432 lines
13 KiB
Go
432 lines
13 KiB
Go
// Copyright 2020 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package embed provides access to files embedded in the running Go program.
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//
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// Go source files that import "embed" can use the //go:embed directive
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// to initialize a variable of type string, []byte, or FS with the contents of
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// files read from the package directory or subdirectories at compile time.
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//
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// For example, here are three ways to embed a file named hello.txt
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// and then print its contents at run time.
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//
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// Embedding one file into a string:
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//
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// import _ "embed"
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//
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// //go:embed hello.txt
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// var s string
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// print(s)
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//
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// Embedding one file into a slice of bytes:
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//
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// import _ "embed"
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//
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// //go:embed hello.txt
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// var b []byte
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// print(string(b))
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//
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// Embedded one or more files into a file system:
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//
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// import "embed"
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//
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// //go:embed hello.txt
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// var f embed.FS
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// data, _ := f.ReadFile("hello.txt")
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// print(string(data))
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//
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// Directives
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//
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// A //go:embed directive above a variable declaration specifies which files to embed,
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// using one or more path.Match patterns.
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//
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// The directive must immediately precede a line containing the declaration of a single variable.
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// Only blank lines and ‘//’ line comments are permitted between the directive and the declaration.
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//
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// The type of the variable must be a string type, or a slice of a byte type,
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// or FS (or an alias of FS).
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//
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// For example:
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//
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// package server
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//
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// import "embed"
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//
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// // content holds our static web server content.
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// //go:embed image/* template/*
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// //go:embed html/index.html
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// var content embed.FS
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//
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// The Go build system will recognize the directives and arrange for the declared variable
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// (in the example above, content) to be populated with the matching files from the file system.
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//
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// The //go:embed directive accepts multiple space-separated patterns for
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// brevity, but it can also be repeated, to avoid very long lines when there are
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// many patterns. The patterns are interpreted relative to the package directory
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// containing the source file. The path separator is a forward slash, even on
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// Windows systems. Patterns may not contain ‘.’ or ‘..’ or empty path elements,
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// nor may they begin or end with a slash. To match everything in the current
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// directory, use ‘*’ instead of ‘.’. To allow for naming files with spaces in
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// their names, patterns can be written as Go double-quoted or back-quoted
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// string literals.
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//
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// If a pattern names a directory, all files in the subtree rooted at that directory are
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// embedded (recursively), except that files with names beginning with ‘.’ or ‘_’
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// are excluded. So the variable in the above example is almost equivalent to:
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//
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// // content is our static web server content.
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// //go:embed image template html/index.html
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// var content embed.FS
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//
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// The difference is that ‘image/*’ embeds ‘image/.tempfile’ while ‘image’ does not.
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// Neither embeds ‘image/dir/.tempfile’.
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//
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// If a pattern begins with the prefix ‘all:’, then the rule for walking directories is changed
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// to include those files beginning with ‘.’ or ‘_’. For example, ‘all:image’ embeds
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// both ‘image/.tempfile’ and ‘image/dir/.tempfile’.
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//
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// The //go:embed directive can be used with both exported and unexported variables,
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// depending on whether the package wants to make the data available to other packages.
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// It can only be used with variables at package scope, not with local variables.
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//
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// Patterns must not match files outside the package's module, such as ‘.git/*’ or symbolic links.
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// Matches for empty directories are ignored. After that, each pattern in a //go:embed line
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// must match at least one file or non-empty directory.
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//
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// If any patterns are invalid or have invalid matches, the build will fail.
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//
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// Strings and Bytes
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//
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// The //go:embed line for a variable of type string or []byte can have only a single pattern,
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// and that pattern can match only a single file. The string or []byte is initialized with
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// the contents of that file.
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//
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// The //go:embed directive requires importing "embed", even when using a string or []byte.
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// In source files that don't refer to embed.FS, use a blank import (import _ "embed").
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//
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// File Systems
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//
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// For embedding a single file, a variable of type string or []byte is often best.
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// The FS type enables embedding a tree of files, such as a directory of static
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// web server content, as in the example above.
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//
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// FS implements the io/fs package's FS interface, so it can be used with any package that
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// understands file systems, including net/http, text/template, and html/template.
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//
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// For example, given the content variable in the example above, we can write:
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//
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// http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.FS(content))))
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//
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// template.ParseFS(content, "*.tmpl")
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//
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// Tools
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//
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// To support tools that analyze Go packages, the patterns found in //go:embed lines
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// are available in “go list” output. See the EmbedPatterns, TestEmbedPatterns,
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// and XTestEmbedPatterns fields in the “go help list” output.
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//
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package embed
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import (
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"errors"
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"io"
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"io/fs"
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"time"
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)
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// An FS is a read-only collection of files, usually initialized with a //go:embed directive.
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// When declared without a //go:embed directive, an FS is an empty file system.
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//
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// An FS is a read-only value, so it is safe to use from multiple goroutines
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// simultaneously and also safe to assign values of type FS to each other.
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//
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// FS implements fs.FS, so it can be used with any package that understands
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// file system interfaces, including net/http, text/template, and html/template.
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//
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// See the package documentation for more details about initializing an FS.
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type FS struct {
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// The compiler knows the layout of this struct.
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// See cmd/compile/internal/staticdata's WriteEmbed.
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//
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// The files list is sorted by name but not by simple string comparison.
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// Instead, each file's name takes the form "dir/elem" or "dir/elem/".
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// The optional trailing slash indicates that the file is itself a directory.
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// The files list is sorted first by dir (if dir is missing, it is taken to be ".")
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// and then by base, so this list of files:
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//
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// p
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// q/
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// q/r
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// q/s/
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// q/s/t
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// q/s/u
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// q/v
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// w
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//
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// is actually sorted as:
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//
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// p # dir=. elem=p
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// q/ # dir=. elem=q
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// w/ # dir=. elem=w
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// q/r # dir=q elem=r
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// q/s/ # dir=q elem=s
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// q/v # dir=q elem=v
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// q/s/t # dir=q/s elem=t
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// q/s/u # dir=q/s elem=u
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//
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// This order brings directory contents together in contiguous sections
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// of the list, allowing a directory read to use binary search to find
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// the relevant sequence of entries.
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files *[]file
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}
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// split splits the name into dir and elem as described in the
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// comment in the FS struct above. isDir reports whether the
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// final trailing slash was present, indicating that name is a directory.
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func split(name string) (dir, elem string, isDir bool) {
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if name[len(name)-1] == '/' {
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isDir = true
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name = name[:len(name)-1]
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}
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i := len(name) - 1
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for i >= 0 && name[i] != '/' {
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i--
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}
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if i < 0 {
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return ".", name, isDir
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}
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return name[:i], name[i+1:], isDir
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}
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// trimSlash trims a trailing slash from name, if present,
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// returning the possibly shortened name.
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func trimSlash(name string) string {
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if len(name) > 0 && name[len(name)-1] == '/' {
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return name[:len(name)-1]
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}
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return name
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}
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var (
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_ fs.ReadDirFS = FS{}
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_ fs.ReadFileFS = FS{}
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)
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// A file is a single file in the FS.
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// It implements fs.FileInfo and fs.DirEntry.
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type file struct {
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// The compiler knows the layout of this struct.
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// See cmd/compile/internal/staticdata's WriteEmbed.
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name string
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data string
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hash [16]byte // truncated SHA256 hash
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}
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var (
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_ fs.FileInfo = (*file)(nil)
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_ fs.DirEntry = (*file)(nil)
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)
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func (f *file) Name() string { _, elem, _ := split(f.name); return elem }
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func (f *file) Size() int64 { return int64(len(f.data)) }
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func (f *file) ModTime() time.Time { return time.Time{} }
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func (f *file) IsDir() bool { _, _, isDir := split(f.name); return isDir }
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func (f *file) Sys() any { return nil }
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func (f *file) Type() fs.FileMode { return f.Mode().Type() }
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func (f *file) Info() (fs.FileInfo, error) { return f, nil }
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func (f *file) Mode() fs.FileMode {
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if f.IsDir() {
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return fs.ModeDir | 0555
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}
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return 0444
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}
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// dotFile is a file for the root directory,
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// which is omitted from the files list in a FS.
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var dotFile = &file{name: "./"}
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// lookup returns the named file, or nil if it is not present.
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func (f FS) lookup(name string) *file {
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if !fs.ValidPath(name) {
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// The compiler should never emit a file with an invalid name,
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// so this check is not strictly necessary (if name is invalid,
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// we shouldn't find a match below), but it's a good backstop anyway.
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return nil
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}
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if name == "." {
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return dotFile
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}
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if f.files == nil {
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return nil
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}
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// Binary search to find where name would be in the list,
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// and then check if name is at that position.
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dir, elem, _ := split(name)
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files := *f.files
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i := sortSearch(len(files), func(i int) bool {
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idir, ielem, _ := split(files[i].name)
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return idir > dir || idir == dir && ielem >= elem
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})
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if i < len(files) && trimSlash(files[i].name) == name {
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return &files[i]
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}
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return nil
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}
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// readDir returns the list of files corresponding to the directory dir.
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func (f FS) readDir(dir string) []file {
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if f.files == nil {
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return nil
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}
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// Binary search to find where dir starts and ends in the list
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// and then return that slice of the list.
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files := *f.files
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i := sortSearch(len(files), func(i int) bool {
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idir, _, _ := split(files[i].name)
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return idir >= dir
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})
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j := sortSearch(len(files), func(j int) bool {
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jdir, _, _ := split(files[j].name)
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return jdir > dir
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})
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return files[i:j]
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}
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// Open opens the named file for reading and returns it as an fs.File.
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//
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// The returned file implements io.Seeker when the file is not a directory.
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func (f FS) Open(name string) (fs.File, error) {
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file := f.lookup(name)
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if file == nil {
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return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
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}
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if file.IsDir() {
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return &openDir{file, f.readDir(name), 0}, nil
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}
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return &openFile{file, 0}, nil
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}
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// ReadDir reads and returns the entire named directory.
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func (f FS) ReadDir(name string) ([]fs.DirEntry, error) {
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file, err := f.Open(name)
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if err != nil {
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return nil, err
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}
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dir, ok := file.(*openDir)
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if !ok {
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return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("not a directory")}
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}
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list := make([]fs.DirEntry, len(dir.files))
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for i := range list {
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list[i] = &dir.files[i]
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}
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return list, nil
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}
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// ReadFile reads and returns the content of the named file.
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func (f FS) ReadFile(name string) ([]byte, error) {
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file, err := f.Open(name)
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if err != nil {
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return nil, err
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}
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ofile, ok := file.(*openFile)
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if !ok {
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return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("is a directory")}
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}
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return []byte(ofile.f.data), nil
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}
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// An openFile is a regular file open for reading.
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type openFile struct {
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f *file // the file itself
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offset int64 // current read offset
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}
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var (
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_ io.Seeker = (*openFile)(nil)
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)
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func (f *openFile) Close() error { return nil }
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func (f *openFile) Stat() (fs.FileInfo, error) { return f.f, nil }
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func (f *openFile) Read(b []byte) (int, error) {
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if f.offset >= int64(len(f.f.data)) {
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return 0, io.EOF
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}
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if f.offset < 0 {
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return 0, &fs.PathError{Op: "read", Path: f.f.name, Err: fs.ErrInvalid}
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}
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n := copy(b, f.f.data[f.offset:])
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f.offset += int64(n)
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return n, nil
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}
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func (f *openFile) Seek(offset int64, whence int) (int64, error) {
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switch whence {
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case 0:
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// offset += 0
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case 1:
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offset += f.offset
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case 2:
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offset += int64(len(f.f.data))
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}
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if offset < 0 || offset > int64(len(f.f.data)) {
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return 0, &fs.PathError{Op: "seek", Path: f.f.name, Err: fs.ErrInvalid}
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}
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f.offset = offset
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return offset, nil
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}
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// An openDir is a directory open for reading.
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type openDir struct {
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f *file // the directory file itself
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files []file // the directory contents
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offset int // the read offset, an index into the files slice
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}
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func (d *openDir) Close() error { return nil }
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func (d *openDir) Stat() (fs.FileInfo, error) { return d.f, nil }
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func (d *openDir) Read([]byte) (int, error) {
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return 0, &fs.PathError{Op: "read", Path: d.f.name, Err: errors.New("is a directory")}
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}
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func (d *openDir) ReadDir(count int) ([]fs.DirEntry, error) {
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n := len(d.files) - d.offset
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if n == 0 {
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if count <= 0 {
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return nil, nil
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}
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return nil, io.EOF
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}
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if count > 0 && n > count {
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n = count
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}
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list := make([]fs.DirEntry, n)
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for i := range list {
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list[i] = &d.files[d.offset+i]
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}
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d.offset += n
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return list, nil
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}
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// sortSearch is like sort.Search, avoiding an import.
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func sortSearch(n int, f func(int) bool) int {
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// Define f(-1) == false and f(n) == true.
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// Invariant: f(i-1) == false, f(j) == true.
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i, j := 0, n
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for i < j {
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h := int(uint(i+j) >> 1) // avoid overflow when computing h
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// i ≤ h < j
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if !f(h) {
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i = h + 1 // preserves f(i-1) == false
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} else {
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j = h // preserves f(j) == true
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}
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}
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// i == j, f(i-1) == false, and f(j) (= f(i)) == true => answer is i.
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return i
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}
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