Author:        Pietro Cerutti <[email protected]>
State:         Withdrawn
Type:          Project
Vote:          Pending
Created:       17-Sep-2026
Post-History:
Tcl-Version:   9.1
Keywords:      tcltest
Tcl-Branch:    gahr-no-hardcoded-ip-addresses
Vote-Summary:
Votes-For:
Votes-Against:
Votes-Present:

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Abstract

This TIP proposes two new functions in the tcltest namespace, for auto-discovery of the IPv4 and IPv6 address of the local interface.

Rationale

Tests in core currently hardcode 127.0.0.1 and ::1 for the local IPv4 and IPv6 address. This is problematic on systems where the local interface uses different addresses, e.g., on a FreeBSD jail with no loopback interface. It also doesn't allow any parameterization by users.

Specification

The two functions localIPv4Address and localIPv6Address are added to the tcltest namespace. The functions perform auto-discovery and returns the first match in the following heuristics, caching the results for subsequent calls.

1. the contents of the TCLTEST_IPV4 or TCLTEST_IPV6 environment variable
2. the addresses on a server socket opened with -myaddr localhost
3. the addresses on a server socket opened without a -myaddr parameter
4. 127.0.0.1 and ::1, respectively

IPv4 and IPv6 are discovered independently, i.e., one can set TCLTEST_IPV6 and rely on the above heuristics for IPv4.

Implementation

See the gahr-no-hardcoded-ip-addresses branch.

Copyright

This document has been placed in the public domain.