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path.go
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path.go
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// MIT License
// Copyright (c) The RAI Authors
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
// Package urlpath matches paths against a template. It's meant for applications
// that take in REST-like URL paths, and need to validate and extract data from
// those paths.
//
// See New for documentation of the syntax for creating paths. See Match for how
// to validate and parse an inputted path.
//
// This package is dirctly copied from the library `https://github.com/ucarion/urlpath`.
package url
import "strings"
// Path is a representation of a sequence of segments.
//
// To construct instances of Path, see New.
type Path struct {
// A sequence of constraints on what valid segments must look like.
Segments []Segment
// Whether additional, trailing segments after Segments are acceptable.
Trailing bool
}
// Segment is a constraint on a single segment in a path.
type Segment struct {
// Whether this segment is parameterized.
IsParam bool
// The name of the parameter this segment will be mapped to.
Param string
// The constant value the segment is expected to take.
Const string
}
// Match represents the data extracted by matching an input against a Path.
//
// To construct instances of Match, see the Match method on Path.
type Match struct {
// The segments in the input corresponding to parameterized segments in Path.
Params map[string]string
// The trailing segments from the input. Note that the leading slash from the
// trailing segments is not included, since it's implied.
//
// An exception to this leading slash rule is made if the Path was constructed
// as New("*"), in which case Trailing will be identical to the inputted
// string.
Trailing string
}
// New constructs a new Path from its human-readable string representation.
//
// The syntax for paths looks something like the following:
//
// /shelves/:shelf/books/:book
//
// This would match inputs like:
//
// /shelves/foo/books/bar
// /shelves/123/books/456
// /shelves/123/books/
// /shelves//books/456
// /shelves//books/
//
// But not any of the following:
//
// /shelves/foo/books
// /shelves/foo/books/bar/
// /shelves/foo/books/bar/pages/baz
// /SHELVES/foo/books/bar
// shelves/foo/books/bar
//
// Optionally, a path can allow for "trailing" segments in the input. This is
// done using a segment simply named "*". For example, this path:
//
// /users/:user/files/*
//
// Would match inputs like:
//
// /users/foo/files/
// /users/foo/files/foo/bar/baz.txt
// /users/foo/files////
//
// But not:
//
// /users/foo
// /users/foo/files
//
// The asterisk syntax for trailing segments only takes effect on the last
// segment. If an asterisk appears in any other segment, it carries no special
// meaning.
//
// In more formal terms, the string representation of a path is a sequence of
// segments separated by slashes. Segments starting with colon (":") are treated
// as "parameter" segments (see Match).
//
// If the final segment is just the character asterisk ("*"), it is treated as
// an indication that the path accepts trailing segments, and not included in
// the Segments of the return value. Instead, Trailing in the return value is
// marked as true.
func New(path string) Path {
inSegments := strings.Split(path, "/")
trailing := inSegments[len(inSegments)-1] == "*"
var outSegments []Segment
if trailing {
outSegments = make([]Segment, len(inSegments)-1)
} else {
outSegments = make([]Segment, len(inSegments))
}
for i := 0; i < len(outSegments); i++ {
if strings.HasPrefix(inSegments[i], ":") {
outSegments[i] = Segment{IsParam: true, Param: inSegments[i][1:]}
} else {
outSegments[i] = Segment{IsParam: false, Const: inSegments[i]}
}
}
return Path{Segments: outSegments, Trailing: trailing}
}
// Match checks if the input string satisfies a Path's constraints, and returns
// parameter and trailing segment information.
//
// The second return value indicates whether the inputted string matched the
// path. The first return value is meaningful only if the match was successful.
//
// If the match was a success, all parameterized segments in Path have a
// corresponding entry in the Params of Match. If the path allows for trailing
// segments in the input, these will be in Trailing.
func (p *Path) Match(s string) (Match, bool) {
params := map[string]string{}
for segmentIndex, segment := range p.Segments {
// s[:i] is the prefix of s which contains the segment that must match
// against the path. s[j:] is the suffix of s which the next iteration of
// the loop will operate on.
//
// In "ordinary" circumstances, s[:i] is everything up to the first slash,
// and s[j:] is everything after it. But when there are no remaining slashes
// in the input, s[:i] is the entire string, and s[j:] is the empty string.
i := strings.IndexByte(s, '/')
j := i + 1
if i == -1 {
i = len(s)
j = len(s)
// If we have run out of slashes before the last element of the segments,
// then the input does not match the path.
//
// Implicitly, allowing for trailing input effectively adds an additional
// required slash to the input that's not captured by p.Segments. If
// trailing input is allowed, it's never ok for an input to have fewer
// slashes than the path has segments (an equal number is ok, and
// corresponds to a trailing part with no slashes in it).
if segmentIndex != len(p.Segments)-1 || p.Trailing {
return Match{}, false
}
} else {
// If we have slashes left over and we are not ok with trailing input,
// then the input does not match the path.
if segmentIndex == len(p.Segments)-1 && !p.Trailing {
return Match{}, false
}
}
if segment.IsParam {
params[segment.Param] = s[:i]
} else {
if s[:i] != segment.Const {
return Match{}, false
}
}
s = s[j:]
}
return Match{Params: params, Trailing: s}, true
}
// Build is the inverse of Match. Given parameter and trailing segment
// information, Build returns a string which satifies this information.
//
// The second parameter indicates whether the inputted match has the parameters
// the path specifies. If any of the parameters in the path are not found in the
// provided Match's Params, then false is returned.
func (p *Path) Build(m Match) (string, bool) {
var s strings.Builder
for i, segment := range p.Segments {
if segment.IsParam {
if param, ok := m.Params[segment.Param]; ok {
s.WriteString(param)
} else {
return "", false
}
} else {
s.WriteString(segment.Const)
}
if i != len(p.Segments)-1 {
s.WriteRune('/')
}
}
// The trailing segment of a match does not include a leading slash. We
// therefore need to add it here.
//
// However, if there are no segments at all in the path, then in this special
// case the match's Trailing is simply the originally inputted string itself,
// and so no leading slash must be inserted.
if p.Trailing && len(p.Segments) > 0 {
s.WriteRune('/')
}
s.WriteString(m.Trailing)
return s.String(), true
}