Reference

API surface

The complete public API in one page. Rendered rustdoc with full signatures is at docs.rs/er7.

Entry points

Item	Signature	Notes
`er7::parse`	`fn(&str) -> Result<Message, Error>`	needs an MSH/FHS/BHS header
`er7::parse_with`	`fn(&str, Separators) -> Message`	headerless fragment; cannot fail
`er7::split_messages`	`fn(&str) -> Vec<&str>`	batch input; slices borrow

er7::parse names both a module and a function. That is legal — they live in different namespaces — so er7::parse(text) calls the function and er7::parse::split_messages resolves the module path.

The value tree

Six types, one per level of the ER7 hierarchy. All fields are pub, so a message can be built from literals as well as parsed. All derive Debug, Clone, PartialEq, Eq; the four below Segment also derive Default.

Message { separators: Separators, segments: Vec<Segment> }
Segment { name: String, fields: Vec<Field> }
Field { repetitions: Vec<Repetition> }
Repetition { components: Vec<Component> }
Component { subcomponents: Vec<Subcomponent> }
Subcomponent { raw: String }

Only Subcomponent holds text, in raw, exactly as sent. Decoding happens on demand — that single decision is what makes the byte-for-byte round trip possible.

`Message`

Method	Returns	Purpose
`segment(&str)`	`Option<&Segment>`	the first segment with that name
`segment_at(&str, usize)`	`Option<&Segment>`	the 1-based Nth of that name
`segment_at_mut(&str, usize)`	`Option<&mut Segment>`	the same, mutable
`segments_named(&str)`	`impl Iterator`	every segment with that name
`header()`	`Option<&Segment>`	the segment that declared the delimiters
`query(&str)`	`Result<Option<String>, Error>`	first match at a path, decoded
`query_all(&str)`	`Result<Vec<String>, Error>`	every match, decoded
`query_path(&Path)`	`Vec<String>`	every match, path pre-parsed
`query_path_raw(&Path)`	`Vec<String>`	every match, exactly as sent
`message_code()`	`Option<String>`	MSH-9.1
`trigger_event()`	`Option<String>`	MSH-9.2
`message_structure()`	`Option<String>`	MSH-9.3
`control_id()`	`Option<String>`	MSH-10
`version()`	`Option<String>`	MSH-12.1
`to_er7()`	`String`	write with default options
`to_er7_with(RenderOptions)`	`String`	write, choosing the terminator

Also impl Display for Message, equivalent to to_er7().

Levels below `Message`

Every level exposes 1-based accessors matching HL7’s own numbering, each returning Option, plus a _mut variant. Index 0 returns None rather than element 1.

Segment: field(n), field_mut(n), component(field, component), is_header(), to_er7(&seps), to_text(&seps)
Field: repetition(n), repetition_mut(n), component(n), is_empty(), is_null(), to_er7, to_text
Repetition: component(n), component_mut(n), is_empty(), is_null(), to_er7, to_text
Component: subcomponent(n), subcomponent_mut(n), is_empty(), is_null(), to_er7, to_text
Subcomponent: new(text), value(&seps), set(value, &seps), is_empty(), is_null(), to_er7, to_text

to_text decodes leaf text but keeps the structural delimiters, so its output is not re-parseable: a decoded \F\ becomes a literal |. Use to_er7 for anything that will be sent, stored, or parsed again.

Configuration

Separators: Fields field, component, repetition, escape, subcomponent: char; truncation: Option<char>. Methods default(), from_header(&str), validate(), is_delimiter(char), encoding_characters(). Derives Copy.
Terminator: Cr (default), Lf, CrLf. Method as_str().
RenderOptions: terminator: Terminator, trailing_terminator: bool. Derives Default (Cr, false).
Path: segment: String; segment_occurrence, field, repetition, component, subcomponent: Option<usize>. Implements FromStr, Display, Hash.

Escape sequences

Module er7::escape.

Item	Signature
`escapes`	`fn(&str, &Separators) -> Escapes`
`unescape`	`fn(&str, &Separators) -> Cow<str>`
`escape`	`fn(&str, &Separators) -> Cow<str>`
`decode_hex`	`fn(&str) -> Option<String>`

Escape variants: Text, Field, Component, Subcomponent, Repetition, EscapeCharacter, Hex, Highlight, Normal, Formatting, Local, SingleByteCharacterSet, MultiByteCharacterSet, Unknown, Unterminated.

The escape-sequence reference →

Errors

Four variants, arising from exactly two situations: a message with no usable header, and a path that is not a path.

Variant	When
`Empty`	the input held no non-blank lines
`MissingHeader(String)`	the first segment is not MSH, FHS, or BHS; carries the name found
`BadHeader(String)`	the declared delimiters are unusable
`BadPath(String)`	a path could not be read

Everything else about ER7 is recovered rather than refused: unknown segments, local Z segments, ragged field counts, undecodable escapes, and missing positions are all data.

Not in the API

No dictionary, no validator, no transport, no dependencies. See the ecosystem for the crates that add the HL7 v2.5 dictionary on top.

API surface

Entry points

The value tree

Message

Levels below Message

Configuration

Escape sequences

Errors

Not in the API

`Message`

Levels below `Message`