Panic on invalid board_manager.additional_urls config value

[per1234]

Describe the problem

The user may specify the URLs of additional package indexes via the board_manager.additional_urls configuration key.

🐛 If the user sets this configuration key to a value with a format like so:

<non-scheme><reserved character><URL>

(where <non-scheme> is any string that does not have the form of a URI scheme, <reserved character> is a URI reserved character, and <URL> is a URL)

Arduino CLI will panic.

To reproduce

$ arduino-cli version

arduino-cli  Version: git-snapshot Commit: 84fc413ad Date: 2024-12-16T17:53:58Z

$ arduino-cli --config-file /tmp/arduino-cli.yaml config set board_manager.additional_urls foo=https://espressif.github.io/arduino-esp32/package_esp32_index.json

$ arduino-cli --config-file /tmp/arduino-cli.yaml core update-index

Error initializing instance: Invalid additional URL: parse "foo=https://espressif.github.io/arduino-esp32/package_esp32_index.json": first path segment in URL cannot contain colon
Downloading index: package_index.tar.bz2 downloaded
Downloading index: foo=https://espressif.github.io/arduino-esp32/package_esp32_index.json Unable to parse URL: parse "foo=https://espressif.github.io/arduino-esp32/package_esp32_index.json": first path segment in URL cannot contain colon
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x8 pc=0xb102b4]

goroutine 1 [running]:
net/url.(*URL).String(0x0)
        C:/Users/per/sdk/go1.22.10/src/net/url/url.go:817 +0x34
github.com/arduino/arduino-cli/commands.(*arduinoCoreServerImpl).UpdateIndex.func1(...)
        E:/git/arduino/arduino-cli/commands/instances.go:539
github.com/arduino/arduino-cli/commands.(*arduinoCoreServerImpl).UpdateIndex(0xc000009038, 0xc002f042c0, {0x19156e0, 0xc002408690})
        E:/git/arduino/arduino-cli/commands/instances.go:567 +0x7d1
github.com/arduino/arduino-cli/internal/cli/core.UpdateIndex({0x1910788, 0xc0002da180}, {0x19218e8, 0xc000009038}, 0xc00012ac60)
        E:/git/arduino/arduino-cli/internal/cli/core/update_index.go:57 +0x265
github.com/arduino/arduino-cli/internal/cli/core.runUpdateIndexCommand({0x1910788, 0xc0002da180}, {0x19218e8, 0xc000009038})
        E:/git/arduino/arduino-cli/internal/cli/core/update_index.go:49 +0xa5
github.com/arduino/arduino-cli/internal/cli/core.initUpdateIndexCommand.func1(0xc000395508?, {0xc000110160?, 0x4?, 0x155faea?})
        E:/git/arduino/arduino-cli/internal/cli/core/update_index.go:40 +0x2c
github.com/spf13/cobra.(*Command).execute(0xc000395508, {0xc000110140, 0x2, 0x2})
        C:/Users/per/go/pkg/mod/github.com/spf13/[email protected]/command.go:989 +0xab1
github.com/spf13/cobra.(*Command).ExecuteC(0xc000198c08)
        C:/Users/per/go/pkg/mod/github.com/spf13/[email protected]/command.go:1117 +0x3ff
github.com/spf13/cobra.(*Command).Execute(...)
        C:/Users/per/go/pkg/mod/github.com/spf13/[email protected]/command.go:1041
github.com/spf13/cobra.(*Command).ExecuteContext(...)
        C:/Users/per/go/pkg/mod/github.com/spf13/[email protected]/command.go:1034
main.main()
        E:/git/arduino/arduino-cli/main.go:92 +0x474

Expected behavior

Panics do not occur under normal operating conditions, including invalid user input.

Note that of course it is not expected that Arduino CLI can download the index file in the face of an invalid configuration. It is only expected that it will handle this gracefully, without panicking.

Arduino CLI version

84fc413

Operating system

Windows

Operating system version

11

Additional context

Originally reported at https://forum.arduino.cc/t/arduino-ide-2-3-4-compilation-error-no-connection-established/1332770

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the nightly build
• My report contains all necessary details