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fix(config): remove trailing newlines in regexes (#373)

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Closes #372

Fun YAML fact of the day:

What is the difference between how these two expressions are parsed?

```yaml
foo: >
  bar
```

```yaml
foo: >-
  bar
```

They are invisible in yaml, but when you evaluate them to JSON the
difference is obvious:

```json
{
  "foo": "bar\n"
}
```

```json
{
  "foo": "bar"
}
```

User-Agent strings, URL path values, and HTTP headers _do_ end in
newlines in HTTP/1.1 wire form, but that newline is usually stripped
before the server actually handles it. Also HTTP/2 is a thing and does
not terminate header values with newlines.

This change makes Anubis more aggressively detect mistaken uses of the
yaml `>` operator and nudges the user into using the yaml `>-` operator
which does not append the trailing newline.

I had honestly forgotten about this YAML behavior because it wasn't
relevant for so long. Oops! Glad I released a beta.

Whenever you get into this state, Anubis will throw a config parsing
error and then give you a message hinting at the folly of your ways.

```
config.Bot: regular expression ends with newline (try >- instead of > in yaml)
```

Big thanks to https://yaml-multiline.info, this helped me realize my
folly instantly.

@aiverson, this is official permission to say "told you so".

Signed-off-by: Xe Iaso <me@xeiaso.net>
This commit is contained in:
Xe Iaso 2025-04-26 10:01:15 -04:00 • committed by GitHub
parent c669b47b57
commit ef52550e70
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GPG key ID: B5690EEEBB952194
8 changed files with 61 additions and 9 deletions
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12
lib/policy/checker.go
View file

@ -110,11 +110,11 @@ func NewUserAgentChecker(rexStr string) (Checker, error) {
}
func NewHeaderMatchesChecker(header, rexStr string) (Checker, error) {
rex, err := regexp.Compile(rexStr)
rex, err := regexp.Compile(strings.TrimSpace(rexStr))
if err != nil {
return nil, fmt.Errorf("%w: regex %s failed parse: %w", ErrMisconfiguration, rexStr, err)
}
return &HeaderMatchesChecker{header, rex, internal.SHA256sum(header + ": " + rexStr)}, nil
return &HeaderMatchesChecker{strings.TrimSpace(header), rex, internal.SHA256sum(header + ": " + rexStr)}, nil
}
func (hmc *HeaderMatchesChecker) Check(r *http.Request) (bool, error) {
@ -135,7 +135,7 @@ type PathChecker struct {
}
func NewPathChecker(rexStr string) (Checker, error) {
rex, err := regexp.Compile(rexStr)
rex, err := regexp.Compile(strings.TrimSpace(rexStr))
if err != nil {
return nil, fmt.Errorf("%w: regex %s failed parse: %w", ErrMisconfiguration, rexStr, err)
}
@ -155,7 +155,7 @@ func (pc *PathChecker) Hash() string {
}
func NewHeaderExistsChecker(key string) Checker {
return headerExistsChecker{key}
return headerExistsChecker{strings.TrimSpace(key)}
}
type headerExistsChecker struct {
@ -180,11 +180,11 @@ func NewHeadersChecker(headermap map[string]string) (Checker, error) {
for key, rexStr := range headermap {
if rexStr == ".*" {
result = append(result, headerExistsChecker{key})
result = append(result, headerExistsChecker{strings.TrimSpace(key)})
continue
}
rex, err := regexp.Compile(rexStr)
rex, err := regexp.Compile(strings.TrimSpace(rexStr))
if err != nil {
errs = append(errs, fmt.Errorf("while compiling header %s regex %s: %w", key, rexStr, err))
continue