[codegeek]

Fixes #121.

Why

The ident appears in every nick!ident@host prefix the server sends: JOIN, PRIVMSG and NOTICE sources, WHO, WHOIS, and NAMES with userhost-in-names. USER only rejected NUL, CR, LF, space and @. Every other control character got through: TAB, the CTCP delimiter \x01, the formatting codes \x02, \x03 and so on, DEL, and C1 controls such as U+0085 (NEL). A client could therefore plant line breaks, CTCP framing or colors inside its hostmask as other users see it. Sourcery found this while reviewing #120.

What

• Hostmask.isValidUsernameContent now rejects any ISO control character (Character.isISOControl: C0, DEL and C1). Space and @ are still rejected. UserCommandHandler already falls back to the ident user for invalid content, and that hasn't changed.
• Ident truncation to IDENT_MAX_CHARS (9 chars) no longer splits a surrogate pair. Before, abcdefgh😀 became abcdefgh plus a lone surrogate, which goes out as ?. Now it becomes abcdefgh.
• The contract text in specs/001-ircv3-server/contracts/irc-protocol-commands.md now matches.

Formatting codes in message text, the realname, topics and reasons are untouched. #122 tracks a channel mode for those.

Validation

• HostmaskUsernameContentTest checks that TAB, \x01, \x1f, DEL, U+0080, U+0085, U+009F, NUL, CR, LF, space and @ are rejected. It also checks that alice, ~ident, 界界 and café are accepted, and that null and empty input are handled.
• UserIdentControlCharacterTest is a socket test. It sends idents containing \x01, U+0085, TAB and DEL, and checks that JOIN, WHOIS 311 and WHO 352 show user. A second case shows the surrogate-safe cut.
• All of the new tests failed before the fix.
• ./gradlew cleanTest build sonar passes, and the local SonarCloud branch scan passed the quality gate with 0 issues.
• Codex reviewed the diff against .github/REVIEW_CHECKLIST.md and found nothing. It also confirmed that UserCommandHandler is the only production caller of setIdent.

🤖 Generated with Claude Code

Summary by Sourcery

Harden USER ident validation and display handling against control characters and malformed Unicode.

Bug Fixes:

• Reject ISO control characters in USER idents so they cannot appear in client-visible hostmasks.
• Prevent ident truncation from splitting surrogate pairs and producing malformed output.

Documentation:

• Update the IRC protocol contract and research documentation to describe the expanded username validation and surrogate-safe ident handling.

Tests:

• Add protocol and integration coverage for control-character rejection, fallback idents, and safe truncation.

[sourcery-ai]

Reviewer's Guide

The PR hardens USER ident handling by rejecting all ISO control characters before they can appear in hostmasks, retains the existing user fallback, safely truncates long idents without splitting surrogate pairs, and adds unit/integration coverage plus matching protocol documentation.

Sequence diagram for safe USER ident handling

sequenceDiagram
    participant Client
    participant UserCommandHandler
    participant Hostmask
    participant ClientSession
    participant IRCResponse

    Client->>UserCommandHandler: handle(USER)
    UserCommandHandler->>Hostmask: isValidUsernameContent(username)
    alt invalid username content
        UserCommandHandler->>ClientSession: setIdent(user)
    else valid username content
        UserCommandHandler->>ClientSession: setIdent(username)
    end
    UserCommandHandler->>ClientSession: setRealname(realname)
    ClientSession->>IRCResponse: render hostmask ident
    IRCResponse-->>Client: JOIN, WHOIS 311, or WHO 352

Loading

Flow diagram for surrogate-safe ident truncation

flowchart LR
    A[USER ident] --> B{Length exceeds IDENT_MAX_CHARS?}
    B -- No --> C["setIdent(ident)"]
    B -- Yes --> D{Character at truncation boundary is high surrogate?}
    D -- Yes --> E[Remove boundary high surrogate]
    D -- No --> F[Keep IDENT_MAX_CHARS boundary]
    E --> C
    F --> C

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File-Level Changes

Change	Details	Files
Reject ISO control characters from USER idents before storing the session ident.	Expanded username validation to reject C0, DEL, and C1 controls while retaining space and @ checks. Preserved existing fallback to user for invalid ident content. Added unit coverage for rejected controls, delimiters, null/empty input, and accepted Unicode/non-control content.	jircd-core/src/main/java/net/jircd/core/session/command/UserCommandHandler.java jircd-protocol/src/main/java/net/jircd/protocol/Hostmask.java jircd-protocol/src/test/java/net/jircd/protocol/HostmaskUsernameContentTest.java
Make ident length truncation safe for UTF-16 surrogate pairs.	Avoided cutting immediately after a high surrogate at the nine-character display limit. Added an integration test verifying emoji truncation produces the valid prefix without replacement characters.	jircd-core/src/main/java/net/jircd/core/session/command/UserCommandHandler.java jircd-integration-tests/src/test/java/net/jircd/integration/UserIdentControlCharacterTest.java
Verify sanitized idents across protocol responses and align the protocol contract.	Added socket coverage for control-character idents in JOIN, WHOIS 311, and WHO 352 output. Updated the USER contract to describe ISO control-character rejection and the nine-character display limit.	jircd-integration-tests/src/test/java/net/jircd/integration/UserIdentControlCharacterTest.java specs/001-ircv3-server/contracts/irc-protocol-commands.md

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#121	Reject USER idents containing any ISO control character and fall back to the safe ident user, preventing those characters from appearing in server-generated identity prefixes.	✅
#121	Verify the rejection through registration and confirm the unsafe ident is not echoed in JOIN, WHO, or WHOIS responses, while retaining support for valid idents.	✅

Possibly linked issues

• [Bug] USER accepts control characters in the ident #121: The PR rejects ISO controls in USER idents, falling back to user as the issue expects; it also safely truncates surrogate pairs.

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[sourcery-ai]

Hey - I've found 1 issue

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path="specs/001-ircv3-server/contracts/irc-protocol-commands.md" line_range="139" />
<code_context>
   ever stating.
 - **Username** (the `<user>` parameter of `USER`, RFC 2812 §2.3.1's
-  `user` production): any octet except NUL, CR, LF, space, and `@` — no
+  `user` production): any character except space, `@`, and ISO control characters (C0 including NUL, CR, LF, TAB and \x01, DEL, and C1) — no
   length limit specified by the RFC itself, but this server MUST apply
   the same 9-character limit as `Hostmask`'s `ident` field for display
</code_context>
<issue_to_address>
**Research gives stale username rule**

When a reader relies on the research document for the USER username rule, `research.md` states the old octet rule while `Hostmask.isValidUsernameContent` rejects TAB, CTCP and C1 characters and `UserCommandHandler` substitutes `user`, so readers expect usernames the server rejects.

Update the registration grammar in `research.md` to match the username rule in the contract and validator.
</issue_to_address>

Sourcery assessment

Approved.

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[sourcery-ai]

Sourcery assessment

Approved.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
92.3% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud