compose_yml 0.0.59

Parse, manipulate and serialize docker-compose.yml in a strongly-typed fashion
Documentation 
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use super::common::*;

/// The size of a block of memory. This can be serialized as a
/// Docker-compatible size string using specifiers like `k`, `m` and `g`.
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub struct MemorySize(usize);

impl MemorySize {
    /// Create a `MemorySize` from a size in bytes.
    pub fn bytes(bytes: usize) -> MemorySize {
        MemorySize(bytes)
    }

    /// Create from a size in kilobytes.
    pub fn kb(kb: usize) -> MemorySize {
        MemorySize(kb * 1024)
    }

    /// Create from a size in megabytes.
    pub fn mb(mb: usize) -> MemorySize {
        MemorySize(mb * 1024 * 1024)
    }

    /// Create from a size in gigabytes.
    pub fn gb(gb: usize) -> MemorySize {
        MemorySize(gb * 1024 * 1024 * 1024)
    }

    /// Convert to a size in bytes.
    pub fn to_bytes(self) -> usize {
        match self {
            MemorySize(bytes) => bytes,
        }
    }
}

impl_interpolatable_value!(MemorySize);

impl fmt::Display for MemorySize {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let bytes = self.to_bytes();
        if bytes == 0 {
            // Just print 0 without any units, because anything else looks
            // weird.
            write!(f, "0")
        } else if bytes % (1024 * 1024 * 1024) == 0 {
            write!(f, "{}g", bytes / (1024 * 1024 * 1024))
        } else if bytes % (1024 * 1024) == 0 {
            write!(f, "{}m", bytes / (1024 * 1024))
        } else if bytes % 1024 == 0 {
            write!(f, "{}k", bytes / 1024)
        } else {
            // `b` is the default specifier, so don't print it.
            write!(f, "{}", bytes)
        }
    }
}

impl FromStr for MemorySize {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self> {
        lazy_static! {
            static ref MEM_SIZE: Regex = Regex::new("^([0-9]+)([bkmg])?$").unwrap();
        }
        let caps = MEM_SIZE
            .captures(s)
            .ok_or_else(|| Error::invalid_value("memory size", s))?;
        let value: usize = caps.get(1).unwrap().as_str().parse().unwrap();
        match caps.get(2).map(|c| c.as_str()) {
            None | Some("b") => Ok(MemorySize::bytes(value)),
            Some("k") => Ok(MemorySize::kb(value)),
            Some("m") => Ok(MemorySize::mb(value)),
            Some("g") => Ok(MemorySize::gb(value)),
            _ => unreachable!("Unexpected error parsing MemorySize <{}>", s),
        }
    }
}

#[test]
fn memory_size_supports_string_serialization() {
    let pairs = vec![
        (MemorySize::bytes(0), "0"),
        (MemorySize::bytes(1), "1"),
        (MemorySize::bytes(1023), "1023"),
        (MemorySize::bytes(1024), "1k"),
        (MemorySize::kb(1), "1k"),
        (MemorySize::bytes(1025), "1025"),
        (MemorySize::mb(1), "1m"),
        (MemorySize::gb(1), "1g"),
    ];
    for (mem_sz, s) in pairs {
        assert_eq!(mem_sz.to_string(), s);
        assert_eq!(mem_sz, MemorySize::from_str(s).unwrap());
    }

    assert_eq!(MemorySize::bytes(10), MemorySize::from_str("10b").unwrap());
}