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Specification 6.0 · Not released · Tested product 5.21.3

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    Library · std.url

    URL.toString

    Serializes all URL components into stable URL text.

    toString() -> string
    Module
    std.url
    Receiver
    URL
    Minimum arity
    0
    Maximum arity
    0

    Declaration and parameters

    Link

    Availability

    Included by default: Pending

    Import std.url in language mode 5.21.

    The current compiler selects std/url.tpz for this language mode. Availability in other released editions and inclusion in each installed distribution are Pending.

    Source evidence

    Receiver

    URL

    Parameter constraints

    Additional contracts are Pending.

    URL.parse takes a string and applies the WHATWG URL parser with UTF-8 input and no base URL. A successful parse returns Ok containing an immutable URL. Relative references need a base and therefore return Err.

    A parser failure returns Err containing a nonempty string. Missing or invalid schemes, invalid hosts, and ports outside 0 through 65535 fail. Error wording is explanatory text and has no fixed spelling.

    URL preprocessing removes leading and trailing code points from U+0000 through U+0020. It then removes U+0009, U+000A, and U+000D throughout the input. Other characters are processed by the URL parser. A validation warning that permits parsing does not become an Err.

    Schemes use lowercase. Special-scheme domain hosts use ASCII domain serialization. Default ports disappear and hierarchical dot segments are removed. Opaque paths retain their distinct path interpretation.

    The default ports are 21 for ftp, 80 for http and ws, and 443 for https and wss. Other valid ports survive serialization as decimal integers. The file scheme has no port.

    URL.toString serializes every stored component. It preserves user information, nondefault ports, query order, and explicit empty query and fragment delimiters. Existing percent escapes retain their spelling. Newly escaped characters use percent-encoded UTF-8 bytes with uppercase hexadecimal digits.

    Parsing the serialization produces the same serialization and component values. Reading a URL does not modify it. Parsing evaluates its argument once before validation and performs no network or filesystem operation.

    Related rule: Parse and serialize absolute URLs

    URL.scheme returns the lowercase scheme without its delimiter. URL.host returns Some containing the serialized host without user information or a port. IPv6 hosts include their square brackets.

    A URL whose host is absent returns None() from URL.host. A present empty host returns Some containing an empty string. A local file URL can have that empty host.

    URL.path returns the serialized path without the query or fragment. A hierarchical path retains its leading slash. An opaque path has no implied slash. Percent escapes stay encoded so an escaped slash remains path data.

    URL.fragment returns None() when there is no fragment delimiter. An explicit empty fragment returns Some containing an empty string. A present fragment excludes its delimiter and retains percent encoding.

    Scheme, host, path, and fragment inspection cannot fail after construction. Each receiver is evaluated once. The returned strings are immutable and inspection has no external effects.

    Read URL.query for decoded query fields. URL.path and URL.fragment do not apply query decoding. In particular, a plus sign in those components remains a plus sign.

    Related rule: Read serialized URL components and their absence

    Result

    Additional contracts are Pending.

    The declared result type is string.

    Effects

    Pending

    Failures

    Pending

    Result and effects

    Link

    Serializes all URL components into stable URL text.

    Resolved contracts

    Link

    Related entries

    Link

    std.url

    Parse and serialize absolute URLs

    Link
    Ruletopaz.stdlib.contract.url-parse.rule

    Parse and serialize absolute URLs

    URL.parse takes a string and applies the WHATWG URL parser with UTF-8 input and no base URL. A successful parse returns Ok containing an immutable URL. Relative references need a base and therefore return Err.

    A parser failure returns Err containing a nonempty string. Missing or invalid schemes, invalid hosts, and ports outside 0 through 65535 fail. Error wording is explanatory text and has no fixed spelling.

    URL preprocessing removes leading and trailing code points from U+0000 through U+0020. It then removes U+0009, U+000A, and U+000D throughout the input. Other characters are processed by the URL parser. A validation warning that permits parsing does not become an Err.

    Schemes use lowercase. Special-scheme domain hosts use ASCII domain serialization. Default ports disappear and hierarchical dot segments are removed. Opaque paths retain their distinct path interpretation.

    The default ports are 21 for ftp, 80 for http and ws, and 443 for https and wss. Other valid ports survive serialization as decimal integers. The file scheme has no port.

    URL.toString serializes every stored component. It preserves user information, nondefault ports, query order, and explicit empty query and fragment delimiters. Existing percent escapes retain their spelling. Newly escaped characters use percent-encoded UTF-8 bytes with uppercase hexadecimal digits.

    Parsing the serialization produces the same serialization and component values. Reading a URL does not modify it. Parsing evaluates its argument once before validation and performs no network or filesystem operation.

    Why

    A single established parser gives URL text one interpretation. Parsing without a hidden base makes acceptance independent of the working directory and browser location. Stable serialization keeps resource identifiers reusable in text and typeset links.

    Examples Normalize the scheme, host, port, and pathHandle invalid absolute URL text as dataCheck both port boundaries and the first invalid portApply URL preprocessing and escape a path spacePreserve serialized escapes and empty components through parsingEvaluate the input once before reporting a parse errorReject a forbidden domain character

    Source evidence

    Normalize the scheme, host, port, and path

    Link

    run · running · Verification: not-run

    main.tpzNormalize the scheme, host, port, and pathOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. match (URL.parse("HTTPS://Example.COM:443/a/./b/../c?x=1#part")) {
    5. case Ok(value) => io.writeLine(value.toString())
    6. case Err(_) => io.writeLine("parse failed")
    7. }
    Expected outputexit 0
    https://example.com/a/c?x=1#part
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. https://example.com/a/c?x=1#part

    This exact example has not been executed.

    Source evidence

    Handle invalid absolute URL text as data

    Link

    run · running · Verification: not-run

    main.tpzHandle invalid absolute URL text as dataOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. for text in (["", "../guide", "1bad:x", "https://", "https://example.com:wrong"]) {
    5. match (URL.parse(text)) {
    6. case Err(message) => io.writeLine("{message != ""}")
    7. case Ok(_) => io.writeLine("accepted")
    8. }
    9. }
    Expected outputexit 0
    true
true
true
true
true
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. true
    2. true
    3. true
    4. true
    5. true

    This exact example has not been executed.

    Source evidence

    Check both port boundaries and the first invalid port

    Link

    run · running · Verification: not-run

    main.tpzCheck both port boundaries and the first invalid portOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. for text in (["https://example.com:0", "https://example.com:65535", "https://example.com:65536"]) {
    5. match (URL.parse(text)) {
    6. case Ok(value) => io.writeLine(value.toString())
    7. case Err(_) => io.writeLine("invalid port")
    8. }
    9. }
    Expected outputexit 0
    https://example.com:0/
https://example.com:65535/
invalid port
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. https://example.com:0/
    2. https://example.com:65535/
    3. invalid port

    This exact example has not been executed.

    Source evidence

    Apply URL preprocessing and escape a path space

    Link

    run · running · Verification: not-run

    main.tpzApply URL preprocessing and escape a path spaceOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. match (URL.parse(" \thttps://EXAMPLE.com/a b\n")) {
    5. case Ok(value) => io.writeLine(value.toString())
    6. case Err(_) => io.writeLine("parse failed")
    7. }
    Expected outputexit 0
    https://example.com/a%20b
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. https://example.com/a%20b

    This exact example has not been executed.

    Source evidence

    Preserve serialized escapes and empty components through parsing

    Link

    run · running · Verification: not-run

    main.tpzPreserve serialized escapes and empty components through parsingOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. for text in (["https://example.com/a%2fb?x=%2b#p%2fq", "https://example.com/?#"]) {
    5. match (URL.parse(text)) {
    6. case Ok(value) => {
    7. io.writeLine(value.toString())
    8. match (URL.parse(value.toString())) {
    9. case Ok(again) => io.writeLine(again.toString())
    10. case Err(_) => io.writeLine("second parse failed")
    11. }
    12. }
    13. case Err(_) => io.writeLine("first parse failed")
    14. }
    15. }
    Expected outputexit 0
    https://example.com/a%2fb?x=%2b#p%2fq
https://example.com/a%2fb?x=%2b#p%2fq
https://example.com/?#
https://example.com/?#
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. https://example.com/a%2fb?x=%2b#p%2fq
    2. https://example.com/a%2fb?x=%2b#p%2fq
    3. https://example.com/?#
    4. https://example.com/?#

    This exact example has not been executed.

    Source evidence

    Evaluate the input once before reporting a parse error

    Link

    run · running · Verification: not-run

    main.tpzEvaluate the input once before reporting a parse errorOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. function inputText() -> string {
    5. io.writeLine("input")
    6. return "../chapter"
    7. }
    8. match (URL.parse(inputText())) {
    9. case Err(_) => io.writeLine("invalid URL")
    10. case Ok(_) => io.writeLine("accepted")
    11. }
    Expected outputexit 0
    input
invalid URL
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. input
    2. invalid URL

    This exact example has not been executed.

    Source evidence

    Reject a forbidden domain character

    Link

    run · running · Verification: not-run

    main.tpzReject a forbidden domain characterOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. match (URL.parse("https://exa[mple.com/")) {
    5. case Err(_) => io.writeLine("invalid host")
    6. case Ok(_) => io.writeLine("accepted")
    7. }
    Expected outputexit 0
    invalid host
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. invalid host

    This exact example has not been executed.

    Source evidence

    Read serialized URL components and their absence

    Link
    Ruletopaz.stdlib.contract.url-components.rule

    Read serialized URL components and their absence

    URL.scheme returns the lowercase scheme without its delimiter. URL.host returns Some containing the serialized host without user information or a port. IPv6 hosts include their square brackets.

    A URL whose host is absent returns None() from URL.host. A present empty host returns Some containing an empty string. A local file URL can have that empty host.

    URL.path returns the serialized path without the query or fragment. A hierarchical path retains its leading slash. An opaque path has no implied slash. Percent escapes stay encoded so an escaped slash remains path data.

    URL.fragment returns None() when there is no fragment delimiter. An explicit empty fragment returns Some containing an empty string. A present fragment excludes its delimiter and retains percent encoding.

    Scheme, host, path, and fragment inspection cannot fail after construction. Each receiver is evaluated once. The returned strings are immutable and inspection has no external effects.

    Read URL.query for decoded query fields. URL.path and URL.fragment do not apply query decoding. In particular, a plus sign in those components remains a plus sign.

    Why

    Component access must preserve delimiters as data and distinguish absence from an empty component. Encoded path and fragment values can be placed back into a URL without turning an escaped separator into structure.

    Examples Read encoded URL components without decoding delimitersDistinguish an absent fragment from an empty fragmentRead IPv6 and file hosts without losing authority dataSerialize a Unicode domain, path, and fragment

    Source evidence

    Read encoded URL components without decoding delimiters

    Link

    run · running · Verification: not-run

    main.tpzRead encoded URL components without decoding delimitersOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. match (URL.parse("HTTPS://EXAMPLE.COM:8443/a%2Fb?q=a+b#x%20y")) {
    5. case Ok(value) => {
    6. io.writeLine(value.scheme())
    7. match (value.host()) {
    8. case Some(host) => io.writeLine(host)
    9. case None() => io.writeLine("no host")
    10. }
    11. io.writeLine(value.path())
    12. match (value.fragment()) {
    13. case Some(fragment) => io.writeLine(fragment)
    14. case None() => io.writeLine("no fragment")
    15. }
    16. io.writeLine(value.toString())
    17. }
    18. case Err(_) => io.writeLine("parse failed")
    19. }
    Expected outputexit 0
    https
example.com
/a%2Fb
x%20y
https://example.com:8443/a%2Fb?q=a+b#x%20y
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. https
    2. example.com
    3. /a%2Fb
    4. x%20y
    5. https://example.com:8443/a%2Fb?q=a+b#x%20y

    This exact example has not been executed.

    Source evidence

    Distinguish an absent fragment from an empty fragment

    Link

    run · running · Verification: not-run

    main.tpzDistinguish an absent fragment from an empty fragmentOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. for text in (["mailto:reader@example.com", "mailto:reader@example.com#"]) {
    5. match (URL.parse(text)) {
    6. case Ok(value) => {
    7. io.writeLine(value.scheme())
    8. match (value.host()) {
    9. case None() => io.writeLine("no host")
    10. case Some(host) => io.writeLine("host={host}")
    11. }
    12. io.writeLine(value.path())
    13. match (value.fragment()) {
    14. case None() => io.writeLine("no fragment")
    15. case Some(fragment) => io.writeLine("fragment={fragment}")
    16. }
    17. io.writeLine("{value.query().length}")
    18. }
    19. case Err(_) => io.writeLine("parse failed")
    20. }
    21. }
    Expected outputexit 0
    mailto
no host
reader@example.com
no fragment
0
mailto
no host
reader@example.com
fragment=
0
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. mailto
    2. no host
    3. reader@example.com
    4. no fragment
    5. 0
    6. mailto
    7. no host
    8. reader@example.com
    9. fragment=
    10. 0

    This exact example has not been executed.

    Source evidence

    Read IPv6 and file hosts without losing authority data

    Link

    run · running · Verification: not-run

    main.tpzRead IPv6 and file hosts without losing authority dataOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. for text in (["https://u:p@[2001:DB8::1]:443/", "file:///tmp/a"]) {
    5. match (URL.parse(text)) {
    6. case Ok(value) => {
    7. match (value.host()) {
    8. case Some(host) => io.writeLine("host={host}")
    9. case None() => io.writeLine("no host")
    10. }
    11. io.writeLine(value.toString())
    12. }
    13. case Err(_) => io.writeLine("parse failed")
    14. }
    15. }
    Expected outputexit 0
    host=[2001:db8::1]
https://u:p@[2001:db8::1]/
host=
file:///tmp/a
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. host=[2001:db8::1]
    2. https://u:p@[2001:db8::1]/
    3. host=
    4. file:///tmp/a

    This exact example has not been executed.

    Source evidence

    Serialize a Unicode domain, path, and fragment

    Link

    run · running · Verification: not-run

    main.tpzSerialize a Unicode domain, path, and fragmentOpen in Playground
    1. import std.url { URL }
    2. import std.io
    4. match (URL.parse("https://bücher.example/한#α")) {
    5. case Ok(value) => {
    6. match (value.host()) {
    7. case Some(host) => io.writeLine(host)
    8. case None() => io.writeLine("no host")
    9. }
    10. io.writeLine(value.path())
    11. match (value.fragment()) {
    12. case Some(fragment) => io.writeLine(fragment)
    13. case None() => io.writeLine("no fragment")
    14. }
    15. io.writeLine(value.toString())
    16. }
    17. case Err(_) => io.writeLine("parse failed")
    18. }
    Expected outputexit 0
    xn--bcher-kva.example
/%ED%95%9C
%CE%B1
https://xn--bcher-kva.example/%ED%95%9C#%CE%B1
    $ topaz run main.tpz · target product 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. xn--bcher-kva.example
    2. /%ED%95%9C
    3. %CE%B1
    4. https://xn--bcher-kva.example/%ED%95%9C#%CE%B1

    This exact example has not been executed.

    Source evidence

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