netget-tool 0.3.5

//! NBD constants (the fixed newstyle handshake, options, transmission) and the read-only export
//! a handler describes: a size, data extents, fill extents and error regions; everything else
//! reads as zeroes.
use anyhow::{bail, ensure, Context, Result};
use serde_json::Value as Json;

pub const NBDMAGIC: u64 = 0x4e42444d41474943;
pub const IHAVEOPT: u64 = 0x49484156454F5054;
pub const REPLY_MAGIC: u64 = 0x0003e889045565a9;
pub const REQUEST_MAGIC: u32 = 0x25609513;
pub const SIMPLE_REPLY_MAGIC: u32 = 0x67446698;
pub const STRUCTURED_REPLY_MAGIC: u32 = 0x668e33ef;

pub const FLAG_FIXED_NEWSTYLE: u16 = 1;
pub const FLAG_NO_ZEROES: u16 = 2;

pub const OPT_EXPORT_NAME: u32 = 1;
pub const OPT_ABORT: u32 = 2;
pub const OPT_LIST: u32 = 3;
pub const OPT_STARTTLS: u32 = 5;
pub const OPT_INFO: u32 = 6;
pub const OPT_GO: u32 = 7;
pub const OPT_STRUCTURED_REPLY: u32 = 8;
pub const OPT_LIST_META_CONTEXT: u32 = 9;
pub const OPT_SET_META_CONTEXT: u32 = 10;

pub const REP_ACK: u32 = 1;
pub const REP_SERVER: u32 = 2;
pub const REP_INFO: u32 = 3;
pub const REP_META_CONTEXT: u32 = 4;
pub const REP_ERR_UNSUP: u32 = 0x8000_0001;
pub const REP_ERR_POLICY: u32 = 0x8000_0002;
pub const REP_ERR_INVALID: u32 = 0x8000_0003;
pub const REP_ERR_UNKNOWN: u32 = 0x8000_0006;
pub const REP_ERR_TOO_BIG: u32 = 0x8000_0009;

pub const INFO_EXPORT: u16 = 0;
pub const INFO_NAME: u16 = 1;
pub const INFO_DESCRIPTION: u16 = 2;
pub const INFO_BLOCK_SIZE: u16 = 3;

pub const TFLAG_HAS_FLAGS: u16 = 1;
pub const TFLAG_READ_ONLY: u16 = 1 << 1;
pub const TFLAG_SEND_FLUSH: u16 = 1 << 2;
pub const TFLAG_SEND_DF: u16 = 1 << 7;
pub const TFLAG_CAN_MULTI_CONN: u16 = 1 << 8;
pub const TFLAG_SEND_CACHE: u16 = 1 << 10;

pub const CMD_READ: u16 = 0;
pub const CMD_WRITE: u16 = 1;
pub const CMD_DISC: u16 = 2;
pub const CMD_FLUSH: u16 = 3;
pub const CMD_TRIM: u16 = 4;
pub const CMD_CACHE: u16 = 5;
pub const CMD_WRITE_ZEROES: u16 = 6;
pub const CMD_BLOCK_STATUS: u16 = 7;
pub const CMD_FLAG_DF: u16 = 1 << 2;

pub const REPLY_FLAG_DONE: u16 = 1;
pub const REPLY_NONE: u16 = 0;
pub const REPLY_OFFSET_DATA: u16 = 1;
pub const REPLY_OFFSET_HOLE: u16 = 2;
pub const REPLY_BLOCK_STATUS: u16 = 5;
pub const REPLY_ERROR: u16 = 0x8001;
pub const REPLY_ERROR_OFFSET: u16 = 0x8002;

pub const EPERM: u32 = 1;
pub const EIO: u32 = 5;
pub const ENOMEM: u32 = 12;
pub const EINVAL: u32 = 22;
pub const ENOSPC: u32 = 28;
pub const ENOTSUP: u32 = 95;
pub const ESHUTDOWN: u32 = 108;

pub const BASE_ALLOCATION: &str = "base:allocation";
pub const STATE_HOLE: u32 = 1;
pub const STATE_ZERO: u32 = 2;

/// One request or option payload at most; a read or block status at most.
pub const MAX_OPTION: usize = 64 * 1024;
pub const MAX_REQUEST: u32 = 32 * 1024 * 1024;
/// Bytes of explicit content one export may carry, and extents.
pub const MAX_CONTENT: usize = 16 * 1024 * 1024;
pub const MAX_EXTENTS: usize = 4096;

pub fn errno(name: &str) -> Option<u32> {
    Some(match name {
        "EPERM" => EPERM,
        "EIO" => EIO,
        "ENOMEM" => ENOMEM,
        "EINVAL" => EINVAL,
        "ENOSPC" => ENOSPC,
        _ => return None,
    })
}

pub fn errno_name(n: u32) -> String {
    match n {
        0 => "OK".into(),
        EPERM => "EPERM".into(),
        EIO => "EIO".into(),
        ENOMEM => "ENOMEM".into(),
        EINVAL => "EINVAL".into(),
        ENOSPC => "ENOSPC".into(),
        75 => "EOVERFLOW".into(),
        ENOTSUP => "ENOTSUP".into(),
        ESHUTDOWN => "ESHUTDOWN".into(),
        n => format!("errno {n}"),
    }
}

#[derive(Clone, Debug, PartialEq)]
pub enum Content {
    Bytes(Vec<u8>),
    Fill(u8),
}

#[derive(Clone, Debug, PartialEq)]
pub struct Extent {
    pub offset: u64,
    pub length: u64,
    pub content: Content,
}

#[derive(Clone, Debug, PartialEq)]
pub struct Export {
    pub size: u64,
    pub description: Option<String>,
    pub extents: Vec<Extent>,
    pub errors: Vec<(u64, u64, u32)>,
    pub block_min: u32,
    pub block_preferred: u32,
    pub block_max: u32,
}

/// A piece of a read: data, or a run of zeroes.
#[derive(Clone, Debug, PartialEq)]
pub enum Piece {
    Data(u64, Vec<u8>),
    Hole(u64, u32),
}

fn u64_of(v: &Json, key: &str) -> Result<u64> {
    v.get(key)
        .and_then(Json::as_u64)
        .with_context(|| format!("{key} is a non-negative number"))
}

impl Export {
    /// The export an `nbd_export` action describes.
    pub fn from_action(v: &Json) -> Result<Self> {
        let size = u64_of(v, "size")?;
        ensure!(size <= 1 << 40, "size is at most 1 TiB");
        let mut extents = Vec::new();
        let mut content = 0usize;
        let list = |key: &str| -> Result<Vec<Json>> {
            match v.get(key) {
                None | Some(Json::Null) => Ok(vec![]),
                Some(Json::Array(a)) => {
                    ensure!(
                        a.len() <= MAX_EXTENTS,
                        "{key} has more than {MAX_EXTENTS} entries"
                    );
                    Ok(a.clone())
                }
                _ => bail!("{key} is an array"),
            }
        };
        for e in list("extents")? {
            let offset = u64_of(&e, "offset")?;
            let content_of = if let Some(t) = e.get("text").and_then(Json::as_str) {
                Content::Bytes(t.as_bytes().to_vec())
            } else if let Some(h) = e.get("hex").and_then(Json::as_str) {
                Content::Bytes(hex::decode(h).context("hex is not hex")?)
            } else if let Some(f) = e.get("fill") {
                Content::Fill(
                    f.as_u64()
                        .and_then(|f| u8::try_from(f).ok())
                        .context("fill is a byte value 0-255")?,
                )
            } else {
                bail!("each extent has text, hex or fill");
            };
            let length = match &content_of {
                Content::Bytes(b) => {
                    content += b.len();
                    b.len() as u64
                }
                Content::Fill(_) => u64_of(&e, "length")?,
            };
            ensure!(
                content <= MAX_CONTENT,
                "extents carry more than {MAX_CONTENT} bytes"
            );
            ensure!(
                offset.checked_add(length).is_some_and(|end| end <= size),
                "an extent at {offset} runs past the export size {size}"
            );
            if length > 0 {
                extents.push(Extent {
                    offset,
                    length,
                    content: content_of,
                });
            }
        }
        let mut errors = Vec::new();
        for e in list("errors")? {
            let (offset, length) = (u64_of(&e, "offset")?, u64_of(&e, "length")?);
            ensure!(
                offset.checked_add(length).is_some_and(|end| end <= size),
                "an error region runs past the export size"
            );
            let name = e.get("error").and_then(Json::as_str).unwrap_or("EIO");
            errors.push((
                offset,
                length,
                errno(name).context("error is EIO, EPERM, ENOMEM, EINVAL or ENOSPC")?,
            ));
        }
        let bs = v.get("block_size").filter(|b| !b.is_null());
        let get = |k: &str, d: u32| -> Result<u32> {
            match bs.and_then(|b| b.get(k)).filter(|x| !x.is_null()) {
                None => Ok(d),
                Some(x) => x
                    .as_u64()
                    .and_then(|x| u32::try_from(x).ok())
                    .with_context(|| format!("block_size.{k} is a number")),
            }
        };
        let (block_min, block_preferred, block_max) = (
            get("minimum", 1)?,
            get("preferred", 4096)?,
            get("maximum", MAX_REQUEST)?,
        );
        ensure!(
            block_min.is_power_of_two() && block_min <= 65536,
            "block_size.minimum is a power of two up to 64 KiB"
        );
        ensure!(
            block_preferred.is_power_of_two()
                && block_preferred >= block_min
                && block_preferred <= MAX_REQUEST,
            "block_size.preferred is a power of two between the minimum and 32 MiB"
        );
        ensure!(block_max >= block_preferred && block_max <= MAX_REQUEST && block_max % block_min == 0, "block_size.maximum is a multiple of the minimum, at least the preferred size, at most 32 MiB");
        let description = v
            .get("description")
            .and_then(Json::as_str)
            .map(str::to_owned);
        ensure!(
            description.as_ref().is_none_or(|d| d.len() <= 4096),
            "description is at most 4096 bytes"
        );
        Ok(Self {
            size,
            description,
            extents,
            errors,
            block_min,
            block_preferred,
            block_max,
        })
    }

    /// The first errored byte in a range, with its errno.
    pub fn error_in(&self, offset: u64, length: u64) -> Option<(u64, u32)> {
        self.errors
            .iter()
            .filter(|(o, l, _)| *o < offset + length && offset < o + l)
            .map(|(o, _, e)| ((*o).max(offset), *e))
            .min_by_key(|(o, _)| *o)
    }

    /// The bytes of a range, zeroes where no extent covers it.
    pub fn read(&self, offset: u64, length: u32) -> Vec<u8> {
        let mut out = vec![0u8; length as usize];
        let end = offset + length as u64;
        for e in &self.extents {
            let (s, t) = (e.offset.max(offset), (e.offset + e.length).min(end));
            if s >= t {
                continue;
            }
            let dst = &mut out[(s - offset) as usize..(t - offset) as usize];
            match &e.content {
                Content::Bytes(b) => {
                    dst.copy_from_slice(&b[(s - e.offset) as usize..(t - e.offset) as usize])
                }
                Content::Fill(f) => dst.fill(*f),
            }
        }
        out
    }

    /// Covered (data) and uncovered (zero) runs of a range, in order.
    pub fn runs(&self, offset: u64, length: u64) -> Vec<(u64, u64, bool)> {
        let end = offset + length;
        let mut cuts = vec![offset, end];
        for e in &self.extents {
            for p in [e.offset, e.offset + e.length] {
                if p > offset && p < end {
                    cuts.push(p);
                }
            }
        }
        cuts.sort_unstable();
        cuts.dedup();
        let mut runs: Vec<(u64, u64, bool)> = Vec::new();
        for w in cuts.windows(2) {
            let data = self
                .extents
                .iter()
                .any(|e| e.offset < w[1] && w[0] < e.offset + e.length);
            match runs.last_mut() {
                Some(last) if last.2 == data => last.1 += w[1] - w[0],
                _ => runs.push((w[0], w[1] - w[0], data)),
            }
        }
        runs
    }

    /// A read as structured-reply pieces: data where extents are, holes elsewhere.
    pub fn pieces(&self, offset: u64, length: u32) -> Vec<Piece> {
        self.runs(offset, length as u64)
            .into_iter()
            .map(|(o, l, data)| {
                if data {
                    Piece::Data(o, self.read(o, l as u32))
                } else {
                    Piece::Hole(o, l as u32)
                }
            })
            .collect()
    }
}