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[SR-5784] JSONEncoder is lossy for URL type #4075

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swift-ci opened this issue Aug 28, 2017 · 5 comments
Open

[SR-5784] JSONEncoder is lossy for URL type #4075

swift-ci opened this issue Aug 28, 2017 · 5 comments
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@itaiferber
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@swift-ci
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Previous ID SR-5784
Radar rdar://problem/34138907
Original Reporter ylin (JIRA User)
Type Bug
Environment

macOS, Swift 4 08-21 snapshot

Additional Detail from JIRA
Votes 0
Component/s Foundation
Labels Bug
Assignee @itaiferber
Priority Medium

md5: e6d42a434f747ae22d710ada3ecdf7b6

Issue Description:

While playing around JSONEncoder/JSONDecoder, I found that the `URL` type is lossy on encode -> decode.

Example:

ylin@youming-mbpr:~/Swift/Configuration$ swift
Welcome to Apple Swift version 4.0-dev (LLVM 2dedb62a0b, Clang b9d76a314c, Swift 61ad3c07ef). Type :help for assistance.
  1> import Foundation 
  2. let url = URL(string: "../", relativeTo: URL(string: "http://example.com/test"))! 
  3. let url2 = JSONDecoder().decode([URL].self, from: JSONEncoder().encode([url]))[0] 
  4. url == url2
$R0: Bool = false
url: URL = "../ -- ttp://example.com/test"
url2: URL = "http://example.com/../"

The same URL is read back losslessly using the `PropertyList` version, however:

ylin@youming-mbpr:~/Swift/Configuration$ swift
Welcome to Apple Swift version 4.0-dev (LLVM 2dedb62a0b, Clang b9d76a314c, Swift 61ad3c07ef). Type :help for assistance.
  1> import Foundation 
  2. let url = URL(string: "../", relativeTo: URL(string: "http://example.com/test"))! 
  3. let url2 = PropertyListDecoder().decode([URL].self, from: PropertyListEncoder().encode([url]))[0] 
  4. url == url2 
$R0: Bool = true
url: URL = "../ -- ttp://example.com/test"
url2: URL = "../ -- ttp://example.com/test"

Even more oddly, on Ubuntu 14.04 the same 08-21 snapshot produces the correct result:

ylin@ylin-VirtualBox:~$ swift -I/home/ylin/.swiftenv/versions/4.0-DEVELOPMENT-SNAPSHOT-2017-08-21-a/usr/lib/swift/clang/include
Welcome to Swift version 4.0-dev (LLVM 2dedb62a0b, Clang b9d76a314c, Swift 61ad3c07ef). Type :help for assistance.
  1> import Foundation 
  2. let url = URL(string: "../", relativeTo: URL(string: "http://example.com/test"))! 
  3. let url2 = JSONDecoder().decode([URL].self, from: JSONEncoder().encode([url]))[0] 
  4. url == url2
$R0: Bool = true
url: Foundation.URL = <redacted>
url2: Foundation.URL = <redacted>
@belkadan
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cc @itaiferber

@itaiferber
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This is actually done on purpose — overall, it would be significantly more surprising to people if {{URL}}s they got from potentially arbitrary sources encoded as a dictionary instead of as a string. We encode {{URL}}s as absolute strings because most consumers of JSON would expect that; unfortunately, it means that we lose the relativeness.

We can potentially add a strategy to tell JSONEncoder to preserve the structure as-is for round-tripping.

The Linux behavior can actually be considered a bug; it will be fixed once PR-11315 is pulled into a Swift release.

@itaiferber
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@swift-ci Create

@swift-ci
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Comment by Youming Lin (JIRA)

@itaiferber Thanks for the explanation. And +1 on the new option; I could see this being used for debug logging in JSON format, in which case a lossless archival of the object state might be beneficial.

Also, for future reference, are there any other native/Foundation types that aren't losslessly encoded by JSONEncoder?

@itaiferber
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ylin (JIRA User) There shouldn't be, no. All other types which have multiple potential representations encode as a dictionary; URL is just unique in that most consumers of the JSON would be expecting a string, so we do this for maximum compatibility.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@shahmishal shahmishal transferred this issue from apple/swift May 5, 2022
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@itaiferber @belkadan @swift-ci