feat(connect): add --server-name flag for tunneled connections

[jimmystridh]

Problem

When connecting to Azure SQL through an SSH tunnel or proxy (e.g., 127.0.0.1:11433), connections fail because SQL Server validates the hostname in the TDS LOGIN7 packet. The server receives 127.0.0.1 as the server name and rejects it with "Cannot open server '127.0.0.1' requested by the login".

Current workaround requires adding /etc/hosts entries mapping the real server name to 127.0.0.1.

Fixes #576

Solution

Add a --server-name flag that specifies the server name to send in the login packet, separate from the dial address (-S).

# Connect via tunnel on localhost:11433, authenticate as the real server
sqlcmd -S 127.0.0.1,11433 --server-name myserver.database.windows.net \
    -U myuser -P mypass -N -C

Implementation

• Add ServerNameOverride field to ConnectSettings
• Build the connection string using the override host/instance (so LOGIN7 uses the override)
• Use a proxy dialer that rewrites the network dial target back to the original -S host/port
• Skip override for named pipes

[jimmystridh]

@microsoft-github-policy-service agree

[Copilot]

Pull request overview

Adds support for overriding the server name used during TDS login (and related connection metadata) so sqlcmd can connect through tunnels/proxies (e.g., 127.0.0.1:11433) while authenticating as the real Azure SQL hostname.

Changes:

• Introduces ConnectSettings.ServerNameOverride and applies it when building the connection string.
• Adds a proxyDialer to rewrite the actual dial target while keeping the overridden server name for login.
• Adds unit tests covering the new connection string behavior and dialer behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/sqlcmd/connect.go	Adds ServerNameOverride and applies it during connection string construction.
pkg/sqlcmd/sqlcmd.go	Attempts to attach a custom dialer when ServerNameOverride is set.
pkg/sqlcmd/dialer.go	Implements a dialer that rewrites dial host/port while reporting an overridden hostname.
pkg/sqlcmd/dialer_test.go	Adds unit tests for proxyDialer.
pkg/sqlcmd/sqlcmd_test.go	Extends connection string tests to cover ServerNameOverride.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

[jimmystridh]

Addressed the remaining review notes:

• If --server-name is set but the connector isn’t *mssql.Connector, we now return an explicit error instead of silently changing the DSN host (commit c6f6ec4).
• proxyDialer now embeds a zero-value net.Dialer to avoid a race on lazy init (commit c6f6ec4).
• Added a named-pipe override test to ensure ServerNameOverride is ignored for np connections (commit c6f6ec4).
• The --server-name flag wiring is included in cmd/sqlcmd/sqlcmd.go in the same commit.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

[shueybubbles]

localizer.Errorf(

run build\build to generate localization files with the new strings

[shueybubbles]

or maybe just go generate but I'm not sure