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|
// This example demonstrates both dictionary- and visitor-based parsing of the
// Priority header according to https://httpwg.org/specs/rfc9218.html.
const KEY_U: &str = "u";
const KEY_I: &str = "i";
const DEFAULT_URGENCY: u8 = 3;
const DEFAULT_INCREMENTAL: bool = false;
#[derive(Debug, PartialEq)]
struct Priority {
urgency: u8,
incremental: bool,
}
impl Default for Priority {
fn default() -> Self {
Self {
urgency: DEFAULT_URGENCY,
incremental: DEFAULT_INCREMENTAL,
}
}
}
fn parse_urgency(v: Option<sfv::Integer>) -> u8 {
v.and_then(|v| u8::try_from(v).ok())
.filter(|v| *v <= 7)
.unwrap_or(DEFAULT_URGENCY)
}
fn parse_incremental(v: Option<bool>) -> bool {
v.unwrap_or(DEFAULT_INCREMENTAL)
}
impl<'de> sfv::visitor::DictionaryVisitor<'de> for Priority {
type Error = std::convert::Infallible;
fn entry(
&mut self,
key: &'de sfv::KeyRef,
) -> Result<impl sfv::visitor::EntryVisitor<'de>, Self::Error> {
Ok(match key.as_str() {
KEY_U => Some(PriorityParameter::U(&mut self.urgency)),
KEY_I => Some(PriorityParameter::I(&mut self.incremental)),
// Per https://httpwg.org/specs/rfc9218.html#parameters unknown
// dictionary keys are ignored.
_ => None,
})
}
}
enum PriorityParameter<'a> {
U(&'a mut u8),
I(&'a mut bool),
}
impl<'de> sfv::visitor::ItemVisitor<'de> for PriorityParameter<'_> {
type Error = std::convert::Infallible;
fn bare_item(
self,
bare_item: sfv::BareItemFromInput<'de>,
) -> Result<impl sfv::visitor::ParameterVisitor<'de>, Self::Error> {
// Per https://httpwg.org/specs/rfc9218.html#parameters values of
// unexpected types and out-of-range values are ignored. Since the same
// dictionary key can appear multiple times in the input, and only the
// last value may be considered per Structured Field semantics, we
// overwrite any existing value with the default on error.
match self {
Self::U(urgency) => *urgency = parse_urgency(bare_item.as_integer()),
Self::I(incremental) => *incremental = parse_incremental(bare_item.as_boolean()),
}
// Neither https://httpwg.org/specs/rfc9218.html#urgency nor
// https://httpwg.org/specs/rfc9218.html#incremental defines parameters.
Ok(sfv::visitor::Ignored)
}
}
impl<'de> sfv::visitor::EntryVisitor<'de> for PriorityParameter<'_> {
fn inner_list(self) -> Result<impl sfv::visitor::InnerListVisitor<'de>, Self::Error> {
// Per https://httpwg.org/specs/rfc9218.html#parameters values of
// unexpected types are ignored. Since the same dictionary key can
// appear multiple times in the input, and only the last value may be
// considered per Structured Field semantics, we overwrite any existing
// value with the default.
match self {
Self::U(urgency) => *urgency = DEFAULT_URGENCY,
Self::I(incremental) => *incremental = DEFAULT_INCREMENTAL,
}
// Per https://httpwg.org/specs/rfc9218.html#parameters values of
// unexpected types are ignored.
Ok(sfv::visitor::Ignored)
}
}
impl From<&sfv::Dictionary> for Priority {
fn from(dict: &sfv::Dictionary) -> Self {
Self {
urgency: parse_urgency(match dict.get(KEY_U) {
Some(sfv::ListEntry::Item(sfv::Item { bare_item, .. })) => bare_item.as_integer(),
_ => None,
}),
incremental: parse_incremental(match dict.get(KEY_I) {
Some(sfv::ListEntry::Item(sfv::Item { bare_item, .. })) => bare_item.as_boolean(),
_ => None,
}),
}
}
}
#[allow(clippy::too_many_lines)]
fn main() -> Result<(), sfv::Error> {
let examples = [
// From https://httpwg.org/specs/rfc9218.html#parameters: "When
// receiving an HTTP request that does not carry these priority
// parameters, a server SHOULD act as if their default values were
// specified."
(
"",
Priority {
urgency: 3,
incremental: false,
},
),
// https://httpwg.org/specs/rfc9218.html#incremental
(
"u=5, i",
Priority {
urgency: 5,
incremental: true,
},
),
// Unknown key
(
"x;a, u=5, i",
Priority {
urgency: 5,
incremental: true,
},
),
// Unexpected type for urgency
(
"u=(), i",
Priority {
urgency: 3,
incremental: true,
},
),
// Unexpected type for urgency
(
"u=6.5, i",
Priority {
urgency: 3,
incremental: true,
},
),
// Urgency below minimum
(
"u=-1, i",
Priority {
urgency: 3,
incremental: true,
},
),
// Urgency above maximum
(
"u=8, i",
Priority {
urgency: 3,
incremental: true,
},
),
// Unexpected type for incremental
(
"i=(), u=5",
Priority {
urgency: 5,
incremental: false,
},
),
// Unexpected type for incremental
(
"i=1, u=5",
Priority {
urgency: 5,
incremental: false,
},
),
// Parameters are ignored
(
"u=5;x, i;y",
Priority {
urgency: 5,
incremental: true,
},
),
// When duplicate keys are encountered, only last's value is used
(
"u=6, i, u=5, i=?0",
Priority {
urgency: 5,
incremental: false,
},
),
// When duplicate keys are encountered, only last's value is used
(
"u=6, i, u=(), i=()",
Priority {
urgency: 3,
incremental: false,
},
),
];
for (input, expected) in examples {
assert_eq!(
Priority::from(
&sfv::Parser::new(input)
.with_version(sfv::Version::Rfc8941)
.parse()?
),
expected,
"{input}"
);
assert_eq!(
{
let mut priority = Priority::default();
sfv::Parser::new(input)
.with_version(sfv::Version::Rfc8941)
.parse_dictionary_with_visitor(&mut priority)?;
priority
},
expected,
"{input}"
);
}
Ok(())
}
|
