = { version = "0.3.9", features = ["formatting", "parsing", "macros", "large-dates"] }
+bitvec = "1.0.1"
 
 [dev-dependencies]
 assert_matches = "1.2"
@@ -78,4 +79,4 @@ chrono = { version = "0.4", features = ["serde", "clock", "std"], default-featur
 
 [package.metadata.docs.rs]
 all-features = true
-rustdoc-args = ["--cfg", "docsrs"]
+rustdoc-args = ["--cfg", "docsrs"]

serde-tests/json.rs

@@ -48,7 +48,7 @@ fn all_types_json() {
         "undefined": { "$undefined": true },
         "code": { "$code": code },
         "code_w_scope": { "$code": code_w_scope.code, "$scope": scope_json },
-        "decimal": { "$numberDecimalBytes": v.decimal.bytes() },
+        "decimal": { "$numberDecimal": v.decimal.to_string() },
         "symbol": { "$symbol": "ok" },
         "min_key": { "$minKey": 1 },
         "max_key": { "$maxKey": 1 },

src/bson.rs

@@ -455,7 +455,7 @@ impl Bson {
                 "$date": { "$numberLong": v.timestamp_millis().to_string() },
             }),
             Bson::Symbol(v) => json!({ "$symbol": v }),
-            Bson::Decimal128(_) => panic!("Decimal128 extended JSON not implemented yet."),
+            Bson::Decimal128(v) => json!({ "$numberDecimal": v.to_string() }),
             Bson::Undefined => json!({ "$undefined": true }),
             Bson::MinKey => json!({ "$minKey": 1 }),
             Bson::MaxKey => json!({ "$maxKey": 1 }),
@@ -474,9 +474,6 @@ impl Bson {
     }
 
     /// Converts the Bson value into its [canonical extended JSON representation](https://www.mongodb.com/docs/manual/reference/mongodb-extended-json/).
-    ///
-    /// Note: extended json encoding for `Decimal128` values is not supported. If this method is
-    /// called on a case which contains a `Decimal128` value, it will panic.
     pub fn into_canonical_extjson(self) -> Value {
         match self {
             Bson::Int32(i) => json!({ "$numberInt": i.to_string() }),
@@ -705,6 +702,14 @@ impl Bson {
                 _ => {}
             },
 
+            ["$numberDecimal"] => {
+                if let Ok(d) = doc.get_str("$numberDecimal") {
+                    if let Ok(d) = d.parse() {
+                        return Bson::Decimal128(d);
+                    }
+                }
+            }
+
             ["$numberDecimalBytes"] => {
                 if let Ok(bytes) = doc.get_binary_generic("$numberDecimalBytes") {
                     if let Ok(b) = bytes.clone().try_into() {

src/de/serde.rs

@@ -466,10 +466,15 @@ impl<'de> Visitor<'de> for BsonVisitor {
                 }
 
                 "$numberDecimal" => {
-                    return Err(Error::custom(
-                        "deserializing decimal128 values from strings is not currently supported"
-                            .to_string(),
-                    ));
+                    let string: String = visitor.next_value()?;
+                    return Ok(Bson::Decimal128(string.parse::<Decimal128>().map_err(
+                        |_| {
+                            V::Error::invalid_value(
+                                Unexpected::Str(&string),
+                                &"decimal128 as a string",
+                            )
+                        },
+                    )?));
                 }
 
                 "$numberDecimalBytes" => {