Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1496 insertions, 0 deletions

diff --git a/third_party/rust/wasmparser/src/parser.rs b/third_party/rust/wasmparser/src/parser.rs
new file mode 100644
index 0000000000..227530abba
--- /dev/null
+++ b/third_party/rust/wasmparser/src/parser.rs
@@ -0,0 +1,1496 @@
+use crate::CoreTypeSectionReader;
+use crate::{
+    limits::MAX_WASM_MODULE_SIZE, BinaryReader, BinaryReaderError, ComponentCanonicalSectionReader,
+    ComponentExportSectionReader, ComponentImportSectionReader, ComponentInstanceSectionReader,
+    ComponentStartFunction, ComponentTypeSectionReader, CustomSectionReader, DataSectionReader,
+    ElementSectionReader, ExportSectionReader, FromReader, FunctionBody, FunctionSectionReader,
+    GlobalSectionReader, ImportSectionReader, InstanceSectionReader, MemorySectionReader, Result,
+    SectionLimited, TableSectionReader, TagSectionReader, TypeSectionReader,
+};
+use std::convert::TryInto;
+use std::fmt;
+use std::iter;
+use std::ops::Range;
+
+pub(crate) const WASM_MODULE_VERSION: u16 = 0x1;
+
+// Note that this started at `0xa` and we're incrementing up from there. When
+// the component model is stabilized this will become 0x1. The changes here are:
+//
+// * [????-??-??] 0xa - original version
+// * [2022-01-05] 0xb - `export` introduces an alias
+// * [2022-02-06] 0xc - `export` has an optional type ascribed to it
+pub(crate) const WASM_COMPONENT_VERSION: u16 = 0xc;
+
+/// The supported encoding formats for the parser.
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+pub enum Encoding {
+    /// The encoding format is a WebAssembly module.
+    Module,
+    /// The encoding format is a WebAssembly component.
+    Component,
+}
+
+/// An incremental parser of a binary WebAssembly module or component.
+///
+/// This type is intended to be used to incrementally parse a WebAssembly module
+/// or component as bytes become available for the module. This can also be used
+/// to parse modules or components that are already entirely resident within memory.
+///
+/// This primary function for a parser is the [`Parser::parse`] function which
+/// will incrementally consume input. You can also use the [`Parser::parse_all`]
+/// function to parse a module or component that is entirely resident in memory.
+#[derive(Debug, Clone)]
+pub struct Parser {
+    state: State,
+    offset: u64,
+    max_size: u64,
+    encoding: Encoding,
+}
+
+#[derive(Debug, Clone)]
+enum State {
+    Header,
+    SectionStart,
+    FunctionBody { remaining: u32, len: u32 },
+}
+
+/// A successful return payload from [`Parser::parse`].
+///
+/// On success one of two possible values can be returned, either that more data
+/// is needed to continue parsing or a chunk of the input was parsed, indicating
+/// how much of it was parsed.
+#[derive(Debug)]
+pub enum Chunk<'a> {
+    /// This can be returned at any time and indicates that more data is needed
+    /// to proceed with parsing. Zero bytes were consumed from the input to
+    /// [`Parser::parse`]. The `usize` value here is a hint as to how many more
+    /// bytes are needed to continue parsing.
+    NeedMoreData(u64),
+
+    /// A chunk was successfully parsed.
+    Parsed {
+        /// This many bytes of the `data` input to [`Parser::parse`] were
+        /// consumed to produce `payload`.
+        consumed: usize,
+        /// The value that we actually parsed.
+        payload: Payload<'a>,
+    },
+}
+
+/// Values that can be parsed from a WebAssembly module or component.
+///
+/// This enumeration is all possible chunks of pieces that can be parsed by a
+/// [`Parser`] from a binary WebAssembly module or component. Note that for many
+/// sections the entire section is parsed all at once, whereas other functions,
+/// like the code section, are parsed incrementally. This is a distinction where some
+/// sections, like the type section, are required to be fully resident in memory
+/// (fully downloaded) before proceeding. Other sections, like the code section,
+/// can be processed in a streaming fashion where each function is extracted
+/// individually so it can possibly be shipped to another thread while you wait
+/// for more functions to get downloaded.
+///
+/// Note that payloads, when returned, do not indicate that the module or component
+/// is valid. For example when you receive a `Payload::TypeSection` the type
+/// section itself has not yet actually been parsed. The reader returned will be
+/// able to parse it, but you'll have to actually iterate the reader to do the
+/// full parse. Each payload returned is intended to be a *window* into the
+/// original `data` passed to [`Parser::parse`] which can be further processed
+/// if necessary.
+pub enum Payload<'a> {
+    /// Indicates the header of a WebAssembly module or component.
+    Version {
+        /// The version number found in the header.
+        num: u16,
+        /// The encoding format being parsed.
+        encoding: Encoding,
+        /// The range of bytes that were parsed to consume the header of the
+        /// module or component. Note that this range is relative to the start
+        /// of the byte stream.
+        range: Range<usize>,
+    },
+
+    /// A module type section was received and the provided reader can be
+    /// used to parse the contents of the type section.
+    TypeSection(TypeSectionReader<'a>),
+    /// A module import section was received and the provided reader can be
+    /// used to parse the contents of the import section.
+    ImportSection(ImportSectionReader<'a>),
+    /// A module function section was received and the provided reader can be
+    /// used to parse the contents of the function section.
+    FunctionSection(FunctionSectionReader<'a>),
+    /// A module table section was received and the provided reader can be
+    /// used to parse the contents of the table section.
+    TableSection(TableSectionReader<'a>),
+    /// A module memory section was received and the provided reader can be
+    /// used to parse the contents of the memory section.
+    MemorySection(MemorySectionReader<'a>),
+    /// A module tag section was received, and the provided reader can be
+    /// used to parse the contents of the tag section.
+    TagSection(TagSectionReader<'a>),
+    /// A module global section was received and the provided reader can be
+    /// used to parse the contents of the global section.
+    GlobalSection(GlobalSectionReader<'a>),
+    /// A module export section was received, and the provided reader can be
+    /// used to parse the contents of the export section.
+    ExportSection(ExportSectionReader<'a>),
+    /// A module start section was received.
+    StartSection {
+        /// The start function index
+        func: u32,
+        /// The range of bytes that specify the `func` field, specified in
+        /// offsets relative to the start of the byte stream.
+        range: Range<usize>,
+    },
+    /// A module element section was received and the provided reader can be
+    /// used to parse the contents of the element section.
+    ElementSection(ElementSectionReader<'a>),
+    /// A module data count section was received.
+    DataCountSection {
+        /// The number of data segments.
+        count: u32,
+        /// The range of bytes that specify the `count` field, specified in
+        /// offsets relative to the start of the byte stream.
+        range: Range<usize>,
+    },
+    /// A module data section was received and the provided reader can be
+    /// used to parse the contents of the data section.
+    DataSection(DataSectionReader<'a>),
+    /// Indicator of the start of the code section of a WebAssembly module.
+    ///
+    /// This entry is returned whenever the code section starts. The `count`
+    /// field indicates how many entries are in this code section. After
+    /// receiving this start marker you're guaranteed that the next `count`
+    /// items will be either `CodeSectionEntry` or an error will be returned.
+    ///
+    /// This, unlike other sections, is intended to be used for streaming the
+    /// contents of the code section. The code section is not required to be
+    /// fully resident in memory when we parse it. Instead a [`Parser`] is
+    /// capable of parsing piece-by-piece of a code section.
+    CodeSectionStart {
+        /// The number of functions in this section.
+        count: u32,
+        /// The range of bytes that represent this section, specified in
+        /// offsets relative to the start of the byte stream.
+        range: Range<usize>,
+        /// The size, in bytes, of the remaining contents of this section.
+        ///
+        /// This can be used in combination with [`Parser::skip_section`]
+        /// where the caller will know how many bytes to skip before feeding
+        /// bytes into `Parser` again.
+        size: u32,
+    },
+    /// An entry of the code section, a function, was parsed from a WebAssembly
+    /// module.
+    ///
+    /// This entry indicates that a function was successfully received from the
+    /// code section, and the payload here is the window into the original input
+    /// where the function resides. Note that the function itself has not been
+    /// parsed, it's only been outlined. You'll need to process the
+    /// `FunctionBody` provided to test whether it parses and/or is valid.
+    CodeSectionEntry(FunctionBody<'a>),
+
+    /// A core module section was received and the provided parser can be
+    /// used to parse the nested module.
+    ///
+    /// This variant is special in that it returns a sub-`Parser`. Upon
+    /// receiving a `ModuleSection` it is expected that the returned
+    /// `Parser` will be used instead of the parent `Parser` until the parse has
+    /// finished. You'll need to feed data into the `Parser` returned until it
+    /// returns `Payload::End`. After that you'll switch back to the parent
+    /// parser to resume parsing the rest of the current component.
+    ///
+    /// Note that binaries will not be parsed correctly if you feed the data for
+    /// a nested module into the parent [`Parser`].
+    ModuleSection {
+        /// The parser for the nested module.
+        parser: Parser,
+        /// The range of bytes that represent the nested module in the
+        /// original byte stream.
+        range: Range<usize>,
+    },
+    /// A core instance section was received and the provided parser can be
+    /// used to parse the contents of the core instance section.
+    ///
+    /// Currently this section is only parsed in a component.
+    InstanceSection(InstanceSectionReader<'a>),
+    /// A core type section was received and the provided parser can be
+    /// used to parse the contents of the core type section.
+    ///
+    /// Currently this section is only parsed in a component.
+    CoreTypeSection(CoreTypeSectionReader<'a>),
+    /// A component section from a WebAssembly component was received and the
+    /// provided parser can be used to parse the nested component.
+    ///
+    /// This variant is special in that it returns a sub-`Parser`. Upon
+    /// receiving a `ComponentSection` it is expected that the returned
+    /// `Parser` will be used instead of the parent `Parser` until the parse has
+    /// finished. You'll need to feed data into the `Parser` returned until it
+    /// returns `Payload::End`. After that you'll switch back to the parent
+    /// parser to resume parsing the rest of the current component.
+    ///
+    /// Note that binaries will not be parsed correctly if you feed the data for
+    /// a nested component into the parent [`Parser`].
+    ComponentSection {
+        /// The parser for the nested component.
+        parser: Parser,
+        /// The range of bytes that represent the nested component in the
+        /// original byte stream.
+        range: Range<usize>,
+    },
+    /// A component instance section was received and the provided reader can be
+    /// used to parse the contents of the component instance section.
+    ComponentInstanceSection(ComponentInstanceSectionReader<'a>),
+    /// A component alias section was received and the provided reader can be
+    /// used to parse the contents of the component alias section.
+    ComponentAliasSection(SectionLimited<'a, crate::ComponentAlias<'a>>),
+    /// A component type section was received and the provided reader can be
+    /// used to parse the contents of the component type section.
+    ComponentTypeSection(ComponentTypeSectionReader<'a>),
+    /// A component canonical section was received and the provided reader can be
+    /// used to parse the contents of the component canonical section.
+    ComponentCanonicalSection(ComponentCanonicalSectionReader<'a>),
+    /// A component start section was received.
+    ComponentStartSection {
+        /// The start function description.
+        start: ComponentStartFunction,
+        /// The range of bytes that specify the `start` field.
+        range: Range<usize>,
+    },
+    /// A component import section was received and the provided reader can be
+    /// used to parse the contents of the component import section.
+    ComponentImportSection(ComponentImportSectionReader<'a>),
+    /// A component export section was received, and the provided reader can be
+    /// used to parse the contents of the component export section.
+    ComponentExportSection(ComponentExportSectionReader<'a>),
+
+    /// A module or component custom section was received.
+    CustomSection(CustomSectionReader<'a>),
+
+    /// An unknown section was found.
+    ///
+    /// This variant is returned for all unknown sections encountered. This
+    /// likely wants to be interpreted as an error by consumers of the parser,
+    /// but this can also be used to parse sections currently unsupported by
+    /// the parser.
+    UnknownSection {
+        /// The 8-bit identifier for this section.
+        id: u8,
+        /// The contents of this section.
+        contents: &'a [u8],
+        /// The range of bytes, relative to the start of the original data
+        /// stream, that the contents of this section reside in.
+        range: Range<usize>,
+    },
+
+    /// The end of the WebAssembly module or component was reached.
+    ///
+    /// The value is the offset in the input byte stream where the end
+    /// was reached.
+    End(usize),
+}
+
+const CUSTOM_SECTION: u8 = 0;
+const TYPE_SECTION: u8 = 1;
+const IMPORT_SECTION: u8 = 2;
+const FUNCTION_SECTION: u8 = 3;
+const TABLE_SECTION: u8 = 4;
+const MEMORY_SECTION: u8 = 5;
+const GLOBAL_SECTION: u8 = 6;
+const EXPORT_SECTION: u8 = 7;
+const START_SECTION: u8 = 8;
+const ELEMENT_SECTION: u8 = 9;
+const CODE_SECTION: u8 = 10;
+const DATA_SECTION: u8 = 11;
+const DATA_COUNT_SECTION: u8 = 12;
+const TAG_SECTION: u8 = 13;
+
+const COMPONENT_MODULE_SECTION: u8 = 1;
+const COMPONENT_CORE_INSTANCE_SECTION: u8 = 2;
+const COMPONENT_CORE_TYPE_SECTION: u8 = 3;
+const COMPONENT_SECTION: u8 = 4;
+const COMPONENT_INSTANCE_SECTION: u8 = 5;
+const COMPONENT_ALIAS_SECTION: u8 = 6;
+const COMPONENT_TYPE_SECTION: u8 = 7;
+const COMPONENT_CANONICAL_SECTION: u8 = 8;
+const COMPONENT_START_SECTION: u8 = 9;
+const COMPONENT_IMPORT_SECTION: u8 = 10;
+const COMPONENT_EXPORT_SECTION: u8 = 11;
+
+impl Parser {
+    /// Creates a new parser.
+    ///
+    /// Reports errors and ranges relative to `offset` provided, where `offset`
+    /// is some logical offset within the input stream that we're parsing.
+    pub fn new(offset: u64) -> Parser {
+        Parser {
+            state: State::Header,
+            offset,
+            max_size: u64::MAX,
+            // Assume the encoding is a module until we know otherwise
+            encoding: Encoding::Module,
+        }
+    }
+
+    /// Attempts to parse a chunk of data.
+    ///
+    /// This method will attempt to parse the next incremental portion of a
+    /// WebAssembly binary. Data available for the module or component is
+    /// provided as `data`, and the data can be incomplete if more data has yet
+    /// to arrive. The `eof` flag indicates whether more data will ever be received.
+    ///
+    /// There are two ways parsing can succeed with this method:
+    ///
+    /// * `Chunk::NeedMoreData` - this indicates that there is not enough bytes
+    ///   in `data` to parse a payload. The caller needs to wait for more data to
+    ///   be available in this situation before calling this method again. It is
+    ///   guaranteed that this is only returned if `eof` is `false`.
+    ///
+    /// * `Chunk::Parsed` - this indicates that a chunk of the input was
+    ///   successfully parsed. The payload is available in this variant of what
+    ///   was parsed, and this also indicates how many bytes of `data` was
+    ///   consumed. It's expected that the caller will not provide these bytes
+    ///   back to the [`Parser`] again.
+    ///
+    /// Note that all `Chunk` return values are connected, with a lifetime, to
+    /// the input buffer. Each parsed chunk borrows the input buffer and is a
+    /// view into it for successfully parsed chunks.
+    ///
+    /// It is expected that you'll call this method until `Payload::End` is
+    /// reached, at which point you're guaranteed that the parse has completed.
+    /// Note that complete parsing, for the top-level module or component,
+    /// implies that `data` is empty and `eof` is `true`.
+    ///
+    /// # Errors
+    ///
+    /// Parse errors are returned as an `Err`. Errors can happen when the
+    /// structure of the data is unexpected or if sections are too large for
+    /// example. Note that errors are not returned for malformed *contents* of
+    /// sections here. Sections are generally not individually parsed and each
+    /// returned [`Payload`] needs to be iterated over further to detect all
+    /// errors.
+    ///
+    /// # Examples
+    ///
+    /// An example of reading a wasm file from a stream (`std::io::Read`) and
+    /// incrementally parsing it.
+    ///
+    /// ```
+    /// use std::io::Read;
+    /// use anyhow::Result;
+    /// use wasmparser::{Parser, Chunk, Payload::*};
+    ///
+    /// fn parse(mut reader: impl Read) -> Result<()> {
+    ///     let mut buf = Vec::new();
+    ///     let mut parser = Parser::new(0);
+    ///     let mut eof = false;
+    ///     let mut stack = Vec::new();
+    ///
+    ///     loop {
+    ///         let (payload, consumed) = match parser.parse(&buf, eof)? {
+    ///             Chunk::NeedMoreData(hint) => {
+    ///                 assert!(!eof); // otherwise an error would be returned
+    ///
+    ///                 // Use the hint to preallocate more space, then read
+    ///                 // some more data into our buffer.
+    ///                 //
+    ///                 // Note that the buffer management here is not ideal,
+    ///                 // but it's compact enough to fit in an example!
+    ///                 let len = buf.len();
+    ///                 buf.extend((0..hint).map(|_| 0u8));
+    ///                 let n = reader.read(&mut buf[len..])?;
+    ///                 buf.truncate(len + n);
+    ///                 eof = n == 0;
+    ///                 continue;
+    ///             }
+    ///
+    ///             Chunk::Parsed { consumed, payload } => (payload, consumed),
+    ///         };
+    ///
+    ///         match payload {
+    ///             // Sections for WebAssembly modules
+    ///             Version { .. } => { /* ... */ }
+    ///             TypeSection(_) => { /* ... */ }
+    ///             ImportSection(_) => { /* ... */ }
+    ///             FunctionSection(_) => { /* ... */ }
+    ///             TableSection(_) => { /* ... */ }
+    ///             MemorySection(_) => { /* ... */ }
+    ///             TagSection(_) => { /* ... */ }
+    ///             GlobalSection(_) => { /* ... */ }
+    ///             ExportSection(_) => { /* ... */ }
+    ///             StartSection { .. } => { /* ... */ }
+    ///             ElementSection(_) => { /* ... */ }
+    ///             DataCountSection { .. } => { /* ... */ }
+    ///             DataSection(_) => { /* ... */ }
+    ///
+    ///             // Here we know how many functions we'll be receiving as
+    ///             // `CodeSectionEntry`, so we can prepare for that, and
+    ///             // afterwards we can parse and handle each function
+    ///             // individually.
+    ///             CodeSectionStart { .. } => { /* ... */ }
+    ///             CodeSectionEntry(body) => {
+    ///                 // here we can iterate over `body` to parse the function
+    ///                 // and its locals
+    ///             }
+    ///
+    ///             // Sections for WebAssembly components
+    ///             ModuleSection { .. } => { /* ... */ }
+    ///             InstanceSection(_) => { /* ... */ }
+    ///             CoreTypeSection(_) => { /* ... */ }
+    ///             ComponentSection { .. } => { /* ... */ }
+    ///             ComponentInstanceSection(_) => { /* ... */ }
+    ///             ComponentAliasSection(_) => { /* ... */ }
+    ///             ComponentTypeSection(_) => { /* ... */ }
+    ///             ComponentCanonicalSection(_) => { /* ... */ }
+    ///             ComponentStartSection { .. } => { /* ... */ }
+    ///             ComponentImportSection(_) => { /* ... */ }
+    ///             ComponentExportSection(_) => { /* ... */ }
+    ///
+    ///             CustomSection(_) => { /* ... */ }
+    ///
+    ///             // most likely you'd return an error here
+    ///             UnknownSection { id, .. } => { /* ... */ }
+    ///
+    ///             // Once we've reached the end of a parser we either resume
+    ///             // at the parent parser or we break out of the loop because
+    ///             // we're done.
+    ///             End(_) => {
+    ///                 if let Some(parent_parser) = stack.pop() {
+    ///                     parser = parent_parser;
+    ///                 } else {
+    ///                     break;
+    ///                 }
+    ///             }
+    ///         }
+    ///
+    ///         // once we're done processing the payload we can forget the
+    ///         // original.
+    ///         buf.drain(..consumed);
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    ///
+    /// # parse(&b"\0asm\x01\0\0\0"[..]).unwrap();
+    /// ```
+    pub fn parse<'a>(&mut self, data: &'a [u8], eof: bool) -> Result<Chunk<'a>> {
+        let (data, eof) = if usize_to_u64(data.len()) > self.max_size {
+            (&data[..(self.max_size as usize)], true)
+        } else {
+            (data, eof)
+        };
+        // TODO: thread through `offset: u64` to `BinaryReader`, remove
+        // the cast here.
+        let mut reader = BinaryReader::new_with_offset(data, self.offset as usize);
+        match self.parse_reader(&mut reader, eof) {
+            Ok(payload) => {
+                // Be sure to update our offset with how far we got in the
+                // reader
+                self.offset += usize_to_u64(reader.position);
+                self.max_size -= usize_to_u64(reader.position);
+                Ok(Chunk::Parsed {
+                    consumed: reader.position,
+                    payload,
+                })
+            }
+            Err(e) => {
+                // If we're at EOF then there's no way we can recover from any
+                // error, so continue to propagate it.
+                if eof {
+                    return Err(e);
+                }
+
+                // If our error doesn't look like it can be resolved with more
+                // data being pulled down, then propagate it, otherwise switch
+                // the error to "feed me please"
+                match e.inner.needed_hint {
+                    Some(hint) => Ok(Chunk::NeedMoreData(usize_to_u64(hint))),
+                    None => Err(e),
+                }
+            }
+        }
+    }
+
+    fn parse_reader<'a>(
+        &mut self,
+        reader: &mut BinaryReader<'a>,
+        eof: bool,
+    ) -> Result<Payload<'a>> {
+        use Payload::*;
+
+        match self.state {
+            State::Header => {
+                const KIND_MODULE: u16 = 0x00;
+                const KIND_COMPONENT: u16 = 0x01;
+
+                let start = reader.original_position();
+                let header_version = reader.read_header_version()?;
+                self.encoding = match (header_version >> 16) as u16 {
+                    KIND_MODULE => Encoding::Module,
+                    KIND_COMPONENT => Encoding::Component,
+                    _ => bail!(start + 4, "unknown binary version: {header_version:#10x}"),
+                };
+                let num = header_version as u16;
+                self.state = State::SectionStart;
+                Ok(Version {
+                    num,
+                    encoding: self.encoding,
+                    range: start..reader.original_position(),
+                })
+            }
+            State::SectionStart => {
+                // If we're at eof and there are no bytes in our buffer, then
+                // that means we reached the end of the data since it's
+                // just a bunch of sections concatenated after the header.
+                if eof && reader.bytes_remaining() == 0 {
+                    return Ok(Payload::End(reader.original_position()));
+                }
+
+                let id_pos = reader.position;
+                let id = reader.read_u8()?;
+                if id & 0x80 != 0 {
+                    return Err(BinaryReaderError::new("malformed section id", id_pos));
+                }
+                let len_pos = reader.original_position();
+                let mut len = reader.read_var_u32()?;
+
+                // Test to make sure that this section actually fits within
+                // `Parser::max_size`. This doesn't matter for top-level modules
+                // but it is required for nested modules/components to correctly ensure
+                // that all sections live entirely within their section of the
+                // file.
+                let section_overflow = self
+                    .max_size
+                    .checked_sub(usize_to_u64(reader.position))
+                    .and_then(|s| s.checked_sub(len.into()))
+                    .is_none();
+                if section_overflow {
+                    return Err(BinaryReaderError::new("section too large", len_pos));
+                }
+
+                match (self.encoding, id) {
+                    // Sections for both modules and components.
+                    (_, 0) => section(reader, len, CustomSectionReader::new, CustomSection),
+
+                    // Module sections
+                    (Encoding::Module, TYPE_SECTION) => {
+                        section(reader, len, TypeSectionReader::new, TypeSection)
+                    }
+                    (Encoding::Module, IMPORT_SECTION) => {
+                        section(reader, len, ImportSectionReader::new, ImportSection)
+                    }
+                    (Encoding::Module, FUNCTION_SECTION) => {
+                        section(reader, len, FunctionSectionReader::new, FunctionSection)
+                    }
+                    (Encoding::Module, TABLE_SECTION) => {
+                        section(reader, len, TableSectionReader::new, TableSection)
+                    }
+                    (Encoding::Module, MEMORY_SECTION) => {
+                        section(reader, len, MemorySectionReader::new, MemorySection)
+                    }
+                    (Encoding::Module, GLOBAL_SECTION) => {
+                        section(reader, len, GlobalSectionReader::new, GlobalSection)
+                    }
+                    (Encoding::Module, EXPORT_SECTION) => {
+                        section(reader, len, ExportSectionReader::new, ExportSection)
+                    }
+                    (Encoding::Module, START_SECTION) => {
+                        let (func, range) = single_item(reader, len, "start")?;
+                        Ok(StartSection { func, range })
+                    }
+                    (Encoding::Module, ELEMENT_SECTION) => {
+                        section(reader, len, ElementSectionReader::new, ElementSection)
+                    }
+                    (Encoding::Module, CODE_SECTION) => {
+                        let start = reader.original_position();
+                        let count = delimited(reader, &mut len, |r| r.read_var_u32())?;
+                        let range = start..reader.original_position() + len as usize;
+                        self.state = State::FunctionBody {
+                            remaining: count,
+                            len,
+                        };
+                        Ok(CodeSectionStart {
+                            count,
+                            range,
+                            size: len,
+                        })
+                    }
+                    (Encoding::Module, DATA_SECTION) => {
+                        section(reader, len, DataSectionReader::new, DataSection)
+                    }
+                    (Encoding::Module, DATA_COUNT_SECTION) => {
+                        let (count, range) = single_item(reader, len, "data count")?;
+                        Ok(DataCountSection { count, range })
+                    }
+                    (Encoding::Module, TAG_SECTION) => {
+                        section(reader, len, TagSectionReader::new, TagSection)
+                    }
+
+                    // Component sections
+                    (Encoding::Component, COMPONENT_MODULE_SECTION)
+                    | (Encoding::Component, COMPONENT_SECTION) => {
+                        if len as usize > MAX_WASM_MODULE_SIZE {
+                            bail!(
+                                len_pos,
+                                "{} section is too large",
+                                if id == 1 { "module" } else { "component " }
+                            );
+                        }
+
+                        let range =
+                            reader.original_position()..reader.original_position() + len as usize;
+                        self.max_size -= u64::from(len);
+                        self.offset += u64::from(len);
+                        let mut parser = Parser::new(usize_to_u64(reader.original_position()));
+                        parser.max_size = len.into();
+
+                        Ok(match id {
+                            1 => ModuleSection { parser, range },
+                            4 => ComponentSection { parser, range },
+                            _ => unreachable!(),
+                        })
+                    }
+                    (Encoding::Component, COMPONENT_CORE_INSTANCE_SECTION) => {
+                        section(reader, len, InstanceSectionReader::new, InstanceSection)
+                    }
+                    (Encoding::Component, COMPONENT_CORE_TYPE_SECTION) => {
+                        section(reader, len, CoreTypeSectionReader::new, CoreTypeSection)
+                    }
+                    (Encoding::Component, COMPONENT_INSTANCE_SECTION) => section(
+                        reader,
+                        len,
+                        ComponentInstanceSectionReader::new,
+                        ComponentInstanceSection,
+                    ),
+                    (Encoding::Component, COMPONENT_ALIAS_SECTION) => {
+                        section(reader, len, SectionLimited::new, ComponentAliasSection)
+                    }
+                    (Encoding::Component, COMPONENT_TYPE_SECTION) => section(
+                        reader,
+                        len,
+                        ComponentTypeSectionReader::new,
+                        ComponentTypeSection,
+                    ),
+                    (Encoding::Component, COMPONENT_CANONICAL_SECTION) => section(
+                        reader,
+                        len,
+                        ComponentCanonicalSectionReader::new,
+                        ComponentCanonicalSection,
+                    ),
+                    (Encoding::Component, COMPONENT_START_SECTION) => {
+                        let (start, range) = single_item(reader, len, "component start")?;
+                        Ok(ComponentStartSection { start, range })
+                    }
+                    (Encoding::Component, COMPONENT_IMPORT_SECTION) => section(
+                        reader,
+                        len,
+                        ComponentImportSectionReader::new,
+                        ComponentImportSection,
+                    ),
+                    (Encoding::Component, COMPONENT_EXPORT_SECTION) => section(
+                        reader,
+                        len,
+                        ComponentExportSectionReader::new,
+                        ComponentExportSection,
+                    ),
+                    (_, id) => {
+                        let offset = reader.original_position();
+                        let contents = reader.read_bytes(len as usize)?;
+                        let range = offset..offset + len as usize;
+                        Ok(UnknownSection {
+                            id,
+                            contents,
+                            range,
+                        })
+                    }
+                }
+            }
+
+            // Once we hit 0 remaining incrementally parsed items, with 0
+            // remaining bytes in each section, we're done and can switch back
+            // to parsing sections.
+            State::FunctionBody {
+                remaining: 0,
+                len: 0,
+            } => {
+                self.state = State::SectionStart;
+                self.parse_reader(reader, eof)
+            }
+
+            // ... otherwise trailing bytes with no remaining entries in these
+            // sections indicates an error.
+            State::FunctionBody { remaining: 0, len } => {
+                debug_assert!(len > 0);
+                let offset = reader.original_position();
+                Err(BinaryReaderError::new(
+                    "trailing bytes at end of section",
+                    offset,
+                ))
+            }
+
+            // Functions are relatively easy to parse when we know there's at
+            // least one remaining and at least one byte available to read
+            // things.
+            //
+            // We use the remaining length try to read a u32 size of the
+            // function, and using that size we require the entire function be
+            // resident in memory. This means that we're reading whole chunks of
+            // functions at a time.
+            //
+            // Limiting via `Parser::max_size` (nested parsing) happens above in
+            // `fn parse`, and limiting by our section size happens via
+            // `delimited`. Actual parsing of the function body is delegated to
+            // the caller to iterate over the `FunctionBody` structure.
+            State::FunctionBody { remaining, mut len } => {
+                let body = delimited(reader, &mut len, |r| {
+                    let size = r.read_var_u32()?;
+                    let offset = r.original_position();
+                    Ok(FunctionBody::new(offset, r.read_bytes(size as usize)?))
+                })?;
+                self.state = State::FunctionBody {
+                    remaining: remaining - 1,
+                    len,
+                };
+                Ok(CodeSectionEntry(body))
+            }
+        }
+    }
+
+    /// Convenience function that can be used to parse a module or component
+    /// that is entirely resident in memory.
+    ///
+    /// This function will parse the `data` provided as a WebAssembly module
+    /// or component.
+    ///
+    /// Note that when this function yields sections that provide parsers,
+    /// no further action is required for those sections as payloads from
+    /// those parsers will be automatically returned.
+    pub fn parse_all(self, mut data: &[u8]) -> impl Iterator<Item = Result<Payload>> {
+        let mut stack = Vec::new();
+        let mut cur = self;
+        let mut done = false;
+        iter::from_fn(move || {
+            if done {
+                return None;
+            }
+            let payload = match cur.parse(data, true) {
+                // Propagate all errors
+                Err(e) => {
+                    done = true;
+                    return Some(Err(e));
+                }
+
+                // This isn't possible because `eof` is always true.
+                Ok(Chunk::NeedMoreData(_)) => unreachable!(),
+
+                Ok(Chunk::Parsed { payload, consumed }) => {
+                    data = &data[consumed..];
+                    payload
+                }
+            };
+
+            match &payload {
+                Payload::ModuleSection { parser, .. }
+                | Payload::ComponentSection { parser, .. } => {
+                    stack.push(cur.clone());
+                    cur = parser.clone();
+                }
+                Payload::End(_) => match stack.pop() {
+                    Some(p) => cur = p,
+                    None => done = true,
+                },
+
+                _ => {}
+            }
+
+            Some(Ok(payload))
+        })
+    }
+
+    /// Skip parsing the code section entirely.
+    ///
+    /// This function can be used to indicate, after receiving
+    /// `CodeSectionStart`, that the section will not be parsed.
+    ///
+    /// The caller will be responsible for skipping `size` bytes (found in the
+    /// `CodeSectionStart` payload). Bytes should only be fed into `parse`
+    /// after the `size` bytes have been skipped.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the parser is not in a state where it's
+    /// parsing the code section.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use wasmparser::{Result, Parser, Chunk, Payload::*};
+    /// use std::ops::Range;
+    ///
+    /// fn objdump_headers(mut wasm: &[u8]) -> Result<()> {
+    ///     let mut parser = Parser::new(0);
+    ///     loop {
+    ///         let payload = match parser.parse(wasm, true)? {
+    ///             Chunk::Parsed { consumed, payload } => {
+    ///                 wasm = &wasm[consumed..];
+    ///                 payload
+    ///             }
+    ///             // this state isn't possible with `eof = true`
+    ///             Chunk::NeedMoreData(_) => unreachable!(),
+    ///         };
+    ///         match payload {
+    ///             TypeSection(s) => print_range("type section", &s.range()),
+    ///             ImportSection(s) => print_range("import section", &s.range()),
+    ///             // .. other sections
+    ///
+    ///             // Print the range of the code section we see, but don't
+    ///             // actually iterate over each individual function.
+    ///             CodeSectionStart { range, size, .. } => {
+    ///                 print_range("code section", &range);
+    ///                 parser.skip_section();
+    ///                 wasm = &wasm[size as usize..];
+    ///             }
+    ///             End(_) => break,
+    ///             _ => {}
+    ///         }
+    ///     }
+    ///     Ok(())
+    /// }
+    ///
+    /// fn print_range(section: &str, range: &Range<usize>) {
+    ///     println!("{:>40}: {:#010x} - {:#010x}", section, range.start, range.end);
+    /// }
+    /// ```
+    pub fn skip_section(&mut self) {
+        let skip = match self.state {
+            State::FunctionBody { remaining: _, len } => len,
+            _ => panic!("wrong state to call `skip_section`"),
+        };
+        self.offset += u64::from(skip);
+        self.max_size -= u64::from(skip);
+        self.state = State::SectionStart;
+    }
+}
+
+fn usize_to_u64(a: usize) -> u64 {
+    a.try_into().unwrap()
+}
+
+/// Parses an entire section resident in memory into a `Payload`.
+///
+/// Requires that `len` bytes are resident in `reader` and uses `ctor`/`variant`
+/// to construct the section to return.
+fn section<'a, T>(
+    reader: &mut BinaryReader<'a>,
+    len: u32,
+    ctor: fn(&'a [u8], usize) -> Result<T>,
+    variant: fn(T) -> Payload<'a>,
+) -> Result<Payload<'a>> {
+    let offset = reader.original_position();
+    let payload = reader.read_bytes(len as usize)?;
+    // clear the hint for "need this many more bytes" here because we already
+    // read all the bytes, so it's not possible to read more bytes if this
+    // fails.
+    let reader = ctor(payload, offset).map_err(clear_hint)?;
+    Ok(variant(reader))
+}
+
+/// Reads a section that is represented by a single uleb-encoded `u32`.
+fn single_item<'a, T>(
+    reader: &mut BinaryReader<'a>,
+    len: u32,
+    desc: &str,
+) -> Result<(T, Range<usize>)>
+where
+    T: FromReader<'a>,
+{
+    let range = reader.original_position()..reader.original_position() + len as usize;
+    let mut content = BinaryReader::new_with_offset(reader.read_bytes(len as usize)?, range.start);
+    // We can't recover from "unexpected eof" here because our entire section is
+    // already resident in memory, so clear the hint for how many more bytes are
+    // expected.
+    let ret = content.read().map_err(clear_hint)?;
+    if !content.eof() {
+        bail!(
+            content.original_position(),
+            "unexpected content in the {desc} section",
+        );
+    }
+    Ok((ret, range))
+}
+
+/// Attempts to parse using `f`.
+///
+/// This will update `*len` with the number of bytes consumed, and it will cause
+/// a failure to be returned instead of the number of bytes consumed exceeds
+/// what `*len` currently is.
+fn delimited<'a, T>(
+    reader: &mut BinaryReader<'a>,
+    len: &mut u32,
+    f: impl FnOnce(&mut BinaryReader<'a>) -> Result<T>,
+) -> Result<T> {
+    let start = reader.position;
+    let ret = f(reader)?;
+    *len = match (reader.position - start)
+        .try_into()
+        .ok()
+        .and_then(|i| len.checked_sub(i))
+    {
+        Some(i) => i,
+        None => return Err(BinaryReaderError::new("unexpected end-of-file", start)),
+    };
+    Ok(ret)
+}
+
+impl Default for Parser {
+    fn default() -> Parser {
+        Parser::new(0)
+    }
+}
+
+impl Payload<'_> {
+    /// If this `Payload` represents a section in the original wasm module then
+    /// the section's id and range within the original wasm binary are returned.
+    ///
+    /// Not all payloads refer to entire sections, such as the `Version` and
+    /// `CodeSectionEntry` variants. These variants will return `None` from this
+    /// function.
+    ///
+    /// Otherwise this function will return `Some` where the first element is
+    /// the byte identifier for the section and the second element is the range
+    /// of the contents of the section within the original wasm binary.
+    ///
+    /// The purpose of this method is to enable tools to easily iterate over
+    /// entire sections if necessary and handle sections uniformly, for example
+    /// dropping custom sections while preserving all other sections.
+    pub fn as_section(&self) -> Option<(u8, Range<usize>)> {
+        use Payload::*;
+
+        match self {
+            Version { .. } => None,
+            TypeSection(s) => Some((TYPE_SECTION, s.range())),
+            ImportSection(s) => Some((IMPORT_SECTION, s.range())),
+            FunctionSection(s) => Some((FUNCTION_SECTION, s.range())),
+            TableSection(s) => Some((TABLE_SECTION, s.range())),
+            MemorySection(s) => Some((MEMORY_SECTION, s.range())),
+            TagSection(s) => Some((TAG_SECTION, s.range())),
+            GlobalSection(s) => Some((GLOBAL_SECTION, s.range())),
+            ExportSection(s) => Some((EXPORT_SECTION, s.range())),
+            ElementSection(s) => Some((ELEMENT_SECTION, s.range())),
+            DataSection(s) => Some((DATA_SECTION, s.range())),
+            StartSection { range, .. } => Some((START_SECTION, range.clone())),
+            DataCountSection { range, .. } => Some((DATA_COUNT_SECTION, range.clone())),
+            CodeSectionStart { range, .. } => Some((CODE_SECTION, range.clone())),
+            CodeSectionEntry(_) => None,
+
+            ModuleSection { range, .. } => Some((COMPONENT_MODULE_SECTION, range.clone())),
+            InstanceSection(s) => Some((COMPONENT_CORE_INSTANCE_SECTION, s.range())),
+            CoreTypeSection(s) => Some((COMPONENT_CORE_TYPE_SECTION, s.range())),
+            ComponentSection { range, .. } => Some((COMPONENT_SECTION, range.clone())),
+            ComponentInstanceSection(s) => Some((COMPONENT_INSTANCE_SECTION, s.range())),
+            ComponentAliasSection(s) => Some((COMPONENT_ALIAS_SECTION, s.range())),
+            ComponentTypeSection(s) => Some((COMPONENT_TYPE_SECTION, s.range())),
+            ComponentCanonicalSection(s) => Some((COMPONENT_CANONICAL_SECTION, s.range())),
+            ComponentStartSection { range, .. } => Some((COMPONENT_START_SECTION, range.clone())),
+            ComponentImportSection(s) => Some((COMPONENT_IMPORT_SECTION, s.range())),
+            ComponentExportSection(s) => Some((COMPONENT_EXPORT_SECTION, s.range())),
+
+            CustomSection(c) => Some((CUSTOM_SECTION, c.range())),
+
+            UnknownSection { id, range, .. } => Some((*id, range.clone())),
+
+            End(_) => None,
+        }
+    }
+}
+
+impl fmt::Debug for Payload<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use Payload::*;
+        match self {
+            Version {
+                num,
+                encoding,
+                range,
+            } => f
+                .debug_struct("Version")
+                .field("num", num)
+                .field("encoding", encoding)
+                .field("range", range)
+                .finish(),
+
+            // Module sections
+            TypeSection(_) => f.debug_tuple("TypeSection").field(&"...").finish(),
+            ImportSection(_) => f.debug_tuple("ImportSection").field(&"...").finish(),
+            FunctionSection(_) => f.debug_tuple("FunctionSection").field(&"...").finish(),
+            TableSection(_) => f.debug_tuple("TableSection").field(&"...").finish(),
+            MemorySection(_) => f.debug_tuple("MemorySection").field(&"...").finish(),
+            TagSection(_) => f.debug_tuple("TagSection").field(&"...").finish(),
+            GlobalSection(_) => f.debug_tuple("GlobalSection").field(&"...").finish(),
+            ExportSection(_) => f.debug_tuple("ExportSection").field(&"...").finish(),
+            ElementSection(_) => f.debug_tuple("ElementSection").field(&"...").finish(),
+            DataSection(_) => f.debug_tuple("DataSection").field(&"...").finish(),
+            StartSection { func, range } => f
+                .debug_struct("StartSection")
+                .field("func", func)
+                .field("range", range)
+                .finish(),
+            DataCountSection { count, range } => f
+                .debug_struct("DataCountSection")
+                .field("count", count)
+                .field("range", range)
+                .finish(),
+            CodeSectionStart { count, range, size } => f
+                .debug_struct("CodeSectionStart")
+                .field("count", count)
+                .field("range", range)
+                .field("size", size)
+                .finish(),
+            CodeSectionEntry(_) => f.debug_tuple("CodeSectionEntry").field(&"...").finish(),
+
+            // Component sections
+            ModuleSection { parser: _, range } => f
+                .debug_struct("ModuleSection")
+                .field("range", range)
+                .finish(),
+            InstanceSection(_) => f.debug_tuple("InstanceSection").field(&"...").finish(),
+            CoreTypeSection(_) => f.debug_tuple("CoreTypeSection").field(&"...").finish(),
+            ComponentSection { parser: _, range } => f
+                .debug_struct("ComponentSection")
+                .field("range", range)
+                .finish(),
+            ComponentInstanceSection(_) => f
+                .debug_tuple("ComponentInstanceSection")
+                .field(&"...")
+                .finish(),
+            ComponentAliasSection(_) => f
+                .debug_tuple("ComponentAliasSection")
+                .field(&"...")
+                .finish(),
+            ComponentTypeSection(_) => f.debug_tuple("ComponentTypeSection").field(&"...").finish(),
+            ComponentCanonicalSection(_) => f
+                .debug_tuple("ComponentCanonicalSection")
+                .field(&"...")
+                .finish(),
+            ComponentStartSection { .. } => f
+                .debug_tuple("ComponentStartSection")
+                .field(&"...")
+                .finish(),
+            ComponentImportSection(_) => f
+                .debug_tuple("ComponentImportSection")
+                .field(&"...")
+                .finish(),
+            ComponentExportSection(_) => f
+                .debug_tuple("ComponentExportSection")
+                .field(&"...")
+                .finish(),
+
+            CustomSection(c) => f.debug_tuple("CustomSection").field(c).finish(),
+
+            UnknownSection { id, range, .. } => f
+                .debug_struct("UnknownSection")
+                .field("id", id)
+                .field("range", range)
+                .finish(),
+
+            End(offset) => f.debug_tuple("End").field(offset).finish(),
+        }
+    }
+}
+
+fn clear_hint(mut err: BinaryReaderError) -> BinaryReaderError {
+    err.inner.needed_hint = None;
+    err
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    macro_rules! assert_matches {
+        ($a:expr, $b:pat $(,)?) => {
+            match $a {
+                $b => {}
+                a => panic!("`{:?}` doesn't match `{}`", a, stringify!($b)),
+            }
+        };
+    }
+
+    #[test]
+    fn header() {
+        assert!(Parser::default().parse(&[], true).is_err());
+        assert_matches!(
+            Parser::default().parse(&[], false),
+            Ok(Chunk::NeedMoreData(4)),
+        );
+        assert_matches!(
+            Parser::default().parse(b"\0", false),
+            Ok(Chunk::NeedMoreData(3)),
+        );
+        assert_matches!(
+            Parser::default().parse(b"\0asm", false),
+            Ok(Chunk::NeedMoreData(4)),
+        );
+        assert_matches!(
+            Parser::default().parse(b"\0asm\x01\0\0\0", false),
+            Ok(Chunk::Parsed {
+                consumed: 8,
+                payload: Payload::Version { num: 1, .. },
+            }),
+        );
+    }
+
+    #[test]
+    fn header_iter() {
+        for _ in Parser::default().parse_all(&[]) {}
+        for _ in Parser::default().parse_all(b"\0") {}
+        for _ in Parser::default().parse_all(b"\0asm") {}
+        for _ in Parser::default().parse_all(b"\0asm\x01\x01\x01\x01") {}
+    }
+
+    fn parser_after_header() -> Parser {
+        let mut p = Parser::default();
+        assert_matches!(
+            p.parse(b"\0asm\x01\0\0\0", false),
+            Ok(Chunk::Parsed {
+                consumed: 8,
+                payload: Payload::Version {
+                    num: WASM_MODULE_VERSION,
+                    encoding: Encoding::Module,
+                    ..
+                },
+            }),
+        );
+        p
+    }
+
+    fn parser_after_component_header() -> Parser {
+        let mut p = Parser::default();
+        assert_matches!(
+            p.parse(b"\0asm\x0c\0\x01\0", false),
+            Ok(Chunk::Parsed {
+                consumed: 8,
+                payload: Payload::Version {
+                    num: WASM_COMPONENT_VERSION,
+                    encoding: Encoding::Component,
+                    ..
+                },
+            }),
+        );
+        p
+    }
+
+    #[test]
+    fn start_section() {
+        assert_matches!(
+            parser_after_header().parse(&[], false),
+            Ok(Chunk::NeedMoreData(1)),
+        );
+        assert!(parser_after_header().parse(&[8], true).is_err());
+        assert!(parser_after_header().parse(&[8, 1], true).is_err());
+        assert!(parser_after_header().parse(&[8, 2], true).is_err());
+        assert_matches!(
+            parser_after_header().parse(&[8], false),
+            Ok(Chunk::NeedMoreData(1)),
+        );
+        assert_matches!(
+            parser_after_header().parse(&[8, 1], false),
+            Ok(Chunk::NeedMoreData(1)),
+        );
+        assert_matches!(
+            parser_after_header().parse(&[8, 2], false),
+            Ok(Chunk::NeedMoreData(2)),
+        );
+        assert_matches!(
+            parser_after_header().parse(&[8, 1, 1], false),
+            Ok(Chunk::Parsed {
+                consumed: 3,
+                payload: Payload::StartSection { func: 1, .. },
+            }),
+        );
+        assert!(parser_after_header().parse(&[8, 2, 1, 1], false).is_err());
+        assert!(parser_after_header().parse(&[8, 0], false).is_err());
+    }
+
+    #[test]
+    fn end_works() {
+        assert_matches!(
+            parser_after_header().parse(&[], true),
+            Ok(Chunk::Parsed {
+                consumed: 0,
+                payload: Payload::End(8),
+            }),
+        );
+    }
+
+    #[test]
+    fn type_section() {
+        assert!(parser_after_header().parse(&[1], true).is_err());
+        assert!(parser_after_header().parse(&[1, 0], false).is_err());
+        assert!(parser_after_header().parse(&[8, 2], true).is_err());
+        assert_matches!(
+            parser_after_header().parse(&[1], false),
+            Ok(Chunk::NeedMoreData(1)),
+        );
+        assert_matches!(
+            parser_after_header().parse(&[1, 1], false),
+            Ok(Chunk::NeedMoreData(1)),
+        );
+        assert_matches!(
+            parser_after_header().parse(&[1, 1, 1], false),
+            Ok(Chunk::Parsed {
+                consumed: 3,
+                payload: Payload::TypeSection(_),
+            }),
+        );
+        assert_matches!(
+            parser_after_header().parse(&[1, 1, 1, 2, 3, 4], false),
+            Ok(Chunk::Parsed {
+                consumed: 3,
+                payload: Payload::TypeSection(_),
+            }),
+        );
+    }
+
+    #[test]
+    fn custom_section() {
+        assert!(parser_after_header().parse(&[0], true).is_err());
+        assert!(parser_after_header().parse(&[0, 0], false).is_err());
+        assert!(parser_after_header().parse(&[0, 1, 1], false).is_err());
+        assert_matches!(
+            parser_after_header().parse(&[0, 2, 1], false),
+            Ok(Chunk::NeedMoreData(1)),
+        );
+        assert_matches!(
+            parser_after_header().parse(&[0, 1, 0], false),
+            Ok(Chunk::Parsed {
+                consumed: 3,
+                payload: Payload::CustomSection(CustomSectionReader {
+                    name: "",
+                    data_offset: 11,
+                    data: b"",
+                    range: Range { start: 10, end: 11 },
+                }),
+            }),
+        );
+        assert_matches!(
+            parser_after_header().parse(&[0, 2, 1, b'a'], false),
+            Ok(Chunk::Parsed {
+                consumed: 4,
+                payload: Payload::CustomSection(CustomSectionReader {
+                    name: "a",
+                    data_offset: 12,
+                    data: b"",
+                    range: Range { start: 10, end: 12 },
+                }),
+            }),
+        );
+        assert_matches!(
+            parser_after_header().parse(&[0, 2, 0, b'a'], false),
+            Ok(Chunk::Parsed {
+                consumed: 4,
+                payload: Payload::CustomSection(CustomSectionReader {
+                    name: "",
+                    data_offset: 11,
+                    data: b"a",
+                    range: Range { start: 10, end: 12 },
+                }),
+            }),
+        );
+    }
+
+    #[test]
+    fn function_section() {
+        assert!(parser_after_header().parse(&[10], true).is_err());
+        assert!(parser_after_header().parse(&[10, 0], true).is_err());
+        assert!(parser_after_header().parse(&[10, 1], true).is_err());
+        assert_matches!(
+            parser_after_header().parse(&[10], false),
+            Ok(Chunk::NeedMoreData(1))
+        );
+        assert_matches!(
+            parser_after_header().parse(&[10, 1], false),
+            Ok(Chunk::NeedMoreData(1))
+        );
+        let mut p = parser_after_header();
+        assert_matches!(
+            p.parse(&[10, 1, 0], false),
+            Ok(Chunk::Parsed {
+                consumed: 3,
+                payload: Payload::CodeSectionStart { count: 0, .. },
+            }),
+        );
+        assert_matches!(
+            p.parse(&[], true),
+            Ok(Chunk::Parsed {
+                consumed: 0,
+                payload: Payload::End(11),
+            }),
+        );
+        let mut p = parser_after_header();
+        assert_matches!(
+            p.parse(&[10, 2, 1, 0], false),
+            Ok(Chunk::Parsed {
+                consumed: 3,
+                payload: Payload::CodeSectionStart { count: 1, .. },
+            }),
+        );
+        assert_matches!(
+            p.parse(&[0], false),
+            Ok(Chunk::Parsed {
+                consumed: 1,
+                payload: Payload::CodeSectionEntry(_),
+            }),
+        );
+        assert_matches!(
+            p.parse(&[], true),
+            Ok(Chunk::Parsed {
+                consumed: 0,
+                payload: Payload::End(12),
+            }),
+        );
+
+        // 1 byte section with 1 function can't read the function body because
+        // the section is too small
+        let mut p = parser_after_header();
+        assert_matches!(
+            p.parse(&[10, 1, 1], false),
+            Ok(Chunk::Parsed {
+                consumed: 3,
+                payload: Payload::CodeSectionStart { count: 1, .. },
+            }),
+        );
+        assert_eq!(
+            p.parse(&[0], false).unwrap_err().message(),
+            "unexpected end-of-file"
+        );
+
+        // section with 2 functions but section is cut off
+        let mut p = parser_after_header();
+        assert_matches!(
+            p.parse(&[10, 2, 2], false),
+            Ok(Chunk::Parsed {
+                consumed: 3,
+                payload: Payload::CodeSectionStart { count: 2, .. },
+            }),
+        );
+        assert_matches!(
+            p.parse(&[0], false),
+            Ok(Chunk::Parsed {
+                consumed: 1,
+                payload: Payload::CodeSectionEntry(_),
+            }),
+        );
+        assert_matches!(p.parse(&[], false), Ok(Chunk::NeedMoreData(1)));
+        assert_eq!(
+            p.parse(&[0], false).unwrap_err().message(),
+            "unexpected end-of-file",
+        );
+
+        // trailing data is bad
+        let mut p = parser_after_header();
+        assert_matches!(
+            p.parse(&[10, 3, 1], false),
+            Ok(Chunk::Parsed {
+                consumed: 3,
+                payload: Payload::CodeSectionStart { count: 1, .. },
+            }),
+        );
+        assert_matches!(
+            p.parse(&[0], false),
+            Ok(Chunk::Parsed {
+                consumed: 1,
+                payload: Payload::CodeSectionEntry(_),
+            }),
+        );
+        assert_eq!(
+            p.parse(&[0], false).unwrap_err().message(),
+            "trailing bytes at end of section",
+        );
+    }
+
+    #[test]
+    fn single_module() {
+        let mut p = parser_after_component_header();
+        assert_matches!(p.parse(&[4], false), Ok(Chunk::NeedMoreData(1)));
+
+        // A module that's 8 bytes in length
+        let mut sub = match p.parse(&[1, 8], false) {
+            Ok(Chunk::Parsed {
+                consumed: 2,
+                payload: Payload::ModuleSection { parser, .. },
+            }) => parser,
+            other => panic!("bad parse {:?}", other),
+        };
+
+        // Parse the header of the submodule with the sub-parser.
+        assert_matches!(sub.parse(&[], false), Ok(Chunk::NeedMoreData(4)));
+        assert_matches!(sub.parse(b"\0asm", false), Ok(Chunk::NeedMoreData(4)));
+        assert_matches!(
+            sub.parse(b"\0asm\x01\0\0\0", false),
+            Ok(Chunk::Parsed {
+                consumed: 8,
+                payload: Payload::Version {
+                    num: 1,
+                    encoding: Encoding::Module,
+                    ..
+                },
+            }),
+        );
+
+        // The sub-parser should be byte-limited so the next byte shouldn't get
+        // consumed, it's intended for the parent parser.
+        assert_matches!(
+            sub.parse(&[10], false),
+            Ok(Chunk::Parsed {
+                consumed: 0,
+                payload: Payload::End(18),
+            }),
+        );
+
+        // The parent parser should now be back to resuming, and we simulate it
+        // being done with bytes to ensure that it's safely at the end,
+        // completing the module code section.
+        assert_matches!(p.parse(&[], false), Ok(Chunk::NeedMoreData(1)));
+        assert_matches!(
+            p.parse(&[], true),
+            Ok(Chunk::Parsed {
+                consumed: 0,
+                payload: Payload::End(18),
+            }),
+        );
+    }
+
+    #[test]
+    fn nested_section_too_big() {
+        let mut p = parser_after_component_header();
+
+        // A module that's 10 bytes in length
+        let mut sub = match p.parse(&[1, 10], false) {
+            Ok(Chunk::Parsed {
+                consumed: 2,
+                payload: Payload::ModuleSection { parser, .. },
+            }) => parser,
+            other => panic!("bad parse {:?}", other),
+        };
+
+        // use 8 bytes to parse the header, leaving 2 remaining bytes in our
+        // module.
+        assert_matches!(
+            sub.parse(b"\0asm\x01\0\0\0", false),
+            Ok(Chunk::Parsed {
+                consumed: 8,
+                payload: Payload::Version { num: 1, .. },
+            }),
+        );
+
+        // We can't parse a section which declares its bigger than the outer
+        // module. This is a custom section, one byte big, with one content byte. The
+        // content byte, however, lives outside of the parent's module code
+        // section.
+        assert_eq!(
+            sub.parse(&[0, 1, 0], false).unwrap_err().message(),
+            "section too large",
+        );
+    }
+}